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Gainclones (c)

Andrew L Weekes

Andrew L Weekes

Reverse Engineer
Anyone built one, if so how did you find it?

What type did you build?

I've a couple of monoblocks in progress, as a work lunchtime filler project and as is the norm for me I've taken absolutely no notice of the consensus of opinion out there and decided to do it my own way ;)

Basically I'm building a pair of monoblocks, with exactly the same gain, input impedance and frequency response as my NAP150, such that I can drop them straight in and listen solely to the underlying topology with hopefully less confusion about other aspects of the sound.

I also have eschewed the general consensus w.r.t PSU's and have gone for something that's likely to maintain some transient power and LF performance :)

More details once te first one is up and running.

Andy.
 
How much do these Gainclone things cost to make for a complete amp, i.e. a pre/power?

Tony.
 
Hi Andy and Tony

I have built a chip amp using the TDA2050 chip just for fun. I built this about 5 years ago before I knew anything about gainclone. The PCB's were bought from RS and they still sell them for the TDA2030. I only had to change the component values to suit the TDA2050.

I have just put some new smoothing caps made by Rubycon to the power supply section. The amp sounds really good with plenty of bass for the LS35a speakers. However the treble is not as smooth as I would like. I use a 50K log potentiometer as a passive pre when I use the amp.

The cost is about 60 to 100 pounds depending on how much you want to spend on a case.

Regards
Hon

TDA2050newcaps.jpg
 
Andy,
I think I have tried a few configurations while building the GC; the most obvious differences I could hear resulted from

-the type of resistor used from feedback to ground
-the decoupling capacity (type/size/number of capacitors)
-filtering/not filtering RF from the power rails
-the coupling cap (if one is used at all)

My GC has settled now with a 22.1K/820R/22.1K-configuration and 2.000uF per rail. I use a Mundorf MCAP (polypropylene, 4.7uF) as coupling cap, which I feel is a much better match than the Solen ones I tried before.
Decoupling caps are 16 Elna Simics (470uF), four of them soldered directly to the chips' pins. The pot is an Alps 'Blue', 47k.
The feedback resistors are 'Morganite' carbon films; they were a big improvement on the Vishay-Dales I used everywhere else.

The sound is now quite 'natural' (no edginess, no grain) and very detailed. I used it with 2 kinds of speakers so far, IBLs and Mission 751s. To put it bluntly, the amp sounds too thin with the IBLs; although the tops are adorable due to the amp's superior resolution, there is some drive missing and some of the 'presence' Naim amps excel at. It does not seem to be a matter of power though (I blamed the low capacitance at first); I have tried a couple of records that are quite demanding (e.g. "Two Months Off" by Underworld, which is a very dense mix consisting of many sound layers) and the amp never seemed to run out of steam.
The Missions, however, sounded quite pleasant with the GC. I think that these have a more distinct sound than the IBLs, being not as transparent and a bit bass heavy. This 'fullness' somewhat compensated the lean midrange of the GC, while the Mission's slightly raspy tweeter benefitted from its resolution.
My GF was pleased enough to overcome her aversion towards home-made electrical stuff and asked my to build her such an amp as a birthday present (the Mission speakers are hers).

Best regards,

Oliver
 
The cost is about 60 to 100 pounds depending on how much you want to spend on a case.
Click to expand...

Hmmm, I’m starting to get interested! So how good is it? What level of commercial amp would one compare it to performance wise? How much is the preamp? If it was likely to beat my Beat I might be interested in making one.

Tony.
 
Tony wrote:
If it was likely to beat my Beat I might be interested in making one.
Click to expand...
Sorry, but I for one find that highy unlikely.

Best regards,

Oliver
 
Just got my LM3875 Opamps about two days ago.

Need enough spare time....(spending it listening to music!!!)
 
One of my first projects was a sort of gainclone - a 4 channel power amp for surround channels.

As it was a first project, I actually used some littel kits for the power amp modules from Quasar Electronics - they're 25w modules based on the LM1875. I wouldn't say they're "true" gainclones, as the signal paths are way too long, but (to be perfectly honest), as they're just for surround duty, they'll do.

link

Since I took the pics in the link above, I've actually redone the wiring - I made up a cable that goes straight from the PC (which supplies the input) to a pair of DIN plugs wired in Naim configuration - so it's all a bit tidier in there. I've also got all sorts of mad things going on with signals being muted by relay, which is powered by a delayed turn on 5v feed from the PC to alleviate power on thumps.
 
I also feel it's unlikely to beat the Beat in all areas.

I'm going to be using the 56W LM3875T, running from a minimum of about 25V supply (300VA transformer + 2x10,000uF). This voltage is chosen to keep the power dissipation / current limits in the safe operating area under low-load conditions and is a bit lower than the norm, I think.

Cost so far is £30 for the transformer, £20 for caps and £6 for a cheap Maplin case. Also need to factor in mains inlet / fuse + the chip itself (about £3 from Farnell!).

Even if I find myself unhappy with the performance in ultimate terms, I need some amps for my bedroom system and these are cheap and simple to build!

