New PCB boards made with new method. New boards have soldering mask.
Images:
Friday, April 27, 2012
Monday, February 20, 2012
4 input headphone amplifier with TPA6120 chip
I already have schematic and PCB design with TPA6120 chip with 2 inputs. Now I made same design but with 4 inputs and one line output. The new design contains PCB transformer, dual +/- 15V power supply, 4 channel mixer without preamplifiers, unbalanced/balanced converters, and line output with level adjustment.
The schematic:
The device contains 4 audio inputs with volume adjustment. The input connector must be soldered to the bottom of PCB (blue) and the volume must be potentiometers soldered to the top (yellow) of PCB. The input and line output connectors can be 6.3mm jack OR stereo RCA connector. The headphone output can be 6.3mm jack only. The PCB contains header for 4 power filter circuits (whats are optional if not required) for 4 dual operational amplifiers. The operational amplifier chips are compatible with TL072 for cheapest solution, NE5532 for better quality, and with LT1124 for the best quality. These chips used for the input mixer, for unbalanced/balanced converters, and for the line output amplifiers.
The PCB design:
See also:
The schematic:
The device contains 4 audio inputs with volume adjustment. The input connector must be soldered to the bottom of PCB (blue) and the volume must be potentiometers soldered to the top (yellow) of PCB. The input and line output connectors can be 6.3mm jack OR stereo RCA connector. The headphone output can be 6.3mm jack only. The PCB contains header for 4 power filter circuits (whats are optional if not required) for 4 dual operational amplifiers. The operational amplifier chips are compatible with TL072 for cheapest solution, NE5532 for better quality, and with LT1124 for the best quality. These chips used for the input mixer, for unbalanced/balanced converters, and for the line output amplifiers.
The PCB design:
See also:
- More unbalanced to balanced converters
- Simulation of unbalanced-balanced converter
- 2 input headphone amplifier
- Headphone amplifier with TPA6120
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Sunday, February 19, 2012
More unbalanced to balanced converters
At my previous post I simulated the unbalanced/balanced converter I using for unbalanced microphone inputs and headphone amplifier. The used chips (INA217 and TPA6120) have symmetrical inputs. These chips with balanced source have much better dynamics, noise, and sound quality. I think the selected converter I used is very good, but I wanted to simulate another solutions just for fun.
1.
This very simple schematic without required capacitors. This is the reason why the AC analysis have very good result, but with required parts the result of stability and the phases would be changed:
The AC analysis of the pure schematic:
2.
This sample is more complex, but the result is not the best. The reason is that the operation amplifiers not same with inverted and non-inverted mode, but the schematic is symmetrical for - and + outputs:
The result of AC analysis:
3.
Simple "pure" solution again without capacitors and another required parts. This "base" circuit working well but with whole system have to be modified:
The AC analysis is perfect, but we got another result with required parts:
4.
On the previous 3 examples have different method negative feedback on operational amplifier. Sometime the input connected to inverted and non-inverted inputs, and the required amplifiers have several feedback. By this example the inverter circuit getting the input signal from the output of first stage. Very stable example with really good AC analysis result:
The AC analysis:
5.
The final example have more than one versions. The benefit of these schematics are the symmetrical solution of + and - outputs, which have same (or very closed) frequency responses and phases. The previous circuits have no capacitors on the negative feedback, or if have the capacitors modified the inverted stage only, the original signal more linear than the inverted. With the current solution, the frequency response and the phase of inverted and non-inverted stages are relative parallel, not like in the 2nd example what is serious problem.
