I'm currently using 300k Caddock resistor for feedback. There is more gain and the sound seems to be the same. Since the non inverting input connects directly to ground, the DC offset went down to 8mV with this resistor, comparing to 28mV with 220k feedback resistor I had previously.
My current setup includes Caddock for feedback, Cardas wire for PS connection and 1000u/50V BG N caps in PS. I tried to bypass the big caps with small 4.7 BG N directly at the chip, but it was not improvement. I noticed lost of resolution in trebles, which became more etched. Overall it is an improvement comparing to previous implementation. I like Caddock MK132 in feedback location, it's better than Vishay S102.
BTW, we just hit 200,000 mark today
My current setup includes Caddock for feedback, Cardas wire for PS connection and 1000u/50V BG N caps in PS. I tried to bypass the big caps with small 4.7 BG N directly at the chip, but it was not improvement. I noticed lost of resolution in trebles, which became more etched. Overall it is an improvement comparing to previous implementation. I like Caddock MK132 in feedback location, it's better than Vishay S102.
BTW, we just hit 200,000 mark today
Actually, according to BG technical info, you can do super E configuration without paralleling caps and using single caps. So, even if I have 2 caps per channel, I'm also super E conigured. I think the important thing is not to use parallel caps, as I noticed it degrades sonics somehow (at least with BG). As to the sound of big N type caps, I think it's in a different league, with more refinements and liquidity and bass, but I still didn't do side by side comparisons. Also, with Cardas wire, in my recent comparisons it seems like MSR860 is not such a good choice after all. The presence and vocals seem to be better especially on jazz and classical material, but when I tried some industrial and rock recordings, it seems to be more etchy and annoying, with extreme highs loosing resolution. So I will be converting back to MUR860 probably.
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Peter Daniel said:I tried to bypass the big caps with small 4.7 BG N directly at the chip, but it was not improvement. I noticed lost of resolution in trebles, which became more etched. BTW, we just hit 200,000 mark today
Peter, I don't think it's a good idea to bypass an electrolythic with another one for that purpose.
And 4.7uf is too high.
To have better results, you could try 0.1uf poly or even ceramics.
They have very good properties at high frequencies.
But I never used BGs, so I can't say if it will sound better.
It works very well with normal electrolythics.
fedde said:I am somewhat surprised that you didn't hear differences in sound with the 300 k feedback resistor (compared to 220 k). Not that I tried it out myself, but I expected some difference.
Tried the resistor on the + input already ?
Fedde
I can't comment much on a difference because it is a different setup (different resistor and electrolytics). I just find nothing wrong with using that higher value. I still didn't try + to ground resistor. I also tried 2u BG cap (2 x 4.7 BG N in series) between + and - rail and didn't find it desirable. Again, the highs lost resolution.
Certain approaches might seem to be proper from technical and engineering POV, yet, when you try them in a circuit and evaluate subjectively, they don't bring improvement if not degradation.
Peter Daniel said:
I have 4 batteries, but still didn't have a chance to try them
I may be a bit slow in coming to this conclusion but I don't see how it's possible to get a satisfactory earthing arrangment using only four 12V batteries for two channels.
the best compromise might be to have everything in one large box
but for me I think I will be ordering another 4 so I can keep the earths separate.
any comments or ideas welcome
mike
No, because you have built an inverting amp. The forumula is -RF/RI, giving -22 in your case...Matttcattt said:
This is discussed a bit on my page. The issue is the input impedance of the amplifier - determined by RI. You could make it as low as 10 ohms if you had a preamp that was capable of driving itMatttcattt said:
That's why 10K is a popular choice - although I went for 4K7. Once you've decided this, then choose RF based on how much gain you require. I don't know what the safest upper limit for RF is, but personally I wouldn't want to go above a few hundred K
Cheers,
Mark
Input Impedance
Hi Mark,
My preamp's output impedance is 500 ohms. Does this mean that I could use say a 680 ohm resistor for RI and the relative gain companion for RF?
Are not the values of RI and RF, provided kept in the same ratio, responsible for the signal to noise; lower values lower noise?
Then again, aren't you moving your low frequency roll off f-3db point higher if you use a lower value resistor and thus would have to increase the dc blocking capacitor to 68uf to acheive the same f-3db? I guess I see why you selected a RI=4.7K as you would only need a Cdc =10uF. Am I understanding all of this?
Thanks, I am new to this form so please excuse the nube questions,
Gregory
Hi Mark,
My preamp's output impedance is 500 ohms. Does this mean that I could use say a 680 ohm resistor for RI and the relative gain companion for RF?
Are not the values of RI and RF, provided kept in the same ratio, responsible for the signal to noise; lower values lower noise?
Then again, aren't you moving your low frequency roll off f-3db point higher if you use a lower value resistor and thus would have to increase the dc blocking capacitor to 68uf
to acheive the same f-3db? I guess I see why you selected a RI=4.7K as you would only need a Cdc =10uF. Am I understanding all of this?Thanks, I am new to this form so please excuse the nube questions,
Gregory
mhennessy said:
No, because you have built an inverting amp. The forumula is -RF/RI, giving -22 in your case...
This is discussed a bit on my page. The issue is the input impedance of the amplifier - determined by RI. You could make it as low as 10 ohms if you had a preamp that was capable of driving it
what do you mean "if you had a preamp that was capable of driving it"?
