I’ve been away, advise requested, rehearsal report added.

[Bob-I]

Hi folks, I’ve been away for a few years. Retired from my day job, playing a ton using amps I’ve build, restoring a 1948 Ford truck, and mostly enjoying time with my granddaughter.

A few years ago I build a hi-plate non HRM ODS in a Princeton Reverb chassis. The clean side is really great but the OD side not so much. Since I’ve been playing in an Allman Brothers Tribute band, I’ve mostly been using a Marshall type amp, either the 45 watter I built, or (gasp) a DSL40C I bought. To be fair to the amp builder in me, the DSL was broken when I bought it, easy repair and a few mods.

With the recent news on HAD passing, I pulled this amp out again, hoping to tweak the OD. I’ve got it sounding ok, but it doesn’t scream “Dumble” to my ears. There’s a buzzy, mushy sound I just can’t get past.

Give a listen please. Just me noodling using a LP type, single PU, Duncan JB. Cab is a 2x12 with WGS Veteran 30s. Cell phone recording.

For the first 50 seconds I’m playing in the clean side. At about a minute I hear a woolly/buzzy sound peaking out. Any thoughts on what’s happening are appreciated. Again, it simply doesn’t sound like a Dumble to my ears.

https://drive.google.com/file/d/1P8SuQZ ... p=drivesdk

Thx in advance for your help.

[Vintagelove]

Far from an electronics expert here, but my 2 cents.


It did have a bit of a "splatty" sound to the distortion that reminds me of a tube being hit too hard. Your cleans sound fine, so it makes me think you should try backing down the level hitting the OD circuit with the internal OD trim, and/or lowering the bypass cap on v1b.

Hope it helps.

[Bob-I]

I agree it sounds like a tube being hit too hard. I did adjust the OD input trim, no change. Now the bypass cap might make sense. I have a 5uF now, I’ll try a 1uF and see what happens.

Looking at the waveforms on the scope, it appears to be overdriving as expected, no hard clipping. Here’s a pic of the output of v2a.

[martin manning]

Which circuit do you have and what are the component values around the OD stages?

[bepone]

base of the sound is ok... try to remove all bright caps from the first volume pot, and put simple vintage brown ceramic cap 470pF 500-1000v for the treble control.. also to put carbon film in od section.. resisitors in od circuit can be increased from 100k to 150-330k to the drive pot according to taste .. all this is changing top end...trim pot for od 30-40k doesnt matter.. lead dress is more important.. grid wires in the air makes difference... output transformer secondary wires, where are they passing, shouldt be below of half of the preamp..

[talbany]

Hi folks, I’ve been away for a few years. Retired from my day job, playing a ton using amps I’ve build, restoring a 1948 Ford truck, and mostly enjoying time with my granddaughter.

A few years ago I build a hi-plate non HRM ODS in a Princeton Reverb chassis. The clean side is really great but the OD side not so much. Since I’ve been playing in an Allman Brothers Tribute band, I’ve mostly been using a Marshall type amp, either the 45 watter I built, or (gasp) a DSL40C I bought. To be fair to the amp builder in me, the DSL was broken when I bought it, easy repair and a few mods.

With the recent news on HAD passing, I pulled this amp out again, hoping to tweak the OD. I’ve got it sounding ok, but it doesn’t scream “Dumble” to my ears. There’s a buzzy, mushy sound I just can’t get past.

Give a listen please. Just me noodling using a LP type, single PU, Duncan JB. Cab is a 2x12 with WGS Veteran 30s. Cell phone recording.

For the first 50 seconds I’m playing in the clean side. At about a minute I hear a woolly/buzzy sound peaking out. Any thoughts on what’s happening are appreciated. Again, it simply doesn’t sound like a Dumble to my ears.

https://drive.google.com/file/d/1P8SuQZ ... p=drivesdk

Thx in advance for your help.

Hello Bob
I had a similar problem with my HRM's do you have any pictures handy?

Tony

[Bob-I]

Thx guys for jumping in. I’ll snap some pics later, and see if I can locate the schematic I used.