The simplest version:
The AC analysis where the frequency responses are same, the phases are not linear, but running parallel, and the difference is very closed to required 180 degree:
The first modification is the active feedback between the outputs and inverted input for the adjust of inverted stage output level by the R15 resistor:
The final version of this really interesting converter is two operational amplifiers added for the output. This modification have same AC result than the previous version:
The AC analysis:
This example have gain from 707mV to 11V what is not required. If this gain is too much, modify R4/R5 and R9/R11 resistors to adjust the output gain. When the gain of stages modified, set again the output amplitude to exactly same by R15 resistor what can be trimmer potentiometer:
The result of AC analysis is very closed but modified when the gain changed:
The question is, what is the best solution if unbalanced/balanced converter required. The most simple versions are looks like perfect solutions, but with additional (and required) capacitors and with non exactly same resistors the phase and the amplitudes has been shifted. The another reason of differences is the difference between inverted and non-inverted mode of same operational amplifier stage. The simplest (and the best) schematics are block diagrams only, very good base but have to be modified. The useful solutions have two useful version: the input signal connected to same inverted and non-inverted stage. The another one is the input signal connected to non-inverted stage, and the output of this stage connected to inverted-mode operational amplifier. The another differences between the negative feedback. The second example, where the original input signal uses same stage but one with inverted one with non-inverted mode, the result is not really useful. This is the difference between modes of operational amplifiers.
The another question is the same frequency response of - and + outputs. If the original signal uses the simplest solution with direct negative feedback (like in the 1st example), and the inverted stage have negative feedback with capacitor, the frequency response (and the phases) will be different. If the difference shows after 40kHz by AC analysis, I think the result is very useful.
The last 5th example is interesting only. Not the simplest solution, and the problem is, the phase modified by the input frequency. The difference between + and - outputs is constant 180 degree, but always modified the phase values. This is the reason why I think the one of the best result for balanced conversion is on my previous post.
See also:
1.
This very simple schematic without required capacitors. This is the reason why the AC analysis have very good result, but with required parts the result of stability and the phases would be changed:
The AC analysis of the pure schematic:
2.
This sample is more complex, but the result is not the best. The reason is that the operation amplifiers not same with inverted and non-inverted mode, but the schematic is symmetrical for - and + outputs:
The result of AC analysis:
3.
Simple "pure" solution again without capacitors and another required parts. This "base" circuit working well but with whole system have to be modified:
The AC analysis is perfect, but we got another result with required parts:
4.
On the previous 3 examples have different method negative feedback on operational amplifier. Sometime the input connected to inverted and non-inverted inputs, and the required amplifiers have several feedback. By this example the inverter circuit getting the input signal from the output of first stage. Very stable example with really good AC analysis result:
The AC analysis:
5.
The final example have more than one versions. The benefit of these schematics are the symmetrical solution of + and - outputs, which have same (or very closed) frequency responses and phases. The previous circuits have no capacitors on the negative feedback, or if have the capacitors modified the inverted stage only, the original signal more linear than the inverted. With the current solution, the frequency response and the phase of inverted and non-inverted stages are relative parallel, not like in the 2nd example what is serious problem.
The simplest version:
The AC analysis where the frequency responses are same, the phases are not linear, but running parallel, and the difference is very closed to required 180 degree:
The first modification is the active feedback between the outputs and inverted input for the adjust of inverted stage output level by the R15 resistor:
The final version of this really interesting converter is two operational amplifiers added for the output. This modification have same AC result than the previous version:
The AC analysis:
This example have gain from 707mV to 11V what is not required. If this gain is too much, modify R4/R5 and R9/R11 resistors to adjust the output gain. When the gain of stages modified, set again the output amplitude to exactly same by R15 resistor what can be trimmer potentiometer:
The result of AC analysis is very closed but modified when the gain changed:
The question is, what is the best solution if unbalanced/balanced converter required. The most simple versions are looks like perfect solutions, but with additional (and required) capacitors and with non exactly same resistors the phase and the amplitudes has been shifted. The another reason of differences is the difference between inverted and non-inverted mode of same operational amplifier stage. The simplest (and the best) schematics are block diagrams only, very good base but have to be modified. The useful solutions have two useful version: the input signal connected to same inverted and non-inverted stage. The another one is the input signal connected to non-inverted stage, and the output of this stage connected to inverted-mode operational amplifier. The another differences between the negative feedback. The second example, where the original input signal uses same stage but one with inverted one with non-inverted mode, the result is not really useful. This is the difference between modes of operational amplifiers.
The another question is the same frequency response of - and + outputs. If the original signal uses the simplest solution with direct negative feedback (like in the 1st example), and the inverted stage have negative feedback with capacitor, the frequency response (and the phases) will be different. If the difference shows after 40kHz by AC analysis, I think the result is very useful.
