Build Your Own Clone Message Board

Hi

Just finished up this module and did the bias adjustment. Instructions specify 1.5 - 1.7 volts, but at 1.7V the effect is barely audible. I get unity volume with the pot at 12 o'clock with a bias voltage of 4.0V. Not sure now that the effect is that apparent. There is a volume boost but not sure about compression...

Any and all advice appreciated

Matt

Please post photos of the module--they need to be LARGE, well-lit, well-focused shots of BOTH sides of the PCB.

_________________
“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2

Sorry - here...

Don't see anything that looks amiss there. Have you run other modules in that same Crown Jewel to know that the boost stage works? Have you checked the DC voltages on the four voltage supply pins (+9, -9, +4.5 & +18) on the Mimosa module when it's plugged in and powered?

_________________
“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2

-9 = 7.88
4.5 = 4.14
+18 = 15.6
+9 = 8.29

All a bit low obviously

Voltage at the power lead is 9.01V so not a supply issue.

My octave up module has the same readings fyi

Those are all well within normal operational ranges, given modest voltage losses through the diodes in the CJ circuit.

Could you get voltage readings on each of the legs of both transistors and also the op amp pins?

_________________
“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2

VOLTAGES

Transistor 1 (next to trim pot)

E - 4.04
B - 4.04
C - 0.45

Transistor 2

E - 8.30
B - 6.78
C - 4.04

Op Amp

1 - 7.9
2 - 4.48
3 - 3.46
4 - 0
5 - 0
6 - 4.53
7 - 8.30
0 - 3.33

Cheers

The problem could be that you are expecting too much volume boost. Unity gain should be closer to full turn than noon. Bias for compression, not volume boost.

_________________
*patience is a virtue*

Please do not PM me. email is prefered. keith@buildyourownclone.com

Thanks to both of you for your advice. If the voltages look normal then I can rule out a problem with the main CJ board.

Keith - if you have a copy of the mimosa module to hand would you mind giving me an o'clock position for the boost level knob for unity gain? If the level knob controls gain and not compression, then I guess you have to set for gain via the knob and compression via the trim pot?

Thanks again

Matt

I don't have a mimosa module handy. Sorry. Yes, the "boost" knob is a level knob. The term "boost" is a bit of a misnomer in this case as the Mimosa module is not a boost. You set the trimpot for the best compression. It's possible that with enough tolerance build up, 1.5V ~ 1.7V may not be the optimal setting for your particular module. Maybe it's 1.8 ~ 2.0?

_________________
*patience is a virtue*

Please do not PM me. email is prefered. keith@buildyourownclone.com

Not Keith, but I can pass along how my Mimosa module is set up. I have the trimpot set slightly CCW of dead center (about 11 o'clock if dead center is 12 noon) and the source (middle) leg of Q2 reads 1.62 VDC, right about in the middle of the target range. The module compresses well at this setting. Unity gain for the boost level pot is about 1:30 - 2 o'clock, again based upon a mid-point setting = 12 noon. I base this upon comparison of the output volumes AFTER the initial note attack which is, of course, suppressed when the Mimosa is engaged.

_________________
“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2

OK, let's clarify these transistor voltages. First of all, the Mimosa module uses JFETs, not BJTs, so the pins are not emitter/base/collector but rather drain/source/gate. The pinout for the 2N5457 JFET is shown below:



Secondly, the trimpot biasing info in the instructions is for the source (middle leg) of Q2, which is what you have referred to as "transistor 1". See labeled PCB map following:



So you may need to re-visit your Q2 voltage biasing based upon this information.

_________________
“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2

Hi, I just finished my CJ, which works perfectly.
The Mimosa module though is behaving exactly as you described, voltages are similar and good, the Octave up module works fine, but the Mimosa biased at 1.5-1.7 doesn’t get any sound. Only at >4V.
Have you guys found a solution for this?
Thank you so much!
Zoot

Please start a new thread with pics.

_________________
*patience is a virtue*

Please do not PM me. email is prefered. keith@buildyourownclone.com