That's why 10K is a popular choice - although I went for 4K7. Once you've decided this, then choose RF based on how much gain you require. I don't know what the safest upper limit for RF is, but personally I wouldn't want to go above a few hundred K
Cheers,
Mark
Aham...
Matttcattt,
10 ohms is almost a short-circuit for a preamp, and it will not be able to drive such a low impedance.
Ideally a preamp should have low impedance output and a power amp (the circuit the pre is going to drive) a high impedance input.
The same with any source component (as a CD player), it must have a low output impedance, and the preamp a high impedance input.
Resuming, you should have low impedance on the output and high impedance on the input.
Clear?
Matttcattt said:
Matttcattt,
10 ohms is almost a short-circuit for a preamp, and it will not be able to drive such a low impedance.
Ideally a preamp should have low impedance output and a power amp (the circuit the pre is going to drive) a high impedance input.
The same with any source component (as a CD player), it must have a low output impedance, and the preamp a high impedance input.
Resuming, you should have low impedance on the output and high impedance on the input.
Clear?
Re: Input Impedance
Probably not - the output impedance of something doesn't necessarily define its drive capability. For example, the output impedance of a power amplifier might be 0.1 ohms, but of course you wouldn't connect it to a speaker with 0.1 ohms impedance (even assuming you could find such a thing!)
With most things audio, you normally use the lo-Z out, hi-Z in princible. Of course, with higher frequencies you would match imput and output impedance - examples might be an SPDIF connection, or a video signal.
I should say that my 10 ohm example was (hopefully!) obviously silly. The point I was trying to make was that this resistor should ideally be as low as possible, but the lower limit is defined by the preamp or source equipment...
Yes, within limits. All resistors generate noise - without getting too mathematical, the noise is broadly proportional to the square-root of the resistance (assuming Johnson noise is the main contributor)
To analyse the noise in a circuit, you need to look at the combined resistance seen by the input to a gain stage. So the key fact in the case of the GainClone is that the inverting input "sees" RI in parallel with RF. So while you can be forgiven for thinking that RF will contribute most noise because it is the largest resistor, in reality, RI is the dominant resistance.
A good "rule of thumb" value of resistance is around 2K. Try to keep your impedances to around this value, and you can be happy that your signal to noise ratio isn't being needlessly compromised by Johnson noise. After than, the residual noise will mostly be coming from the active devices in your circuit...
Yes, this is exactly what's happening. Ever wondered why engineering is sometimes called "compromise-managment"
No problem! And don't feel that these are "nube" questions - you seem to have a good understanding of the issues here
Cheers,
Mark
gregorx said:
Probably not - the output impedance of something doesn't necessarily define its drive capability. For example, the output impedance of a power amplifier might be 0.1 ohms, but of course you wouldn't connect it to a speaker with 0.1 ohms impedance (even assuming you could find such a thing!)
With most things audio, you normally use the lo-Z out, hi-Z in princible. Of course, with higher frequencies you would match imput and output impedance - examples might be an SPDIF connection, or a video signal.
I should say that my 10 ohm example was (hopefully!) obviously silly. The point I was trying to make was that this resistor should ideally be as low as possible, but the lower limit is defined by the preamp or source equipment...
gregorx said:
Yes, within limits. All resistors generate noise - without getting too mathematical, the noise is broadly proportional to the square-root of the resistance (assuming Johnson noise is the main contributor)
To analyse the noise in a circuit, you need to look at the combined resistance seen by the input to a gain stage. So the key fact in the case of the GainClone is that the inverting input "sees" RI in parallel with RF. So while you can be forgiven for thinking that RF will contribute most noise because it is the largest resistor, in reality, RI is the dominant resistance.
A good "rule of thumb" value of resistance is around 2K. Try to keep your impedances to around this value, and you can be happy that your signal to noise ratio isn't being needlessly compromised by Johnson noise. After than, the residual noise will mostly be coming from the active devices in your circuit...
gregorx said:Then again, aren't you moving your low frequency roll off f-3db point higher if you use a lower value resistor and thus would have to increase the dc blocking capacitor to 68uf
Yes, this is exactly what's happening. Ever wondered why engineering is sometimes called "compromise-managment"
gregorx said:
No problem! And don't feel that these are "nube" questions - you seem to have a good understanding of the issues here
Cheers,
Mark
Matttcattt said:
do you know how to use an opamp?
here, the gainclone chip acts like a high power opamp
so, in inverting mode, the gain is set by 2 resistors, Ri at the -in, and Rf between out and -in
Gain=-Rf/Ri
Try with Ri shortened, you'll have -220/0-> infinite gain
you'll clip your amp with a few mV at the input (don't try this with speakers connected to the amp!)
Because the inverting input is a "virtual earth"Matttcattt said:
I really recommend getting hold of a copy of "The Art of Electronics" by Horowitz and Hill, and reading through chapter 4. It's a really good non-mathematical explanation of basic op-amp theory. I don't mean to be patronising, but this will answer your question and teach you lots more at the same time.
I'll attempt to sumarise - due to the action of negative feedback, the two inputs of the op-amp are always at the same voltage. This is one of the "golden rules" of op-amp operation. Believing this is the first step to understanding. Now, as the non-inverting (+) input is tied to ground, it follows that the inverting (-) input will always be at ground. This is why it is called a "virtual earth".
This is only part of the story, but the book will tell it better
Cheers,
Mark
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