The last 5th example is interesting only. Not the simplest solution, and the problem is, the phase modified by the input frequency. The difference between + and - outputs is constant 180 degree, but always modified the phase values. This is the reason why I think the one of the best result for balanced conversion is on my previous post.
See also:
Saturday, February 18, 2012
Simulation of unbalanced - balanced converter
I using unbalanced/balanced converters with my circuits like microphone preamplifiers and headphone amp because the used chips (INA217 and TPA6120) have symmetrical balanced inputs. This is very important, the sound and the dynamics are much better with this solution. I simulated the schematic of converter, and here are the results:
With scope and AC voltmeter on real time simulation:
AC analysis:
See also:
With scope and AC voltmeter on real time simulation:
AC analysis:
See also:
Tuesday, February 7, 2012
Simulation of UREI LP/HP filter module
Maybe this is the last post about UREI parametric filter projects. On the previous post I finalized the design of modular parametric EQ. I have only one idea for the future, the stereo version of this project, but the biggest problem the potentiometer with 4 adjustable resistors, what is not impossible. The simulation of parametric EQ successfully done, but the original values of high pass/low pass filter have to be modified. This filter circuit with original values started too high, and the possible highest frequency is around 15 kHz what is too low.
This is the schematic of HP/LP filter module:
In this module the most important parts are C2 C3 and C4 C5 capacitors. Noted, this equalizer made for instruments amplification like guitar and vocal, not for home hi-fi, for these applications the middle range of audible frequency is good (better) solution than the full frequency range. But I wanted more, because this module is adjustable like all others in this project. I think, if the middle positions of potentiometers have good result, I have reserved range and more possibilities.
On the first version, the capacitor values like in the schematic, and the simulation result of LP filter is here:
This solution with the end position of potentiometer cutting the highest frequency around 40kHz what is too much. Not a big failure, because the value is adjustable, but not required - compared to the original EQ where the end value is around 15kHz. This is the reason why the capacitors changed to 5.6 nF.
The AC analysis of HP filter:
The start value is around 14Hz what is too low. The end value of this filter is around 326Hz what is too low again. This is the reason why decreased the capacitor value to 330nF.
The simulation of both LP/HP filter at one graph:
With the new simulation the capacitors of LP filter changed to 5.6nF, the capacitors of HP filter changed to 330nF. Here is the AC analysis of HP filter:
The LP filter with 5.6 nF:
Both analysis at one graph:
Not impossible to use this filter module alone, but I analyzed how modified the frequency response of parametric EQ modules. The potentiometers of LP/HP filters set to 50% middle positions:
This is the schematic of HP/LP filter module:
In this module the most important parts are C2 C3 and C4 C5 capacitors. Noted, this equalizer made for instruments amplification like guitar and vocal, not for home hi-fi, for these applications the middle range of audible frequency is good (better) solution than the full frequency range. But I wanted more, because this module is adjustable like all others in this project. I think, if the middle positions of potentiometers have good result, I have reserved range and more possibilities.
On the first version, the capacitor values like in the schematic, and the simulation result of LP filter is here:
This solution with the end position of potentiometer cutting the highest frequency around 40kHz what is too much. Not a big failure, because the value is adjustable, but not required - compared to the original EQ where the end value is around 15kHz. This is the reason why the capacitors changed to 5.6 nF.
The AC analysis of HP filter:
The start value is around 14Hz what is too low. The end value of this filter is around 326Hz what is too low again. This is the reason why decreased the capacitor value to 330nF.
The simulation of both LP/HP filter at one graph:
With the new simulation the capacitors of LP filter changed to 5.6nF, the capacitors of HP filter changed to 330nF. Here is the AC analysis of HP filter:
The LP filter with 5.6 nF:
Both analysis at one graph:
Not impossible to use this filter module alone, but I analyzed how modified the frequency response of parametric EQ modules. The potentiometers of LP/HP filters set to 50% middle positions:
- The red line if all modules off (bypassed)
- The blue is the result if only LP/HP filter on with middle positioned potentiometers
- The green line if all EQ modules on but the LP/HP filter module off
- The maroon line if all modules on.