No I've not built a NAP150, but I do own one, so have intended to reduce variables initially by making the 'clone have a similar response. Unlike most of the basic stripped down circuits out there mine is much more conventional. The main difference is I can use much higher quality components since the expense is small compared to building a discrete amp, and I want to put the 'Linn' approach to amp building to the test.

Maybe they'll grow SMPSU's later ;)

Once I have these units up-and-running I'll probably strip them down to a more basic circuit in order to evaluate the changes.
 
Rico,
basically it is more or less a clone of the 27 Labs' Gaincard; if you're interested, RJM's homepage might be a good start.
 
I built two Gainclones last year, one uses a valve buffer and the other is based on peter Daniels (diyaudio.com) minimized clone.
I also built the diy stepped Attenuator from Decibeldun site.
For the price they cost to build the sound is very good although both like fairly sensitive speakers.

Ron
 
Maplin used to do a board kit based on the TDA2035. I used at as my virgin DIY project.

RS list a suitable bare PCB for pennies as a "development" board.
I think its's listed as discontinued, but have always found them in stock.

How does it sound? Bright and quite punchy but little real bass. It was my first project as a present for my son, so it hasn't been updated to incorporate what I now know courtesy of this Forum! It would be interesting to upgrade the power supply and go to dual rail to get rid of the output blocking capacitor.

Price wise, £30-40, but don't do it because of the price. For that money I've got two Creek 4040's in my den powering a Quadraphonic system.

http://homepage.ntlworld.com/p.mew/Bens amp inner plan(red).jpg

http://homepage.ntlworld.com/p.mew/Bens amp ext(red).jpg

http://homepage.ntlworld.com/p.mew/Bens amp inner oblique(red).jpg
 
Originally posted by Tony L
Hmmm, I’m starting to get interested! So how good is it? What level of commercial amp would one compare it to performance wise? How much is the preamp? If it was likely to beat my Beat I might be interested in making one.

Tony.
Click to expand...

Hi Tony

I can't comment on how good my TDA2050 single chip amp compared to the commercial amps because I haven't got one to compare to! I doubt if the chip amp will beat your BEAT in sound quality. However building such an amp is fun and rewarding. Go to www.diyaudio.com if you want to learn more about chip amps. There are a lot of experienced builders there.

There was a Hi Fi World DIY supplement which detailed the construction of a TDA2050 amp. I was inspired by this article to build such amp. I have put some details in my web page.

http://homepages.tesco.net/h.w.lau/TDA2050amp.html

My passive pre amp is just a 50K log blue Alps potentiometer in a black metal box. The only wiring required is 8 wires from four RCA phono sockets to the Alps pot. See attached photos. The Alps pot costs about 16 pounds and the box between 3 to 10 pounds. Phono sockets can be bought from Maplins or CPC. You can try better wires than what I have used which are only standard tin copper wire.

Regards
Hon

passivepre.jpg


passiveprepotentiometer.jpg
 
Interesting to see a few comments about the lack of real bass, or thinness into IBL's.

Has anyone tried a more sensible PSU than the weedy ones that are the norm, I'm sure this is the reason for the bass problems.

Andy.
 
Andy,

I have also tried 4*10.000uF BC caps + 4*470uF Silmics at the chips' pins. the result was an excellent, bouncy bass with real PRaT; but the midrange was so thin and 'cold' I couldn't stand it. Actually, the midrange sounded much better with only little decoupling capacity (please try it, otherwise you wouldn't believe the difference it makes).
BTW, I wouldn't say it has 'no bass'; I think pm1961 referred to a TDA2035 based GC, which probably has a different sonic signature.

Oliver
 
Hi, this is my first post in this forum.

There is a lot of material concerning chip amps (called "gainclones" for a number of not always logic reasons) on the www.diyaudio.com forum. If you are interested browse there (it is a lot though..)

I was bitten by the GC-bug about two years ago because of the strange and raving reviews of the 47labs Gaincard Amplifier which basically consists of a humble PowerOP for a few Euros. So after some now older "Naim-clones" I made a few attemps with chip amps.
The main reasons:
They are very easy to make
They are very cheap
One can try several versions
etc.etc.

My last version is again a non-inverted version (more stable and better sounding than the inverted version featured by the ampchip forum IMO) with a different psu. It uses the minimum amount of parts and is therefore not recommended for beginners (for a number of reasons).
In brief:
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), 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 which are wired for full wave rectification (like Naim does) with 4 double schottky diodes. Lots of cables... I will draw a schematic and post fotos in the next weeks (no time at the moment).
The amp is DC coupled and can only be driven by completely DC free sources.
A preamp is not necessary at all (with my NAC42.5 it sounds actually worse), so I use a "passsive pre", with 2 x 20k carbon potentiomenters in shunt 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).

This technology blows my mind! How can an amp sound so good with a chip and weak power supply like this? It definitely sound better with the smaller caps! And with carbon resistors!

This is by far the best sounding chip amp I have ever made. I sounds fast and full, with lots of bass, 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, but who cares with amps which are so easy and cheaply to make. The amp is 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...
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.

So stop waxing lyric. Try one yourself.
I will post more details later, if you are interested and if time permits.

all the best
Klaus
 
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