DuMars OD special

[10thTx]

I built this amp trying to combine ideas from a Marshall, a Dumble style approach and my Tweed Overdrive Special using a low wattage cathode biased approach & a 5879 in the OD.

I like the results. Nice cleans that are harmonically rich. The OD does not have quite the blooming as the Tweed Overdrive Special but it is more harmonically sweet in it's tone. On clean, it sound Marshallish. With OD engaged, I can get a range from a quasi-clean slightly overdriven tone all the way to a more OD with a vowel tone and slight blooming where the notes swell and open up.

IF any of the moderators would prefer I post "D-inspired amps" in the technical discussion instead of here just let me know & I will do that in the future.

With respect, 10thtx

[10thTx]

This is the new D'Mars OD special amp. I started off on just clean withOUT the mid boost on. Then switched to the OD with midboost switch on.

http://www.soundclick.com/player/single ... i&newref=1

For illustration purposes, ......... if 0 is clean and "10" is the OD fully cranked ................ the OD here is around 7. I purposely somewhat cranked the OD to illustrate the range of contrast that the amp can have.

There is a sweet spot that sounds alot like the "clean" channel except with more harmonics, sustain and blooming to it where the notes sort of open up. On that same scale the OD sweet spot would be maybe "3.5 to 4". So this OD tone is cranked beyond that and not as "sweet".

On this clip, the trim is around 7, the drive is around 5 and the level is slightly less than 3. The OD sweet spot is more with the trim around 3-4, the drive around 4 and the level around 7. The clean volume was 5 and the PPIMV was around "5.5-6".

The guitar volume was around 7. At 8 and higher audibly increases the blooming. And when the amp clean volume is at "7", there is a significant increase in blooming also.

Anyhow, excuse the mediocre playing. Hopefully, this will show some of the diversity of the amp. No pedals were used. I added some EQ, very slight compression and some delay in the mix.

8/21/12 Here is another soundclip:
http://soundclick.com/share.cfm?id=11842172

It starts off with the clear OD tone, then clean, then FAT OD & then back to clear OD tone.

With respect, Tubenit

[da Geezer]

I built Tubenit's DuMars preamp (only) into a gutted Epi Valve Jr head, using the existing chassis & PT.

I changed it up a bit by adding a "pseudo" channel (switchable presets of Gain/Drive/Level controls on the OD channel), so with the foot-switchable PAB (ground-lift type), I have 6x basic tones available on the 3-button footswitch. That, along with varying the pickup selection, pick attack & volume/tone controls on the guitar, I can get pretty much ANY tone from the amp without touching the amp...EVER!

Here's a poor quality soundclip, recorded straight thru with no editing (some clipping here & there....sorry) but it gives a pretty good rep of what the amp can do.

Amp settings were NOT changed at all....all the different tones were achieved by channel switching, varied pick attach, pickup selection & guitar volume/tone control. Recorded dry with a little verb & delay added in Mixcraft.

0:00 thru 4:11 is an ES-150DC hollowbody
4:12 on is an '87 maple neck Tele with Bill Lawrence pickups

skip ahead to the Tele when you get tired if the endless 1st part....it's very "spanky"

http://soundcloud.com/dageezer/dumars-noodles1-0

Thanks for listening, & MUCH THANKS to Tubenit for all the work he put into the design....I LOVE this amp!

BTW, the preamp is being run into a 2x6AQ5A power amp, cathode biased @~10w, so the overall volume of the amp is very low (you can hear me stepping on the footswitches & flipping the pickup selector @ about the same volume as the amp), but it sounds & feels MUCH bigger. Cab is a 1x12 closed back ported with a Texas Heat.

[lovetone]

Can you tell me the purpose of the IRF 820 mosfet transistor?

Thanks

[Jack Hester]

Can you tell me the purpose of the IRF 820 mosfet transistor?

Cathode follower. I had quizzed him early on about its use, instead of a tube. I believe it's installation may have been out of convenience (not having to add another tube to an existing build), but he can speak up and tell better. Anyway, it stuck, and is doing a good job.

Jack

[10thTx]

Not sure, but Geezer may have OD PS caps and RD65 resistors in that D'Mars preamp?

For anyone interested, there is a lengthy thread (241 posts) on the Hoffman forum about this amp, schematics, layouts, relay switching, cap foil orientation, etc.......

http://www.el34world.com/Forum/index.php?topic=14201.0

And there is some additional editable SCH schematic and layout, voltages, here along with Bill of Materials:

http://www.el34world.com/Forum/index.php?topic=14302.0

Also Doug Hoffman will have a turret board for the D'Mars OD Special. Just send him a PM if interested because it's not listed in his catalog yet.

With respect, 10thtx (Tubenit on the Hoffman forum)

[da Geezer]

Not sure, but Geezer may have OD PS caps and RD65 resistors in that D'Mars preamp?

Correct!

And on the Mosfet CF, it's a real space saver & performs perfectly in that function, but a triode could easily be subbed.

G