Opinions on ModWright PH 9.0 Tube Phono Stage (and others)

This is the result of not using negative feedback! What happens when you apply negative feedback to control a gain stage, a pop or tic comes by (non-audio event) greatly exceeding the slew rate of the forward gain, thereby breaking the loop. What happens is that you now have an out of control loop which has to recover. This exaggerates a tic into a huge event.

When non-feedback gain stages are used there is no loss of control. A tic is amplified as though it was an audio signal. You don't get the prolonged recovery period, during which no music flows.

This is clearly reproducible in testing. Easy to ABX.

 

Interesting! So, then, presumably, the Graham Slee pre *is* using negative feedback?

 

Like most modern phono preamp designs, the GS products are all opamp- based, so all would use very high levels of negative feedback (he does have some strong opinions on the matter, if interested ... Discrete components and Ops Amp ). There are a few exceptions around in the solid state field, some nice low or no negative feedback discrete designs, and we've talked about some of them around here in other threads. But the no-feedback approach is much more prevalent in the tube phono preamp field. I have a couple no-feedback phono preamp designs from Conrad Johnson, one tube and one transistor, both really nice sounding, so I tend to favor that approach.

 

The 'tic' effect is even more prominent when EQ is applied in the feedback network. Fast opamps with purely proportional feedback are not too bad, zipping through the issue via sheer speed.