freestompboxes.org

Hi Mat,

may you post the updated schematic.
That would be very much appreciated.

Cheers
Manfred

With 1k between pins 4 & 6 pin 6 reads 0V and pin 7 is 8,7V.

Mat

Hi Manfred,

I used Joses shem from this thread. The power section is bit different because of the different transformer.

Mat

Manfred wrote:Hi Mat,

may you post the updated schematic.
That would be very much appreciated.

Cheers
Manfred

Jose, I think I (You!) got it. Pin9 of the tube socket seemed to touch slightly the part holding the socket to the chassis. Now the voltages seem to be ok

Can't wait to test the pedal when I get to home from work ! ! !

Will report asap..

Mat

mat wrote:Can't wait to test the pedal when I get to home from work ! ! !

Congratulations Mat !!!!!!!!!

Please comment about what this unit is capable to do.

Cheers,
Jose

Ok, here comes- volume pot started working after I put a wire to ground from the side lug. Then the gain pot stopped working ? I moved wires around the IC and foot switch. I touched couple of the IC pins with srew driver and after a little pop sound the gain pot started to work but the voltage on the input of the IC dropped from 4,6V to 1,8V ?? Anyway the pedal seems to work now and the sound is insane The amount of the volume AND gain could be shared between 10 fuzz and 20 overdrive pedals

I recorded just (mindless) noodling with my DIY guitar (two humbuckers with split switches) to my DIY 86Special-amp with my iPhone. I did not find a pick so I played with my fingers Hope the clip would give a hint how the pedal sounds but I will record something better quality clips later when I go to our bands rehearsal place.



I would like to thank You Jose for guiding me trough this long lasting build Lots of respect !

Mat

I measured the plate voltage adjusting the bias pot and it ranges from 109V to 134V. How can I calculate the proper bias range for the EF86 ?

Mat

mat wrote:Ok, here comes- volume pot started working after I put a wire to ground from the side lug. Then the gain pot stopped working ? I moved wires around the IC and foot switch. I touched couple of the IC pins with srew driver and after a little pop sound the gain pot started to work but the voltage on the input of the IC dropped from 4,6V to 1,8V ??

Don't worry about the value at input pins of the opamp. The only voltage that really matter is that the pin 6 must rest at half the supply voltage.

mat wrote:Anyway the pedal seems to work now and the sound is insane The amount of the volume AND gain could be shared between 10 fuzz and 20 overdrive pedals

Glad to read that your unit is alive...

mat wrote:I recorded just (mindless) noodling with my DIY guitar (two humbuckers with split switches) to my DIY 86Special-amp with my iPhone. I did not find a pick so I played with my fingers Hope the clip would give a hint how the pedal sounds but I will record something better quality clips later when I go to our bands rehearsal place.

http://soundcloud.com/mattit-1/ef86pedal

Your fingerstyle isn't bad at all !!! (but let us know how you play using a pick... )

At some passages of your soundclip the sound is similar to a tube amp at the verge to blow a fuse: a kind of distortion not normally produced by the majority of pedals.

Also this unit looks like prefer the chords instead single notes, but it's only my first impression.

mat wrote:I would like to thank You Jose for guiding me trough this long lasting build Lots of respect !

I am delighted to have deciphered the diagram of this pedal based on the photos posted in January by a participant of this forum.

I'm happy for you to have undertaken this project despite being handled hazardous voltages, and you were able to emerge victorious from this challenge...

You think I'm one of the most elderly in this forum (I'm close to my birthday 52) and I'm one of those few who prefer to play with vacuum tubes rather than semiconductors.

Cheers,
Jose

mat wrote:I measured the plate voltage adjusting the bias pot and it ranges from 109V to 134V. How can I calculate the proper bias range for the EF86 ?

In a previous page someone measure that the bias pot value is 100K

Also in these same page other forum member say that the optimal plate voltage must be around 2/3 of the +B present at the last filter capacitor, but the idea is to put this tube in an operating point that add their own distortion to the sound previously clipped by the couple of schottky diodes.

