Ampbooks Phase Inverter calculator

[überfuzz]

Hi!

I'm messing about with a phase inverter. Doing so I play around with this phase inverter calculator. What are the figure presented just in front of the dB figure?

[pdf64]

They're the straight Vout / Vin voltage gain ratio, then the figures in brackets are the same number expressed as dB of voltage gain.

[überfuzz]

Okay! Is there some rule of thumb to how hard a phase inverter can/should be pushed?

[Enzo]

Well, not so far as to make it clip.

[DRH1958]

Just as a small bit about that site, hit the back button on that page for some other great resources. They have some super info on that site.

[überfuzz]

I've messed around now with the phase-inverter in my tinker-amp. I didn't do any simulations with frequency sweeps, but is there much filtering going on in the phase-inverter? Judging by the probing equipment placed on the side of my head the voicing of the amplifier is affected by the tinkering I did.

[DRH1958]

I suppose we need to know what "tinkering" you did. It should pass all frequencies just fine given the proper value of coupling caps and proper bias. Have you applied NFB to it? This is a common place to tie in the NFB resistor. How about a presesce control tied in also? Other parts of the amp can affect the operation of the LTP. As Enzo said, don't drive it to distortion. Also tied in with coupling caps value is blocking distortion.

[J M Fahey]

FWIW I simulated classic first plate resistors 82k , 91k , and 100k ; with the secondary plate kept at 100k.
There was a slight gain adjustment, but very small, doubt I can hear it.

[pdf64]

I find that an LTP can sound great when overdriven; a dual 'Trainwreck type 2' master volume between it and the power tubes reveals that there can be little tonal difference between power amp overdrive and the LTP. Rather it's more of a feel / dynamic response / squish / sag that makes power amp overdrive better.
12AX7 tend to sound nicer when overdriven than 12AT7, and a reasonable amount of source impedance driving it is good, eg 220k mixers.
I've not tried driving one with a large signal swing / low output impedance source, eg cathode follower, but suspect it may not be beneficial.

[überfuzz]

I tried different plats and grid resistors. The setup that I ended up with, this time, was 91-100kOhms plate and 220k grid. I dont think i have much gain distortion going on. There might be a tad more treble...