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Old 13th April 2003, 02:51 AM   #21
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Default Re: When ground is not ground....

Quote:
Originally posted by Tube_Dude


I'm not surprised...you have connected the input ground to the negatif speaker terminal...where the loudspeaker retourning currents, retourn to the filter capacitors...and that current produces spurious voltages at that point...

The input ground must be conected to the ground terminal of the IC(in this case the noninverting input) ...that is also conected to the comum ground point(in a inverting amp)...!!

Whatever my reply was previously, I went down to my cave and re-run the input ground: I conected it directly to noninverting input (which is connected to common point). The result? No improvement at all, if not degradation.

Tube Dude was so certain however that it makes a difference, like if he's been working on those type of amps every day. Which makes me wonder if he has the same type of conviction on every issue (like DBT and null testing for instance.).

I did one additional change though, after checking grounds. I installed the 50k pot at the input and now the amp reminds me much more the sonic signature of my other gainclones. Which is another issue, either the pot has such a big influence on sonics, or the amp simply needs a sort of resistor at input to the ground?
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Old 13th April 2003, 02:54 AM   #22
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Quote:
Originally posted by Steve Eddy


Ah. Did you find those somewhere already cut and anodized?


When I started figuring the design of this in my head, I had only the transformers at hand and I was looking for nice heatsinks to implement them here. I found those at local surplus store, anodised. This is pretty common extrusion and I saw it in local stores on more than one occasion over the years.
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Old 13th April 2003, 03:05 AM   #23
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Default Re: Re: When ground is not ground....

Koinichiwa,

Quote:
Originally posted by Peter Daniel

I did one additional change though, after checking grounds. I installed the 50k pot at the input and now the amp reminds me much more the sonic signature of my other gainclones. Which is another issue, either the pot has such a big influence on sonics, or the amp simply needs a sort of resistor at input to the ground?
Well, if the source is reliably connected and low DRC/ACR you need no resistor (but that is easy to try).

BTW, I forgot to congratulate on your excellence of implementation. If I could, I'd make you an honarable German.

I rather suspect these Alps plastic pots are to blame. They have a very "manipulative" influence on sound in my experience. I'm afraid I still adhere to the "straight wire" ideas and hence (for example) after much testing no IT coupling in my SE Amp, instead LCL coupling, all IT's I tried where to "manipulative", though thoroughly decent, enjoyable and musical. And hence a preference for $1 Alps carbon trac pots from RS over black beauty or alps blue.

BTW, take the gold BG out and replace the bootstrap with a minimum of BG-N, better BG-NX or best MKT or film & foil (just kidding - I'd use an ERO MKT 22uF anyway).

I'm interested in more comments on the mosfet output TDA Chips. I know they where rejected elsewhere and why and agree from parallel experience, but I have enough "ominous Valve Work" to do to get involved deeply with the SS....

Sayonara
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Old 13th April 2003, 03:06 AM   #24
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Quote:
Originally posted by Peter Daniel
When I started design of this in my head, I had only the transformers at hand and I started looking for nice heatsinks to implement them here. I found those at local surplus store, anodised. This is pretty common extrusion and I saw it in local stores on more than one occasion over the years.
Ah. Have you (or the local store) any left? If so, I might be interested in buying a couple. Currently I'm just using samples I got from Accel and they've already been plated (gold). I'll be buying a whole 9 foot bar from them sometime later but I've got some Bolivian rosewood left and thought it'd be nice to build just one pair in black/rosewood (I'm going to stop using tropical hardwoods once my stock of rosewood is gone).

se
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Old 13th April 2003, 03:13 AM   #25
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Default The amp with a new grounding technic...

Quote:
Whatever my reply was previously, I went down to my cave and re-run the input ground: I conected it directly to noninverting input (which is connected to common point). The result? No improvement at all, if not degradation.
So ...maybe your system doesn't have enough resolution...

Quote:
Tube Dude was so certain however that it makes a difference, like if he was working on those amps every day. Which makes me wonder if he has the same type of conviction on every issue (like DBT and null measurements for instance.).
So you think that your amp need grounding technics that viole the grunding principles that are comum to any amplifier design...and only you know the way it must be grounded... Fine!!

If you are so sure why you go to the cave to try it???

PS:you never see me to defend the DBT...if so point it!!!

For me not all amps sound the same...but the ones that have a better null...sound allways better...

And if for you the null teste is so complicated...for me is logical and intuitive...
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Old 13th April 2003, 03:13 AM   #26
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I will check, but I'm sure they have at least 4 left.
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Old 13th April 2003, 03:16 AM   #27
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Default Re: The amp with a new grounding technic...

Quote:
Originally posted by Tube_Dude




If you are so sure why you go to the cave to try it???

Although I might give the impression that I was sure, in reality I wasn't, that's why I decided to check it. But now I am sure that it doesn't affect anything, at least in that type of layout
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Old 13th April 2003, 03:38 AM   #28
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Default The amp tuned by ear....

Quote:
Although I might give the impression that I was sure, in reality I wasn't, that's why I decided to check it. But now I am sure that it doesn't affect anything, at least in that type of layout
And now i am sure that you have golden ears....
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Old 13th April 2003, 03:46 AM   #29
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Quote:
Originally posted by Steve Eddy


..... Currently I'm just using samples I got from Accel and they've already been plated (gold). I'll be buying a whole 9 foot bar from them sometime later ....

steve - at the risk of hijacking the thread... ...how do you go about getting samples from accel - just ask them? or do you have to have a tax ID or something? ....also, do you happen to have a price list for their profiles?

ObTopic: nice lookin' monoblocks! it looks like you really have fun with your amp-making. salut!
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Old 13th April 2003, 03:49 AM   #30
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So far I tried LM3875, OPA549 and today TDA7294.

I've seen grading on a forum of the gainclone chips, where TDA was listed as best sounding, others claimed that OPA was better than LM chip, but my feeling is that LM sounds better than the other two chips mentioned.


The OPA549, IMO, produces the sound that is very clean, completely free of any discernible aberration, but unfortunately also free of too much emotion for my taste. While very clean and taut, the sound lackes involvement, as if the op amps were doing their jobs very professionally, but without emotion - all business, nothing personal. This is not a very big difference over LM chip, and sometimes, depending on listening material, I couldn't decide which chip I prefer, but this is the bias I have.

The TDA chip, although today is the first day I listen to it, seems somewhat lacking coherence (if this is best description). It's very dynamic, with lots of bass, but somewhat bloomy midbass and the midrange seems to be out of phase (for lacking better words). It's sort of bothering and whenever I try to listen, it makes me restless. There is detail, but highs seem a bit edgy also.

It offers somewhat thick and veiled sound, as if I were looking for something through a thin mist, more like a haze. Obviously, it lacks involvement and I really don't know if this can improve after burn in time.

I also understand that the construction of this amp is different than the other clones I made so far. This is the first amp that is using parallel 1000u caps, and my feeling is that a single cap works better. I'm not sure about the bootstrap cap as well. Maybe placing better one would improve things.
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