See also:
- Modular, expandable parametric equalizer based on UREI546
- Simulation of 8 band parametric equalizer
- Simulation and software analysis of UREI 546
- UREI546 parametric EQ like URS VST EQ bundle
- 6 and 10 bands for UREI 546 parametric equalizer
- Math expression for UREI546 parametric EQ design
- Parametric EQ Project - Modular UREI545 and 546
- Modular equalizer with gyrator filter
- PDF manual of modular gyrator EQ
- PDF manual of UREI 545 and 546 EQ clone
Tuesday, January 24, 2012
Updates of PDF manuals
In these days I updated PDF manuals. The benefit of the PDF documents is the vector based schematic and PCB design for unlimited magnification, and the project is not separated to articles, there are all in one documents. Here are the updated documents:
- TDA7293 modular project: modified the wrong parallel schematic and PCB module, and inserted offer to make amplifier up to 800W with more than one parallel modules. Two new PWM fan controller and speaker protection design included.
- Headphone amplifier with TPA6120: Two schematic for the simplest and full featured solutions, but four PCB designs available.
My next "project" is to finish PDF manual for my parametric EQ.
Download manuals from the right side.
Tuesday, January 17, 2012
Modular, expandable parametric equalizer based on UREI546
I posted about the equalizer called UREI545 and UREI546. This is the one of my favorite project. These devices are not same, but very similar. The differences between 545 and 546, the LP/HP filter on the input, and the number of bands. On the original UREI545 have 3 parametric EQ filters, and one switchable filter with 3 different middle frequencies. The UREI546 have 4 bands without switchable frequencies, but this is dual device. Can be used as mono 8 band parametric EQ, or as 4 band stereo parametric EQ. These devices used by musicians for guitar and vocal equalization.
The current project based on the UREI546, but modified. The new design is an expandable parametric equalizer with modular system for smaller PCBs with no limitations. The maximum number of bands are not limited, but the current project made for 4 to 8 band equalizer, with optional input and output gain modules, optional HP/LP filter module, and optional clipping LED module. The design is similar as my previous modular expandable audio mixer or modular amplifier. The current project started with software simulation of filter circuit, and continued to get capacitor values for 8 band EQ by simulation. This is the post where I publish the schematic and PCB design of expandable modular parametric equalizer.
For the expandable feature, 2 mainboards required for this project. The first is for 4 modules, contains connectors for inputs (Conn2), outputs (Conn3), and +/-15V power supply (Conn1). This mainboard designed for 4 band EQ only, without additional modules:
Because between EQ modules and other modules requires serial connection, (not parallel like in the modular audio mixer), the last module on the whole system must be connected to the output bus. This is the reason why W1 and W2 jumpers are required. With these jumpers, the last module must be wired to the system output, without jumpers, the output of module connecting to the input of next module. The jumper must be used only on the last EQ or Output Gain module of the whole system. The connector P2 is 10 pin female connector, the next mainboard must be connected here if required. Conn4....Conn7 is 2x6 L headers for the EQ or Gain modules.
The PCB of first mainboard:
The second mainboard is more simple, contains only one 2x6 L header for one module, on the left one 10 pin male connector, on the right one 10 pin female connector:
W1 and W2 jumpers must used if the connected module is the last on the whole system. If last, the current module output connected to the system output bus by W1 and W2. The one and only exception, if the last module is the clipping detector. If more modules required, this mainboard must be connected to the previous one.
The PCB design:
The modules can be soldered to these two mainboards with 2x6 pins L header. The most important module is the parametric filter:
This filter based on UREI546 with some modifications. The Conn2 must be connected to the mainboard, the Conn1 is the connector for "power filter" module for less noise. This is the reason why the filter capacitor missing from the OpAmp. The C3 is coupling capacitor, 10uF or 22uF is better than 100nF in the original design. No need to change on several EQ modules. For EQ bands with different middle frequency, only 2 pieces of Ca capacitors must be changed. This is the reason, why the footprint accept 200 and 300 mil pins. Sw1 is the bypass switch, D2 diode is connected for the clipping detector bus. P1 adjust Q, P2 adjust the middle frequency, P3 adjust cut/boost of the EQ module.
