tonepad.com Ross Compressor - no signal but getting radio when touching Q1?!?!?!

[sweetwilly]

Hi all.  I've been playing guitar for 15+ years and have been doing minor repairs and rewiring on all my guitars (and bandmates) for the last 5 years or so and decided to jump into the wonderful world of effects building.  I practiced with perf board and a component kit I pinched from a mate's old school stuff and got a few little circuits working so felt ready to take on a full build.  I decided to go for the tonepad.com layout of the Ross Compressor.  This posting is after my 2nd attempt at this build.

1st Attempt.

I ordered the PCB from tonepad and parts from combination of small bear and maplin here in the UK.  I couldn't get a 0.05uf cap so I used a 0.047 and a 0.0047 in parallel.  I also left out the 220pf cap marked CD as a lot of the build reports on tonepad mentioned this let through more highs.  I used 2N5088 transistors and a metal can CA3080A IC.  As this was my first attempt I made a few errors in choosing components.  All the values were correct but I got high voltage caps instead of 16v so they were quite large!

I got all the components and the board and started work.  I socketed the trannies and the IC and spent several hours soldering.  I had several mishaps and ended up with quite a few lifted pads so had to run component leads to the next pad. When done, in went a battery, the guitar was plugged in and nothing!  Looked at the solder side of the board for ages then realised there were 2 shiny pads without anything in them.  It was where CD should have been.  I put a jumper in and I had an amazing compressor!  I set the trim pot, had a little play (very smooth!) then set about fitting it in it's box. After squeezing it all in to the box my lovely compressor had disappeared!  There was no signal whatsoever.  I checked for any possible shorts, but had been pretty liberal with my electrical tape use (totally covered inside of box) and couldn't see any obvious faults.  I took it all out and tried it again but still nothing.  Then I noticed that when I picked it up I started getting a local radio station coming through and that the level and sustain pots worked on this.  After a bit of "probing" with fingertip found that it was when I was touching the pins of Q1 and the trim pot that I got the radio.  When I strummed the guitar the guitar signal interfered with the radio but no notes.  You could hear the sound when scratching the wound strings though.  The PCB was such a mess that I decided to write it off as practice and a lesson and started again with a new board.

2nd Attempt.

This time I got 16v caps, tantalum for electrolytics (for size mainly) and the CA3080E "spider" IC and a larger, pre-drilled box.  Because the box had 3 holes for pots I decided to attempt Mark Hammer's release mod using a SPDT toggle switch, 150k, 10k and 52k resistors.  Started work.  As I soldered each resistor I checked the joints.  I used a jumper to test the joints of the sockets.  I'm not entirely sure how to test caps with the DMM I have (or any for that matter!) so just checked each joint visually and all seemed fine.  Anyway, this time I skipped the working compressor bit and went straight back to local radio!!!  It is EXACTLY the same as my 1st attempt.  Touching the pins of Q1 and the trimpot is the only way to get any sound out of it and am getting the same string noises again. 

These are the readings I get using a battery that reads 8.78 and the power input on the board reads this as well.

IC

P1 - 0       
P2 - 3.77 
P3 - 3.77
P4 - 0
P5 - 0.60
P6 - 2.42
P7 - 8.79
P8 - 0

Q1

C - 6.83
B - 1.37
E - 1.89

Q2

C - 6.47
B - 2.44
E - 2.25

Q3

C - 8.71
B - 0
E - 0

Q4

C - 8.71
B - 0
E - 0

Q5

C - 8.80
B - 8.71
E - 8.28

D1

A - 0
K - 8.80

D2

A - 0
K - 0

D3

A - 0
K - 0

Apologies for the epic post, but figured the more info the better.  Just hope it's the right info!

Thanks in advance!
S.Willy...

[Papa_lazerous]

Hi I've just had a little look at your voltages,  I assume your battery was a little low? as you where only getting around 8.8volts on +supply on CA3080 and on collectors of Q3,4 and 5.

Mostly everything seems pretty nice and within what you would expect to see.  the voltages you get will vary form mine for example as it makes a difference where the pots are set and if there is a signal runnign through it. Q1 however seems wrong as your emitter is higher than the base which shouldnt be as there is a diode drop between B & E so the emmiter should be about 0.60Volts lower than the base.

this may be a problem or you may have written it down wrong.

Although at the moment you are saying you are getting radio interference, do you still have a working effect despite this?  You may have possibly said but after reading all that my brain is pickled  If it still works but with interference it may just be wise not to probe the circuit with your fingers    your body is a huge antenna!!.  But it in a ncice hammond box and that should screen it from interference

hope this helps

[sweetwilly]

Hey thanks for speedy reply!

