D'Mars ODS & FX & 2CF

[tubenit]

I decided to try something ..................  and I like how it turned out!

The D'Mars ODS with on board FX  sort of had two cathode followers in series & I wondered what would happen if I removed one? 

Please NOTE that Doug Hoffman came up with a FX for Marshall type using one triode in a recovery stage. 

So I decided to move the "redundant" CF to the overdrive stage and see what happens?  One of the TOS (Tweed Overdrive Special) that I did had 2 CF's with one of those being connected to a 5879 in the overdrive section. (I really wish this D'Mars amp had been punched out and laid out better, so I could have had a triode into a 5879 with triode CF.  But, there isn't room.)

So, what is the results tone wise of moving this?   I can not say that it is unequivocally "better".  However, I can say the harmonics in the OD section are quite a bit superior to the OD without the CF. 

AND the 2CF gave the amp increased touch sensitivity, a lot more harmonics,  & a bigger "cranked" tone that is more compressed.  This is a very very musical tone with a very transparent OD tone.

What it lost was some of the "blooming" feature that the Dumblish OD had.  The sustain is about the same, but the notes don't open up and "blossom"  when the CF is added.   (I would describe this blooming and blossoming thing as an audio version of fast photography of a rose bud opening up.)  And it does not have the "vowel" tone as much using the 2CF version OD. (I'd describe the vowel tone sort of like you hear with a wah wah pedal notched about half way)

It's a different tone and very harmonically musically sweet. I think it would allow for more aggressive playing.  The dumblish OD with blossoming almost requires a different pick and attack that is more subtle  and restrained to sound it's best.  This CF versions sounds the sweetest to me really digging in!

I'd dub this version 65% Marshall tone and 35% Dumblish tone giving the edge to a sweet Marshall touch sensitive tone, IMO.  Very cool tone.

There is a great deal more transparent OD tone to my ears with the 2CF version.  And a very slight improvement in transparency in the clean channel.   I am thinking that the V3a in the original FX structure might actually detract or siphon off some transparency/tone?

The amp does seem somewhat louder also.  I noticed needing to turn the FX level knob down a little.

With respect, Tubenit

[kagliostro]

Hi Jeff

good and interesting experiment  

looking to the difference between the two solutions the first thing that appears is that moving the CF between the OD channel and his Tone Control

you have less load on V2b and so you preserve the gain to be tamed by the tone control

this, almost certainly, is the reason for which you need to turn the FX level knob down

Franco

[tubenit]

I experimented a little more.   V2 is a 5751 that I am using for the OD.  V3 is a 12AY7 that I was using for the FX.

So essentially what I have in the OD is a 5751 V2a into a V2b with a 12AY7 V3a cathode follower. 

I wondered IF that was going to be an issue with 5751 V2b/ 12AY7 V3a?  So I tried a 5751 in V3 to match V2b.
It was quite a bit louder but not as musically sweet to my ears.  I then tried a reverse 12DW7 and did not care for that.

So, I went back to the 12AY7 and feel like the sweet spot is more with that combination.  Ironically, I am finding the amp significantly louder with the FX send triode moved into the CF position on the OD.

Just an FYI.     With respect, Tubenit

[kagliostro]

Ciao Jeff

Ironically, I am finding the amp significantly louder with the FX send triode moved into the CF position on the OD.

Why ironically ? This is exactly what I would have expected

Franco

[Tone Junkie]

Jeff is that schematic as built. I just did the Effects loop that way on another build with a cathodyne PI, if thats the right term.    I didnt have room for another tube and wanted the Effects loop, it worked real nice . I like to use the effects loop volume at the end for my master it sounds so much better than the other versions ive used.
Bill
 

[tubenit]

Yes, that is the schematic as built pretty much.  I made two minor changes.  V1-1 is now 180k instead of 120k. Drive pot is wired differently.  And the V2-8 cathode cap is switched by a relay now.

With respect, Tubenit