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Thinking DIY: DX-AMP aka Destroyer X Audio Power Amplifier

Wharfedale EVO 4.1 4.2 Speakers

omishra

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Hello everybody.

This discussion is to replace - discrete, solid state, medium power and transistor based power amp module. I already have +/-33V, 200VA PS with output protection relay and chassis in place. Dimension of PCB < 80mm * 80mm

Since many years I was using power amplifier designed with HEXFET. It was running with 100mA quotient current and used for moderate power levels ~20W/ch. This was sounding very nice but somehow I could not avoid problem of thermal runaway. International Rectifier (Manufacturer of HEXFET) does not recommend using these devices for audio power output device. Same thing mentioned at DIYAudio discussions and Rod-Elliot website. MOSFET/HEXFET have positive thermal coefficient against normal negative thermal coefficient of BJT/semiconductors in general.
ref - International Rectifier - HEXFET Power MOSFET Product Information
ref - Using HEXFETs in High Fidelity Audio

Eventually right channel of my power amp died couple of days back and I am now using standby t-amp with limited power of 10W/ch. I can add temp compensation to existing kit but now thinking to go away from HEXFET. That why looking at low quotient current (30-50mA) and no cross over distortion.

After looking into many designs, I came across this Destroyer x Amplifier...Dx amp...my amplifier - diyAudio - designed by forum member Carlos and few suggestions on forum.

Schematic and original work here -
Greg's Web Site

One ebay clone (search DX-AMP in consumer electronics section) TOSHIBA A1943/C5200 DX-AMP Power amplifier Kit 2-CH | eBay

My plan is to buy ready-made kit or ebay clone and upgrade components if not satisfied.

If anybody has experience or thought with this particular kit then please narrate here.

Thanking in advance,
 

kanwar

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Hello everybody.
Since many years I was using power amplifier designed with HEXFET. It was running with 100mA quotient current and used for moderate power levels ~20W/ch. This was sounding very nice but somehow I could not avoid problem of thermal runaway. International Rectifier (Manufacturer of HEXFET) does not recommend using these devices for audio power output device. Same thing mentioned at DIYAudio discussions and Rod-Elliot website. MOSFET/HEXFET have positive thermal coefficient against normal negative thermal coefficient of BJT/semiconductors in general.

Thanking in advance,

Well don't blame HEXFETs for thermal runaway, if done correctly they are hard to beat in performance. Elektor designs such as by T.Giesberts using Hexfets are flawed in many ways and have associated compensation difficulties in stability for Diyers. People try to drive HEXFETs like a bipolar and end up with stability issues.:D

Carlos's amp is a bipolar transistor based one similar to Aspen kit amps. Its a basic and simple amp good for Diyers. Easy to setup and construct. Try the Ebay kit if you want to go for easy way to setup.



Kanwar
 

omishra

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Carlos's amp is a bipolar transistor based one similar to Aspen kit amps. Its a basic and simple amp good for Diyers. Easy to setup and construct. Try the Ebay kit if you want to go for easy way to setup.
BTW can you please point out few other DIY amps which sound good, for internal home music listening and difficult setup as well.

Update:
I repaired existing circuit.
Lowered gain of my original HEXFET amp and found the issue. It was not thermal runaway but bad preset made changes to quotient current which blown output devices. Now both channels are running fine and musical. Effect of voltage gain reduction is - earlier 0.7V p-p was giving 42Vp-p output, now 1Vp-p gives the same. So usual listening position on dial moved from 9'0 clock position to 10-11'o position.
 
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kanwar

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BTW can you please point out few other DIY amps which sound good, for internal home music listening and difficult setup as well.

To name a few:-

FC-100 by Roender,[Its a folded cascode CCS loaded frontend and CFP drivers]

Leach double barrel amp,[Cascode loading and series output stage]


NVMOS by myself[Its an N-channel Mosfet amp with a unique Push pull gate drive]


Update:
I repaired existing circuit.
Lowered gain of my original HEXFET amp and found the issue. It was not thermal runaway but bad preset made changes to quotient current which blown output devices. Now both channels are running fine and musical. Effect of voltage gain reduction is - earlier 0.7V p-p was giving 42Vp-p output, now 1Vp-p gives the same. So usual listening position on dial moved from 9'0 clock position to 10-11'o position.

Better substitute the preset with a fixed value resistor combination in order to ensure stability in long run, presets are prone to failure.

Kanwar
 

omishra

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To name a few:-
FC-100 by Roender,[Its a folded cascode CCS loaded frontend and CFP drivers]
Leach double barrel amp,[Cascode loading and series output stage]
NVMOS by myself[Its an N-channel Mosfet amp with a unique Push pull gate drive]
Can you please post some links, including the last one.
Better substitute the preset with a fixed value resistor combination in order to ensure stability in long run, presets are prone to failure.
That would be better, but I am not sure if somehow re-tune will require or not. Now thinking of designing new pcb of same size inclusive of Vgs temp compensator.
 

kanwar

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