Ulbrick - 12AXE

popstudioguitar · Post by **popstudioguitar** » 01 Oct 2008, 00:52

Anyone ever tried, borrowed and/or open one of these ?!

Heard a couple of nice clip with it on U Tube !

Greg · Post by **Greg** » 01 Oct 2008, 14:37

Sorry no... but i think it's a YATS.

Post by **gurishka** » 07 Nov 2008, 02:50

Yes, I've opened one at my local music store to see what was in it. They are a very transparent overdrive, like a TS but without the TS low end drop off.

Fuzzer · Post by **Fuzzer** » 08 Nov 2008, 14:32

I wouldn't say a TubeScreamer is transparent, but anyway, opinions and tastes Galore...

blackbunny · Post by **blackbunny** » 21 May 2012, 12:53

I opened up one of these last week and traced the circuit. It's another TS9 variant - remove the clipping diodes from the feedback loop of the first op-amp stage and fit 2N7000 MOSFETs back to back and you're pretty much there. Almost exactly like a Fulldrive MOS-Silicon without the Boost circuit or the diode clippers.

The sound is very fat and "tubey"...I really like the sound of this pedal. A 12AXE clone is now on my list of things to do.

Steven_M · Post by **Steven_M** » 21 May 2012, 16:35

Gut Shot:

: 12axe.jpg (60.59 KiB) Viewed 2955 times

bigorangefan79 · Post by **bigorangefan79** » 21 May 2012, 18:18

blackbunny wrote:I opened up one of these last week and traced the circuit. It's another TS9 variant - remove the clipping diodes from the feedback loop of the first op-amp stage and fit 2N7000 MOSFETs back to back and you're pretty much there. Almost exactly like a Fulldrive MOS-Silicon without the Boost circuit or the diode clippers.

The sound is very fat and "tubey"...I really like the sound of this pedal. A 12AXE clone is now on my list of things to do.

Schematic?

blackbunny · Post by **blackbunny** » 22 May 2012, 00:14

Just swap the 1N914 (or whatever) diodes for 2N7000 MOSFETs with the Gate & Drain legs tied together, like I did on this TS9-TS808 schematic by Jack Orman.

bigorangefan79 · Post by **bigorangefan79** » 14 Jul 2012, 03:22

I had to open one of these up to repair a bad output cap today.
It has Jfet clippers, not mosfet. Other than that... YATS

candletears7 · Post by **candletears7** » 14 Jul 2012, 12:45

Yep, Dave Ulbrick is based here in Melbourne, Australia and he makes excellent amps.
I've played the 12AXE, and compared it to my Deaj Yats and vintage spec BYOC Tubescreamer. Virtually identical except for the fatter "tube" sound, which the mosfet clippers would contribute to.

blackbunny · Post by **blackbunny** » 14 Jul 2012, 17:01

bigorangefan79 wrote:I had to open one of these up to repair a bad output cap today.
It has Jfet clippers, not mosfet. Other than that... YATS

That's interesting.What was marked on the cases or the JFET's, and did you notice how they were wired into the circuit, ie, which legs were shorted?

bigorangefan79 · Post by **bigorangefan79** » 15 Jul 2012, 04:45

blackbunny wrote:
bigorangefan79 wrote:I had to open one of these up to repair a bad output cap today.
It has Jfet clippers, not mosfet. Other than that... YATS
That's interesting.What was marked on the cases or the JFET's, and did you notice how they were wired into the circuit, ie, which legs were shorted?

J201's Drain and source tied together in standard antiparrallel...
ds g
g sd

The Rotagilla · Post by **The Rotagilla** » 16 Jul 2012, 19:17

blackbunny wrote:I opened up one of these last week and traced the circuit. It's another TS9 variant - remove the clipping diodes from the feedback loop of the first op-amp stage and fit 2N7000 MOSFETs back to back and you're pretty much there. Almost exactly like a Fulldrive MOS-Silicon without the Boost circuit or the diode clippers.

The sound is very fat and "tubey"...I really like the sound of this pedal. A 12AXE clone is now on my list of things to do.

Would you mind posting your trace? Words like "pretty much" and "almost" leave too much wiggle room for those of us suffering from OCD.

blackbunny · Post by **blackbunny** » 17 Jul 2012, 00:44

The Rotagilla wrote:Would you mind posting your trace? Words like "pretty much" and "almost" leave too much wiggle room for those of us suffering from OCD.

I mean really close as in virtually identical to a TS9.
I went through the PCB from input to output and compared it part by part to a TS9 schematic. The ONLY differences I found were:
- the TS9 clipping diodes were replaced by 2N7000 MOSFETs as shown in my notes on J.O.'s diagram
- a 100uF 16v electro and a 1N4004 diode have been added across the power supply from V+ to ground
- both 0.22uF capacitors which are tantalum in a TS9 are MKT box type in the 12AXE (values are still .22)

The 8 pin DIP op amp has been sanded to remove the part number, so it may be a 4558 or it may be something else.

All other values are identical to a TS9. The output resistors are 100 ohm and 10k ohm, and the buffer transistors are 2SC1815.

This particular 12AXE was bought new in 2008 and was probably made in late 2007.
Later ones may have some changes - bigorangefan79 saw JFET clippers in one he opened up recently.

bigorangefan79 · Post by **bigorangefan79** » 18 Jul 2012, 01:21

TS9 indeed. I believe there was an extra small value cap around the clippers. I have pictures somewhere. I'll see if I can find them. But yes, other than that and the clippers, it was a ts9.

blackbunny · Post by **blackbunny** » 18 Jul 2012, 10:29

The 2007/2008 12AXE even had the same capacitor as a TS9 in the feedback loop with the clippers - 51pf ceramic.
Alert TS clonewatchers will have noticed that the Fulltone Fulldrive MOSFET edition is the same circuit as the 2007 12AXE, except the Fulldrive has a 1 Meg Drive pot instead of the TS9 500K.

roseblood11 · Post by **roseblood11** » 18 Jul 2012, 19:06

Did I get this right:
If 2n7000 Mosfets are used, gate and drain are connected, but if J201 Jfets are used, source and drain are connected?

bigorangefan79 · Post by **bigorangefan79** » 18 Jul 2012, 20:30

roseblood11 wrote:Did I get this right:
If 2n7000 Mosfets are used, gate and drain are connected, but if J201 Jfets are used, source and drain are connected?

Correctamundo. I've never used jfets for clippers before but that is how they were used in the circuit. Evidently you can use Jfets as clippers by going from 1. gate to drain 2. gate to source 3. or gate to drain and source tied together (like in this circuit). I'm more used to Mosfets like in the Zendrive and Fulldrive. I guess I'll have to play around with jfets now.

bigorangefan79 · Post by **bigorangefan79** » 21 Jul 2012, 02:34

blackbunny wrote:The 2007/2008 12AXE even had the same capacitor as a TS9 in the feedback loop with the clippers - 51pf ceramic.
Alert TS clonewatchers will have noticed that the Fulltone Fulldrive MOSFET edition is the same circuit as the 2007 12AXE, except the Fulldrive has a 1 Meg Drive pot instead of the TS9 500K.

The small value cap that I was remembering was actually a 3.9pf cap in parallel with a 47pf cap. I guess he ran out of 51's and thought that the 4pf difference would be audible. So yes, other than the clippers, it is part for part a TS9 clone. All the way down to the buffers and 51pf cap.