Gainclone heaven ?

[juanpmar]

Thanks Peter, yes we were talking about the Y cables but in that case they were to be used with my Spectron amps in the monoblock configuration (this is basically a stereo amp  that can be bridged inside to be used as monoblock).

I understand that different reactance/feedback problems could appear using a combination of different amps. I don´t have more amps so I can´t test it, maybe someone else in the forum could do it and let us know if the use of two different pairs of monoblocks affect the sound.

I guess that if I want to test the Gainclone I´ll have to buy it or build it  and see if they work in combination with the Specton. Anyway, I´m very happy with Spectron and I feel quite lazy to start with this new path. The only temptation I have is the Gainclone price (if I could build it by myself).

Juan

[PeterSt]

Since I was measuring a DAC this morning anyway, I captured this screenshot. *This* is how I want to see a noise line, and not one spike else.

Notice this is measured from the DAC output, and not from the amp's output. But it really looks the same, with the difference of the gain - hence noise level highered by that gain.

If this line has spikes to begin with, or is not straight over the full frequency range as shown here, sound will be dead.

Peter

PS: For the knowledgeable : this is a normal 8K FFT, so no tricks or anything to lower the noise line (which can be dropped by 20dB easily with a deep FFT).

[manisandher]

OK Peter, I'm dying to ask you this: would you see this level of performance from the output of your power amps? Actually, with your 115dB/W@1m speakers, I wouldn't be at all surprised if the answer is 'yes'...

Mani.

[GerardA]

For a cheap gainclone offer:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=160590654250#ht_4487wt_1235

[PeterSt]

OK Peter, I'm dying to ask you this: would you see this level of performance from the output of your power amps? Actually, with your 115dB/W@1m speakers, I wouldn't be at all surprised if the answer is 'yes'...

Hey Mani,

Although the answer should be Yes, this is not 100% honest. I mean, a few months back I never looked into it for a couple of years. I *had* to though, when things appeared to be wrong-sounding (and it was wrong, never mind for now why).

Do, today the answer would be Yes. This, while the honest answer from a few years back would be "impossible !". So here too, all is about the reference.

PS:
Please notice this is all in the context of a zillion thing wrong anyway. I'll be back on this soon (the Bass thing).

[Scroobius]

Hi Peter & Juan,

  Lastly, we must be careful. Because now I think of it ... it formally will need twice the current output to drive the interlinks. I don't say it won't work, but theoretically it will work less (or the allowed interlink length will be less).

Maybe by now we must wonder how Paul did it, because he must have done something similar ...

Into my GC amp there is just one pair of RCA as normal but inside I simply connected the amp inputs in parallel - so just the same as Peter's "Y" connector (but v short distance). OK not ideal because as Peter points out my poor old NOS1 has to provide twice the current and also sees the reactance of two GC inputs. I am sure that this is the way Nick connected his active set up and as Peter points out it is (maybe) not ideal. Peter has pointed out elsewhere in this thread he used a different arrangement with the LF unit GC taking the output of the HF unit GC as its input and a volume pot to control the output to the LF unit (well I am sure Peter explains it better elsewhere here). I am waiting a dark rainy evening to try this arrangement - so being in the UK that should not be too long ha ha.

Thinking about it there is an easy way to see if the above paralleled input to the GC from NOS1 adversely affects the sound. With the inputs from NOS1 connected together (as in my GC amp now and described above) connect the speakers as normal (ie not bi amp) to the outputs of one stereo pair of the GC amp and take listen. Then remove the link (paralleled input links) and take another listen - better still put a temporary switch to aid the comparison. The comparison is not perfect because one GC amp pair will not have an output load - but if a difference is heard then it would prove that paralleling the inputs is not ideal. When I get some enthusiasm I will try it over the next few days and report back. Too busy listening to music at the moment though 

P

[GerardA]

I tired to check the inputimpedance of the gainclones, but it looks like they are at least higher then 100k.
As long as it is not changed by an extra inputresistor.
I guess that is high enough for the NOS1 to deliver into two parallel gainclones?

[Scroobius]

Hi Gerard  -  The input resistance is not a problem but possibly the "reactance" or different varying voltages appearing on the two inputs is - well maybe.

