Cathode Follower after One Gain Stage

[RockinRocket]

Can you drive a dc cathode follower after one gain stage for a Tone Stack?

If so what would be the negatives. The gain is less than one correct? So if used in a marshall 18 watt or similar amp where there would be an extra triode going to waist would the PI be driven not as hard?

Sure I could use it as a 2nd gain stage but I don't really want more pre amp gain but would like some compression of the follower to experiment with.

[martin manning]

Sure, no problem. The gain is only slightly less than 1, so it will only cost you a couple tenths of a dB. You could also experiment with bootstrapping as described at the bottom of this page, and get a gain boost: http://www.valvewizard.co.uk/dccf.html Reducing the size of the bootstrap cap will get you a treble boost.

[RockinRocket]

I thought it would be a no issue. Surprisingly ive never seen a amp with this configuration.

[pdf64]

The brown bassman used a dc cf on the 2nd stage of its bass channel http://bmamps.com/Schematics/fender/bas ... _schem.pdf

[Kagliostro]

Surprisingly ive never seen a amp with this configuration.

Do you mean the CF or the bootstrapped ?

a DC coupled CF driving a ToneStack after a gain stage is the TopBoost Vox AC30, not very rare


K

[10thTx]

I have NOT built this amp and it is simply a DRAFT idea.

I had the same thought about a CF after a V1 pentode

with respect, 10thtx

[martin manning]

Surprisingly ive never seen a amp with this configuration.

Do you mean the CF or the bootstrapped ? a DC coupled CF driving a ToneStack after a gain stage is the TopBoost Vox AC30, not very rare

AC30 w/ TB and many others (from Fender Bassman on) have a DC coupled CF driving the tone stack, but the usual arrangement is G-G-CF-TS, i.e. two gain stages before the CF. The 6G6 Bassman pdf linked is the odd one with G-CF-TS.

[RockinRocket]

Yes the 2 gain stage is very popular. However still never seen a cathode follower following only ONE gain stage.
As in amps that leave a free triode open and use some simple treble control could be replaced with a CF and Tone stack.

[martin manning]

However still never seen a cathode follower following only ONE gain stage.

Fender 6G6-B which pdf64 linked above has exactly that in the bass channel.

[RockinRocket]

However still never seen a cathode follower following only ONE gain stage.

Fender 6G6-B which pdf64 linked above has exactly that in the bass channel.

Oh yes that is it. I overlooked it when I saw it. Thanks guys

[strelok]

How easy would it be to overdrive the CF in this case? I've been tossing around a similar idea in my head and was thinking you might need to put the volume control at the input of the amp since obviously it can't go right after the first gain stage and it might be possible to clip the CF before anything else does if the volume knob is set low enough if its placed after the CF/tone stack.

[RockinRocket]

Wouldn't putting the Vol pot at the input of the amp be redundant since that is basically the guitars Vol pot?

[Tobyk]

Will this second stage CF create as much compression and H2 as one with two stages before it?

[Tobyk]

Will this second stage CF create as much compression and H2 as one with two stages before it?

I think not.. an earlier stage would render less compression

[cdemike]

Almost certainly less compression. The signal swing won’t be as large since there’s less amplification, so less bias shifting effect as the CF’s grid becomes more positive and draws more grid current.

In addition to the Blonde/Brown Bassman, Hiwatt SAP’s also use a CF immediately after the input gain stage. However, the Hiwatt design uses it as part of a volume cut operated via foot switch rather than to drive a tone stack. I actually prefer my SAP clone with a boot up front, though, since I really like CF compression.