Goldpoint SA4M-47 passive 'preamp' winging its way to Marco Towers...

[PaulStewart]

A certain Mr R Dunn and his cesspit. Need I say more?

Marco.

Bit of advice you gave me mate, use the ignore button.......

[DSJR]

I need a qualified engineer to confirm what's going on here please as I'm shocked that just ONE series resistor in each channel can make such a sonic difference (I think I really am going deaf now, as resistor tolerance would count more to me than type or maker in this case)...

A 'shunt' passive attenuator has ONE fixed value resistor in the signal path and each volume 'step' has a different resistor each step to 'load' or 'shunt' the signal further to adjust volume. This means the input and output impedance varies with each volume 'step,' doesn't it?

Again, confirmation needed please by an experienced engineer! More conventional attenuators have either a step ladder, the volume 'tapping' being taken from different 'rungs' on the ladder, giving a roughly equal impedance (in series AND across the load) to input and output at each 'step,' and lastly, an individual 'pair' of resistors at each 'step,' one in series and one across the load, maintaining constant impedance with each defined 'step.'

It just strikes me that a 'shunt' type is only half done, but if the varying load with each volume 'step' to both source and amp doesn't matter, then it's not a problem at all I expect.

HELP PLEASE!!!

[lurcher]

I need a qualified engineer to confirm what's going on here please as I'm shocked that just ONE series resistor in each channel can make such a sonic difference (I think I really am going deaf now, as resistor tolerance would count more to me than type or maker in this case)...

Not sure what qualification you need, but I certainly have experience of this. Not entirly sure if you are asking a question with the above sentence or just saying what you expect to happen. Yes, you can clearly hear the differences in the shunted resistor in this sort of setup. All this was tried ten years ago on the WAD forum with just the same results. Its worth pointing out that you can (and I often do) use a shunt with a conventional pot to remove much of the sound of the pot. I do have to point out that I sugested that this was the best solution some pages ago and was told it "just didnt feel right" or some such. But hey ho.

A 'shunt' passive attenuator has ONE fixed value resistor in the signal path and each volume 'step' has a different resistor each step to 'load' or 'shunt' the signal further to adjust volume. This means the input and output impedance varies with each volume 'step,' doesn't it?

Yes.

It just strikes me that a 'shunt' type is only half done, but if the varying load with each volume 'step' to both source and amp doesn't matter, then it's not a problem at all I expect.

Again, yes, as I said some time ago, if you need fixed resistances in the input and output, then the shunt is not the best choice. Likewise if you need max output to be 0dB then a shunt is no use, if neither of these, then it can and does work well.

You may have thought that places like HiFi collective sell their wide range of components just to pander to fools, no, these things do matter, the reason manufactures don’t normally use them is simple, cost and the effect on their profit margin. If you looked inside Gary's 300b amp, you would find that the resistors in the signal path are all better types than the nasty metal film that sell for 1p a resistor, likewise the caps and so on. I use metal film in places like the power supply where the cost of something better is more than the benefit they bring. I dont do that just so I can charge more for the amp, I do it because it sounds better.

[brian2957]

+1 on Gary's new amp . I've heard it a couple of times now and it's stunning . Gary tells me that it sounds even better since the last time I heard it

[lurcher]

+1 on Gary's new amp . I've heard it a couple of times now and it's stunning . Gary tells me that it sounds even better since the last time I heard it

Yes, ironically given this thread, but we have just found out that the noise floor of his preamp is now a limiting factor.

[brian2957]

Well it still sounded stunning to me Nick and I'm pretty sure Gary is grinning like a Cheshire cat as I write this If ever I get the cash together you'll be getting a call from me

[DSJR]

Sincere thanks for your considered replies

[awkwardbydesign]

Bit of advice you gave me mate, use the ignore button.......

Yes, please do, it's not helping this thread.

[Ali Tait]

Yes, ironically given this thread, but we have just found out that the noise floor of his preamp is now a limiting factor.

Is it the pre causing the hiss Nick?

[awkwardbydesign]

I need a qualified engineer to confirm what's going on here please as I'm shocked that just ONE series resistor in each channel can make such a sonic difference (I think I really am going deaf now, as resistor tolerance would count more to me than type or maker in this case)...

A 'shunt' passive attenuator has ONE fixed value resistor in the signal path and each volume 'step' has a different resistor each step to 'load' or 'shunt' the signal further to adjust volume. This means the input and output impedance varies with each volume 'step,' doesn't it?

An engineer can certainly explain the circuit, but won't necessarily understand the sonic implications. In fact, an engineering background may well bias against hearing any difference. Not in all cases, obviously, or there would be very few advances in sonics.

Not sure what qualification you need, but I certainly have experience of this. Not entirly sure if you are asking a question with the above sentence or just saying what you expect to happen. Yes, you can clearly hear the differences in the shunted resistor in this sort of setup. All this was tried ten years ago on the WAD forum with just the same results. Its worth pointing out that you can (and I often do) use a shunt with a conventional pot to remove much of the sound of the pot. I do have to point out that I sugested that this was the best solution some pages ago and was told it "just didnt feel right" or some such. But hey ho.

I don't know if this is germaine, but using a log law faking resistor on a linear pot not long ago completely squashed the sonics. I have no idea why, as the overall resistances were maintained correctly. Buying a log pot of the same type restored the quality.