When a boost is a bust :(

[moid]

Hello everyone

Those of you of a certain age who remember the cartoon character Penelope Pitstop, who when presented with a death threat by the dreaded Hooded Claw would utter the plaintive cry of 'Hay-ulp, hay-ulp!' will now be aware of the position I found myself stuck in (although fortunately, I have avoided the clutches of the Hooded Claw). So, if Penelope Pitstop was a middle aged overweight bloke with bad eyesight who couldn't build effects pedals properly, she might be making sounds like I am currently

I'm trying to build a Mr Black Tiger Boost:

Schematic

Veroboard layout I'm using

What could be easier I thought? I need a clean boost, and (for later nefarious purposes, one that won't invert the phase of the signal like a transistor boost might do) and this seemed like a good idea. I've built LPB1s before and they all worked, although I wasn't keen on their tonal qualities, I really want something that will be loud but not change the tone of my guitar much. I've built this creation on veroboard and rather unsurprisingly, it doesn't work - but not in the way I'd expect. Normally when a pedal doesn't work for me, no sound comes out. This time, sound does indeed come out, but it does so at unity and the one potentiometer does nothing - it neither decreases or increases the volume.

Maybe I've made a buffer circuit instead? I reflowed all the solder today. I knifed between the traces to ensure that there are no tiny solder bridges anywhere. I checked the pot with my DMM and it shows that as I turn the shaft the resistance does change within the expected range. Is it possible that the IC (JRC4558P) is busted? I mounted it in a socket so my soldering didn't fry it. Are these chips that might be upset if I wasn't grounded when I touched them? The only other changes I made to the vero layout was I didn't have a 51K resistor, so tied two 25K resistors together in series (wrapped two of their legs together and soldered them) so that shouldn't be too bad, and also I used a huge capacitor in place of the 100n (it is a 100n, but the size is way larger than I usually expect them to be, so I must've screwed up on my ordering as I know have a bag of them - it says Suntan 2A104K on it and are rated at 100v) would this be the issue?

EDIT: I took the IC out of the socket to swap in another (to see if the chip was faulty) and the sound carried on playing straight through the damn circuit when the chip wasn't there - so presumably this means the audio is not getting to the chip? And is somehow bypassing that part of the circuit and coming straight out? Weird!

Here's the top of the board


Here's the back (taken before I filled a couple of small holes with more solder)


There are a couple of extra wires (not connected to anything) because I was hoping to use this pedal to blend with a Noise Ensemble (another pedal that I have failed to get working, grrrrr!). There's no footswitch attached yet because I thought I had better make sure the sound works before getting keen and boxing the damn thing!

If you have any suggestions I'd be very grateful (apart from chuck it at the nearest wall as hard as you can, I've already considered that one!)

Thanks

[GibsonGM]

Hi Moid, go here: http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

Post the info they ask you to collect back here!  Pin voltages....careful not to short 2 pins together when you get in there with a meter.

Likely just a small mistake somewhere!

[moid]

Thanks, I'll try that after some sleep then, my eyes are getting blurry Should I have music running through the chip when I test each pin?

[thermionix]

Signal not needed, the requested voltages are DC.

[slacker]

EDIT: I took the IC out of the socket to swap in another (to see if the chip was faulty) and the sound carried on playing straight through the damn circuit when the chip wasn't there - so presumably this means the audio is not getting to the chip? And is somehow bypassing that part of the circuit and coming straight out? Weird!

It could mean the signal is bypassing the chip, a wiring problem perhaps. With the chip removed signal can sneak through R4, R6, R5 and the pot to the output though so there might not be a problem. When the chip is in and powered up "vcc/2" looks like ground to the signal so it can't sneak though there.
With the chip out measure the resistance between pins 1 and 2 of the socket, it should change between about 1k and 50k depending on where the pot is set. Also check the connections to R6 and check that it's the right value, an error there could cause the problem you're having.

[Chris S]

Maybe check the potentiometer is working. When its at 0K the signal should be unity when it's at 50k it should be fully boosted. If you replaced the pot with a 20 something K resistor you should notice a volume change if everything else is working. Persist it's a great and very loud boost.

[anotherjim]

Check that wire link going under the chip to pins 6 & 7. It should connect the top row (with R4 & R6) to both of those pins, so is really 2 links. It's behaving as though there is no connection from R4/R6 to Vcc/2, which could well be an error in those links.

Without the chip, there is still a path through the other components, so you could hear something even if there were no faults.

[GibsonGM]

Need DC voltages for supply, and each pin of the chip.  The numbers can often REALLY point out if something is wrong.

[moid]

Hi Moid, go here: http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

Post the info they ask you to collect back here!  Pin voltages....careful not to short 2 pins together when you get in there with a meter.

Likely just a small mistake somewhere!

Thanks Therminonix and GibsonGM for the tips

I used this diagram to measure the pinout voltage from:


pin1 - 524mV
pin2 - 0mV
pin3 - 000.6mV
pin4 - 0mV
pin5 - ~6.3mV (this kept changing, but never hit 0)
pin6 - ~3.0mV (this kept changing, but never hit 0)
pin7 - ~30.0mV (this kept changing, but never hit 0)
pin8 - 300.0mV

[GibsonGM]

Ok....is your meter set to measure DC (I hope?). 

