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Old 25th March 2004, 04:05 PM   #1
lohk is offline lohk  Europe
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Default my new chip amp version

My last chip amp is again a non-inverted version (more stable and better sounding than the inverted version IMO) with a different psu with eight secondaries. It otherwise uses the minimum amount of parts and is therefore not recommended for beginners (for a number of well known reasons).
I therefore do not show a schematic diagram here - but it is not necessary anyway.

In brief (non-inverted amp):
OP: LM3875
Cin: none
Rin: 150R
Rin_ground: 22k
Rnfb: 22k
Rnfb_ground: 680R
C_ground: none
Zobel: none
PSU: 2 x 1000yF FRAKO

All resistors are subminiature carbon resistors (best sound so far, I never tried Rikens and the like because I think that the amp must sound good also with "normal" parts), the Rnfb is soldered directly to the chip, all other parts p2p to the chip, no PCB of course, one star ground between the psu caps.
The amp uses four torrodial transformers (Avel Lindberg, two for each channel) with 2 x 15V / 50VA each, which are wired for full wave rectification (like Naim does) with 4 double schottky diodes. Lots of cables, which in fact hide all other electronics.
A preamp is not necessary at all (with my NAC42.5 it actually sounds worse), so I use a "passsive pre", with 2 x 20k carbon potentiomenters in shunt (4k5 and 20k pot) configuration.
The two diodes and the chip are screwed to a small heatsink which forms part of the "case", the whole amp is very small... (actually only 6 x 6 x 20 cm with heatsinks and lots of air in between, without the transformers of course).
The case actually consists of two heatsinks with horizontal finns and a wooden front and back of oiled multiplex, glued together with neopren glue. It normally has a loosly fitted in oiled cork cover and bottom.
The transformers, which can be seen behind the amp, are temporarly mounted on a multiplex board, but will later be mounted upright in a dedicated box when the amp will be finished.

This technology continues to blow my mind! How can an amp sound so good with a chip and weak power supply like this? It definitely sounds better with the smaller caps! And with carbon resistors!
Now most of you have made similar experiences anyway.

This is by far the best sounding chip amp I have ever made.
It sounds fast and full, with lots of bass, it drives my not very sensitive speakers with such an ease, it is amazing! There is much soundstage AND musicality, the PRAT factor is definitely there. Ok, I really do no know if they sound better than my Naim clones at the end of the day, but who cares with amps which are so easy and cheaply to make. The amp is completely noise and humfree, I almost cannot hear if it is switched on by listening very closely to the tweeter, no switch-in thump etc. I cannot say how loud it will go before clipping...
Inspite of different experiences the mentioned chip amp version has NO OFFSET like its predecessors, although there are no caps to prevent that. The reason? The topology overall, I suppose.

This amp is like a gracile dancer, it can start and stop on the spot, energy flows though it in a very seemless way, easy, effortless, quick.

Have a look here http://www.8ung.at/alohka/alohka_new_chipamp.htm


Klaus
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Old 26th March 2004, 08:26 AM   #2
Ropie is offline Ropie  United Kingdom
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Very nice looking amp! The heatsinks you are using look quite hefty - do they get warm at all?

I had similar experiences with my first inverted gainclone but am planning to try the non-inverted version next. Currently I have a valve buffered version which is a significant improvement over the non-buffered amp.

Do you have the amp on any feet? Have you played around with different feet configurations and noticed any effect on the sound? This is often cited as having a big effect on the sound quality of a gainclone.
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Old 26th March 2004, 02:40 PM   #3
lohk is offline lohk  Europe
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Thanks for the reply.

The amp sits on four small roundheaded M3 screws in the moment, two underneath the heatsink of each side/channel, lateron I will substitute one with a cone and the other one with a rubber pad maybe or something like it. I personally think that this talking about different feet is a mixed bag. It maybe more important when the transformers are incorporated with the amp, in my case I think it should be enough to have a sensible rigid/damped structure. But I will listen to the difference between different feet.
The heatsinks can get warm, you have to consider the miniature size of the amp. Each heatsink is 6x4x9cm exactly (to correct my first post). That is not very big. During normal use the heatsinks are quite cool, they only get hot when I push the amp heavily. And this little beast can play very loud, although it uses only 15V secondaries.
Valve buffering is considered as a next step for a new gainclone. I already have another new goldpin E88CC for this job. But I think it makes much sense to get as much quality out of the basic circuit first.

Klaus
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Old 26th March 2004, 07:53 PM   #4
Ropie is offline Ropie  United Kingdom
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Quote:
[i]Valve buffering is considered as a next step for a new gainclone. I already have another new goldpin E88CC for this job. But I think it makes much sense to get as much quality out of the basic circuit first.

Agreed
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