The PCB:
The module cutted on the bottom because this required for mechanical assembly. The bypass switch and the 3 required potentiometers are soldered to the PCB. D1 is the connector for LED displays the bypassed or connected status of the module. The both mainboards made for stereo circuits, but this module (and currently all others) is mono. The reason of this difference, that in the future I would like to design stereo filters for stereo EQ, but I would like to use these mainboards. The lion in the way, that 4 potentiometers required to adjust the frequency if this EQ module going stereo.
The most important question about this module, the values of Ca (C1 and C2) capacitors. These values depend on the required middle frequency. I have no math expression, but I done software simulation for 8 bands with values.
With this design the bypass switch with LED, and the header for power filter are available too. The output connected to the clipping detector via D2, like all other filter modules. The C1 capacitor changed to 47pF to get better Q for higher frequency of LP filter. The potentiometers changed from 55kOhm to 22kOhm for smaller adjustment range. High adjustment range is not too important, because numerous adjustable filters can be connected after this module. The highest value of filter depend on C2 and C3 capacitor, what changed from 6.8nf to 4.7nF, but maybe 5.6 nF is the best because the new endpoint of frequency range is around 40kHz what is too much, but the original is around 15 kHz, what is low.
The capacitors of high pass filer is C4 and C5 changed to 470nF instead of the original 220nF to get lowest frequency. With this new value the filter starts from 15Hz, what is too low. Maybe 330nF would be the best, I will do simulation for several values soon.
The result of current AC analysis (470nF and 4.7nF):
The PCB of LP/HP filter module:
The next is a very simple and noiseless preamplifier module with jFET. I really like the sound of this circuit for guitar. This module can be used as first module (for input gain) and (or only) at the end of device as output gain:
This circuit can be bypassed by the switch, and can be ignored if not required.
The PCB:
The last module is the clipping detector what monitor all outputs of applied modules by the pin2 of 2x6 L header:
Clipping detector PCB:
The power filter, required for all modules for less noise except clipping detector:
I have 8 versions of power filter PCB where the difference is only the size of board. This is the version 6 with SMD resistors and transistors:
The required power supply and the PCB:
By these boards can be built like this (for example):
The current project based on the UREI546, but modified. The new design is an expandable parametric equalizer with modular system for smaller PCBs with no limitations. The maximum number of bands are not limited, but the current project made for 4 to 8 band equalizer, with optional input and output gain modules, optional HP/LP filter module, and optional clipping LED module. The design is similar as my previous modular expandable audio mixer or modular amplifier. The current project started with software simulation of filter circuit, and continued to get capacitor values for 8 band EQ by simulation. This is the post where I publish the schematic and PCB design of expandable modular parametric equalizer.
For the expandable feature, 2 mainboards required for this project. The first is for 4 modules, contains connectors for inputs (Conn2), outputs (Conn3), and +/-15V power supply (Conn1). This mainboard designed for 4 band EQ only, without additional modules:
Because between EQ modules and other modules requires serial connection, (not parallel like in the modular audio mixer), the last module on the whole system must be connected to the output bus. This is the reason why W1 and W2 jumpers are required. With these jumpers, the last module must be wired to the system output, without jumpers, the output of module connecting to the input of next module. The jumper must be used only on the last EQ or Output Gain module of the whole system. The connector P2 is 10 pin female connector, the next mainboard must be connected here if required. Conn4....Conn7 is 2x6 L headers for the EQ or Gain modules.
The PCB of first mainboard:
The second mainboard is more simple, contains only one 2x6 L header for one module, on the left one 10 pin male connector, on the right one 10 pin female connector:
W1 and W2 jumpers must used if the connected module is the last on the whole system. If last, the current module output connected to the system output bus by W1 and W2. The one and only exception, if the last module is the clipping detector. If more modules required, this mainboard must be connected to the previous one.
The PCB design:
The modules can be soldered to these two mainboards with 2x6 pins L header. The most important module is the parametric filter:
This filter based on UREI546 with some modifications. The Conn2 must be connected to the mainboard, the Conn1 is the connector for "power filter" module for less noise. This is the reason why the filter capacitor missing from the OpAmp. The C3 is coupling capacitor, 10uF or 22uF is better than 100nF in the original design. No need to change on several EQ modules. For EQ bands with different middle frequency, only 2 pieces of Ca capacitors must be changed. This is the reason, why the footprint accept 200 and 300 mil pins. Sw1 is the bypass switch, D2 diode is connected for the clipping detector bus. P1 adjust Q, P2 adjust the middle frequency, P3 adjust cut/boost of the EQ module.
