First impression: Herron VTPH-2A phono preamp

@georgehifi
So you had enough volume with the passive even though you had a very low 0.24mV MC cartiridge, you didn’t have >100db horn speakers? also what was your amps gain or sensitivity? And the VP1 is the same gain and even higher output impedance.

George..I have a lot of volume on tap as it sits. My speakers are not all that efficient @ 87.5 db or something like that, they are Revel F52.
I had everything spec wise when I was looking for a buffer but I may have tossed them.
The amp is an ATI 3002

scm

Thanks for that info.

There you go Al, even with .24mV MC and 87db speakers plenty of volume on tap. And the ATI amp seems to be 1.8v sensitivity.

Your calculations have a hicup somewhere.

Cheers George

No problem Al. I'm having a great time being a bystander as you and George go back and forth. It's entertaining and somewhat educational. I'm pleased to have started a thread where folks can have a hearty, decent conversation.

@georgehifi

What really seemed to help was adding the tube buffer. The volume level on the numeric display was usually  maxed out at about 54-56 by..."maxed out" I mean what I felt was loud enough.
Now though the display shows 40-42 for the same level.

I think I can flex the walls if I wanted to, there seems to be a lot of pedal left :)

Thank you, Professor.

George, there are no hiccups in my calculations. Note that I referred to not being able to drive the power amp to full power, in some and perhaps many circumstances. I did not say that users in those circumstances would necessarily be unable to achieve a volume level that is satisfactory to them.

A quick search I did for specs on the ATI 3002 seemed to turn up specs on the ATI 3000 instead. But presuming the specs for the two model numbers are the same the 1.8 volt sensitivity spec you cited is correct, and the gain of the amp from its unbalanced input is 34 db, which is probably about 8 db higher than average for a power amp.

The gain provided by the LOMC input of SCM’s VTPH-1MC+ is 66 db. That corresponds to a voltage multiplication of 1995x. That would raise a 0.24 mv cartridge output to 1995 x 0.24 = 479 mv, far less than the 1.8 volts that is necessary to drive the amp to its maximum power capability. To be precise, about 11.5 db less than what is necessary, which means that his amp that is rated at 300 watts into 8 ohms would only be putting out about 21 watts into 8 ohms when the cartridge is providing its rated output and the passive preamp’s volume control is set at max!

But let’s assume that high volume dynamic peaks of some recordings may cause the cartridge output to be in the area of 3x the rating, corresponding to about 10 db more than the cartridge’s output under the standard test conditions. Those peaks would result in an output from the phono stage of 479 mv x 3 = 1.44 volts, which would still be significantly less than what is required to drive the amp to full power.

And, again, the power amp would only see voltages as high as those numbers when the volume control of the passive preamp is at max!!

IMO, in most circumstances if the front end of a system cannot drive a power amp to full power the system has not been configured in an optimal manner.

Best regards,
-- Al