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:

• Simulation of favorite unbalanced/balanced converter
• 4 input headphone amplifier
• 2 input headphone amplifier
• Modifier microphone preamplifier
  

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:

• Simulation of several unbalanced/balanced converters
  
• 4 input headphone amplifier
• 2 input headphone amplifier
• Modifier microphone preamplifier

Modified microphone preamplifier with INA217

I really like the microphone preamplifier with INA217. No noise, very good sound and dynamic, no feedback, very high (max 10.000x) gain, very simple application. Lot of websites testing and comparing this design with another industrial devices. The article, when this is the best mic preamp and the cost is USD5 only, maybe not true. Not only the INA217 required, you need PCB, transformer, 2 potentiometers, input and output connectors, power supply.

I modified the original design recommended on the datasheet. The original application circuit on datasheet is really simple and very good microphone preamplifier. I added a better unbalanced/balanced converter after unbalanced jack input. I have this feature before, but now I have better circuit. The another modification is the output. Because this preamp is mono, the simple connection to stereo system is not the best. The result may increase the crosstalk between left and right channels. This is the reason why I included two line driver circuits to separate left and right channels. Finally because this new design contains 3 integrated circuit, I inserted 3 "power filter" for less noise.

The modified preamp design with input unbalanced/balanced converter and output line drivers:


The PCB with simple connectors:


The same design without connectors, because this PCB can be inserted to the mainboards of modular mixers. The connectors changed to P4 header:


Now here is the list of features:

• Balanced input
  
• 6.3 jack as Unbalanced input, but with unbalanced/balanced converter
  
• Gain adjustment
• Volume adjustment
• Connector for 48V phantom power
  
• Switch for 48V phantom power
  
• Switch between unbalanced jack and balanced XLR input
  
• Divided line driver inputs connect to stereo systems
  
• Power filter circuits for all 3 integrated circuits for less noise
  

PCB sales of this project Module name Size (mm) Area (cm2) PDF SCH PCB image Tested Price (US$) Des. Sim.1 Full2 Sim.1 Full2 Man3 Mic preamp pro with connectors 79x104 82 Yes Yes Yes - - No 13 21 Ask Mic preamp pro as mixer module 67x103 69 Yes Yes Yes - - No 11 19 Ask How to order? Please read the rules carefully!

Expandable, modular audio mixer for any number of channels

This is my second audio mixer project. The difference between current and previous design is, that this design can be expandable to any number of channels, the previous is made for 4 or 8 input channels only. At the end of the PDF manual of this project I inserted examples how to build audio mixer for any number of input and output channels.

I made paper models of my design to check how possible to build the complex device:



This gallery is funny, but very cheap to find mechanical problems before manufacturing the PCBs. With this test, I detected the problem, that the PCBs of "power filter" circuits are too big, have to be smaller than 25mm. This is the reason why I have 5 several power filter PCBs, and here is the smallest, with 22mm height, and 25mm width for the modular mixers:



The schematic of power filter module to decrease the preamplifier's noise and the crosstalk between left and right channels:


This PCB is very small, much harder to build....

The required preamplifiers for input channels are exactly same as than my simplest mixer project. The new on this design, that the small mainboards can be expanded with female/male connectors to build bigger than 8 channel audio mixer.

The first module of expandable mainboard:


...and the PCB for the first mainboard module:


This design is simple 4 channel audio mixer. Possible to finalize with 4 several preamplifiers. The blue potentiometers on the bottom of PCB is the L/R balance adjustment, but these parts are ignorable if not important. These potentiometers have blue color, because must be soldered to the bottom layer. There are mono, metal case parts. The first mainboard contains connectors for powers, phantom powers, line outputs, and balanced microphone input for all channels if mic preamp inserted. The main difference is the P1 female connector. This is the part where possible to connect another mixer mainboard to make more input or output channels. This first 4 channel module working without another connected boards, but on this one no connectors for outputs, only one stereo line output on the PCB via H5 connector.