The PCB:
The module cutted on the bottom because this required for mechanical assembly. The bypass switch and the 3 required potentiometers are soldered to the PCB. D1 is the connector for LED displays the bypassed or connected status of the module. The both mainboards made for stereo circuits, but this module (and currently all others) is mono. The reason of this difference, that in the future I would like to design stereo filters for stereo EQ, but I would like to use these mainboards. The lion in the way, that 4 potentiometers required to adjust the frequency if this EQ module going stereo.
The most important question about this module, the values of Ca (C1 and C2) capacitors. These values depend on the required middle frequency. I have no math expression, but I done software simulation for 8 bands with values.
- Math expression required to get frequency values among the lowest and highest bands. This expression is used for Excel spreadsheet if the first and last frequency, and the number of other bands decided:=IF(C8<$D$5,$D$3*10^((LOG10($D$4)-LOG10($D$3))*(C8-1)/($D$5-1)), IF(C8=$D$5,$D$4,IF(C8>$D$5," ","?")))
- The next is that we need the Ca capacitor value for the module frequency. This value is linear on the logarithmic scale with the frequency, but the best method is the software simulation. Here is an example for 8 band equalizer:
The input of this spreadsheet is on the green fields on the top, contains the highest frequency of the first and last modules, and the number of all EQ modules. I always working with the highest frequency, the middle and the lowest value getting by the software simulation using modified standard capacitor values. - The real value of the module frequencies depend on the standard values of the capacitors. The best result is the software simulation again to getting the lowest and highest values of filters:
- The number of possible requirements are very high. Not only the number of EQ bands, the lowest and highest frequency of the bands can be different. This is the reason, why I can publish and simulated 8 band EQ only. If you like another versions, for example less or more bands, or higher frequency of the lower band, software simulation required to get the capacitor values and the resistor values to setting Q.
With this design the bypass switch with LED, and the header for power filter are available too. The output connected to the clipping detector via D2, like all other filter modules. The C1 capacitor changed to 47pF to get better Q for higher frequency of LP filter. The potentiometers changed from 55kOhm to 22kOhm for smaller adjustment range. High adjustment range is not too important, because numerous adjustable filters can be connected after this module. The highest value of filter depend on C2 and C3 capacitor, what changed from 6.8nf to 4.7nF, but maybe 5.6 nF is the best because the new endpoint of frequency range is around 40kHz what is too much, but the original is around 15 kHz, what is low.
The capacitors of high pass filer is C4 and C5 changed to 470nF instead of the original 220nF to get lowest frequency. With this new value the filter starts from 15Hz, what is too low. Maybe 330nF would be the best, I will do simulation for several values soon.
The result of current AC analysis (470nF and 4.7nF):
The PCB of LP/HP filter module:
The next is a very simple and noiseless preamplifier module with jFET. I really like the sound of this circuit for guitar. This module can be used as first module (for input gain) and (or only) at the end of device as output gain:
This circuit can be bypassed by the switch, and can be ignored if not required.
The PCB:
The last module is the clipping detector what monitor all outputs of applied modules by the pin2 of 2x6 L header:
Clipping detector PCB:
The power filter, required for all modules for less noise except clipping detector:
I have 8 versions of power filter PCB where the difference is only the size of board. This is the version 6 with SMD resistors and transistors:
The required power supply and the PCB:
By these boards can be built like this (for example):
- 4 bands mainboard, 4 pieces of EQ filters with the oroginal values of UREI546 can be the clone of original device but without preamplifier module, LP/HP filter, and clipping detector.
- Start the whole device with 4 band mainboard, use the jFET gain module first, the second is the LP/HP filter module, and continue with 2 parametric EQ module. Connect mainboard 2 to mainboard 1, and use parametric EQ modules. When the maximum number of EQ modules connected, use one more jFET gain module for output gain (with W1 and W2 jumpers) and the last possible module is the clipping detector.
By software simulation the result of these circuits can be changed. The schematic samples on this post maybe set to wide values, but all modules adjustable, so I think this is not a big problem.