The voltages are all correct and yes, the battery read 8.78.  I read only today about voltage drops in transistors and noticed that  Q1 didn't seem right.  Will try a few different trannies to see if it makes any difference. 

I'm not getting any guitar signal through at all, it's only when I touched the pins of Q1 (something I did accidentally the 1st time) that I even get the radio interference.  Again with Q1!!!  I am going to go and swap it out and see what readings I get.

Thanks again.

[sweetwilly]

OK, I've changed out Q1 with a couple of other 2N5088s and am getting the same readings.  Well pretty close.  The emitter is still higher than the base.  What would cause this? 

Also tested all the electrolytics.  Apart from 1 they all show a voltage on the + side and nothing on the -.  1 shows around 6v on the + and about 2 on the -.  Is this normal?

Thanks again.

[Papa_lazerous]

I could have told you it wasnt the transistor,

Erm well Q1 the only way you can be getting that voltage at the emmiter isif you have done something really basic and silly so it should be an easy fix.  you should have 1 10K resistor going to ground and a 1uF electrolytic cap connected to it and nothing else.  if the transistor where removed and you powered the circuit up you should get no voltage on that point whatsoever.  So look there!

Did you use a bought PCB?  or etch your own or made your own layout?


can you post pics of both sides of your board

[sweetwilly]

I bought the boards from tonepad.  I've only got a very low quality camera phone so wouldn't be any good.  Will try to get my hands on a camera and post photos asap.

cheers...

[sweetwilly]

Erm well Q1 the only way you can be getting that voltage at the emmiter isif you have done something really basic and silly so it should be an easy fix.  you should have 1 10K resistor going to ground and a 1uF electrolytic cap connected to it and nothing else.  if the transistor where removed and you powered the circuit up you should get no voltage on that point whatsoever.  So look there!

Yep, just the 10k and 1uf and when transistor removed no voltage at that point.  I did forget to mention I managed to lift one of the pads of Ra - 470k so I ran it's lead straight to the base of Q1.  I followed the copper track and it's definitely not touching anything else so not sure if it would be causing the issue.  When I soldered the socket for Q1 I tested the resistor attached directly to it and it was fine...

Really appreciating your help here!
Many thanks!

[sweetwilly]

I checked the electrolytic caps again.  Am only getting a voltage reading on the negative lead of 1 of them.  The + is about 3 (not 6 as posted earlier) and the - is about 2.  Should I be getting voltage readings on the -s of the other electrolytics as well?

cheers...

[frokost]

Since you lifted the (I assume) right pad of Ra - is there continuity between the Q1 base and the 10K resistor too? That connection could be broken now...

EDIT: Nevermind. Reread a few posts and saw that the connection is fine. Sorry.

[sweetwilly]

no worries, thanks for the input!

[deadspeaker]

Idk if you already did this, but here is a little story:
I printed out a schematic of the box I was building and used my eyes and an ohms meter to trace the circuit. I used a highlighter to mark of the connections on the schematic. I traced all the way through the circuit(including the pots and switch) and the schematic was looking pretty yellow. Then I realized that one part was not connected to ground! That was the only thing missing. It stood out to me because it was the only non-yellow part left. Once I made the connection my box worked amazingly. Try that(even if you just looked at it, use the highlighter method) and good luck.

[Yazoo]

I built a Ross Compressor using a Tonepad pcb. Just a thought in case it's the same thing I experienced. Is there continuity between the Q5 emitter and the Sustain 500K pot terminal 3 (left-most on the layout file PDF)?

[sweetwilly]

Hey hey.  Cheers, will give it a go.  Will test my schematic reading skills, but gotta learn.  

Excuse me if this is a stupid quesiton, but when you say traced the circuit with an ohm meter was it a continuity test or did you test each component?  My multi meter doesn't have a continuity test function and I'm not 100% sure how test caps  

[sweetwilly]

The voltage readings at both points are the same so assume that means there's continuity?

cheers...

[frokost]

Not necessarily. Your meter doesn't measure continuity? Then I reraise my question  . Is the base of Q1 connected to the 10K resistor coming from the input? Anyways, get yourself a decent meter. It'll save you lots of trouble.

[deadspeaker]

well the meter is just to make sure that the parts are connected. You won't get a good ohms reading on most caps. You are just testing if there is a connection. You can do this visually, but an ohms meter will help.

[sweetwilly]

thanks again, will look at it tomorrow with fresh eyes...