PWM amplifier 1 - The PWM modulator design III.

On my previous analysis, I didn't pleased with the quality of triangle signal, but a little modification made better result. In the second article, the triangle (and the PWM) signal is better, but not perfect. This is the reason why I simulated the modulator design with another oscillator circuit.



The design is very simple, simplest then the previous signal generator version. This new contains simple CMOS oscillator. The design is small, simple, and the output signal is perfect. The duty-cycle is always 50%, the amplitude of square signal is 5...15V if required. The frequency setting is very easy, on 10 MHz the square signal is really nice.

The red is the square output of CMOS circuit, the green is the triangle signal.

The triangle and the square signal is much better compared to the analog oscillator circuit.

This is the schematic, the difference between R1 and R2 is 10x, the capacitor can be very small value, the frequency is very stable.

Unfortunately, the upper ideal stage will be wrong if I continues the design with comparator circuit on the simulation. (See the schematic, I did not continued the triangle output to the comparator input). If the triangle signal after CMOS (or TTL) circuit wired to the comparator, the signal will be non-usable:

The square signal stay good, but the triangle signal going wrong on the simulation.

 The usefulness triangle signal.

I did nothing else, I just continued the signal with comparator.

The upper problem can be solved with a small modification, see the images and the power source of the comparator on the schematic:

On the circuit, I using independent DC power source for comparator chip only. After I getting back the nice signals, but with this design the comparator doesn't made PWM signal from sources. If I used common ground, the comparator started to work, but the triangle (and the PWM) signal is going wrong again:

Transient analysis result when the CMOS oscillator and the comparator have common ground:

At this moment I don't know how to solve the problem on the simulator. I wonder, (and not sure) about the result of real circuit. The simulation is usefulness, but the oscillator design is better and simpler before using comparator. So at this moment, the analog oscillator design is much better than this new one.

PWM amplifier 1 - The PWM modulator design II.

I have successfully cleared the last design example of PWM modulator circuit. This PWM modulator will be used before TAS H-bridge chip. In this article, I don't really like the signal at the end, and I made mistakes about power sources (with Zener diodes) on the last simulation schematic. Not too much, but I modified the design, and I got better result. I deleted the dead-time logic, because for the TAS chip not required, the soft start only is easier. At the end of this newer design, I got nice signal from both TTL and CMOS outputs and comparator without dead-time logic. See images.

In this image the green is the triangle signal, the red is 10 kHz sinus, a yellow is the PWM output on the CMOS 4009 inverter.

I know, that not really important, but how I know about the quality of modulated PWM signal? I have to convert back to the original with RLC network. This is the blue line.

I changed the CMOS 4009 (15V power for comparator and CMOS circuit) to TTL 7414 (5V power for comparator and TTL circuit). The TTL output is the yellow line.

 The decoded result at the end of TTL circuit is the blue signal.

I made small modifications on the circuit around the comparator. I changed Z diodes DC power sources, the output of the comprator continued with only one TTL or CMOS gate (inverter). I analyzed the PWM signal after the TTL/CMOS chip, but the output of comparator is really good too with this schematic:

PWM amplifier 1 - The PWM modulator design I.

Newly detected TAS5630 chip can solve my problems about the PWM amplifier. This chip have analog inputs, the package contains all required parts (A/D converter, PWM modulator), and the parallel mode is possible if less than 4 Ohm output impedance required. with this package we have one paralleled mono or one stereo poweramp with analog input.

But I have TAS5261 chips, without analog input. For this design required TAS55xx PWM modulators and analog/digital converters. These chips recommended for home DVD  players, the power supply is 3.3 volts only. I don't think that this solution is ideal for instrument amplification.

In this post, I writing about the method and simulation of analog PWM modulator.

First I need a triangle function generator. I found too much... The clock of PWM input TAS chip is 192-384 kHz, what is understandable if digital chips placed before chip. For this frequency, not too easy to find triangle signal generator with very good output.

Can be found one-chip function generators. One of them is LM566 (with this chip I found a schematic) not available here and now, or we can use XR2206 or ICL8038 chips. These chips are very simple solutions for triangle output, maybe I will try some of them. The maximum frequency on the datasheet is 0.5MHz, typical is 1MHz, but the 8038 have 300kHz maximum. I have no experiences with these function generator chips, so I don't know about the output quality. This is the reason, why I seek discreet analog function generator for triangle output. The another reason, is, function generator chips are not available on Multisim.


The first tryouts I have no success:

This function generator promised for perfect output, but the triangle with 20 kHz only is really bad. So I don't need to try this design for 200-300 kHz.

I tried more triangle generators with op-amps, but the output is not good enough. Finally I found a really good analog triangle generator with nice triangle and square outputs. This circuit can be used up to 4MHz what is more than enough.