For more inputs, here is the required module can be connected to the right edge of the first board to the connector P1:


and the really small PCB with P21 male connector:


This is an input channel for 2 arbitrary preamplifiers. Upper left is the male connector can be connected to the first, to the same, or to the output boards too. Here is the reason why expandable this device to any input or output channels.

If output channels required, here is the new schematic:


And I have 2 PCB design for upper schematic:


The difference between two PCBs is the L/R balance potentiometer only. This mainboard-module made for output circuits. The board can be connected to anywhere and anytime within the whole system. I offer several output modules:

The line outputs with master volume adjustment:


...and the PCB:


The difference between this, and the previous version of line output board, that this board contains line driver circuits, not the mixer's mainboard. This board contains adjustable master output of mixer with volume potentiometer with following variations:

• 2 6.3mm jack
• 1 6.3mm and 1 3.2mm jack
• 1 6.3mm jack and 1 stereo RCA
• 1 3.2mm jack and 1 stereo RCA

This board contains only one stereo volume adjustment, but possible to soldering to the board with L/R balance potentiometer if this feature required.

Another output circuit:

This is headphone amplifier with TPA6120. I modified my previous design of this module.

The PCB:

This is the simplest application of this really good IC with 6.3mm jack output and volume adjustment feature.

I made another version of this output for my audio mixer. The difference, here is an unbalanced/balanced converter for less noise, higher dynamics, higher possible volume. The official 120dB dynamics range is really high quality.


The required PCB is bigger, with two power filter module on P3 and P4 connectors:

• PDF manual of expandable mixer with examples.

PCB sales of this project Module name Size (mm) Area (cm2) PDF SCH PCB image Tested Price (US$) Des. Sim.1 Full2 Sim.1 Full2 Man3 Power filter module 17x25 4 Yes Yes Yes - - No 3 11 Ask 1st mixer module 103x95 98 Yes Yes Yes - - No 15 24 Ask 2nd mixer module 51x93 47 Yes Yes Yes - - No 8 16 Ask 3rd mixer module 26x93 24 Yes Yes Yes - - No 5 13 Ask Line outout board 65x76 49 Yes Yes Yes - - No 9 16 Ask Headphone output board 56x71 40 Yes Yes Yes - - No 7 15 Ask Balanced headphone output board 58x105 61 Yes Yes Yes - - No 10 18 Ask Microphone preamp module V2 67x103 69 Yes Yes Yes Yes - No 11 19 Ask Microphone preamp module V3 67x103 69 Yes Yes Yes - - No 11 19 Ask 1 dual opamp preamp module 61x103 63 Yes Yes Yes - - No 10 18 Ask 2 single opamp preamp module 64x103 66 Yes Yes Yes Yes - No 11 19 Ask HQ 2 single opamp module 67x103 69 Yes Yes Yes - - No 11 19 Ask jFET guitar preamp module 65x102 66 Yes Yes Yes - - No 11 19 Ask Switch module 18x34 6 Yes Yes Yes Yes - No 3 11 Ask Simple Power supply 121x57 69 Yes Yes Yes Yes - No 11 20 Ask Power supply with 48V phantom 168x89 150 Yes Yes Yes - - No 22 32 Ask How to order? Please read the rules carefully!

Modular audio mixer for 8 and 4 input channels

I uploaded two new PDF documents about my audio mixer projects (1 - 2). The circuit called "audio mixer" is really simple, the required preamplifiers are little harder, if you need poweramp and EQ the device will more harder. But already I have tested and passed preamplifier project with headphone amplifier. And I have two modular equalizers ready to build. So I need audio mixer to collect these circuits to the simplest solution.

As I wrote already I have two of audio mixer project, because first time I designed very simple, with 4 or 8 input channels only, with master volume and line two outputs only. This project contains 2 very simple mainboards for 4 and 8 channel inputs, two output panels, and preamplifiers as module. The preamplifiers for mixer is same as my first designs, but can be connected with 12 pin male connectors to selected mixer mainboard.

