Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: kagliostro on September 05, 2013, 03:52:32 pm

Title: Adding a stage with the intention to add harmonics and not gain is a good idea ?
Post by: kagliostro on September 05, 2013, 03:52:32 pm

I would like to know if the addiction of a stage can be done with the purpose to add harmonics and not gain

and I've some question about

for this purpose a CF stage is useful ?

is better to build an anode follower with some gain and to drop it via a partition resistor or to use an = to 1 gain architecture ?

is better a triode or a pentode for this use ?

Thanks

K

Title: Re: Adding a stage with the intention to add harmonics and not gain is a good idea ?
Post by: jjasilli on September 06, 2013, 01:02:07 pm

Yes, this is a major purpose of cascading gain stages, and pioneered by Mesa Boogie.  Each 12AX7 stage amplifies its input signal by a net of about 60X.  So after one gain stage a 200mV guitar signal is 12V, after the next stage 720V!!!  Clearly this amount of gain is being attenuated and thrown away for some other purpose.  One purpose is to saturate the signal with harmonics.  Another purpose is to smooth out overdrive tone:  it's the bottom half of the signal wave that gets clipped.  The next gain stage is out of phase, and clips the other half of the signal.  The 2 clips may be purposefully designed to be symmetric, or asymmetric.  Each individual clip will produce its own set of  harmonics.  And, specific harmonics will be determined by the symmetry or asymmetry of the cascaded gain circuits.

Title: Re: Adding a stage with the intention to add harmonics and not gain is a good idea ?
Post by: kagliostro on September 07, 2013, 09:25:14 am

Many thanks for the answer jjasilli

That is a very interesting matter, not easy to manage, but very, very interesting

Franco

Title: Re: Adding a stage with the intention to add harmonics and not gain is a good idea ?
Post by: jjasilli on September 07, 2013, 12:59:54 pm

To quote PRR, plagiarize from a known circuit you like.  :icon_biggrin:

Title: Re: Adding a stage with the intention to add harmonics and not gain is a good idea ?
Post by: kagliostro on September 07, 2013, 04:37:58 pm

Ohhhh Yesssss !

:thumbsup:

Franco