I have good result on 300kHz:

See the simulation output, this is 235 kHz. Very easy to set the frequency and duty cycle.

I tested this discreet (but easy to set) schematic  on higher frequency. Here ate the test results:

1.3 MHz:

2MHz:

3.5 MHz:

6 MHz:

I think, if the upper schematic is good enough on 2-4 MHz, then this is good for around 300 kHz only.

The triangle output of this circuit wired to the fast comparator. the most of comparators doesn't worked on Multisim for me, but finally I found one what is very good for output simulation:
 

Example about the signals in the circuit:

The purple line is the triangle output of function generator, the green is the part of 1kHz sinus (audio) input, the red is the TTL PWM modulated square with variable duty cycle.

In this image can be seen how duty cycle modulated by the sinus input signal:

Continued the circuit simulation, the next is the comparator. This part AD8611 is good on Multisim, but I think another comparator (for example LM311) is good on real life too. The triangle signal and the audio (sinus) input have to be connected to the comparator's inputs.

The most important question is, the quality of the PWM modulated output. What I get back, if the PWM modulated square signal converted back to the original sinus wave. The quality of this method cannot seen by the quality of the PWM modulated output. See the image:

The green line is the original audio sine wave signal. I have to get back this wave from the PWM outputs. The dark-red is the (good) result if the PWM output converted back to the original sine. What is the blue line, I will tell you soon....

After the comparator chip, I put TTL logic. This logic made soft start while the triangle generator up, and disabled the input of TAS H-bridge. This method made inverted and non-inverted PWM outputs. Finally this is the "deat time" logic. The TAS5261 contains "dead time" logic, and the most if comparators have inverted and non-inverted outputs. This TTL logic required, if the output of PWM amplifier is simple MOSFETs, not H-bridge chips with internal logic what I want to use.

......the blue line (what is really wrong and distorted) is the converted output of TTL chips.

Here are the signals in this design: The sine is 20 kHz now, the blue line is the triangle signal on 235 kHz, the red line is the TTL PWM output, the tall brown line is the output of comparator. The result is much better on the comparator output.

After simulation results I have many problems.

The first question is about the precision of simulation. How about the simulation and the  reality, whats about the differences, depending on the PCB design and the quality of parts.

After these PWM modulated square waves, I have to put TAS H-bridhe chips, and I can use these outputs for audio. Maybe this method have good result, but maybe not. Maybe the TTL outputs (what is really wrong after decoding on the simulation result) good enough for discreet MOSFET drivers. Finally I have to test the DC offset of comparator inputs and outputs, and the linear frequency range of the decoded output. These solutions is on the next post.

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:

• More unbalanced to balanced converters
• Simulation of unbalanced-balanced converter
• 2 input headphone amplifier
• Headphone amplifier with TPA6120
  

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 4 input headphone amplifier 189x112 212 No Yes Yes - - No 30 39 Ask How to order? Please read the rules carefully!

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.

Modular TDA7293 bridge/parallel amplifier

I finished the project of the most simplest and cheaper modular instrument amplifier. The final amplifier have output power between 70W and 300W for 4 and 8 ohm speakers. Three several modules required for this project if bridged and paralleled modes required. The 4th module is the speaker protection. The amplifier can be built as:

• Single amplifier with only one module with 1 TDA7293 or TDA7294 / channel
  
• Bridged amplifier with 2 modules / channel
  
• Paralleled amplifier with 2 modules / channel
  
• Combined bridged and paralleled with 4 modules / channel
  
• Paralleled simple or bridged amplifier, but with 2 paralleled module
  

The modules can be connected with 15 pin connectors instead of wires. The single, bridged, and paralleled amplifier modules are not same, one for the first and the most important "main" module, one for bridge connection, and one for parallel connection what can be used for both main and bridged modules. The last 4th module is the speaker protection, must be placed to the middle of stereo configuration between left and right channels.

The official datasheet contains all modes of TDA729x circuits. The TDA7294 is very cheap, but cannot use for paralleled mode, and no clipping led output. The recommended max. power supply voltage is +-40V. The TDA7293 have paralleled mode (where only the power stage works, the preamp stages off), the max. power supply voltage is +-47V, and clipping led output available. The maximum output power of one circuit is 70-75W of TDA7294, and about 80-100W of TDA7293.

The possible output powers of bridged application:


The V column is the power supply voltage, 1 means: 1 IC paralleled, 2 means: 2 IC paralleled with all others. Without superscripted number have no parallel connections, this is only bridged.

The possible output power with single (non bridged) application:

The V is the power supply voltage, 1 means: 1 IC paralleled, 2 means: 2 IC paralleled. Without superscripted number have no parallel connections.

