ThermalTrak+TMC amp

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All PCBs are ready. Now is time to start some measurements, but first I will listen some music over this PCBs connected together. ThermalTrak bias current is very stable from 25 degree to 60 degree centigrade. I will show a result after I finish test measurements. For now here are all needed PCBs.
dado
 

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Gad,
the thickness of the L angle for connecting to the heatsink is too thin.
4 devices can dissipate a lot of heat.
Try for at least 50% thicker and if you can source it, double the thickness.

The two device version is possibly OK.

Thanks Andrew, the thickness is 3 mm and I never have any problem with heat transfer to the heatsink. By the way I could not find thicker alumina here in Zagreb.
Two device version is the Power Suply Regulator, a kind of a capacitor multiplier.
dado
 
Listening

Both channels are playing now. It is to early to final comment of the sound, but I like it, very punchy bass well controlled clean mid and heights.
I wanted very well thermal control of the output stage bias. I divided this in two part. First the drivers are situated on separate heatsink together with the bias transistor (BD139). The bias spreader use ThermalTrak diodes connected in the bias transistor emitter. In this way I tried to separate thermal drift of the drivers from the output ThermalTrak transistors. The bias spreader transistor it self has to compensate thermal drift of the drivers and ThermaTrak diodes have to compensate thermal drift of the ThermalTrak output transistor only.
And I think the result is quite good. In first seconds after power on the bias current will go up from 60 mA (per output pair) to 130 mA and after the driver temperature have settled, temperature increment of the output transistor will no influences the bias current. It stays at between 125 mA to 130 mA. I was measuring the voltage drop on the output transistors emitter resistor and it stay quite firmly at 20 mV.
Next, I m going to do some measurements with sinus, triangle and square waves. I will insert different value capacitors parallel to the dummy load.
Dado
 

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Congratulations!
the sound is better than from your JHLs?

Not sure yet, this amp has to play some time as electrolytic caps need a time to reform(thay stayed in my drawer) One think is certain, bass is more puchy and better controled.
JLH amp realy a treasure (after my modest improvement) and I like it. It uses original Hitachi lateral, I am not sure how it will work with other producers lateral.
dado
 
TT-triple

I've been building the amp in parallel with Dadod, on my side of the Atlantic. He has been very helpful answering my questions and guiding me through my first fully discrete DIY amp. He was kind enough to send me the amplifier PCBs and heatsinks (not available in the USA).

Many thanks, Dadod!

So far I've constructed the power supply, DC regualtor/speaker protection, and almost have one channel complete. After I have the first channel operational, I will begin the second.

I made a parts list, which I've shared on Google Docs.

A few more steps I should be ready for the light bulb test.

Here are a few photos:
 

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Last edited:
Some measuremts here. Sinus 1kHz and 20kHz at a level just below the clipping.
Next are square waves 10kHz and 20kHz on the 8 ohm load.
dado
 

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Next is 1uF parallel to the 8 ohm load at 20kHz. Durin the test I overloaded the amp and the power supply protection switched off the power. Reset was done by switch off and after some seconds switch on again, and all worked.
dado
 

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meaurements

Hi, Dado.

The amp is sounding worderful: punchy bass, smooth mids, and aggressive highs. I'm looking forward to completing the second channel.

A few questions in regard to the TT-Triple:
  1. Do you happen to know the input sensitivity?
  2. Have you been able to measure real-world THD?
Also, an unrelated observation/question not specific to this amplifier. On most of my amps, I can hear very low level Johnson Noise (white noise) with no input signal, and my ear pressed up to the speaker. I'm not sure if this is from the speakers themselves, noise from amplifier RC components, or a combination. It's definitely not a ground loop, but low volume white noise. My living space ambient noise is MUCH louder, but I'm just curious about the source of the white noise.....

With headphones I don't notice white noise with line level portable media players and computer audio output.

/Mason
 
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