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Notes on a 1997 Dumble OD 100

9/4/1999 3:01 AM
Steve A.
Notes on a 1997 Dumble OD 100
To all of you Dumb(le) bunnies out there:  
    I just posted the text of some e-mail correspondence from an AMPAGER who wishes to remain anonymous. He had the opportunity to look over a friend's 1997 OD100 and noted many of the voltages and parts values. He has built a Dumble clone (with Dumbleator) himself and included some notes on his experiments, too:  
Steve Ahola  
P.S. The TXT file is 11k so I didn't want to hog the bandwidth here.
9/4/1999 3:47 AM

For what it's worth, the transformers are Pacific Transformers.  
I've opened a couple at my shop myself and this 1052 transformer is not a regular thing!  
Go figure.  
9/10/1999 2:15 PM
Re: Notes on a 1997 Dumble OD 100, abput the 2nd tone stack...
Hi Bruce  
Did you by any chance, see any Dumbles with 2nd tone stack(the one in the overdrive section), and how it was laid out? any cap values, etc. the notes here discribe a marshall type TS, 250K treble, 1Meg bass and 25K Mid. and I have just tried it, ( 500p treble cap, 33K slope res. and .022uf bass and mid) and it works ok , but if you have any info to share, I and alot of others would greatly appreciate it! Thanks Ed  
9/10/1999 3:21 PM

Hi ya Ed..  
The most recent ones I've seen have an area boxed off in the tone stack department and filled to the brim with a couple-three tubes of blue RTV! YUK! Very ugly.  
Since they were not my amps, I was not in a position to slice away at it for a peak!  
The last one had a 25K pot in between the two plate resistors of the PI/driver... who's wiper was fed with the B+ thus allowing you to balance the PI/driver sections a little better. Interesting but big deal.  
Yes, the Dumble amps sound great, but in truth, I've had homebuilders, who knew nothing about Dumble's amps, bring their 25 watt homemade amp projects in to have me help them with a noise problem, (or what ever..etc.) that sounded wonderfull and cost them $150.00 to build.  
Since that's anything from a 20:1 to 40:1 cost reduction, I would be thinking that anyone with the time and interest to tweak their own amps will be getting a GREAT sounding amp at 1/20th to 1/40th the cost of any Dumble.... even if they don't ever think Dumble... Dumble... gotta get a Dumble!  
Reminds me of the dog marching into the kitchen on mission from god thinking...Kibbles and Bits..kibbles and Bits...  
The tone stack combination you mentioned is a little off from what I use but still sounds pretty good.  
I'd consider going back to a 500K bass pot and use a .047uF cap instead of the .022uF cap in the bass section.  
And also, I'm not a big fan of using a Marshall type tone stack configuration in a Fender type amp.  
Sometimes it works good and other times it just OK.  
Ed, most of the things I know about Dumbles are common knowledge, the things I know that are not common knowledge, aren't going to make a big difference in a homebrew version of it anyhow and aren't worth repeating just to get everyone all fired up about Dumbles or how much "I" know about them. :>)  
9/10/1999 3:50 PM

Thanks Bruce:  
I agree about tweeking in a home brew. I find a lot gratification, in doimg your own, and I have learned a lot here at the AMPAGE, I also realize that every one is going to have a different tonal taste, which is good for variety,thank God we all don't sound the same. I have always been interested in "how do you get such great tone dude?" especialy when you can get good results from tour own amp, by changing some components here and there. I think that is the beauty here at the ampage. Thanks Bruce again for your reply, Ed
9/10/1999 8:05 PM
Gil Ayan

"Ed, most of the things I know about Dumbles are common knowledge, the things I know that are not common knowledge, aren't going to make a big difference in a homebrew version of it anyhow and aren't worth repeating just to get everyone all fired up about Dumbles or how much "I" know about them. :>)  
So, Bruce, you are going on record saying that you're holding out on us. Fine, be that way... "if you don't tell me what I don't know about Dumble's amps, then I won't tell you what *I* don't know about them." (not that I coudl anyway, right?) ://  
A cpmment though, never underestimate the b;ack magic art of amplifier making. It really works both ways...  
1. I had a Mark IIC+ that I was going through and found that one of the cathobe bypass caps (15uF in that amp, for the most part) was shorte out and read 4 ohms on the meter. That means the tube was running with its cathode at DC ground (mu gain). I replaced the cap and? No diffence in sound that I could hear.  
2. Parts of overdrive cicuits are so sensitive that using two caps of the same value and type will make an audible difference; or, changing a gain pot from say 100K to 250K can sweeten up the sound a great deal (not necessarily intuitive until you sit down and figrue out why), while affording more gain (very intuitive).  
So, if you're holding back to save bandwidth, remember that thus far, bandwidth is free and there is always something to be gained by receiving a new piece of information. :)  
9/11/1999 3:56 AM
Steve A.

    I agree with you completely about the sounds that you can get from a home-made amp, especially compared with the typical amps you find in a music store. When I first rebuilt my abused '65 Pro as a Torres SuperTexan I was amazed at all of the sounds that I had never been able to get out of any store-bought amp. And that was just the starting point for me since I later scrapped the Torres design and started following ideas I picked up here at AMPAGE with much better results.  
    It's like the mfgs "neuter" their amp designs before they put them into production because they don't want the sound to offend anyone, and in doing so they manage to offend everyone who has ears! ("Design by committee" and all that.)  
    However, there is only so far that you can go in tweaking a particular design so sometimes you have to reach out and try to grab the brass ring. While most of us have been able to get some pretty good sounds out of our homebrews, there still seems to be that elusive smooth OD sound that many people are looking for: the Robben Ford Skyliner sound is what it is usually called. And just tweaking what we have now probably won't get us that sound.  
    But I do agree with you that if there wasn't such a mystery around the Dumble designs it would not be such a big deal... And there are plenty of other great guitar tones besides the Dumble Skyliner sound (only that seems to be one of the hardest to duplicate, hence all of the interest here in what is going on under all of that silicone!)  
Steve Ahola  
P.S. BTW how many amps do you think that Dumble has made over the years? Of all of those amps, I bet that a lot of them have been retubed without fine-tuning the trimmer pots inside. So I bet that a lot of the older Dumbles out there may not be performing up to their potential. ("Don't mess with those parts, manó they were set by Dumble himself!") Well, if Mr. Dumble was using the tubes you are using now he probably would have set those pots differently...

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