Cathode Follower Feed to Tonestack in Dumble Circuit

[David Root]

Anyone tried this? Does it have anything to offer vs. the conventional plate feed from V1A? Did HAD ever use it eg in SSS?

I am wondering if it would improve the amp's ability to project in a mix.

Also what about a CF feed to the OD section ie between V1B and the OD relay? Any perceived benefit there?

[Max]

Did HAD ever use it eg in SSS?

As far as I remember right now he did not, at least not in one of the amps I am familiar with.

Max

[talbany]

Also what about a CF feed to the OD section ie between V1B and the OD relay? Any perceived benefit there?

Dave
Iv'e done some experimenting with CF within various gain stages and here is what I concluded..
CF set up like a buffer (Marshall type) lower impedance so in this situation( a low-level signal application), you want maximum voltage transfer, not maximum power transfer (Like output section) in order to achieve this the source impedance must be at least 10 times lower than the load impedance, you're okay, because you'll get 90% of signal transfer so you need to be aware of this when implementing the low impedance source within the gain stages..If not you will end up loosing quite a bit of voltage/gain and the amp will sound choked..Also The lower the source impedance, the less high end you'll lose in the preceding gain stages so the buffer becomes a sort of treble booster (Generally a no no when designing a OD stage)..CF generally work best when using long cables like the front of your pedal board, or effects loops for outboard gear or in the caes of the Bassman driving tone stacks that preceed the OP section and of coarse feeding the OP tubes grids for greater headroom..The only place where a CF might be implemented in an ODS style amp is before the HRM tonestack.. I remember several trying this and commenting that it really didn't buy them much in the way of tone..Everybody is different your ears might be different... Good Luck!!
Layout provided by Normster

[dogears]

Carlton's amp.... Sort of.....

Also what about a CF feed to the OD section ie between V1B and the OD relay? Any perceived benefit there?

Dave
Iv'e done some experimenting with CF within various gain stages and here is what I concluded..
CF set up like a buffer (Marshall type) lower impedance so in this situation( a low-level signal application), you want maximum voltage transfer, not maximum power transfer (Like output section) in order to achieve this the source impedance must be at least 10 times lower than the load impedance, you're okay, because you'll get 90% of signal transfer so you need to be aware of this when implementing the low impedance source within the gain stages..If not you will end up loosing quite a bit of voltage/gain and the amp will sound choked..Also The lower the source impedance, the less high end you'll lose in the preceding gain stages so the buffer becomes a sort of treble booster (Generally a no no when designing a OD stage)..CF generally work best when using long cables like the front of your pedal board, or effects loops for outboard gear or in the caes of the Bassman driving tone stacks that preceed the OP section and of coarse feeding the OP tubes grids for greater headroom..The only place where a CF might be implemented in an ODS style amp is before the HRM tonestack.. I remember several trying this and commenting that it really didn't buy them much in the way of tone..Everybody is different your ears might be different... Good Luck!!
Layout provided by Normster

[talbany]

Carlton's amp.... Sort of.....

Scott
I can see where you could sub V2A for the CF drive the HRM low impedance and have only 3 gain stages when in OD for those who don't like alot of gain in their OD tone (depending on how you set it up).. You would no doubt have to make several other design changes.. I imagine the BM stack/NFB would work well here and could let the amp run a bit more open in OD...Take Care!!

Tony

[David Root]

Thanx to all, I knew someone had to have looked at this before.

I was interested in voltage transfer from V1A to the tonestack, ~37K V1A plate into ~4.5M CF, out of CF at 600 ohms, now a source into way more than 6K ohms in the tonestack has to pass more signal than ~37K V1A plate would directly into the tonesatck, yes/no?

Or did I miss something?

[talbany]

Dave

Do you plan on doing it like the layout I posted?.. If it's different can you write out the topology..

Tony

[David Root]

I would put it ahead of the non-HRM tonestack.

V1A is CL1. V1B is the CF. V1B cathode feeds slope resistor and treble pot coupling resistor etc., treble pot wiper to vol pot in, vol pot wiper to V2A, which is CL2.
V3 is OD, V4 has to be added for the PI. V2B is not used.

