Modded SL1200's

Anyway, getting back to the electronics...

The third part of my slightly off-topic ramblings considers the distortion produced by the input stages of the phono preamp...

That is to say, before the application of negative feedback - the open loop distortion.

Taking solid-state, or more accurately, an input transistor (a bipolar transistor): these offer the lowest noise which is a prerequisite of a phono preamp input.

Unless steps are taken to avoid it, a transistor input (whether discrete or in an op-amp) is only linear for a 60mV peak to peak input voltage.

Taking the output of a moving magnet cartridge we see it's around 5mV rms, which is about 14mV peak to peak, so that should be OK? Wrong!

Let's look at its output at 20kHz. Due to RIAA and the fact that magnetic cartridges give an output proportional to velocity. As the frequency increases the output does also. And by 20dB per decade, which all boils down to an output of ten times that rated at 20kHz.

What will that be? 140mV p-p. Ouch!

Never mind, we have negative feedback? Just how much negative feedback will it take to cure extreme clipping? About 40dB according to Nyquist (Bell Telephone Labs). And most op-amps have that amount of gain "headroom", and a discrete stage can be arranged to do so too.

But hang on, are we not in the territory of mending something that just broke?

Yes we are. And the sound isn't going to be all that natural.

What is needed is an input stage that is more linear - that allows a larger input signal without clipping it. Then, when we apply negative feedback it is to address slight irregularities rather than glueing a broken vase back together.

This should therefore explain why - if the electronics is suspect - why loud passages and high frequencies can sound distorted, while ordinarilly everything is just sweetness and light.

This may not be the case here, but it will be in some systems.

Thanks for the progress report, don't forget that the DL-160 will work direct into your 2 SE and is quite a step up from the DL-110 (if the Goldring is defunct).

I considered the BPS at one time but ultimately came across too many conflicting reports.

Enjoy the music.