Brunetti Mercury

[Frank_NH]

Hey all.  Here's another layout for an effect that I recently built - the Brunetti Mercury distortion.  There is a vero of this already at Harald Sabro's site.  Mine differs in some key ways:

* I use trimmers for the jfets so you can bias the drains
* There is a slight mod for the output capacitor (3.3nF --> 330 pF) which removes less high end
* Some differences in the potentiometer values based on my tastes (Gain is 50K rather than 250K, and the Volume is 100K versus 50K)
* I also used all 2N5457s in my build rather than j201s as it tames the distortion somewhat (along with a lower drive pot) making it less "wooly".  It's got plenty of muscle though!

The effect uses a charge pump for higher voltage and more headroom, and is relatively low noise as far as dirt boxes go.  And the Bite and Body controls are very effective in controlling treble and bass.

In anyone builds this, let me know if there are problems with this layout.  My original layout was slightly larger and I managed to shrink it by one column.  Have fun!  

Additional notes: 2/19/2016

* Updated the vero layout with minor edits.  Verified by building it again!

[Frank_NH]

Quick note.  Adjust the trimmers so that the Q1, Q2 jfet drains are ~9V.

[rocket88]

awesome job man.

[motterpaul]

Frank - here is a demo of this pedal (in Thai, but he shows all the controls) and it really sounds great. I am going to build this one based on your recommendation. If he can get that much OD out of a Strat that is a powerful little "Scatola"

https://www.youtube.com/watch?v=EDw0L93lGYI

By the way - the Catalinbread Wiio knocked the Wampler Plexi off my pedalboard. It is louder & cleaner.

[motterpaul]

Frank - Just built this and I am not getting any throughput. I can bias the 5457s to 12v and I am pretty sure the build is as given (pics are in the links below) - any problems or ideas?

I am using a CPAZ 7660S, otherwise all parts are as specified. Caps are tant & correctly oriented except 2.2u (MMC) with a small bridge just to make the leg longer.

Tranys are Fairchild. Only sockets are re-used since I need new ones.

Here are the pics: http://s1304.photobucket.com/user/Paul_Motter/library/Brunetti

[motterpaul]

FYI: as far as I can tell the audio throughput ends in the tl071 (which is right in the beginning). It is getting 12v, and voltage is fine throughout the circuit afaik.

[Frank_NH]

Hi Paul,

Thanks for hires photos.  If you have an audio probe, check the following points:

* pins 3 and 6 of the IC.  That's where the signal enters and exits the op amp.
* the gate of Q1 (very bottom leg)
* the drain of Q1 (top leg)

That's enough to check to see where the signal is getting lost in the IC.

Also, you should be getting ~18V (less diode voltage drop) from the charge pump, so pin 7 of the IC should be close to that.  The bias voltage should be half that (~9V) and you should see something like that voltage at pins 2, 3, ans 6 of the IC.  Also, pin 4 should be ground.  Pins 1, 5 and 8 are not connected.

Let me know what you find.  We'll go through this step by step and figure out where the problem is.

And, as always, check for solder bridges and cold solder joints.  A solder bridge got me in a recent OD808 build...

[Frank_NH]

One more thing - I used a LT1054 for the charge pump.  Your chip may or may not work.  For the 7660 series, I think you have to have pins 1 and 8 connected, like this:

[motterpaul]

My charge pump has that link (as I recall), it is in your plans. All voltages look good, I am getting over 18v output.

I get audio signal at pin 3 of 071, but nothing at pin 6. And I tried a few different chips - all from a "new" tube of tl071s.

EDIT - also, as mentioned I am able to bias the trans to 9v, and I see them going up as high as 12+ voltage available at the trimpots. I seems to be the audio. Could be bad chips - would you recommend another opamp?

[motterpaul]

OH, I see, I was thinking about the link between 3 and 5 you have (connected being the key word I misunderstood). You mean to remove the cut at the top of the chip - but I am still getting correct voltage throughout the circuit, but I will look into this.

[motterpaul]

actually - now that you mention it. I am seeing voltages as high as 12v at the tlo71, is that wrong? Maybe I need to LOWER those voltages and removing that cut will do that?

[Frank_NH]

Pin 7 of the TL071 should be getting near 18V (perhaps a little less due to the diodes).  So 12V seems too low.  Did you check all your IC voltages?  How about the audio probe - is the signal not coming out of pin 6 of the TL071?  Print out all of your voltages here so I can see what's going on.  Thanks!

[motterpaul]

I was just going by memory so I am not sure about all voltages at 072 (I think I did see an 18+) , but I am sure I am not getting audio out of pin 6.

Anyway - I will re-check and let you know. Should I bridge that cut between 1-8  first?

[motterpaul]

Okay - bridged 1-8 on 7660s

I am thinking maybe this just isn't compatible with 7660s? Anyway - here are readings...

IC 1:

9.23
4.48
-3.3m
3.2m
.6m
5.20
7.12
9.23

Output of D1:  13.18
Output of D2: 17.35

IC 2:

10.55
~ (too jumpy to read, low)
5.82
.5
~
~
12.83
11.77

Q1: D 9v, .76v, .6v
Q2: D 9v, .3v, .5v
Q3: D 12.5v, 7v, 5.3 v

[Frank_NH]

I would get a LT1054 and use that.  The voltages are off from what they should be (IC2 is the 7660).

[motterpaul]

Okay-dokey. I don't know the differences between the two chips but I imagine that link changes some things. I just happen to have dozens of 7660s.

[Frank_NH]

Also, check all the connections in the vicinity of the charge pump.  Make sure there isn't a solder bridge or cold solder joint.  I can check the voltages on my build and post them.

[motterpaul]

I did check for bridges & shorts (always do as part of trouble shooting first). With my builds if I get a fault (beyond just making the wrong ptp connections, which I also double-checked already) it is usually failed cap or diode.

I will check again, though. I might try changing the 10uf - have had some trouble with mine before.

[motterpaul]

I get 18+v at the output of D2, but the 220R resistor drops it down to about 12v and that is what seems to feed the Tl071. That is the max voltage I see through the rest of the circuit.

[Frank_NH]

Check for a solder bridge.  When I had a low voltage like this, that was the problem.  From your pictures there may be a few potential spots where you may have a solder bridge between adjacent tracks.  Check it with your DVM using the continuity tester.

I fired up my Mercury tonight and it's still works.  After playing with it some, I think I may recommend the original gain pot (A250K).  It gets fuzzy but in a good way.

I also checked my voltages with a fresh 9V battery and I only drop about 1.3V across the 220 ohm resistor (implying a current draw of 6 mA).  I get ~18.3 V from the charge pump as my battery reads 9.5V.  Q1 and Q2 have their drains biased at 9.4V.  For Q1, the source voltage is 1.0V and for Q2, it's 0.26V.  Q3 is a source follower (buffer) with drain at ~18V.