On the EQ modules and LP/HP filter modules maybe very important the logarithmic potentiometers. The resistor and capacitor values are linear, but with logarithmic scale of graph. On the simulation and on the schematic I used TL071...TL074, but for the best quality I offer using LT or NE series instead, what is much better for filter designs. For example for single OpAmp use LT1028/LT1128/LT1115, for quad or dual OpAmps can be changed to LT1124/LT1125.
See also:
- Simulation of UREI LP/HP filter module
- Simulation of 8 band parametric equalizer
- Simulation and software analysis of UREI 546
- UREI546 parametric EQ like URS VST EQ bundle
- 6 and 10 bands for UREI 546 parametric equalizer
- Math expression for UREI546 parametric EQ design
- Parametric EQ Project - Modular UREI545 and 546
- Modular equalizer with gyrator filter
- PDF manual of modular gyrator EQ
- PDF manual of UREI 545 and 546 EQ clone
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Saturday, January 7, 2012
Simulation of 8 band parametric equalizer
On the previous post I talking about software simulation of parametric EQ filter. The simulation result is exactly same as the original official datasheet of 4 band EQ (with really small differences on the lowest frequencies). But I would like to design parametric EQ with more than 4 bands. No math expression, but the simulation is easier solution for this modification.
For the first design, I modified the original 4 band schematic to 8 bands, and the simulation works with this modification very fast, the required time is same as like with 1 filter only (while several software running on the background). The schematic simplified, I removed virtual batteries, used VCC/VEE power sources instead. Deleted the on/off switch which is really needless. This simplified schematic without virtual instruments working well for AC analysis.
First of all, I need math expression (again :) for getting frequency values between 20 Hz and 20 kHz for 8 bands. I think about 10 bands, but for parametric EQ where the middle frequency and the Q are adjustable, I think 10 bands are too much. The parametric EQ of URS software have 5 bands only. The first solution to get middle values between the lowest and highest band I found on the NET by this page. This webpage counts the geometric mean between f1 and f2, which are the lowest and highest frequencies on the system.
This solution is not the best for 8 bands, because first I can get the middle of the lowest and highest value which are 3 bands, but after, I have to get all middles between these 3 values, finally I have 5 or 9 results instead of 8. Maybe the possible solution if the highest frequency is around 40 kHz, get 9 results with this page, and delete the last (40 kHz) value. So you can have 8 results, where the highest around 20 kHz.
The really tricksy solution is the Excel spreadsheet. This table is not my own work, I got help from Frank Walker. I just enter the start and end values to this spreadsheet, and the required numbers between these values, and the table getting back the solutions.
First, compare the result of this expression with the original 4 band UREI EQ:
Compared with the UREI datasheet and the result of simulation, we can see, the datasheet values contains the result of expression not the simulation. The trust, on the UREI schematic I can found capacitor with 27.5 nf value, which is not the standard value.
Tables for more than 4 bands:
Finally, here is the expression of spreadsheet from the cell where we got the results of bands:
=IF(C8<$D$5,$D$3*10^((LOG10($D$4)-LOG10($D$3))*(C8-1)/($D$5-1)), IF(C8=$D$5,$D$4,IF(C8>$D$5," ","?")))
This expression counts the required frequencies between the lowest and highest bands. The lowest frequency is on the cell no. D3, the highest on D4, the number of bands is on the D5. The column C is the serial number of bands from 1 to 8.
More than 8 channels have problem with Q, what must be very high if the number of bands are too much. If less than 8 band required, all channels have bypass switch and the Q parameter can be set to lower.
For the current design, I need the table of 8 bands EQ. The range of frequency adjustment must be smaller than with 4 bands only, modifications of the schematic required:
The important aspect, that we have to work with standard values of capacitors and potentiometers. The first modification requires for possible higher Q value, and less possible range of the adjustment of Q:
For the first design, I modified the original 4 band schematic to 8 bands, and the simulation works with this modification very fast, the required time is same as like with 1 filter only (while several software running on the background). The schematic simplified, I removed virtual batteries, used VCC/VEE power sources instead. Deleted the on/off switch which is really needless. This simplified schematic without virtual instruments working well for AC analysis.
