DOD FX80B Compressor Sustainer sounds like a tremolo?

[JohnForeman]

Hi all.
I have just dusted off a old FX80B compressor that has been in the closet for about 15 years (new family stopped me from doing much playing).  Anyway. I put a new battery in it, plugged it into the amp and yes, it worked and sounded as sweet as I remember it.  For about an hour, then I noticed i was getting a tremolo effect.  At first I thought it was my amp, but nope, it turned out to by FX80B.  I really liked this pedal so I've been searching and emailing around on the net to find someone who can fix it.  I might add, until I started this search, I had no idea there was such a large community of pedal modders and developers out there.  Anyway, I was not having any luck finding anyone that wanted to try to fix it.  So I started looking for a replacement.  Then I found Tonepad, then I found this forum.  I'm thinking i'm a lucky man today.  OK enough of that. Back to my FX80B problem.

As i mentioned earlier, it no longer works like a compressor (that I can tell at least) and works more like a tremolo effect.  The tremolo effect can be sped up and slowed down by using the compression knob.  I really like this pedal and want to keep this one (not buy a used one off ebay).  I mostly want to keep it because of sentimental reasons.  What I was hoping i could do is find someone on here that would be willing to take this on as a project for me.  Since I was not able to find anyone that had mod kits for it, and people who have this pedal really like it, I thought perhaps someone would like to clone it and at the same time, fix it and mod it if they could find way to improve it.  the pedal is pretty quite as is.  It gets a little noisy when the compression is cranked up and perhaps that could be improved upon.  Perhaps I was not able to find any mod kits for this compressor because it's already a clone of something else.  My guess, this is the place to find these answers.

If someone would be willing to take this repair/mod/clone project on.  Let me know.  Perhaps it could turn into a group forum project.

I have several pictures of the pedal and PCB but i'm not able to see how to attach them to this post.  Perhaps I can get some help with that also.

I don't expect anything for free.  So if anyone decides they want to take this project on, we can work those details out.

Thanks for taking the time to read this.

Quick Update:  I plugged it in one last time before posting this hoping the it had fixed itself.  An now a new problem, when I switch it from effect to bypass, I get a horrible pop.  Tremolo effect is still there.

-John

About me:  I'm not an electrical engineer but have dabbled with soldering things together over the years.

[SISKO]

Here you have a schematic http://personal.inet.fi/musiikki/echoserver/pics/Kytkikset/FX80-BAttack.jpg (do you know how to read schematics?)

Your problem sounds like a cold solder or a broken transistor, I think probably near Q5.
I have the same unit. If you  measure the voltages inside of it, then we can compare them with mines. (do you know how to read voltages?)

To upload pictures you have to host them on a server and then paste the link here. I used photobucket and/or 4shared. You need to be registered to be able to use it.

[JohnForeman]

Here's a link to the images.  I have located Q5.  I have a multimeter to check the voltages.  you will have to show me where you would like me to probe for them.

http://s203.photobucket.com/albums/aa112/t2436jf/

thanks for taking the time to respond.  I have that same schematic but no nothing about circuit design so would not even know where to start looking based on my problem.
Thanks

[JohnForeman]

Here's a picture showing where the Q5 is located.  after i marked up the image I saw that it is marked on the underside of PCB.  So, I guess i was somewhat successful in reading the schematic.

http://i203.photobucket.com/albums/aa112/t2436jf/Q5.jpg

John

[SISKO]

Yes, thats Q5. Any bad solder surrounding it?
To check the voltages you should place the black probe on the negative terminal of your battery, with the red probe take this measueres:

Battery: (place the red probe on the + terminal)
All the diodes, ICs, and transistors pins voltages.
This should give you an example of how to do it http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

So, check the voltages and we´ll compare them with mines!

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Edit: Yes!! Thats Q5!

[JohnForeman]

ok.  I'll read the debugging thread and start taking some measurements.  It will be later today since technically i'm at work (work from home).  There are are a couple spots that look like the solder may be bad, but i'm not sure.

cap next to QA5
http://i203.photobucket.com/albums/aa112/t2436jf/0425121320.jpg
http://i203.photobucket.com/albums/aa112/t2436jf/0425121321.jpg

Possible repair or mod?
http://i203.photobucket.com/albums/aa112/t2436jf/0425121321a.jpg

Thanks again

[SISKO]

We have diferents PCB revisions. Yours is "D", mine is "K". That means that the layout is a little bit diferent in some places. I dont know  precisely if those components solderded on the solder side of the pcb are stock, a mod or a repair.

That big capacitor is a supply filter. Its connected across the V+ rail to ground in case your power adapter is unregulated or bad filtered. My unit doesnt has it (not even on the other side), but it does appear on the schematic, so theres a great porbability that its stock.

One way to check if its a bad solder is to reflow or to resolder it. The other is to move the suspicious component while you play and see if there is some audible difference

[JohnForeman]

A little off topic.  do you have other compressors and if so, how does this one compare?  Mainly transparency, noise.. overall sound?  This is the only one i've ever had and I like it but now my interests are peaking and i'm wondering if I should start trying some others.
-John

[JohnForeman]

when i do the voltage test, should i have all the knobs  up/down or middle?
-John

[SISKO]

A little off topic.  do you have other compressors and if so, how does this one compare?  Mainly transparency, noise.. overall sound?  This is the only one i've ever had and I like it but now my interests are peaking and i'm wondering if I should start trying some others.
-John

Right now, I dont have any other compressor at hand to compare with, but Ive played trough some others compressor (built the DynaComp), mainly the Dyna and the Boss CS-3.
This one sits right in the middle of them in terms of tone (tone not tone as in transparency but in attack and response, the DC is agressive and the CS-3 is mellower). Its the quietest  of them (good!), altough most compressors do hiss when the comp knob is on max.
In term of Tone, its seems to me a little dull and dark (like some of the shimmery higs are lost when the comp is activated, its not the most transparent compressor in the world) but again, the Dyna had this problem too.