For example, here is the microphone preamplifier with INA217:


The "original" PCB for this device is here:


But for modular mixer I have to modify the board design, the input and power connectors are removed, and changed to P4 connector on the bottom of board:


These preamplifier modules are smaller than the original versions, and contains "power filter" circuits as module (P5 and P6 connector at upper board). The preamplifier modules can be connected to the mixer mainboards, any preamplifier can be connected to the any connector of the mixer. The distance between preamplifiers is 25mm. This is the reason, why I have to design new versions of PCB for circuit called "power filter". This module must be smaller than 25mm. I have 5 versions of this module, with several sizes. All my preamplifiers (mic preamp with INA217, stereo dual jFET preamp, Dual OpAmp, 2 versions of single OpAmp) re-designed for modular mixer system.

The picasa gallery:


For the simplest version of my mixer project I have two mainboards with connectors for preamps, outputs, power supply, and balanced inputs for microphones:


4 channel mainboard for 4 inputs and 2 outputs:

For this board required 2 "power filter" modules, 4 preamplifiers, 1 volume board, and 1 line output board.

For the board can be connected two output PCBs. The one is for the master volume:

This PCB must be soldered after the 4th preamplifier via P5 male connector. This board working as 2 separated volume potentiometer for left and right channel, and possible to use only one stereo potentiometer for both channels on the pins of P1.

The another output module made for 2 line level outputs:

This board must be soldered to the last connector of mixer board via P1 header. The line level circuit designed to the mainboard, so this PCB contains the connectors only. The board useful for:

• 2 6.3mm jack
• 1 6.3mm jack and 1 stereo RCA
• 1 6.3mm jack and 1 3.2mm jack
• 1 3.2mm jack and 1 stereo RCA

The main output of full mixer is connected to the mainboard. This is the output for equalizers, poweramps, headphone amps, etc....

I designed 8 channel mainboard:


This circuit is same as than the upper 4 channel design. But here is 8 connectors for input channels can be connected to preamplifiers. The two of output boards is same too. This board width is 25cm, I think this is something big, very hard to manufacture, this is the reason why i designed "expandable" version of my audio mixer with connectable small mainboards for more than 8 channel inputs.

PDF manuals for audio mixers:

• Simple 4 or 8 channel audio mixer
  
• Expandable, any number of channels audio mixer
  

PCB sales of this project Module name Size (mm) Area (cm2) PDF SCH PCB image Tested Price (US$) Des. Sim.1 Full2 Sim.1 Full2 Man3 Power filter module 17x25 4 Yes Yes Yes - - No 3 11 Ask 4 channel mixer mainboard 149x84 125 Yes Yes Yes - - No 19 28 Ask 8 channel mixer mainboard 240x80 192 Yes Yes Yes - - No 27 36 Ask I/O board 37x60 22 Yes Yes Yes - - No 5 12 Ask 2 Potmeter board 31x62 19 Yes Yes Yes - - No 5 12 Ask Microphone preamp module V2 67x103 69 Yes Yes Yes Yes - No 11 19 Ask Microphone preamp module V3 67x103 69 Yes Yes Yes - - No 11 19 Ask 1 dual opamp preamp module 61x103 63 Yes Yes Yes - - No 10 18 Ask 2 single opamp preamp module 64x103 66 Yes Yes Yes Yes - No 11 19 Ask HQ 2 single opamp module 67x103 69 Yes Yes Yes - - No 11 19 Ask jFET guitar preamp module 65x102 66 Yes Yes Yes - - No 11 19 Ask Switch module 18x34 6 Yes Yes Yes Yes - No 3 11 Ask Simple Power supply 121x57 69 Yes Yes Yes Yes - No 11 20 Ask Power supply with 48V phantom 168x89 150 Yes Yes Yes - - No 22 32 Ask How to order? Please read the rules carefully!

