1st build problems - help required.

[Rodders]

Hi folks
I'm new here, so feel free to hurl abuse at me and get me to do all the crappy jobs like sweeping the workshop floor and making the coffee

I'm just starting out with some DIY stompboxes and have got a whole load of components lined up for making some of the projects from Tonepad.

My first attempt is the Ross Compressor clone - Project page layout/schematic (hope that 2nd link works)

I've got zero experience of building/modding electronic circuits, but I did study the theory of resistors/capacitors/transistors etc at school here in the UK. I'm pretty quick at picking things up, but I'll admit that I was hoping the first couple of projects would be as simple as just following the instructions. I expected the difficulty to come from my soldering ability, rather than not following the instructions correctly or using the wrong component.

OK, so what stage am I at?
I've populated the board with all of the components. I've had to make 1 or 2 minor substitutions to the original specification:

• Instead of 0.05uF capacitors I used 0.047uF.
• My pots are 470K and 47K rather than the 500K and 50K specified. They are the correct type - linear/log

Where else might I have deviated from the schematic?
Well, I'm not 100% sure I put the transistors in correctly. I assumed that the legs were located precisely how the board was expecting them so I just made sure that the flat edge of the transistor matched up to the flat edge on the board's printed layout.

I did a similar thing with the pots as the lugs don't seem to be labelled.

Also, when I was soldering one of the pot wires I managed to lose the copper ring around the hole on the PCB. Maybe I used too much heat. There was a bit of the copper still exposed so I soldered to that. It's an ugly joint, but I've tested the continuity of it and it appears to be fine. My other joints seem to be fine.

Next potential error is that I have tried to follow this guide for the "offboard" wiring - gaussmarkov. At this moment in time I haven't put the stuff into the enclosure, so it's a bit of a web of wires which is awkward for sure. To make sure that the jacks are both grounded I've used a wire to attach their sleeves together.

What's the problem?
OK, my true bypass works perfectly.
And, my LED shines nice and bright when I operate the footswitch.

Problems:

• When it's on, there is no signal getting through to the output jack. I mean, I've plugged it into an amp and I get silence.
  I've tried turning the pots all the way up and all the way down. I've also adjusted the trim point up and down to no avail.
• When I haven't plugged in anything to the input jack, my LED will still come on indicating that I haven't used the stereo jack as a switch. I think this is missing from the offboard wiring diagram.

I've placed some photos of the board on my Picasaweb account. You can view them here - http://picasaweb.google.co.uk/RodriguezUK/RossCompressorClone# Sorry they're not great photos - especially of the solder side.

What I'm hoping for is some advice on how to star debugging this. Should I remove certain things (LED, footswitch etc.) in order to simplify and close in on the issue?

I thank you in advance.....

Rich

[Zben3129]

Welcome!

First of all, do you have a multimeter? Do you have an audioprobe?


I don't see any glaring problems in the pictures (don't have time to really look hard at them right now, sorry, will do later). Are you positive all tantalum caps are correctly oriented?

If you have an audio probe probe the "input" of the board to see if your switch is wired correctly. Also put your finger on the output" on the board and you should hear 'that sound' come out of your amp.




Zach

[Rodders]

Welcome!

Thanks

First of all, do you have a multimeter? Do you have an audioprobe?

Yes. No - not yet but I can make one.

I don't see any glaring problems in the pictures (don't have time to really look hard at them right now, sorry, will do later).

No problem, when you're ready - or anyone else.

Are you positive all tantalum caps are correctly oriented?

Hmmm, maybe not. I'll check which ones are the tantalums and then check the orientation. Could be tricky now that I've chopped the legs off.

If you have an audio probe probe the "input" of the board to see if your switch is wired correctly. Also put your finger on the output" on the board and you should hear 'that sound' come out of your amp.

OK, will do and I'll report back. My amp isn't small enough to bring into my work area (kitchen) so I need to run upstairs! It's not ideal, so I'll look into getting a small amp (headphone amp) for this job.


Back in a bit.

[Zben3129]

Welcome!

Thanks

First of all, do you have a multimeter? Do you have an audioprobe?

Yes. No - not yet but I can make one.

Definitely do this. It will be your best friend.

Are you positive all tantalum caps are correctly oriented?

Hmmm, maybe not. I'll check which ones are the tantalums and then check the orientation. Could be tricky now that I've chopped the legs off.

Should be marked on the body of the cap. Looks like all the 1uf caps are tantalum, except for the electro one. Check all the caps of that shape as they are usually tantalum.

If you have an audio probe probe the "input" of the board to see if your switch is wired correctly. Also put your finger on the output" on the board and you should hear 'that sound' come out of your amp.

OK, will do and I'll report back. My amp isn't small enough to bring into my work area (kitchen) so I need to run upstairs! It's not ideal, so I'll look into getting a small amp (headphone amp) for this job.


Back in a bit.

Another way to test this is to use the continuity setting on your DMM, but I always think its easier for beginners to be able to hear what is going on. Headphone amp is a very good idea as well.


Zach

[Rodders]

Tantalums. I've checked the data sheet and it indicates that the long leg is +ve (normal) and it's marked on the casing. I've checked my board and I'm certain that they are correctly oreinted.

I don't have an audio probe currently, but I checked the continuity of the input side of my switch and that's correct.

I touched the output of the board and got a nice bit of hum. Other parts of the circuit also caused humming when touched. At one particular point, I even picked up a radio station but I couldn't get a clear signal so that wasn't much use

[Rodders]

I've got a few crappy patch leads - are they useful for making an audio probe? If so, I can do that now.....though I don't have a spare clip so I'll have to "make" one somehow....

