About the top of my new guitar amplifier design

This project stopped for years, but the wood case of my new guitar amplifier is ready. The rason of long time delay while I did nothing is that I used my old amplifiers. One is my previous DIY guitar amp have been disasembled, and I have a Carlsbro GLX100 amplifier with Eminence ReadCoat speaker, whats are very good solutions. This is the reason why I don't hurry with my new idea, but now I take apart my old DIY amplifier and the power supply have been moved to the new wood-case.

My old rack mounted amplifier was stereo for guitar, because I  using multieffect. I have Boss GT8, where not only the effects have stereo outputs, this is dual guitar effect, where I can use different amplifiers for left and right channels. This is the reason, why I have combo design but with two speakers for stereo solution:

After the wood case, I have metal cases for electronic circuits:

This is the back of the wood case:

....now without the middle slat because I need space to fix the speakers.

 The power supply built to the bottom of wood-case. I know that all other industrial solution have same case with other circuits on the top, but now I have more space on the top for amplifiers and equalizers. I think the larger distance between transformer and circuits have benefits:

The design of wood case was realy good, I made model of paper, and got to the professional carpenter, who manufactured and assembled:

The bottom of this amplifier is done, this is the power supply. From the power supply the required voltages wired to the top of amplifier case:

Here I have +/- 40V for poweramps, +/-18V for preamps, +24V for LED-s relays, and coolers.

But the most important question is what I have on the top

Because the power supply built to the bottom, I have more space on the top. The power of toroid transformer is 1200VA. I want to place guitar preamplifiers and amplifier (stereo for multieffect), and one more stereo poweramp for additional cabinets for vocal or keyboards. I need parametric equalizer, if I have enough space on the top-case, separated for left and right channels. I need audio mixer with mic preamps for vocal or another audio sources with headphone and line outputs.


But the most important question is, what will be the power amplifier on the top case. On this time, I want to build some digital class-D poweramp maybe for vocal only not for guitar. I have PWM power bridges, what is 1x315W, and I have 2x210W TAS chips:

1x350W with TAS5261 is would be enough for guitar, but this power available for 4 Ohm only. The guitar speakers are 8 or 16 Ohms. On 8 Ohm this chip have 125W output power. Now I think, for guitar (where the speaker is 8 Ohm) I will use bridged TDA7293 chips, where I got 200-220W for 8 Ohm speakers. This chip is very popular on guitar amplifier market, Marshall, Carlsbro using this solution. And for example the Crate Powerblock is PWM poweramp.


Because the vocal or additional guitar speakers have less than 8 Ohm impedance, the PWM chip is good solution. The benefit of PWM chip is the very high efficiency. But the disadvantage is the very small size of chip, TAS5261 have digital PWM inputs only, so I need PWM modulator like TAS5028 for example. TAS5028 is more small than TAS5261, so more harder to build the PCB. Finally the PWM modulators have digital inputs, so I need A/D converter for analog input devices.

I'm not sure that I can build complex design with these very small chips. The another detriment is that the PWM modulator and the A/D converter need 3.3V only, what is used for DVD players orfor computer soundcards. I don't think that the vocal or guitar amplifier design is same as like the home theater systems. The power stage of this idea need only non-symmetrical power voltage, +50V. I have +/-40V for TDA bridged solution, what is much better. I can bridged the TDA chips, but I can't bridge TAS power chips, because this is already internally bridged. At he moment I think the bridged TDA circuits are better and easier to build for guitar and vocal.

The power supply moved to new amp

The power supply of my stereo guitar amp is moved to the new place and ready. The old circuits can be fixed to the new "box", what is smaller but higher. The toroid transformer is 1200VA, with 4x15V, 4x10V AC for high power circuits, 2x15V AC for small power circuits, 1x18V AC for relay and LED. The DC and 24V AC voltages wired to the top of combo with 5 point cable, the +/-41V DC power for amplifier wired with speakon connector to the top of amplifier case:

TDA7293 for more than 300W (500-600-700W)

My previous post, where I wrote about the TDA7294 and 7293 modular amplifier design, I uploaded a table about the output powers:



By this table, for the maximum 300W amplifier required:

• 1 Main module
  
• 2 Parallel module
  
• 1 Bridge module
  
• 2 Parallel module
  
• Speaker protection with FAN controller
  

This amplifier required 6 pcs TDA7293, but for stereo device 12 pcs needed. The "chip" is really low cost, not too much for 300W amplifier.

But not only 2 parallel chips can be inserted after the main and bridged module. Schematics with 3 parallel modules (after main and bridged modules too) may possible. If the possible output current of one chip is 2.5A, with 4 chips (one main or bridged, and 3-3 paralleled modules after main and bridge circuits) is 4x2.5=10A. With +-40V (80V) the result is 800W like in this schematic. But this is not true. One chip is 75W, 8x75=600W maximum output power.

The official guitar amplifiers (Marshall, Carlsbro, ...) using one TDA729x chips always says 100W output powers what is not true. But for high output power around 550...600W not impossible. For this amplifier required good speaker protection and fan controller and very good power supply with kW-s of transformer and high values of capacitors.

See also:

• Failure in the official datasheet of TDA7293
• New PWM Fan controller with speaker protection
• Modular TDA7293 bridge/parallel amplifier
• PDF manual for TDA7293 amplifiers

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 TDA 7293 main module 59x65 38 Yes Yes Yes - - No 7 15 Ask TDA 7293 bridge module 44x50 22 Yes Yes Yes - - No 5 12 Ask TDA 7293 parallel module 41x47 19 Yes Yes Yes - - No 5 12 Ask Dual speaker protection 51x42 21 Yes Yes Yes - - No 5 12 Ask PWM Fan controller V:1 70x57 40 Yes Yes Yes - - No 7 15 Ask PWM Fan controller V:2 56x57 32 Yes Yes Yes - - No 6 14 Ask Stereo bridged TDA7294 amp (2x200W + speaker protection) 77x184 142 Yes Yes Yes Yes - Yes 21 - Ask Power supply for poweramps 135x98 132 Yes Yes Yes Yes - Yes 19 - Ask Soft start for toroid transformers 67x67 45 Yes Yes Yes Yes - Yes 8 - 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!