Tube Amps / Music Electronics
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|8/5/1999 10:04 AM|
Hi I am attepting the Dumble overdrive
clone circuit and noticed that the clean ch.
is louder and distorts because turning down the master volume does any one have any sugestions ? I seem to have to turn the first volume (1meg) down to 4 or 5 to get an even transition between channels but loose gain in the lead ch.
in the process any help and additional tips would be greatly
appreciated thanks Ed.
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|8/5/1999 7:06 PM|
Hmmm... are you sure the wiring is correct? You should be able to get significantly more volume from the overdrive channel... What do you have feeding the overdrive stages, the 100K trimpot? How do you have that set (i.e., resisotr to ground?)?
|8/8/1999 9:56 AM|
Thanks so much for your reply. I have the
pot so that the bottom lug is to ground,
the center to input of the drive circuit,
and top to in coming signal, maybe its where I
have the master set. I added a typical (overall)
master just before the inverter, I guess what I'm
trying to acomplish is a setting some where that
the 1st volume is some where about 6 or 7 and the
drive in the lead mode starts to overdrive about
3 or 4 (kind of bluesy) with the lead master @ 4 or 5.
Do you think I could put a dual pot in there, on one
pot (in coming trim have a fixed res. for the minimum
amount between the grounded end of pot and ground)
so that the end result would give good cleaner response
on the lower drive setting, and get a stronger drive when
the dual pots are turned up ? or is this not such a good
Idea ? I've been rechecking my work, to see if I goofed
some where in the meantime. By the way do you know what
could be added to get the midrange boost like Robben Fords
modded Dumble ? or is that a totally different beast?
Thanks Gil so much again for you help, and I look foward
to hearing from you soon
|8/8/1999 8:04 PM|
Ed, once again, if you set the trimpot to maximum (so that you feed as much signal as possible into the first OD stage), the volume of the overdrive should be always louder than that of the clean channel, even if you set the Drive control low (as you say, 3 or so) to get a bluesy sound. I don't knwo what else to say, but something is not right in what you describe.
Also, I remember you mentioned that the clean was grainy witht the preamp volume around 6 or so? Did you wire in the negative feedback arrangement, with the .056uF and 22MEg resistor from plate to cathode on the 2nd clean stage? That will really change the character of the amp when it begins to overdrive. I have had good results with 22 Meg, but maybe you want to lower that a bit (say 14 Meg) and see if that sounds more like what you're after....
Regarding the Robben Ford midrange boost, are you talking about the DUmble's preamp boost function? If not, I'm afraid I can't help you because I have no idea what RF's Dumble looks like inside -- though I wish I did.
Hoewever, if it is the preamp boost you're referring to, that feature was put int all Dumbles form the 80s on. I understand there may be more than one way to skin the cat there, but I heard that at least some of those preamp boosts were just tone stack defeat. Now, given the nature of the Dumble tone stack, there are mahy ways to defeat the TS and come up with different configurations.
Personally, I prefer to do a boost so that you eliminate EVERYTHING and the amp looks just like the treble cap was a coupling cap after the first stage. So to put it another way, you would get 1st stage with a 250pF or 330pF or 470pF (whatever you use in the treble cap) and then onto the volume control.
In contrast, Fender tone stacks, which Boogie copied, were used as is for preamp boosts in the early Boogie by merely lifting the ground connection of the midrange control. That sounds way too muddy because you get not only the 250pF treble cap's action, but also the mid (.047uF) and the bass (.1uF) caps' action.
Hope this helps,
|8/8/1999 8:39 PM|
Hi again Gil
I finally got the volume levels to work good together
and I do have the feedback from plate to grid ( I had a .047 and 22meg in series from the plate, then to grid, is this correct?)and having it in does like you say
makes a difference, but I might try your suggestion using
14 meg. Does .056 uf make a difference as opposed to .047 uf?. I also agree about the boogie boost thing being muddy, I'll try these ideas out. thanks again very much Ed
|8/9/1999 4:29 PM|
Glad you're making progress. Regarding the .047 vs .056uF... for THAT application it's probably a wash -- just be sure to use a high viltage capacitor though.
|8/9/1999 6:28 PM|
Hi again Gil;
I have a couple more questions if you don't
mind? In doing the boost you were mentioning,
would it work to just switch the 100k tone stack res.
out where it connnects to the 330 treble cap
so that the bass and mid caps are bypassed?
I like this idea you prefer. Also I was thinking
of adding a prescence control, perhaps the standard
fender (Bassman tweed) circuit? I have seen a block
diagram from one of the websites showing the block
diagram with a different power supply, and some were
skeptical about supplies (power) and the rest of the
amp being from two separate sources, so I might try
experiment with one or the other, but the power supply
schematic from Steve's site works good to my ears.
The supply from Groove tubes looks like it has more
filtering of course, but it also has a heck of a lot
of other things, like tremolo and reverb. Well thats probably a nuff eye twisting now, so again I thank
you for your time, this site is really, really neat,
I like it.
talk with ya soon, Ed G.
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