[Zben3129]

Hmmm,

you could use a crude method to find where you are losing the signal AKA touch the board at multiple points 

Let me know what happens when you touch:

Middle pin of Q1:
Emitter of Q1 (Left pin when looking at the flat side)

Pin 3 of IC:
Pin 6 of IC:

Middle pin of Q2:
Collector (right pin when looking at flat side) of Q2:
Emitter of Q2:

Collector of Q4 (right pin when...):



Don't forget the IC is upside down, so pin 1 is bottom right


Zach

[Rodders]

just about to check those....but can you confirm that pin1 on the IC is bottom right when upside down? the bottom left pin has the square PCB marking which I thought was meaningful....

My thought was that this was the layout from underneath:

4-| |-5
3-| |-6
2-| |-7
1-| |-8

[Rodders]

crackle - very quiet static kind of noise, usually starts with a little pop
buzz - like you get when you touch a guitar cable when it's plugged into a powered up amp
dead - no sound


Q1:
middle - crackles
emitter - crackles

IC (using my pin interpretation):
1-dead
2-crackle
3-smalll crackle
4-small crackle
5-buzz
6-big buzz
7-small crackle
8-dead

Q2:
middle- buzz
collector- crackle
emitter- crackle

Q4:
collector- crackle

[Zben3129]

Ok, sounds to me like the problem is in the IC stage. Both outputs of the IC are connected to the output (loud buzz), but the input isn't (small crackle). Might be time to grab some voltages off the IC. Let me know what you come up with.


Zach

[Rodders]

OK, on some of the pins the meter just goes mad - numbers rise continuously.

1- mad
2- 4.65V
3- 4.65V
4- 0V
5- mad
6- 2.65V
7- 8.92V
8- mad

[oskar]

Pin 5 should be ~0.6V
From pin 5 there is a diod forward voltage drop to pin 4. It should therefore be 0.6v over pin 4.

pin 1 and 8 are not used on this chip I believe.

[Rodders]

Can you explain how you see this "diode forward voltage drop" arrangement?

And, where do you get the 0.6V value from?

Assuming you are correct, then where do you suppose the problem might be?

[oskar]

Can you explain how you see this "diode forward voltage drop" arrangement?

http://www.intersil.com/data/fn/fn475.pdf
page 3, schematic diagram, Q3/ D1

And, where do you get the 0.6V value from?

The voltage drop over a diod ( or transistor, base/emitter) is normally around 0.6-0.7 volt for small or IC silicon
devices.

Assuming you are correct, then where do you suppose the problem might be?

I was sort of hoping you wouldn't ask that question.
With a healthy chip I think pin 5 and 8 would read 0Volts as they are unconnected.

I knew there was something familiar with the ross compressor, this is another ross thread from a year ago.
http://www.diystompboxes.com/smfforum/index.php?topic=59742.0

I can't say for sure what is wrong with your Ross clone thing. I'm tempted to say that your 3080 has gone to IC heaven
but I really don't know. Used sockets?

[Rodders]

Oh dear! I may have a spare.

I didn't use a socket, but perhaps I should in future.

[oskar]

You could try and give us all the voltages though and go audioprobe on it, while you're at it.
Allways start a thread like this with proper voltage readings. You'll almost certainly end up
doing them anyway.

Think you've got problems?
http://www.youtube.com/watch?v=Uh-5piuNy-U

[Zben3129]

OK, on some of the pins the meter just goes mad - numbers rise continuously.

1- mad
2- 4.65V
3- 4.65V
4- 0V
5- mad
6- 2.65V
7- 8.92V
8- mad

Pins 2 and 3 are the inverting and noninverting inputs, which should be biased halfway between V+ (9v) and V- (0v). Approx 4.5v expected, so these pins check out fine.

Pin 7 is V+, so 9v here is correct

Pin 4 is V-, so 0v (ground) is correct.

Pin 6 is the output of the amplifier, this pin looks alright.

However, pins 1 and 8 should read 0v. They have no connections to anything inside the chip itself, so getting voltages here is a bad sign.

Pin 5 is the bias for the amplifier, and gets its voltage from the emitter of Q5 through a 27k resistor and 500k pot. I don't know why you would get wacky readings here, another indication of a bad chip.



I originally feared either a burnt transistor or chip, as your soldering looked great and parts looked correct, but I don't like suggesting that work cause I would hate for you to go through the hassle of replacing it to find it still doesn't work. However, I'm pretty sure you need to replace the IC in this case. And please use a socket! 



Zach

[Rodders]

OK, thanks guys. Sorry for disappearing for a few hours - it was after 1am here when I got to bed.

Before I do replace the IC, is it possible that the mad voltage readings come from crap multi-meter use? I've only got needle probes so having to hold them on tiny, rounded bits of solder isn't easy.

I suppose I'm also saying, is it common to get crazy voltage readings like this with a fried component? What does it mean, when the DMM just spirals out of control like that? I could understand a zero reading or an incorrect fixed reading, but not a reading that rises up beyond 200V.

I'll pick up a few sockets today anyway - these any good? Maplin DIL

EDIT: Thanks for your comment on my soldering, Zben3129. I thought it was a bit messy in places so will do a neater job next time. I'm a bit of a perfectionist, y'see!

[Zben3129]

I am not sure about the multimeter, but mine does wacky things sometimes, though not usually rising that high. It may be the meter, worth checking out. Maybe a way to get voltage on the non connected pins would be by frying the chip from soldering, connecting it to something internally.


Zach

[Rodders]

The multimeter was a very cheap one, so I'll look to replace that in future if I can stay motivated through this steep learning curve.

I was very careful when soldering the IC in place - made sure to only give a couple of seconds heat before touching the solder on and then moving the iron away.

I suppose, if I use a socket in future then I'll know that I haven't fried it. That'll make fault-finding a bit quicker too I guess.

Right, off to the shops to buy some sockets.........