Anyone familiar with Dumble amp?

[Alan0354]

I am building the front end of the 1997 Humble Overdraft Specimen into my Bassman just for comparison. Since I have EL34 in, it's going to be very close to the Dumble. Now I am going to have 3 preamps in the Bassman chassis, this one, Marshall 2204 and my own. I just want to hear first hand what is so special about the Dumble.

I look at 2 other schematics, the 1984 and 1988 models, they all follow the same scheme, basically the BF/SF normal channel front end driving kind of a Marshall front end without the cathode follower to make up 4 stages. With this, it has the PRE-OVERDRIVE tone control that shape the clean signal, then drive two extra stages for OD before driving the final tone stack like the Marshall/Soldano et al.

What is so special and so secretive about Dumble? I read the guy even make buyers to sign an agreement not to open, copy the circuit. I am still a day or two off from completing and testing as I have to drill holes at the back of the chassis to put the pots in. Also new holes for tubes and all.

I just want to explore more different amp configuration before I build the second amp. It's kind of boring to build the Marshall with essentially the same circuit of my first KMD with major difference are the speaker, power tubes and OT.

[jazbo8]

Opening a can of worms again... "What is so special and so secretive about Dumble?"
Nothing and everything, first of all, the Dumbles are very rare amps and typically owned and played by world famous musicians, mere mortals need not apply... They are special because who play them and the famous recordings made with them. If you are talking about the circuit, then sure you can break it down and see like all guitar amps, nothing is "special", after all, they are just a bunch of wires and electronic parts... But even a cursory reading on Dumble amplifier will tell you that the Dumbles are specifically tuned to suit the clients/players, that's where the magic happens, and only great builders like Dumble, Fischer can come up with the goods, time after time. That's the art part...

Design-wise, you can toss out the Humble Overdraft, it bears very little resemblence to the ODS circuit - so if you want to clone one, at least start with the correct schematic, theampgarage is the place to get the correct schematics and information on the Dumble amps.

[Alan0354]

I have the ODS schematic, if you look pass the Jazz/Rock switching, the basic circuit is very similar. I choose this one because I want to get the basic ones. I think to each configuration, there is a certain sound characteristics. Mainly I want to see how the pre distorted tone stack affect the OD sound.

[jazbo8]

Similar is not the same... why not start with the correct one?!

[J M Fahey]

what is so special about the Dumble.

Larry Carlton, Robben Ford and a host other Guitar Gods play them.

Why do they play Dumbles and not something else?

See it this way: why would anybody go to a good tailor to have a suit custom made, while there are millons of cloth suppliers?

Is it worth U$50000 ? ..... looks that for some it does.

Did the Guitar Gods pay U$50000 for theirs?

I'd guess, say, somewhere around U$5000 .

Larry Carlton & Robben Ford - Live In Tokyo - YouTube

enjoy

[jazbo8]

I believe the current record is the Jackson Browne ODS that John Mayer sold (but unfortunately never got paid) through Maverick Music, it went for $275,000 before commissions. Only serious collectors and guitar gods need bother.

[DrGonz78]

Yeah I always heard about amps that had goop to cover up parts of the circuit so other's could not clone the amp. Here is a page that shows blue stuff all over the preamp circuit.
http://www.premierguitar.com/article...rdrive_Special

Also, I had someone send me a link a few weeks back from craigspist in dallas. Damn those amps are expensive. I just can't understand paying that much for anything amp related.
http://dallas.craigslist.org/ndf/msg/4635354392.html

[Alan0354]

Similar is not the same... why not start with the correct one?!

Because I don't want to deal with all the switching. Too much interaction if you have more wires bundled in the same area and it becomes sound through interaction of the wires. I rather modify later for Jazz if the sound intrigue me enough. So start with the Rock first, it would be easy to modify the values to ODS and see how it sounds first.

From the picture in post #7, looks like there is a toroid inductor in the PI section??!! Or is it only a trim pot?

[jazbo8]

Please look again, many of the part values are different and LNFB is misssing. You have to bear in mind that the Humble was drafted before accurate ODS schematics became available, I would not waste any time on it.

[big_teee]

Where are the schematics you guys keep referring to?
How about some links we can all look at?

[Enzo]

There are a bunch here:

Amplifier Schematics

[loudthud]

Where are the schematics you guys keep referring to?
How about some links we can all look at?

At Amp Garage you have to be a member and be logged in to see any atachments. There is a sub forum Dumble Discussion and another Dumble Files.

[Alan0354]

Please look again, many of the part values are different and LNFB is misssing. You have to bear in mind that the Humble was drafted before accurate ODS schematics became available, I would not waste any time on it.

Actually the original 1984 and 1988 did a lot of switching of the ODS, I don't think it's about which one come first.

What is LNFB?

I am not building the whole amp, just the preamp section, just want to get a taste of it. Yes the values are slightly different, but the only major difference is ODS has a bright switch. I side by side compare, the difference is very very little. From my experience, it's not going to make or break one way or the other.

BUT if you actually think the ODS sounds better, then I can just use the values of the ODS and just not building the switching stuffs. I have not complete it yet, so it's easy to do at this point.

I bet Dumble is very particular in the placement of the wires. He might have a recipe of wires interaction that he keep to himself.

[Alan0354]

There are a bunch here:

Amplifier Schematics

One thing is the few schematics are all having the clean channel with tone stack driving and second preamp section to get OD. But in a lot of pictures of Dumble amps, there are no second sets of tone stack ( T,M and B knob).

[jazbo8]

Actually the original 1984 and 1988 did a lot of switching of the ODS, I don't think it's about which one come first.

What is LNFB?

But in a lot of pictures of Dumble amps, there are no second sets of tone stack ( T,M and B knob).

You can skip the various tone shaping switches if you want, but look at the gain setting resistors across the stages, there are quite a bit of difference. LNFB = local negative feedback, it's on the second gain stage. Second set of tonestack was added to some later generations of ODS, there were also versions with trimmers mounted inside the chassis, they allowed tweaking the OD channel's tone, it's up to you whether you want to include it or not. My point is that you should try the circuit as is, since you are trying to find out "what's so special about the Dumble", why modify anything at all before you even hear it?