First of all, I need math expression (again :) for getting frequency values between 20 Hz and 20 kHz for 8 bands. I think about 10 bands, but for parametric EQ where the middle frequency and the Q are adjustable, I think 10 bands are too much. The parametric EQ of URS software have 5 bands only. The first solution to get middle values between the lowest and highest band I found on the NET by this page. This webpage counts the geometric mean between f1 and f2, which are the lowest and highest frequencies on the system.
This solution is not the best for 8 bands, because first I can get the middle of the lowest and highest value which are 3 bands, but after, I have to get all middles between these 3 values, finally I have 5 or 9 results instead of 8. Maybe the possible solution if the highest frequency is around 40 kHz, get 9 results with this page, and delete the last (40 kHz) value. So you can have 8 results, where the highest around 20 kHz.
The really tricksy solution is the Excel spreadsheet. This table is not my own work, I got help from Frank Walker. I just enter the start and end values to this spreadsheet, and the required numbers between these values, and the table getting back the solutions.
First, compare the result of this expression with the original 4 band UREI EQ:
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Tables for more than 4 bands:
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=IF(C8<$D$5,$D$3*10^((LOG10($D$4)-LOG10($D$3))*(C8-1)/($D$5-1)), IF(C8=$D$5,$D$4,IF(C8>$D$5," ","?")))
This expression counts the required frequencies between the lowest and highest bands. The lowest frequency is on the cell no. D3, the highest on D4, the number of bands is on the D5. The column C is the serial number of bands from 1 to 8.
More than 8 channels have problem with Q, what must be very high if the number of bands are too much. If less than 8 band required, all channels have bypass switch and the Q parameter can be set to lower.
For the current design, I need the table of 8 bands EQ. The range of frequency adjustment must be smaller than with 4 bands only, modifications of the schematic required:
The important aspect, that we have to work with standard values of capacitors and potentiometers. The first modification requires for possible higher Q value, and less possible range of the adjustment of Q:
- R2 120 Ohm instead of 390 Ohm
- R3 1.5 KOhm instead of 390 Ohm
The second modification is for the less range of frequency adjustment.
- R5 and R7 potentiometers changed from 55 KOhm to 22 KOhm.
After these changes, on the filters have to be modified the C1 and C2 capacitors only:
- 330 nF
- 150 nF
- 68 nF
- 33 nF
- 15 nF
- 7.5 nF
- 3.6 nF
- C1 = 1.8 nF, C2 = 1.6 nF
Possible to fine tune the required frequency, if the values of C1 and C2 are not same. With this method, the required frequency can be fine shifted to lower or higher value, and can be re-tuned the value of Q.
After analyzing the first band I started to define the second, but before, I wonder how about these bands on the original 4 band EQ:
This is the result of analysis for all 4 bands, with possible lowest, middle, and the possible highest frequencies.
Finally, the graph of AC analysis of 1st, 2nd, and 3rd frequencies not succeed pretty like on the original UREI EQ, because with available standard values this is not possible:
These graphs are not really pretty, but this is no problem, because the parameters are adjustable, and the graph cannot visible during operation :).
The next step is the AC analysis of all 8 bands:
The graphs are really not nice like the original one :(.
With the next analysis I reduced the Q from 100% to 70% on all bands:
This analysis would be more interested, if I bypass some filters, or changing the cut/boost parameter too.
Finally I tried to correct the "errors" of the graph. I reduced the bands frequency to 93...95% from 100, this is the thinner red line. The new line is closer to the green, which is the possible lowest frequencies of all 8 bands:
For this equalizer I have PCB for 4 and 6 bands only, but my next PCB project is the expandable modular parametric equalizer from 4 bands to any.
See also:
- Simulation of UREI LP/HP filter module
- Modular, expandable parametric equalizer based on UREI546
- Simulation and software analysis of UREI 546
- UREI546 parametric EQ like URS VST EQ bundle
- 6 and 10 bands for UREI 546 parametric equalizer
- Math expression for UREI546 parametric EQ design
- Parametric EQ Project - Modular UREI545 and 546
- Modular equalizer with gyrator filter
- PDF manual of modular gyrator EQ
- PDF manual of UREI 545 and 546 EQ clone
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