The bridged or single version is very popular on "official" instrument amplifiers. Carlsbro GLX100, Marshall MG, and Marshall Mode Four contains TDA7293/7294 circuits. I using bridged application long time ago for stereo guitar amplifications and for microphones. This is more than enough for small rooms or rock clubs for live sessions with very good (for example Eminence) speakers.

The four modules (including speaker protection) can be connected by the 15 pin connectors soldered to the edge of the PCB. This is the method to build single, bridged, paralelled, bridged+paralleled, bridged+duble-paralleled, mono or stereo applications with very simple easy to build PCBs.

The first and the most important circuit is complete 70-75W amplifier:

This circuit always be the first of the complete amplifier configuration, which can be continued with parallel, bridge, or speaker protection module.

The PCB of main TDA module:


To the Conn2 on right edge can be connected another module for bridged or parallel application. It this one main module required (for 75W output power) then Conn2 can be used for speaker protection, but this is not required. The nother side have Conn4 connector for the second (right) channel is the setup is stereo. This Conn4 connector can be connected the speaker protection only. For example the simplest stereo setup is: 1 main module for left channel, 1 speaker protection, 1 main module for the right channel. Examples are on the PDF manual. The speaker protection will be protected bot left and right channels.

On this first PCB the Conn5 connector is the stereo audio level inputs, the right channel wired to the input of another main module on the right side of speaker protection. The output connector Conn6 is not stereo. This connector can be user for one channel only (the another output is on the second main module). The single setup uses Out+ and GND, the bridged setup uses Out+ and Out- for speaker connection.

The second circuit for bridge configuration:


And the bridge PCB:


The Conn4 connector of this bridge PCB can be used for the connection of first main circuit. This module can be continued by Conn5 connector with speaker protection (if the channel finalized) or with parallel module if more output current needed.

If the setup must be continued with parallel mode, here is the schematic:


PCB for parallel mode:


This is the simplest module, because the premaplifiers are off within the circuit, only the power FETs working. This mode controlled by Buffer Driver and Slave mode pins of TDA circuit. This module can be connected to the right side of main module, bridge module, or if required can be connected to the parallel module to duplicate the paralleled circuits within the application. The second parallel modules can be continued with speaker protection or with nothing only. The another edge of the speaker protection (if used) can be restart the full setup with main module for right channel.

The speaker protection:


And the PCB:


Here are the examples how to build complete amplifiers with several output powers with these four modules. The "Module 1" is always the first and always required main module, the "Module 2" is the optional bridge module, "Module 3" is the optional parallel module can be duplicated within the setup, and the 4th is the speaker protection.

The simplest mono setup (75W on 4 Ohm, with 8 Ohm about half):

1. Module 1
   
2. Speaker protection (optional)
   

Simple stereo setup (2x 75W on 4 Ohm, with 8 Ohm about half):

1. Module 1
   
2. Speaker protection (required)
   
3. Module 1

Mono bridged application (8 Ohm only, about 150W):

1. Module 1
   
2. Module 2
   
3. Speaker protection (optional)
   

Bridged stereo setup (8 Ohm only 2x150W)

1. Module 1
   
2. Module 2
   
3. Speaker protection
   
4. Module 1
   
5. Module 2
   

Mono paralleled setup (4 Ohm about 100W):

1. Module 1
   
2. Module 3
   
3. Speaker protection (optional)
   

Stereo paralleled setup (2 x 100W on 4 Ohm):

1. Module 1
2. Module 3
3. Speaker protection (required)
   
4. Module 1
   
5. Module 3
   

Mono bridged and paralleled (4 Ohm - 300W, 8 Ohm 200W):

1. Module 1
   
2. Module 3
3. Module 2
4. Module 3
   
5. Speaker protection (optional)
   

Stereo bridged + paralleled setup (About 2 x 300W on 4 Ohm):

1. Module 1
   
2. Module 3
   
3. Module 2
   
4. Module 3
   
5. Speaker protection
   
6. Module 1
   
7. Module 3
   
8. Module 2
   
9. Module 3
   

The parallel module can be connected to the first parallel module for duplication. This increases the maximum current, maybe smaller output impedance possible.

Doubled parallel bridge setup:

1. Module 1
   
2. Module 3
   
3. Module 3
   
4. Module 2
   
5. Module 3
   
6. Module 3
   

and the upper setup can be continued with speaker protection and the another edge of speaker protection can be repeated the same setup for right channel is stereo application required.

See also:

• Failure in the official datasheet of TDA7293
• TDA7293 for more than 300W
• New PWM Fan controller with speaker protection
• 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!

2 input headphone amplifier with TPA6120

I already designed circuit and 3 versions of PCB with TPA6120. I heard only good reviews about this circuit, this is the reason why I made new version again. In this board I want to use all features of this circuit with 2 inputs and one outputs placed to the PCB, with transformer. I want to use this device for my computer sound-card what is EMU1212m, this card shipped without headphone output (and without microphone input). But have very good sound quality, therefore I need this headphone amp.