Perhaps you can lift the parallel resistor placed across your bias pot to increase the range of this control and see what happens.

Cheers,
Jose

Something not right still.. The pin 6 of the IC measured 1,084V and I swapped a fresh one in there and it gave 3V and then the voltage started to drop to little more than 1V ?? The IC supply is 8,07V. I also measured the input of the IC and it was about 2V higher than the previous IC but it dropped aslo to lower value. Hmm...

The pedal works and sounds great but it would be nice to solve the problem of the pin 6.

Mat

I swapped the 10uF in the junction of the two 100K's but no help for getting 4V (8,07V on pin7) on pin6. I have 25k bias pot and no parallel resistor.

Mat

Hi Mat,

Try to lift the 100 ohms resistor that link the output of the operational to the pair of diodes. After do that the pin 6 will be unload and the voltage reading must be normal.

Perhaps the electrolytic capacitor placed in series with this resistor is leaky, and causes the pin 6 goes slowly towards GND. That's my best guess.

Regarding the bias potentiometer, try to replace by another of 100K or at least 50K to have more range to move the bias of the tube to a less linear operating point, increasing the distortion of the EF86.

Keep me informed about what you find.

Cheers,
Jose

I lifted the 100R and pin 6 of the IC is 1,4V.

Mat

I swapped a 100k for the bias pot and got 104V-142V. Too late to test the sound

Mat

Thanks Mat

mat wrote:Hi Manfred,

I used Joses shem from this thread. The power section is bit different because of the different transformer.

Mat

Cheers
Manfred

mat wrote:I lifted the 100R and pin 6 of the IC is 1,4V.

Hi Mat,

I feel like I'm starting to run out of answers ...

The last thing I can think is that there is any part is damaged or different value to the diagram, a defective weld or a short circuit that has not been seen yet.

If you've disconnected the resistance of 100 ohms then the first stage becomes simply a buffer and should have a high level of clean sound, so you'll have to check between the input jack and pin 6 of this IC.

Regarding the problem with solid state section of this unit keep in mind that is a copy of the old MXR Distortion + or DOD 250 Overdrive

For this reason and because it is a circuit topology should be very familiar to many members of this forum, I encourage to ask those who read this post, the following:

PLEASE ... If any of those reading this post comes up with what may be the failure of the first stage of this pedal, I'D LIKE TO READ WHAT IS YOUR SUGGESTION !!!!!!!.

mat wrote:I swapped a 100k for the bias pot and got 104V-142V.

With the change in value of the potentiometer I see that there is more range to vary the polarization, so once you have located and repaired what happens to the IC and solder again the 100 ohms, tell me what you hear as outcome.

Cheers,
Jose

Thanks Jose for your support I will further study the IC part of the circuit next week (weekend at summer house). I thought to try feed the IC with a 9V battery to rule out the faulty power supply - was thinking if the 1000uF/36V might have get damaged while the voltage was more than 40V on the IC.

Ok, You are 6 years older than I. I too love the tube stuff above all. I've built about 10 tube amps and still feel like a noob I've tried several modelling circuits but always come back to the tube stuff. Would like to build a standalone tube tremolo/vibrato and a tube wah

I'll get back next week..

Mat

I again played the pedal and the sound is too distorted even with very low gain pot settings. I purchased new parts for the IC stage. I'll build a new one to see if I will get the pin 6 voltages right.

Will report back ASAP..

Mat

I built the IC part again (and connected it to the input of the EF86) and now with 9,3V battery the TL071 reads:
pin1 - 0,2V
pin2 - 1,6V
pin3 - 4,2V
pin4 - 0V
pin5 - 0,16V
pin6 - 8,77 ??
pin7 - 9,31V
pin8 - 0V

Still the pin6 is not at half of the pin7

Any further suggestions what to check ?

Thanks,
Mat

With low voltage power supply tap:
pin6 - 7,54V
pin7 - 8.04V

Mat