Requires some reorganization on the board, I didn't look at that yet.

OR

V1A and B in parallel is CL1, V2A is the CF, V2B is CL2... etc as before.

[jelle]

IIRC this is the dave funk mod to black face amps. Recovery after the tone stack is the stolen gain stage from the reverb driver. 12AX7.

[David Root]

I was looking at a 6G6 schematic, but that has two tonestack recovery stages (sort of). All I'm doing is putting in the CF between the first stage and the tonestack, it's still CL 1 to CL2, single tonestack recovery stage.

[talbany]

I would put it ahead of the non-HRM tonestack.

V1A is CL1. V1B is the CF. V1B cathode feeds slope resistor and treble pot coupling resistor etc., treble pot wiper to vol pot in, vol pot wiper to V2A, which is CL2.
V3 is OD, V4 has to be added for the PI. V2B is not used.

Requires some reorganization on the board, I didn't look at that yet.

OR

V1A and B in parallel is CL1, V2A is the CF, V2B is CL2... etc as before.

Cool!.. Just my personal preference but I prefer at least 2 gain stages to drive the CF.. it seems to give the stack more range especially low end.. Your ears and style may tell you differently..
Personally I would look at the JTM/Bassman Vol- input then after the 2nd gain stage drive the follower then TS out of the top of the treble pot to the relay then to however you want to set up the OD section..


Tony

[David Root]

OK Tony, that is very interesting, so you have to build up a head of steam, so to speak, with two gain stages, before hitting the CF to the tonestack.

Would a pentode adequately replace two triodes in this, eg 5879? I like 5879s, this does not necessarily have to be a "Dumble-y" solution.

[talbany]

Would a pentode adequately replace two triodes in this, eg 5879? I like 5879s, this does not necessarily have to be a "Dumble-y" solution.

That's a great question Off the top of my head I would say sure or at least worth the try.. If it does work out I imagine it would give you a nice Stratty Voxxy top end..It would sure cut through the mix.. This has been something I've wanted to try but never got around to protoing it.. trying and talking about stuff like this is sooo much fun..Good Luck!!

Tony

[jelle]

I was looking at a 6G6 schematic, but that has two tonestack recovery stages (sort of). All I'm doing is putting in the CF between the first stage and the tonestack, it's still CL 1 to CL2, single tonestack recovery stage.

Exactly, that's what I know as the dave Funk mod.

jelle

[FUCHSAUDIO]

Carlton's amp.... Sort of.....

Also what about a CF feed to the OD section ie between V1B and the OD relay? Any perceived benefit there?

Dave
Iv'e done some experimenting with CF within various gain stages and here is what I concluded..
CF set up like a buffer (Marshall type) lower impedance so in this situation( a low-level signal application), you want maximum voltage transfer, not maximum power transfer (Like output section) in order to achieve this the source impedance must be at least 10 times lower than the load impedance, you're okay, because you'll get 90% of signal transfer so you need to be aware of this when implementing the low impedance source within the gain stages..If not you will end up loosing quite a bit of voltage/gain and the amp will sound choked..Also The lower the source impedance, the less high end you'll lose in the preceding gain stages so the buffer becomes a sort of treble booster (Generally a no no when designing a OD stage)..CF generally work best when using long cables like the front of your pedal board, or effects loops for outboard gear or in the caes of the Bassman driving tone stacks that preceed the OP section and of coarse feeding the OP tubes grids for greater headroom..The only place where a CF might be implemented in an ODS style amp is before the HRM tonestack.. I remember several trying this and commenting that it really didn't buy them much in the way of tone..Everybody is different your ears might be different... Good Luck!!
Layout provided by Normster

Actually pretty "anti-dumble" imho. The whole premise of the D-style OD is a pair of gain stages, each clipping one side of the waveform to produce even order and balanced overdrive. Doing one OD stage and a CF is more Marshall-like, and heaver on the odd-order harmonics, with a harder clip. More aggressive for sure, even when tamed by a post OD stack or trimmer. I haven't much like LC's od tones for the last few years, now I know why...lol.