8 channel mainboard for modular audio mixer

I working on the PDF doc of the modular audio mixer project, but the PCB design is ready to try. This project is same as like the preamplifier project, but the preamplifiers connecting with 12 pins connectors to the mainboard of mixer circuit. First time, I made 4 channel mainboard only, but now I designed new PCB board for 8 channel audio mixer. This new mainboard is bigger, the width is 25cm. This is maximum size what I can finis with my homemade PCB creation method. In the future I will done new PCB design with 4 channel PCB with connectors to 8, 12 or 16 channel mixers.

The 8 channel mainboard:


The 8 connector on the board is for preamplifiers. The last 2 is one for master potentiometers, the another one is for 2 stereo line outputs.

PCB sales of this project Module name Size (mm) Area (cm2) PDF SCH PCB image Tested Price (US$) Des. Sim.1 Full2 Sim.1 Full2 Man3 Power filter module 17x25 4 Yes Yes Yes - - No 3 11 Ask 4 channel mixer mainboard 149x84 125 Yes Yes Yes - - No 19 28 Ask 8 channel mixer mainboard 240x80 192 Yes Yes Yes - - No 27 36 Ask I/O board 37x60 22 Yes Yes Yes - - No 5 12 Ask 2 Potmeter board 31x62 19 Yes Yes Yes - - No 5 12 Ask Microphone preamp module V2 67x103 69 Yes Yes Yes Yes - No 11 19 Ask Microphone preamp module V3 67x103 69 Yes Yes Yes - - No 11 19 Ask 1 dual opamp preamp module 61x103 63 Yes Yes Yes - - No 10 18 Ask 2 single opamp preamp module 64x103 66 Yes Yes Yes Yes - No 11 19 Ask HQ 2 single opamp module 67x103 69 Yes Yes Yes - - No 11 19 Ask jFET guitar preamp module 65x102 66 Yes Yes Yes - - No 11 19 Ask Switch module 18x34 6 Yes Yes Yes Yes - No 3 11 Ask Simple Power supply 121x57 69 Yes Yes Yes Yes - No 11 20 Ask Power supply with 48V phantom 168x89 150 Yes Yes Yes - - No 22 32 Ask How to order? Please read the rules carefully!

Preamplifiers

I finished two of my new projects with preamplifiers. One of them contains independent preamplifier schematics, another one is an audio mixer with modular system where the preamplifier-modules have to be connected to the mainboard.

The simplest preamplifier with very high gain contains only 1 dual opamp. The sound quality depend on the amplifier circuit. Recommended to try the PCB with TL072, NE5532, or LT1124. Maybe the maximum gain will lower with better quality circuits, but the noise and the sound quality will better with NExxxx or LTxxxx dual operational amplifiers. The board of this schematic contains potentiometers for gain and volume adjustment, and 6,3 mm stereo jack input. Stereo circuit, like all others except microphone preamp. The board contains all required potentiometers, jack input, and two switches for stereo/mono and true-bypass. The switches have to be soldered to the small PCB with 12 pins "L" connector. This switch-board have to be connected to the preamplifier's PCB if required, if not, just wire the required pins of the connector on the preamp-board to ignore these switches. This very simple schematic have very big gain, but for microphone is not enough, for guitars too much. The sound of circuit with TL072 dual opamp is good for mixed music, but not for instruments like guitar or guitar effect. This is the reason why I recommended for home music listening. The "P1" connector on board is option for LED output to indicate if something connected to the jack-input.

Schematic:


PCB:


The second version of above schematic with two single operational amplifier instead of one dual:

This PCB is bigger, but very good solution for single operational amplifiers. The ultra low noise single OpAmps are not cheaper, but easier to find than dual. LF356, OPAxxx, LT1028, LT1115 (instead of dual LT1124) are the alternatives for better solutions than the cheapest TL071. The board contains one "power filter" circuit to reduce the noise of power supply.