P

[PeterSt]

About the volume pot ...

There is a trick in order here ...

Although I never tried it without pot (would be useless as well because of too much gain), I am fairly sure that this pot will create anomalies similar to any volume. Now, one could say "hey, this is bass only, so don't worry too much". This by itself would be the wrong idea IMO, but never mind for now.

What happens in my situation is that the woofer -net- will be fed by low passed signal only. So, in my case the roll off starts at 250Hz or so, and beyond that (higher frequencies) all dies out. It is this which makes it the practice case of whatever anomalies the pot would show in the higher frequencies (it is always there where things start to go wild/strange/wong), are not there at all.

Of course any filter behind it (in speaker) would incur for the same, but it is still something to take into consideration. Not that things should be changed, but it may be good to know that IMO the pot here will be harmless (when not too poor).

What we should be worried about more is the low (50 or 60 Hz) mains frequencies which will be "visible". Without an inherent balanced design this will be difficult to avoid. But I think that anyone who starts a Gainclone project now, should especially concentrate on that, because it is there where the potential improvements are.

Peter

[Scroobius]

The sound quality of my GC's is discussed elsewhere but the level of mains hum with no music being played has been just a bit more than I liked (I could hear hum - just - 10 feet away). I thought it was not too bad given that the GC is on full volume all the time (ie no volume pot) with 98db sensitivity speakers. With all the systems I have had in the past if I turned the volume to maximum I would certainly hear hum and that was through low sensitivity speakers (88db typically) and these were big "name" systems. Also RF breakthrough etc.

Well for reasons I will post separately I decided to take apart and rebuild my amps and whilst doing so I created the most perfect "star" earth arrangement that I could. To put it in perspective though the old earth arrangements I really did think were good enough and if you look at the pictures earlier in this thread you will see that there is a 1.5mm2 bus bar arrangement connecting the ground points on each of the circuit boards and then earth points from regulators taken up to the bus bar.

Well now (and I will post pictures soon) I have taken a 2.5mm2 wire from each of the 4 circuit board ground connections separately to a single earth point (SEP) on the chasis. The main incoming earth is connected to the SEP and also each of the 4 regulator earth points is separately wired to the SEP. So there are 9 connections to the SEP. So what is the difference between the previous earth arrangement and the new one? - well electrically not much at all but in terms of mains hum a very big and surprising reduction. Now if I put my ear right next to (3cm away) the LF speaker cone I can hear hum but 1 - 2 feet away I can hardly hear anything. That is a big reduction. I always knew the importance of star earthing but I am surprised at the difference in hum. So if anyone out there is thinking of building a GC it is not possible to pay too much attention to earthing arrangements.

Also I am going to increase the heat sink capacity. Whilst I have not had any problems with the current arrangement they do tend to run a bit warm at extended very high volume. I will post pictures when complete for anyone who is interested.

P

[PeterSt]

gringrinmoregrin
(nose on keyboard)

[Scroobius]

........ but I have to say the heat sinks only get as hot as the hottest in NOS1 even on high volume so maybe not so much of a problem after all.

Peter  -  Hope your nose is OK!!

[Tore]

Hi everyone!

I have been recommended to try a Gainclone amp on my Avantgarde Duo speakers.

Do anybody know someone that can build one for me?

[Bigear]

Interesting thread....

I looked at the web and there are several chips used for Gainclones:
- 1875
- 3875
- 3886
- 4780

Does anyone know what the sonic signature is of each of these?

For instance, would it be an idea to use for bi-amping 2 different kind of gainclones?
F.i. a 3886 for the bass section and a 3875 for mid/high?

[Scroobius]

Hi Bigear,

All I know is that the Peter Daniel 3875 version has been tested, modified and stripped down to the fewest components possible. Components have been removed to the extent that there is only one (3875) in the signal path. There are no caps / resistors in the signal path at all (just like NOS1 - well for NOS1 just one resistor I think). The other components have been carefully selected for best sound quality. So how important is the actual chip type? - I really don't know but the starting point for me would have to be the same layout and minimal components of the right quality before I would even start to consider comparisons. I really don't know the answer.

Not easy to get an equal comparison.

Regards

Paul