Because I would like to use all possible features with all-in-one PCB:

• Small transformer placed to the PCB, with 2 independent symmetrical +/-15V outputs. This is because separated power possible for left and right channels.
  
• 2 inputs on the PCB with volume control and jack or RCA inputs.
• Master volume and output jack.
  
• Mini audio mixer after inputs.
• After the mixer, unbalanced/balanced converter.
  

With this board I can use the features of TPA6120.

The new schematic:


The transformer and the voltage regulators placed to the PCB, with two independent outputs with 4 regulator devices. With inputs, you can choose what you like, 2 pcs 6 .3mm jack, or stereo RCA. Maybe 1 jack and 1 RCA. The balanced converter make better quality and more volume.

This is the PCB:


The longer side of PCB is about 15cm. Around the inputs have something "chaos". You can choose between RCA and Jack inputs this is the reason why 2 footprints on one place, but the inputs have to be placed to the bottom side (must be soldered on the top) and the volume potentiometers placed to the top layer (must be soldered on the bottom). But I think this is no problem on assembly. Because the transformer is on the board, 230V must be connected to the header called "Conn2". The regulators on the edge of the board can be screw to the wall of case or to heatsink. 3 "power filter" circuits required as module for this board, one for mixer, 1-1 for left/right unbalanced/balanced converter.

See also:

• 4 input headphone amplifier with line output
• More unbalanced to balanced converters
• Simulation of unbalanced-balanced converter
• Headphone amplifier with TPA6120
  

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 2 input headphone amplifier 90x160 144 Yes Yes Yes - - No 21 31 Ask How to order? Please read the rules carefully!

Headphone amplifier with TPA6120

This is my first SMD circuit. The small size of SMD parts was my problem before. The opinions about TPA6120 is very good on all other related pages, the official datasheet is unbelievable. I have 5 pcs 6120 circuit, so I have to test it with my own PCBs.



The headphone circuit is very simple. With unbalanced balanced converter is much better, but in this first version this feature is missing from these PCB-s. I have design with unbalanced/balanced converter, but for modular mixer only. Now I posting about "independent" headphone amplifiers. Fortunately, this circuit is not the smallest SMD footprint. The distance between foots is 50 mill, the foot width is 20 mill. This size is no problem for homemade prototype.

The main IC is:


This chip have 20 "foots", but the half of these pins are not internally connected. On the bottom, small heatsink available, but this is not only heatsink, this is the GND as 21st pin. Footprint not available, have to be draw on the CAD software. The full circuit without dual power supply, and unbalanced/balanced converter is very simple:



These modifications possible:

• For both channels (left and right) have + and - inputs for balanced sources. This is optional,
  but maybe the result is better. On this schematic has no input for balanced sources.
• Separated dual power supplies possible for this one circuit. this is reduces the crosstalk between left and right channel. The dynamics of this circuit on the official datasheet is 120 dB, what is very good if true. Class D amplifier. I have "power filter" circuit to separate power sources of left and right channels, but I don`t want to use this for headphone amplifier because maybe the current source is not enough.
  

Therefore I have 3 versions of PCBs:

The first is the biggest one, to screw with another preamplifier circuits. The position of rear hole is the reason why this PCB so large:


If the same hole positions are not important between preamplifiers and the headphone amp, then here is the smaller PCB:


Finlay I have smaller. This PCB have separated inputs for balanced inputs of left and right channels, and inputs for left and right powers. this is the reason why volume potentiometer missing, and the power filter capacitors are too:


This is the smallest PCB, but possible to use after unbalanced/balanced converter and with separated dual power supply. But these solutions are required with another circuits.

6.3mm jack input soldered to all of these boards, the 1st and 2nd version of PCB have volume potentiometers too. This volume pot missing from the 3rd version, because the pot must be soldered before unbalanced/balanced converter. The TPA6120 circuit fitted to the bottom layer of all PCBs (this is the reason why this part mirrored), all another placed to to top.

See also:

• More unbalanced to balanced converters
• Simulation of unbalanced-balanced converter
• 2 input headphone amplifier
• 4 input headphone amplifier
  

PCB sales of this project Module name Size (mm) Area (cm2) PDF SCH PCB image Tested Price (US$) Des./3D Sim.1 Full2 Sim.1 Full2 Man3 TPA6120 headphone amp V:1 67x71 48 Yes Yes Yes - - No 8 16 Ask TPA6120 headphone amp V:2 55x71 39 Yes Yes Yes - - No 7 15 Ask TPA6120 headphone amp V:3 55x49 27 Yes Yes Yes - - No 6 13 Ask Power supply +/- 15V 212x57 69 - Yes Yes Yes - No 11 20 Ask How to order? Please read the rules carefully!