Finally I have version no.3 for the Opamp solutions. The stereo circuit contains 2 single Opamps instead of one dual like above, but two power filter circuits included, one-one for both operation amplifiers. This solution is better for ultra low noise circuits like LT1028 or LT11115.


The small circuit contains switches:

This circuit contains 3 switches, but SW1 and SW2 are same. Only the place of these parts are different. If required only one switch, use SW3 only.

The PCB of switches:

This really small board required for all preamplifiers, except Dual-jFET preamplifier. If the switches are not required, just wire the correct pins of the P1 connector on the amplifier's board.

The dual-jFET preamplifier.

This is my favorite schematic for guitars or guitar-effects. The circuit contains one dual jFET for stereo input. No noise, good dynamics, warm sound. No symmetrical power required, therefore the power filter is smaller and simpler. The gain and volume potentiometers, and the stereo jack input connected to the PCB. The maximum gain is lower than the Opamp preamplifier's, but enough for guitars, guitar effects, and keyboards, or another instruments, except microphones.

See the schematic:


PCB:

This PCB have no bypass and stereo/mono switches. Maybe later will be included. The originally planned part 2N3958 Dual jFET is not available now, but any low frequency dual N-channel jFET compatible with this solution. Here is the table to find another dual jFET.

The next schematic is a microphone preamplifier with very cheap and good quality operational amplifier INA217. This is the recommended application schematic of this integrated instrument preamplifier. The PCB contains two mono potentiometers for gain and volume, and one 6,3mm jack input for unbalanced inputs like guitars. The switch-module contains only one switch to select between unbalanced/balanced inputs. The unbalanced input is the 6,3 jack, the balanced have 3 pins connector, and external XLR input required. For 48V phantom power required an independent external switch to the case if you want to use condenser microphones.

Very cheap and good quality circuit. No noise, no feedback, very high gain, good dynamics. Compared to cheap Phonix mixer, this circuit was much better with Sennheiser and Behringer dynamic vocal microphones. The 48V input for phantom power included to the PCB but power supply required for this feature. Unbalanced to balanced converter circuit included after jack input to the board. This is cheap and simple converter, but with the recommendation of Jensen. Later will be changed this converter to better one. The PCB contains 3 integrated circuits, but one power filter circuit included.

The PCB:


The PCBs of these preamplifier circuits drilled with same positions on the bottom. With these holes possible to fix to the case of mixer or preamplifiers. Later, all of these preamplifiers modified to module of audio mixer. The inputs, outputs, and powers wired to the pins of connectors.

Finally here is the recommended +-15V power supply:


PCB:


The PDF about preamplifier projects.

As I posted, all preamplifiers converted to module of audio mixer with 12 pins connectors. With these connectors the preaplifiers can be connected to the mainboards of mixer. All of the power filter circuits connected as module to the new PCB of preamp-modules. The mixer-mainboard contains only mixing circuits and 2 stereo line outputs:


Gallery about preamplifiers:



Picasa gallery about modular mixer:

PCB sales of this project Module name Size (mm) Area (cm2) PDF SCH PCB image Tested Price (US$) Des. Sim.1 Full2 Sim.1 Full2 Man3 Microphone preamp V:2 130x105 137 Yes Yes Yes Yes - No 20 30 Ask 1 dual opamp preamp 95x104 99 Yes Yes Yes Yes - No 15 24 Ask 2 single opamp preamp 89x110 98 Yes Yes Yes Yes - No 15 24 Ask HQ 2 single opamp 105x112 118 Yes Yes Yes - - No 18 27 Ask jFET guitar preamp 70x108 76 Yes Yes Yes Yes - No 12 20 Ask Switch module 18x34 6 Yes Yes Yes Yes - No 3 11 Ask Simple Power supply 121x57 69 Yes Yes Yes Yes - No 11 20 Ask Power supply with 48V phantom 168x89 150 Yes Yes Yes - - No 22 32 Ask How to order? Please read the rules carefully!