Mod friendly way of building..

[Tdale]

I've been drawing, planning, thinking and wondering for months now. Unfortunately the family budget does not allow any new build project for some time (getting married soon).

But after reading lots of the posts here, I see that there are so many different ways to build a Dumble, since noone really know what is the "correct" way to do it.

So I think that when I finally get to it, I'll build my amp in modules. One board for the pre-amp, one for the OD, one for the PI etc. That way, I can try different components, find out what I like, and even remove boards, withouth having to remove the whole thing. Also, I can make different boards, like a 70's pre amp, a 90's pre amp, a personal modded pre-amp etc.

Does this sound like a bad idea?

Tommy

[pedro]

Tommy,

Ive found on several build that turret boards work well for tweaking post build.
I do a layout using tuttets and ensure Ive got plenty of room to add th eodd turret here and there if I need to squeeze one in - this way its easy to add but very easy to swap components in and out on the tutter tags for tweaking values.

The only downside i see to your plan to build in modular form is that if you have sep boards for clean pre and OD then you will end up maybe having some cable joins between boards which wil add noise/cross talk etc. having OD and clean is part of pre together ensures fairly small runs. Having siad that you have to run cable to relay for channel switching so you may find a way to make it work efficiently on circuit links.
just MHO....

Rgds
Pete

[Icetech]

If you take a look over at turretboards.com i use the hiwatt generic board which is bout 3" wide and i think 18-20 turrents down each side... doing a ods reverb i still have bout 3" of turrets left off the end of the board... plenty of space for modding over and over:)

[Tdale]

I'm thinking about adding a built-in dumbleator, and that makes the board really long! Making modules, enables me to place them so that the chassis don't have to be 2 ft. long!

I have to think about his, it was just an idea.

Tommy

[Normster]

The "standard" Dumble board is only about 8" long and lines up perfectly with the preamp tubes (with tube spacing at 2.5"). Early boards all seemed to use the same 3/8" spacing between components, except the Ck bypass caps which are spaced at 1/2". Adding a Dumblelator or 1-tube reverb should only add about 1.5"-2.5" to the total length of the board based on the number of components and the layout.

As for modular construction, it does make sense to have "piggy-back" boards for added circuits, such as HRM, Dumblelator, or reverb. The only issue I see is attention to lead dress. When I copy a Dumble circuit, I'm less concerned with authenticity than I am with avoiding lead dress issues. I figure I'm safe if I just do what Dumble did.

If you still need extra room inside the chassis, consider using a "stand-up" power tranny rather than the z-mount. Another option is to use a Fender-style cap can outside the chassis.

BTW, the attached layout is about as close as I can get to "real" dumble component layout based on '70s-style ODS amps. It's based on several different photos and the 3/8" - 1/2" pattern that Dumble appears to use. The component values are NOT for any particular amp since I tend to change them to suit the iron at hand. Also note that the first cathode RC in each pair goes to pin 8 and the second goes to pin 3. This seems to be fairly consistent with pics I've seen although there are exceptions.

[Tdale]

On the layout I made, I put all components on the board, and didn't place any on the tube socket, and that could be a reason why it's so long. Also, drawing the board is not the same as actually making it, so I guess it won't be all that long when I finally get around to making it.

However, my schematics has some extra comonents, like negative feedback etc. which adds a little to it.

By the way..what is Ck.?

Tommy

[Tdale]

Nice layout by the way.

I see there are several approaches to the OD entrance..some are simple like this one with a resistor and a trim, other have several resistors to ground, and one across etc..

Any advice on which ones work best?

Tommy

[Normster]

"Ck" is the cathode bypass cap. (Also, "Rk" is the cathode resistor. "RC" is resistor/capacitor network. It took me a while to figure that out. lol) I think the OD circuit depends on which amp you're building. The simple one in this circuit has more gain available than the '70s network in my limited experience. Dogears has done a lot of tweaking in this area some maybe he can shed some light on the subject.

[Bob-I]

"Ck" is the cathode bypass cap. (Also, "Rk" is the cathode resistor. "RC" is resistor/capacitor network. It took me a while to figure that out. lol)

Aiken has lots of good technical documentation where terms like this are listed.


As for the tweakable builds, I'd use this style bread board so the contacts can be added and removed easily. Multiple boards, as already stated, is most likely not the best way.