'80s Dumble?

[Frank W]

Hi everybody, this is my first post here. Great place! Let me introduce me by saying that I understand zilch about electronics (I hope to change that), but have been haunted by Dumble-tones ever since I played an ODS some ten years ago. A friend of mine is building a mod on a Fender Concert "II" platform using the Hybrid A schematics that sounds very promising at the current state. I'll report how it develops.
Now my question: I know of the '77, the Hybrid A and the '97 schematics, but have never seen '80s schematics, although the '80s amps (like Robben's) are often refered to as the "grail" amps. Does anybody know what HAD changed from the '77 schematics? Only some values (so close to Hybrid A) or a different topology? I know every Dumble is different, but maybe there are some common traits?

[Robert]

Here's a great read by the very knowledgeable Steve Ahola written some years ago. It has some of the circuit evolution of the Dumble amps over the years. It should answer some of your questions. I think this is in the Dumble files section but couldn't find it.

[ayan]

Here's a great read by the very knowledgeable Gil Ayan written some years ago. It has some of the circuit evolution of the Dumble amps over the years. It should answer some of your questions. I think this is in the Dumble files section but couldn't find it.

I was not the one who put those notes together, Robert. If I'm not mistaken that was the work of Steve Ahola.

Gil

[jaysg]

A friend of mine is building a mod on a Fender Concert "II" platform using the Hybrid A schematics that sounds very promising at the current state. I'll report how it develops.

Please do. That's what I have. Fwiw, I was extremely pleased when I replaced the OT with an Allen TO2/4/8. The problem there is that it has different feet and one of the through holes has to be moved. (read drilling steel)

[Robert]

I apologize Gil for the error. I have collected many articles regarding Dumbles especially from Ampage. Several of the forum threads from their archives had conversations with you in them. Seemed like you were the most knowledgeable at that time and I must have assumed you wrote it. Anyway, my intent was to provide what had already been written so you or someone else wouldn't have to. Hope it helped.

[Frank W]

Thanks for the Notes on the ODS! They will surely help us to fine-tune the amp. If understand it right, the mods described there are generally made with the intention of making the amp sound smoother. Am I right? However, I'm still confused whether 80's amps are basically different from 70's amps like HRM amps are or if HAD just tweaked his old design. Does anyone know?

[Darkbluemurder]

Fwiw, I was extremely pleased when I replaced the OT with an Allen TO2/4/8. The problem there is that it has different feet and one of the through holes has to be moved. (read drilling steel)

Jay,
what were the difference in sound (louder, smoother, more detailed, more bass/treble etc.)? I have heard from other sources about Allen and Mercury being the top replacement sources for Fender type OTs.

[jaysg]

what were the difference in sound (louder, smoother, more detailed, more bass/treble etc.)? I have heard from other sources about Allen and Mercury being the top replacement sources for Fender type OTs.

The big difference is with the clean channel, which I blackfaced, instead of dumblizing. When dimed, there were some dissonant overtones with the orginal OT that went away with the Allen. There's now better string to string definition and a nicer high end. When played clean, there's no real difference. I had a '66 single Showman for comparison. I feel like it sounded good before, but after swapping OT's it sounds exactly like a BF Fender should.

I had to bring the size of the post PI pass caps down, because it farted with whatever I had in there -- probably 0.1uF's. On the ODS side, the tone improved by becoming less midrangey and clearer with an improved high end. It's not louder. Allen's pricing made it an easier leap of faith than MM's.

I have the boost on a pull switch. I think I have to replace the phono plug/jack switching scheme with a DIN connector and rear-panel toggle switches to add the footswitchable boost. I've got a jumper/switch on the effects loop and reverb, and I can't tell the difference in or out. I'm sure Scott could...lol.

[mlp-mx6]

+1 on the good output from David Allen. I did a new build, not a replacement, but I couldn't be happier w/ that iron.