OMG "Dumble" pedal ?!? ouch

[FUCHSAUDIO]

http://www.youtube.com/watch?v=DB-SUImHU5Y&feature=user

Hysterical.

[JimiB]

that sounds exactly like a dumble to me!

[Structo]

He's got a built in ring modulator in there!

[tele_player]

That video is terrible, but I built one of those a few weeks ago, and it's actually a pretty good stompbox. Like a Dumble clone, you've got to learn where to set the knobs. And you've got to get the right FETs, otherwise it's near impossible to set the bias correctly. You can see in the video, sort of, that he's having trouble getting it to settle at 4.5v. It's easy with proper FET's

That guy did a great job on the graphics - mine's in a plain red box.

For the curious:
http://olcircuits.com/olc_umble.html

[LeftyStrat]

But honestly, I compare it to any amp or pedal builder that relies on the built-in mic on a video camera to relay the sound of their amps/pedals. If you can't hear the overload and compression of that crappy mic, how in the hell can you expect me to believe you have golden ears?

Or posting shootouts of resistors or caps in mp3 format. With all the swirling phasing crap going on with mp3's, how am I supposed to hear anything?

Just reminds me of the old saying, "documentation is like sex, if it is good, it is really good, if it is bad, it's still better than nothing."

I think I could take the crappiest amp in the world and record it well, and the best sounding amp in the world and record it badly, and everyone would want to buy the bad one.

Oh wait, maybe Jimmy Page already did that.

[tele_player]

I don't think the guy who made that video is trying to sell them, just documenting his build for posterity (as if we care!)

It's a lot better than that. A friend played mine onstage recently, with a Les Paul and a Deluxe Reverb. He's a great guitar player, and it sounded really good.

[heisthl]

No camcorder I've owned made any amp sound that bad. I haven't heard tone with that horrid guacamoley sound since Frampton used a talkbox on the Live album.
F.Y.I. Frampton's doing Geico commercials now using a talkbox.

[philmanatee]

If he tweaked it a little more he could have got some of those tones like Henry Kaiser in that other video. Phil

[FUCHSAUDIO]

Good points all. I saw that circuit, and have yet to find the time to build it. I was curious, I am no longer...lol.

I wonder how many people heard it and said "man I don't want a Dumble if it sounds like that !".

I just put it up for hoots. Perhaps a "how not-to" make a demo video....lol.

[Bob-I]

.... And you've got to get the right FETs, otherwise it's near impossible to set the bias correctly. You can see in the video, sort of, that he's having trouble getting it to settle at 4.5v. It's easy with proper FET's
http://olcircuits.com/olc_umble.html

Interesting. Being a tube guy, can you enlighten us on the "correct" FET's? I'd like to build one for situations where I can't bring an amp.

[tele_player]

The schematic lists MPF102 and J201 as equivalent JFETS for this circuit. When my kit arrived, the JFETS were missing, so I went to Radio Shack, and bought what they had, which was one of those (I've forgotten which!).
Couldn't set the bias, the trim pots were way too touchy.

When the replacements came from Officially Licensed Circuits, they were the other number. Dropped them in, set the bias, everything was fine.

I wish I could remember which one was which... I suspect the datasheets for both part numbers would give a clue, and that the lower gain parts work.

I'd check the one I built, but I sold it.

[Fischerman]

Sounds better than that Kaiser clip...so it has that going for it.

[LeftyStrat]

Interesting. Being a tube guy, can you enlighten us on the "correct" FET's? I'd like to build one for situations where I can't bring an amp.

J201's are all over the place in mfg quality. So you need to either use sockets for the transistors and hand select them, or test them up front and pick ones close to the middle of the range of values (article follows). Hand selecting them is probably the best route, since besides characterizing Vp and Idss, you'll want to select for noise and frequency response. Buy three times as many as you think you'll need, they're cheap.

However, personally I've always felt the "stick a fet in place of the tube without changing any other parameters" was hit or miss at best. FET's might behave similar to tubes, but they don't have exactly the same characteristics of a 12AX7, (grid-to-cathode capacitance, etc).

Apparently, even the runffgroove guys revisited this approach:

http://www.runoffgroove.com/fetzervalve.html

The original "Fetzer Valve" was supposed to mimic the input stage of a Fender amp using a j201 with 1.5k/25uf cathode. This article has the measurement setup at the end.

[tele_player]

That's good stuff. I suspect the Umble circuit would benefit from reconsideration of the source resistance and capacitance, according to this analysis.
I think I read somewhere that Umble circuit was used as the jumping-off point for one of the currently popular long-waiting-list overdrive boxes. I don't recall which... maybe the Zen?
Back to my main point - the Umble circuit, in its original form, is WAY better than that Youtube clip would suggest. It's very useable, and I much prefer it to, for instance, a Tube Screamer.

[LeftyStrat]

That's good stuff. I suspect the Umble circuit would benefit from reconsideration of the source resistance and capacitance, according to this analysis.
I think I read somewhere that Umble circuit was used as the jumping-off point for one of the currently popular long-waiting-list overdrive boxes. I don't recall which... maybe the Zen?
Back to my main point - the Umble circuit, in its original form, is WAY better than that Youtube clip would suggest. It's very useable, and I much prefer it to, for instance, a Tube Screamer.

There used to be a version of the Trainwreck based on this technique, Doug Hammond's Meteor. It seems his web site is no longer around, but the clips were pretty impressive, they had the feedback and harmonic bloom thing going.