[Bob-I]

Which circuit do you have and what are the component values around the OD stages?

Here’s the layout.

[Bob-I]

base of the sound is ok... try to remove all bright caps from the first volume pot, and put simple vintage brown ceramic cap 470pF 500-1000v for the treble control.. also to put carbon film in od section.. resisitors in od circuit can be increased from 100k to 150-330k to the drive pot according to taste .. all this is changing top end...trim pot for od 30-40k doesnt matter.. lead dress is more important.. grid wires in the air makes difference... output transformer secondary wires, where are they passing, shouldt be below of half of the preamp..

No bright caps on the first volume pot, only the ratio and I added that to try to combat this issue. All CF except the plate resistors. 220k into the trim pot, 150k into the drive, trim is set at 40k.

I’ve never put grid wires in the air, always down to the chassis the way HAD did it. Look at the pics for more on lead dress.

91ADD823-5728-471B-B275-3EB120FCA265.jpeg

91ADD823-5728-471B-B275-3EB120FCA265.jpeg

12E3F3AB-8C69-4FF0-9C28-0398B754C82D.jpeg

[Bob-I]

Hello Bob
I had a similar problem with my HRM's do you have any pictures handy?

Tony

Thx Tony, pics are posted above, as is the layout. I may have changed a few things after assembly but you get the gist of it.

[bepone]

@bob
my opinion, what i see...
0. remove the capacitor from OD pot..no need
1. cathode wires usually going under the board, not over
2. anode wires usually going under the board, not over
3. tone stack controls usually are separated, not grouped woth others like here, and traveling against the chassis, not over the air, and are grouped with the wire coming from v1b, acting like negative feedback, killing the tone

4. this 2w xicon carbon film i never liked, they are all but not musical
5. i would lift g1 wires from the PI in the air and see the behaviour
6. i would lift g2 V2a tube wire in the air to see the behaviour
7. many pot max wires here traveling unshielded, and over the air..
8. for better sustain, lead dress of V1 can be grouped like in normal Dumble, 3 wires together (positive feedback)

so if this is mine i would have several days of work to make it how i think that need to look...

[mojotom]

6V6 power amp ?

[Bob-I]

Thx for taking the time to look.

@bob
my opinion, what i see...
0. remove the capacitor from OD pot..no need
1. cathode wires usually going under the board, not over
2. anode wires usually going under the board, not over

0. The cap was tacked in to see if it would help. I’ll pull it off, it didn’t help.
1. 2. I agree with this, but if I remember right, someone suggested running the leads this way, didn’t work as expected.

3. tone stack controls usually are separated, not grouped woth others like here, and traveling against the chassis, not over the air, and are grouped with the wire coming from v1b, acting like negative feedback, killing the tone

3. I’ve done tone stacks like this for years, never made a difference. That said, I did have them tie wrapped together, separated them so I could move them and listen for differences. I didn’t hear any. I’ll attack this last.

4. this 2w xicon carbon film i never liked, they are all but not musical

I’ve used them for years, always seem fine. Suggestions?

5. i would lift g1 wires from the PI in the air and see the behaviour
6. i would lift g2 V2a tube wire in the air to see the behaviour
7. many pot max wires here traveling unshielded, and over the air.

Good input. I haven’t found these things made a difference in other amps, but it’s worth looking at.

8. for better sustain, lead dress of V1 can be grouped like in normal Dumble, 3 wires together (positive feedback)

so if this is mine i would have several days of work to make it how i think that need to look...

All my other D-Style amps use this lead dress on V1, I don’t know why I didn’t on this amp, brain fart maybe.

[Bob-I]

6V6 power amp ?

Well…yes and no. It’s using Princeton type voltages, but I have 6Ls in there now,

[Bob-I]

CE19F292-FFF5-4232-A421-DB91C438A15E.jpeg

f

C0AC0F77-894A-433B-A72F-D149498BE3AB.jpeg

I spent some quality time with this amp today, reworked the lead dress on V1 and V2. Very subtle change in tone, and the fuzzy ness is still there.