#1
I recently finished a small amp for my former boss. It is based on a Fender AB763 (Blackface Bandmaster). It has a Dumble ODS overdrive circuit after the preamp. It is single-ended with a 12AU7 as the power tube giving about 2 watts of power. Here it is:

The black socketed tube is the power tube.


Guts (I shielded the crap out of the overdrive adjust pots):


Back:


Front:


He wanted something he could crank without making his wife angry. So I built him this. The blackface circuit has some beautiful clean tones. He's a jazz player, but he also plays some hard rock (Godsmack and Disturbed mainly) so this will do about anything he wants except fill a stadium with sound.
#2
Wow, I was just thinking about how cool a Dumble circuit would sound over a fender amp....

CLIPS!!!!

Edit: Hmmm never heard of 12au7 tubes as power tubes....... very interesting....
Gear:
-Saga strat, modded with guitarfetish p/ups
-epiphone abomination (don't know what it's called) with scalloped neck and power rails gfs p/up
-Fender Twin Reverb
-Blues screamer pedal
-Boss Turbo overdrive
Last edited by The_7th_Nerf at Aug 7, 2009,
#4
so basically, it's a fender power amp that uses a dumble preamp?

sorry for being an amp building noob.
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ANOUNCEMENT: Weird misspellings or words that make no sense? there was a good chance this was sent from my Droid 2 phone.
Quote by SinisterStrieth
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#5
No. It's a fender preamp, with a Dumble Overdrive after the Blackface. The power amp is only 2 watts.

Also, I have clips recorded, but it's .wav format. Does anyone know a good place to upload .wav files?
#6
Quote by end_citizen
No. It's a fender preamp, with a Dumble Overdrive after the Blackface. The power amp is only 2 watts.

Also, I have clips recorded, but it's .wav format. Does anyone know a good place to upload .wav files?



oh, DOH! i'm sorry, i need sleep.
Official Aspie member

ANOUNCEMENT: Weird misspellings or words that make no sense? there was a good chance this was sent from my Droid 2 phone.
Quote by SinisterStrieth
.. You are the man.

RIP Dime RIP Michael Jackson
#8
Cool, nice and compact. Got any bigger internal pics?

The clean channel of a Dumble is basically a modified Fender btw. Just fancy voicing tricks and such.

Whats with all the fuses btw? Mains, heater and HT CT?
#9
Looks cool, nice job.
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#10
Phase inverter or self-split output?
Schematic?
Meadows
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#11
Quote by SomeoneYouKnew
Phase inverter or self-split output?
Schematic?

What do you mean by this?

Since the 12AU7 is a typical dual triode couldn't he have wired the output section two ways. Either class AB push-pull or class A parallel single ended. I guess with the later you just need a "driver". With the PP you need a PI to split. Is that what a self-split PI is, the typical one that takes your signal and splits it into two signals out of phase with each other but of equal strength (more or less).

Sorry just never heard that term.
#12
Quote by kurtlives91
What do you mean by this?
Self-split is where the same valves that do the phase inversion drive the P-P output transformer directly.

But I just re-read the OP. Single Ended. meh.
Meadows
Quote by Jackal58
I release my inner liberal every morning when I take a shit.
Quote by SK8RDUDE411
I wont be like those jerks who dedicate their beliefs to logic and reaosn.
#13
Quote by Invader Jim
Use Nero or smt to convert it to mp3. Or any mp3 converting program.

How much did it cost to bild? I want one


It was $200 for parts, and I just charged him $50 for labor. It is a nice sounding amp, and he knows he's getting a good deal. He's a good friend though, and I'm not doing any cabinet work so I think it's good.

Quote by kurtlives91
The clean channel of a Dumble is basically a modified Fender btw. Just fancy voicing tricks and such.

Whats with all the fuses btw? Mains, heater and HT CT?


I'm aware that the Dumble is a modified Fender, but he loves the sound of the Blackface model on his Cube 60. He wanted the real thing at lower volumes.

Yeah, the fuses are mains, heater, and HT.