I like agressive compression, squeezed attack.. smth you would know when its active only by listening to it. Keep that in mind while you read my opinion. Its not my favourite compressor (I prefer the Dyna cause its character) but its a good candidate when you need a compressor that do what its ask for but no kill you original attack. Yes, it can squeeze your tone when its on max, but its best job its done when its used when you need to just compress a little and add warmth to your sound (a perfect match for a strat!)

The CS-3 was the least preferred. It was sterile compared to the others.

If you would like to diy you compressors, take a look at Merlinb´s fantastic job with the  Engineer´s Thumb here http://www.diystompboxes.com/smfforum/index.php?topic=97123.0
The Dyna and the Ross are good candidates as the Orange Squeezer is. There are a lot of other options too! (WHAT compressor, LA2A, etc)
Here is a thread that might be of your interest http://www.diystompboxes.com/smfforum/index.php?topic=89814.0

when i do the voltage test, should i have all the knobs  up/down or middle?
-John

It doesnt matter in this situation, but only to replicate your results with mines lets have them all down.

[JohnForeman]

Here are the transistor measurements

Q1
E = 2.5 / 3.0
B = 2.5 / 3.0
C = 5.5 / 6.2

Q2
E = 0
B = 0 / .25
C = 1.7

Q3
E = 0
B = .25
C = 1.7

Q4
E = 4.2 / 4.4
B = 4.0 / 4.6
C = .1

Q5
E = 1.2
B = 1.67
C= 8.78

I had the ground probe directly on the battery terminal.
The checks that have two values were jumping erratically during measurement.  I tested with the pots turned up and down.  The values didn't seem to change much.  I was concerned that so many of the checks were zero.
Since I have no idea what the values should be, I don't know if what I have so far is telling us anything.  Let me know if I need to keep measuring.  If so, I'll get the ICs and diodes next

John

[SISKO]

Excellent! Im not at home now, but Ill get my measures as soon as I can. All of your voltages seems fine except Q1. You see, for a transistor to work (lets say, in the most common way or configuartion) the base need to sits somewhere between .3v to .6v from the emitter. That seems to be ok for Q5, Q3 and posibilly for Q2, but not for Q1! (Q4 is a differente beast, a Jfet)
In Q1 it seems that the base and emitter are shorted together. You can check this with your multimeter by placing the balck probe on the emitter and the red probe on the base. If the reading is 0, then the transistor is shorted. If its somewhere from .3v to .6v its working ok.

If it is shorted I can be because of a shot on the pcb or somplace OR the transistor is broken and needs to be replaced.

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Edit: Got time to check the voltages:

Q1
C=6.32
B=3.05
E=2.43

Q2
C=6.32
B=0
E=0

Q3
C=6.32
B=0
E=0

Q5
C=8.8
B=6.55
E=8.22


My diference with your measurements in Q5 is because probably some kind of noise (coming from the air or a wire) was activating your detector circuit thus activating the "reduction of gain".
So, in order to get similiar results as you, I plug a cable trough the input jack and touch the tip with my finger. The reading in Q5 where

Q5
C=8.8
B=2.6
C=1.7

Its a good practice when measuring voltages to short the input to ground so you dont have any intermision coming from noise, etc.
I keep thinking that the problem is in Q1, probably some kind of short circuit between the E and the B.

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Edit numerb 2:
I did not catch the differencs between the collectors of Q2 and Q3. Im leaving now, will seat to think about it when I got home at night
------------------------
Edit 3:
The diferences above is because of the noise activating the compressor. The same thing that happened with Q5. I touched the tip of hte cable and my collectors voltage went down to 2v. Im sorry for all this confusion!

[JohnForeman]

I measured the voltage across E and B on Q1 and got .57.  That's within your target. 

So i flip the board over and start looking for shorts.  I found this break in the circuit.
http://i203.photobucket.com/albums/aa112/t2436jf/breakincircuit.jpg

It almost looks like it was put there intentionally.  It also has the resistor soldered on to that side of the board that does close the trace but at a different location.  Take a look at it and let me know if you think i should drop a dab of solder on it.

[Nasse]

What do you gurus think about such old electrolytic caps? They are small values but some are in the sigal path and others in the conrol.. I have about same unit which seems to be bit tired... must have been unused for long long times

[Nasse]

your pic
http://i203.photobucket.com/albums/aa112/t2436jf/breakincircuit.jpg

I took my dod open and mine is yet another revision, I  T or something

You have that red circle, my board looks much bout the same near the place, my board has jumper wire soldered from that red circle point to the right, next trace

looks like my pedal has 3080 that is replaced by some, looks handmade and all the other board is by machine

[JohnForeman]

Nasse,
can you post a pic of your board in that area?

[Nasse]

http://aijaa.com/0096010084360
http://aijaa.com/0003810084359

i did add small x to point

[JohnForeman]

Nasse
so in the trace to the right of the X, you have a break?

Also, is your middle knob marked "release" or "attack"?  Mine is marked attack.

[Nasse]

http://personal.inet.fi/musiikki/echoserver/PDF/fx80b.pdf

Oops mine must be closer to that circuit, it is release model

I dont see any breaks

[cjonesplay]

I've got the same problem - let me know if I can be of any assistance with pics, etc. Mine is the Attack middle knob.