Sorry, Philip, not to mention you personally.
Maybe I was not putting it right: I just wanted to say, up to my experience, different parts and part inherent qualities do actually make a difference with chipamps, whether more or less than other amps, I do not know. This was not the discussion here.
For me these amplifiers actually sound better with carbon resistors (at least the non-inverted version), but I do not have the slightest clue why. The amps sound good inspite of their "weak" PSUs, or because, I also do not know. I read many possible explanations, the ones from 47labs including, but I was never really convinced.
Maybe I did something wrong with my inverted version. Therefore my question about the + to ground resistor. But I see that I have to find out that alone.
I was expecting much, too much maybe, and was disappointed. Now you may say, make an Aleph or whatever, but this is not the point. I want to tickle out the very best of this chips, because I know that they are good, and because somebody else already seems to have done it already. The only reference are my ears alone - as ever - and I did not have the opportunity to hear the real Gaincard or the Final amps yet.
Klaus
Maybe I was not putting it right: I just wanted to say, up to my experience, different parts and part inherent qualities do actually make a difference with chipamps, whether more or less than other amps, I do not know. This was not the discussion here.
For me these amplifiers actually sound better with carbon resistors (at least the non-inverted version), but I do not have the slightest clue why. The amps sound good inspite of their "weak" PSUs, or because, I also do not know. I read many possible explanations, the ones from 47labs including, but I was never really convinced.
Maybe I did something wrong with my inverted version. Therefore my question about the + to ground resistor. But I see that I have to find out that alone.
I was expecting much, too much maybe, and was disappointed. Now you may say, make an Aleph or whatever, but this is not the point. I want to tickle out the very best of this chips, because I know that they are good, and because somebody else already seems to have done it already. The only reference are my ears alone - as ever - and I did not have the opportunity to hear the real Gaincard or the Final amps yet.
Klaus
Klaus,
I didn't really try to vent, I had just sat down after a fight with the wife and and your post struck a nerve. Sorry. Your right in that this amp design does not follow the normal criteria when considering parts quality. I feel kind of foolish now that that I have spent $150+ for different parts for testing when I could have bought $2.50 poly caps at a local surplus supply and been statisfied with the sound. It certainly satifies my daughter.
I am just going to keep the RTXs and Auricaps for another time. I wasn't originally building this amp for audiophile quality, just a time filler between major projects. I was just suprised by the quality of sound and I am now considering it for a multi-channel H/T amp for the familyroom. It's characteristics are well suited for H/T, dynamic, clean and works well with vocals.
I cannot give you a definitive answer on your question but from what I gather is that the RC circuit from the opposite input leg seems provide some impedence balancing within the amp. I am not using it and have the +IN leg just short to my low voltage ground. I couldn't get the amp to react negatively to this so I have left it out. Maybe I'll put it back in for the final version.
I didn't really try to vent, I had just sat down after a fight with the wife and and your post struck a nerve. Sorry. Your right in that this amp design does not follow the normal criteria when considering parts quality. I feel kind of foolish now that that I have spent $150+ for different parts for testing when I could have bought $2.50 poly caps at a local surplus supply and been statisfied with the sound. It certainly satifies my daughter.
I am just going to keep the RTXs and Auricaps for another time. I wasn't originally building this amp for audiophile quality, just a time filler between major projects. I was just suprised by the quality of sound and I am now considering it for a multi-channel H/T amp for the familyroom. It's characteristics are well suited for H/T, dynamic, clean and works well with vocals. I cannot give you a definitive answer on your question but from what I gather is that the RC circuit from the opposite input leg seems provide some impedence balancing within the amp. I am not using it and have the +IN leg just short to my low voltage ground. I couldn't get the amp to react negatively to this so I have left it out. Maybe I'll put it back in for the final version.
Which one for heavy loads?
I'd like to try these chips, even though I know they won't sound best with my ODINs (MTM speakers - the imp. falls down to 3 Ohms). Maybe they will be a good solution for the summer heats.
Anyway, I'm ready to take the plunge because it seems an easy way to try bi-amping too.
I have a question for those with experience. Which chip will be better for this load - LM3886, or LM3875 will deal with it? I'm talking about modest listening levels - up to 20W (90dB speakers).
Thanks
I'd like to try these chips, even though I know they won't sound best with my ODINs (MTM speakers - the imp. falls down to 3 Ohms). Maybe they will be a good solution for the summer heats.
Anyway, I'm ready to take the plunge because it seems an easy way to try bi-amping too.
I have a question for those with experience. Which chip will be better for this load - LM3886, or LM3875 will deal with it? I'm talking about modest listening levels - up to 20W (90dB speakers).
Thanks
Asen,
I recommend you use the LM3875 in an inverted design but the non-inverted design works very well too. The general consensus I have read is that it (and the LM1875) sound better than the LM3886. Another reason is the mute input on the LM3886 is not present on the LM3875 (or the LM1875). You have to put a small voltage on the leg to turn the mute feature off (IOW have sound come out ). Just one more thing not to have to deal with as clearances are tight enough. You want to keep your other components close to avoid RFI. See Brian's and Peter's pics earlier in the thread. If you don't mind dealing with the extra inputs and voltages and want quite a bit more power take a look at STMicroelectronic's TDA7294. It has 120watts and I have heard it sounds good as long as you stay in the optimum input voltage range. (see the chips white papers). When you get that much stuff going on it might be better to make a PCB. I am using mine right now with some 12 year old B&W DM602s. From my limited but increasing experience with the LM3875 I am satisfied with its performance and it makes a fun little amp with a very high performance to cost ratio.
