Moving Coil into SUP into Passive Amp into Phono Stage into Power Amp

[martinswimmer]

Today I was feeling a bit bored so changed the sequence of components in the audio chain.
I opened the recently bought Sondex passive pre-amp (from the Forum) and found a lot of space above the printed circuit.
I soldered a step up transformer (Otari 1:10) to the input of the Sondex. Then ran the Sondex into the phono stage and then the phono stage directly to the power amp.
Sounds different and very good but obviously there's noise from the phono stage that runs at full whack into the power amp.
It's not noticeable at all unless you put your ear to the speaker - but there it is - a clean hiss.
Has anyone else done this and what would be the pros/cons?

[mayebaza]

Sounds like shorter signal path advantage versus proximity interference cross talk.

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[martinswimmer]

The sound is very open and detailed but subtle and seductive. One interconnect has been removed and the order of components swapped... I think I'm staying with this topology. I can hear from the speakers when I move the stepped volume pot and I wouldn't dare change the input while the power amp is on. I could populate all inputs with various SUTs that I've got and have quick access to them. JUST REALISED - I can have multiple turntables running into my phono stage like this. This is really handy!

[Barry]

Sounds good. An SUT should always be connected directly to the phono preamp, or at least using the shortest length of cable possible. This is so the capacitance of the connecting cable is minimal and the interaction with the secondary coil inductance of the SUT leads to a resonance laying well outside the audio band.

[martinswimmer]

Sounds good. An SUT should always be connected directly to the phono preamp, or at least using the shortest length of cable possible. This is so the capacitance of the connecting cable is minimal and the interaction with the secondary coil inductance of the SUT leads to a resonance laying well outside the audio band.

Hi Barry, the thing that I'm doing differently is that I'm attenuating the signal before the phono stage - and running the signal from the phono stage directly into the power amp.

[Barry]

Ah, so the layout is:

Cartridge > SUT > passive (Sondex?) > phonostage > power amp.

Is that correct? ,If so it is not what I was thinking, and IMO not a good idea for two reasons:

[1] the phono stage is running flat out into the power amp and hence the signal to noise ratio will be poor for low settings of the passive volume control,

[2] the loading of the secondary winding of the SUT will vary with the setting of the volume control, and so too will the load impedance as seen by cartridge. This could affect the tonal balance of the cartridge and make it dependant on volume control setting, though the effect might only be small.


But as the noise/hiss is only noticeable if you put your ear directly up against the speaker, and you like the sound ("Sounds different and very good ... "), then I wouldn't worry.

[martinswimmer]

Ah, so the layout is:

Cartridge > SUT > passive (Sondex?) > phonostage > power amp.

Is that correct? ,If so it is not what I was thinking, and IMO not a good idea for two reasons:

[1] the phono stage is running flat out into the power amp and hence the signal to noise ratio will be poor for low settings of the passive volume control,

[2] the loading of the secondary winding of the SUT will vary with the setting of the volume control, and so too will the load impedance as seen by cartridge. This could affect the tonal balance of the cartridge and make it dependant on volume control setting, though the effect might only be small.


But as the noise/hiss is only noticeable if you put your ear directly up against the speaker, and you like the sound ("Sounds different and very good ... "), then I wouldn't worry.

;-) . Yes, seems like it shouldn't be a good idea, but sounds great. (Maybe the sound improvement is only due to the SUT being wired straight to the passive preamp and nothing to do with the topology change?)
The hiss is not audible from listening position, but now I'll try upping the gain on the phono stage and experimenting without the SUT. I reckon that would exhibit undesirable characteristics, but only one way to find out.