Quote by SYK
But I just re-read the OP. Single Ended. meh


I did it single ended to keep the price down. I found a cheap, yet quality SE O.T. plus one less tube to buy. Also, it's one less gain stage so he can turn it up a little more before he overdrives the output section.
#14
Quote by end_citizen
I did it single ended to keep the price down. I found a cheap, yet quality SE O.T. plus one less tube to buy. Also, it's one less gain stage so he can turn it up a little more before he overdrives the output section.
Yeah, I totally get the advantages, but still. The odd-ordered harmonics of a push-pull are godly.
Meadows
Quote by Jackal58
I release my inner liberal every morning when I take a shit.
Quote by SK8RDUDE411
I wont be like those jerks who dedicate their beliefs to logic and reaosn.
#15
Quote by SomeoneYouKnew
Yeah, I totally get the advantages, but still. The odd-ordered harmonics of a push-pull are godly.

If they don't get cancelled out, or so I understand.

That's why some say matched tubes arent the way to go. The vintage amps we pay thousands for sure didn't have matched tubes.
#16
Well we all know what Mr. Dumble has to say on the matter!

http://www.youtube.com/watch?v=iVTj08qTwGw



But on a more serious note, I never really thought about matched pairs that way. It makes sense, though.......... I better give that a try.....
Gear:
-Saga strat, modded with guitarfetish p/ups
-epiphone abomination (don't know what it's called) with scalloped neck and power rails gfs p/up
-Fender Twin Reverb
-Blues screamer pedal
-Boss Turbo overdrive
#17
Alright, I have a 20 second clip in my profile. First is with the Dumble OD engaged, and then it is just the Blackface channel. Everything is at 12 o'clock. Being a Fender tonestack, there is naturally a bit of a mid scoop.

Specs on recording:

Mic- Senheisser e609 Silver
Speaker- 15" Electro-Voice
Software-Ableton Live 7.0.7 no effects added
Guitar- Washburn P290 (Solid Mahogany, Dimarzio bridge soapbar humbucker)
#18
Quote by kurtlives91
If they don't get cancelled out, or so I understand.

That's why some say matched tubes arent the way to go. The vintage amps we pay thousands for sure didn't have matched tubes.


Perfectly matched output tubes are going to be near impossible to get so you will always have some of the odd-ordered harmonics. There may be some cancellation with matched tubes, but it is also more convenient when it comes to biasing and what not. Its basiaclly a trade off.

I do know someone who uses two sets of matched output tubes in his amp. He modified it so that he biases each individual set, and he swears by this.
#19
it sounds great!

so, when are you going to build me one?
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ANOUNCEMENT: Weird misspellings or words that make no sense? there was a good chance this was sent from my Droid 2 phone.
Quote by SinisterStrieth
.. You are the man.

RIP Dime RIP Michael Jackson
#20
Quote by conor1148
it sounds great!

so, when are you going to build me one?


Thanks. The owner of the amp just picked it up. He's off to guitar center to look for a cab.

I'd love to be able to build amps all year, but a week from wednesday I go back to school. They don't allow you to bring your own soldering iron

Hopefully I can find an apartment in a reasonable amount of time and improve some of my building techniques.
#21
Quote by end_citizen
Thanks. The owner of the amp just picked it up. He's off to guitar center to look for a cab.

I'd love to be able to build amps all year, but a week from wednesday I go back to school. They don't allow you to bring your own soldering iron

Hopefully I can find an apartment in a reasonable amount of time and improve some of my building techniques.


You mean your not supposed to bring one

I know I take mine to school and as long as i keep my desk close to the window i've never been caught.
#22
Sounds pretty cool, the cleans are definitely BF like. Very solid!

Tbh the overdriven tone doesn't scream Dumble to me but it is still good tone. It doesn't have that smooth bloom. No offense.

I'd love to see a schem if you don't mind.


Do you have snubbers in the OD section?
#23
Quote by kurtlives91
If they don't get cancelled out, or so I understand.

That's why some say matched tubes arent the way to go. The vintage amps we pay thousands for sure didn't have matched tubes.
almost sorry i brought this up, here.

Odd-order harmonics are the ones in a symmetrically distorted signal.
Perfect symmetry from perfectly matched tubes would produce nothing but odd-order harmonics.

Even-order harmonics come from asymmetric distortion.
Unmatched tubes or single-ended output.


*leaves to go listen to end_citizen's sound clips*
Meadows
Quote by Jackal58
I release my inner liberal every morning when I take a shit.
Quote by SK8RDUDE411
I wont be like those jerks who dedicate their beliefs to logic and reaosn.