New tone mod for the D'Mars ODS

[tubenit]

The clean channel on the D'Mars is excellent to my ears and has a nice tight punchy bass.  While the OD channel has sounded good, it has sounded quite a bit thinner then the clean channel in the bass response.

The problem was increasing coupling caps or cathode caps in the OD section only added  distortion/mud and the clarity of the OD suffered.

So, today I thought that maybe if I bypassed the tone stack going into the OD that this would help the bass response be tighter and have more punch without the mud/distortion.

I tried using an .02, then .068 and settled on a .1.   I originally tried a 150k after the .02 but the drop in volume was too great.  I then tried a 56k but it did not have a "musical sweet spot" with that value.  Ultimately,  I settled on a .1 into a 10k resistor.  I did try it with NO resistor but thought the 10k actually added some smoothness.

What surprised me was how high a value coupling cap was needed for the bypass to get a similar bass response as the TMB tone stack??  The .1 value was much higher then I expected.   Having this .1 between the clean and the OD has allowed the OD to still have the clarity in the overdrive without turning to distortion or mush,  IMO.

Wished I had stumbled on this mod yrs ago! 

I should add the TMB tone stack on the clean is pretty much a "set and forget" thing for me.  And the OD channel still has a hi-frequency cut that allows some tone shaping as well as the pickup switch and tone pot on the guitar.  So, no loss for me there.

With respect, Tubenit

[tubenit]

I am really loving this mod!  The OD sounds very transparent and MUCH thicker doing this!  This is definitely a "keeper" mod for me.

However, I noticed that the mid-boost feature in the tone stack doesn't work on OD now.  (actually really isn't needed with this mod)

So,  I pondered some different options.

1)  bypass tone stack mod
2)  switchable between bypass tone stack mod ................... or using tone stack
3)  using a pot to mix between bypass of tone stack or using tone stack
4)  using a relay switch to use the tone stack bypass as another boost feature for both clean or OD

With respect, Tubenit

[tubenit]

Here is yet another option.

This allows the THICK OD tone and the normal  clean using the TMB tone stack.

OR .........................

A THICK OD and TMB tone stack combined on the OD ............................... and then just the TMB tone stack on the clean channel.

with respect, Tubenit

[kagliostro]

Hi Tubenit thanks for sharing 


it will be nice if you add schematics and explanations to the original D'Mars ODS tread


Franco

[guitardude57]

There is an option to make a small daughter board
with trimpots and caps to create a tone circuit for just the OD.
Worked for Howard on the HRM...

[guitardude57]

Here is an example of one...

[tubenit]

IIRC, the original HRM was off the plate of the second gain stage of the OD of the D-HRM.   So, I am presuming on the D'Mars that you're thinking of using this off the cathode follower behind the 5879 pentode?

IF so, that sounds like a good idea.  Thanks!

With respect, Tubenit

[JJones]

Tubenit, I'm considering building one.  After a bit of searching, I can't seem to find what size the chassis is.  Any insight?

Thanks for the concepts!

[tubenit]

20" X 8" X 2.5" with outward edges to attach.

There is a current chassis photo, updated information,  schematic and layout in SCH form here in reply #1:

http://el34world.com/Forum/index.php?topic=17305.0

Not a particularly neat wiring job but the amp is very very quiet at idle even when the pot settings have the volume cranked up

With respect, Tubenit

[JJones]

Looks neater than my work... 

Thanks for all your help!

[Ritchie200]

Ahem......  I believe it's time for another recording session?

Jim