http://www.st.com/stonline/books/pdf/docs/6744.pdf
I recommend you use the LM3875 in an inverted design but the non-inverted design works very well too. The general consensus I have read is that it (and the LM1875) sound better than the LM3886. Another reason is the mute input on the LM3886 is not present on the LM3875 (or the LM1875). You have to put a small voltage on the leg to turn the mute feature off (IOW have sound come out
). Just one more thing not to have to deal with as clearances are tight enough. You want to keep your other components close to avoid RFI. See Brian's and Peter's pics earlier in the thread. If you don't mind dealing with the extra inputs and voltages and want quite a bit more power take a look at STMicroelectronic's TDA7294. It has 120watts and I have heard it sounds good as long as you stay in the optimum input voltage range. (see the chips white papers). When you get that much stuff going on it might be better to make a PCB. I am using mine right now with some 12 year old B&W DM602s. From my limited but increasing experience with the LM3875 I am satisfied with its performance and it makes a fun little amp with a very high performance to cost ratio. http://www.st.com/stonline/books/pdf/docs/6744.pdf
-----------------------------------------------------------------------------------protos said:
Thank you protos. This what you are proposing is actually better than the one i wrote, because by having a spread of different capacity values prohibits the (remote) chance of having the PSU resonate at a particular frequency, which may be the case when many equal value and construction capacitors are paralleled.
Regards
George
hifi said:
Howdy Hifi and thanks for watching my back.
I had no idea that a larger xfmr might slow down a PSU, for I am but a lowly newb and these GainClones are the first amps I have ever built and theory is not exactly my strong suit.
Us Texans generally believe bigger is better and we apply that philosophy across the board. That is until someone that actually has a clue informs us otherwise.
Thanks again for informing me otherwise.
I think the subject of inductance and speed of transformers is interesting.
For example Naim uses a 500VA (!) transformer on their pre-amp power supplies which is about as big as some of their transformers in their higher powered amps.
On the other hand on one review of the gaincard I think it was mentioned that adding a second "Power humpty" power supply did not improve the sound.
My gainclone works really well with a 120VA for both channels with more than adequate output for my 90db 4ohm speakers.However if speakers are difficult to drive or one is planning to play the amp at continuous high power levels a 225VA or more for both channels should cover quite easily.
For example Naim uses a 500VA (!) transformer on their pre-amp power supplies which is about as big as some of their transformers in their higher powered amps.
On the other hand on one review of the gaincard I think it was mentioned that adding a second "Power humpty" power supply did not improve the sound.
My gainclone works really well with a 120VA for both channels with more than adequate output for my 90db 4ohm speakers.However if speakers are difficult to drive or one is planning to play the amp at continuous high power levels a 225VA or more for both channels should cover quite easily.
Bridging gainclone
As I am working on some pcbs holding independent and separate non-inverted gainclone versions on the same board, it seemed like a natural idea leaving them prepared for bridging if necessary too.
In spite of using two inverted versions being Thorsten's preferred way, using a transformer to invert one amp input, it's still worth it see how the simpler bridging proposed by National sounds.
What I don't quite get is why the two versions have not the same gain. Can anyone explain why?
Carlos
As I am working on some pcbs holding independent and separate non-inverted gainclone versions on the same board, it seemed like a natural idea leaving them prepared for bridging if necessary too.
In spite of using two inverted versions being Thorsten's preferred way, using a transformer to invert one amp input, it's still worth it see how the simpler bridging proposed by National sounds.
What I don't quite get is why the two versions have not the same gain. Can anyone explain why?
Carlos
Non-inverting vs. Inverting
The gain calculations for the non-inverting and inverting amplifiers are different. Without getting into a lengthy explanation, the gain of the inverting amp is Av=Rf/Ri and the gain of the non-inverting amp is Av=1+(Rf/Ri). Therefore the ratio of Rf/Ri for the inverting amplifier must compensate for the unity gain portion of the non-inverting amp by using a larger feedback resistor.
My calculations say that they aren't quite the same anyway, and for this bridge configuration to be close to "perfect" I would pick through the resistor bin until I found a 51.7k resistor to make the inverting stage gain close to 11 to match the non-inverting stage.
Later,
The gain calculations for the non-inverting and inverting amplifiers are different. Without getting into a lengthy explanation, the gain of the inverting amp is Av=Rf/Ri and the gain of the non-inverting amp is Av=1+(Rf/Ri). Therefore the ratio of Rf/Ri for the inverting amplifier must compensate for the unity gain portion of the non-inverting amp by using a larger feedback resistor.
My calculations say that they aren't quite the same anyway, and for this bridge configuration to be close to "perfect" I would pick through the resistor bin until I found a 51.7k resistor to make the inverting stage gain close to 11 to match the non-inverting stage.
Later,
Re: Non-inverting vs. Inverting
OK. I guessed it was something like that. Thanks.
My intention is to use the "gainclone popular" inverted version as the basis for both amps. That is using 220K/10K to set gain on one amp and a 2.2uF film cap to block DC. The non-inverted stage's gain should be corrected following the Av=1+(Rf/Ri) ratio.
My doubt now is how to compute the Rb resistor from non-inverting pin to ground on U2.
Some claims had been made on this Forum of sound getting more alive if a buffer or preamp was used before the gainclone. Any agreement/disagreement over that?
Carlos
stadams said:
OK. I guessed it was something like that. Thanks.
My intention is to use the "gainclone popular" inverted version as the basis for both amps. That is using 220K/10K to set gain on one amp and a 2.2uF film cap to block DC. The non-inverted stage's gain should be corrected following the Av=1+(Rf/Ri) ratio.
My doubt now is how to compute the Rb resistor from non-inverting pin to ground on U2.
Some claims had been made on this Forum of sound getting more alive if a buffer or preamp was used before the gainclone. Any agreement/disagreement over that?
Carlos
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