With those voltages I think you are not getting power to the chip (or there is a power supply short, or both).   Pin 8 should be near 9V, pin 4, 0V.   Include your battery voltage too, Moid - just in case it's dead!!  lol

Be SURE the tracks you cut have NO continuity to each other.  Make sure that the cuts are done to the right tracks.  So, step 1 - trace 9V from your battery right to pin 8.   
Make sure there is no continuity between that rail and ground (battery minus)!!

[moid]

EDIT: I took the IC out of the socket to swap in another (to see if the chip was faulty) and the sound carried on playing straight through the damn circuit when the chip wasn't there - so presumably this means the audio is not getting to the chip? And is somehow bypassing that part of the circuit and coming straight out? Weird!

It could mean the signal is bypassing the chip, a wiring problem perhaps. With the chip removed signal can sneak through R4, R6, R5 and the pot to the output though so there might not be a problem. When the chip is in and powered up "vcc/2" looks like ground to the signal so it can't sneak though there.
With the chip out measure the resistance between pins 1 and 2 of the socket, it should change between about 1k and 50k depending on where the pot is set. Also check the connections to R6 and check that it's the right value, an error there could cause the problem you're having.

I looked at the schematic and vero layout and it seems to me that there is a route for the audio signal to go right through the circuit without being affected by the IC - or is that just a path to ground perhaps? So possibly that is what I'm hearing? Which is a bit annoying, I want a boost, but also one that I could adjust the potentiometer on and lower the volume to 0 if I wanted to. Maybe if the circuit was working this would be removed? Although I don't think so, I think the boosted signal would be mixed with the original signal...

When you say measure between pins 1 and 2 do you mean stick the positive DMM lead between both pins so it touches them both at the same time?

I'll check R6 later - I'm supposed to be helping my son with his homework at the moment, so it might be a few hours before I can try soldering anything - thanks for the reply though

[moid]

Check that wire link going under the chip to pins 6 & 7. It should connect the top row (with R4 & R6) to both of those pins, so is really 2 links. It's behaving as though there is no connection from R4/R6 to Vcc/2, which could well be an error in those links.

Without the chip, there is still a path through the other components, so you could hear something even if there were no faults.

Thanks, I will need to desolder the socket to get to that bit, I'll try that later tonight

[moid]

Ok....is your meter set to measure DC (I hope?). 

With those voltages I think you are not getting power to the chip (or there is a power supply short, or both).   Pin 8 should be near 9V, pin 4, 0V.   Include your battery voltage too, Moid - just in case it's dead!!  lol

Be SURE the tracks you cut have NO continuity to each other.  Make sure that the cuts are done to the right tracks.  So, step 1 - trace 9V from your battery right to pin 8.   
Make sure there is no continuity between that rail and ground (battery minus)!!

Thanks for the fast reply OK that sounds like power then - I'm not using a battery; I was running from a 9v wall plug. As soon as I'm done helping my son with his homework I will have another look.

[duck_arse]

don't desolder - just use the resistance range on yr meter (with power OFF/battery out) to make sure you have 0R or close to.

we never want two pins shorted together when measuring, unless specifically specified.

squinting at the build photo, it looks to me as tho pin 8 is bent in/under. perhaps lever the IC out and check for leg straights, then refit, and push down firmly until it seats properly.

[moid]

Ok....is your meter set to measure DC (I hope?). 

With those voltages I think you are not getting power to the chip (or there is a power supply short, or both).   Pin 8 should be near 9V, pin 4, 0V.   Include your battery voltage too, Moid - just in case it's dead!!  lol

Be SURE the tracks you cut have NO continuity to each other.  Make sure that the cuts are done to the right tracks.  So, step 1 - trace 9V from your battery right to pin 8.   
Make sure there is no continuity between that rail and ground (battery minus)!!

Thanks for the fast reply OK that sounds like power then - I'm not using a battery; I was running from a 9v wall plug. As soon as I'm done helping my son with his homework I will have another look.

Hallo Duck I might not have to get to that part yet thanks - read on! GibsonGM - I just measured the voltage on the power socket that is powering the circuit and it's only putting out 5mV (which doesn't make any sense to me). I tested a spare power socket that isn't attached to anything else using the same power supply and it reads 9.1V... so maybe I'll remove the power socket later and add my spare one to see if that cures all ills. Hopefully it's just a busted socket?

[GibsonGM]

It could be, or wired wrong if it is a switching kind (?)...many switch when you pull the plug out, so the battery will work.

Get alligator clip jumpers, connect your 9V directly to the power wires for testing.  CAREFUL not to reverse plus and minus or it'll be a worse problem!!! ha ha.   

Once you get power, test the power pins for + and gnd.     Then you can try an audio test again.    If that fails, re-post voltages...good luck! 

[samhay]

>I want a boost, but also one that I could adjust the potentiometer on and lower the volume to 0 if I wanted to.

This circuit won't do that. At minimum, you get unity gain.

[GibsonGM]

>I want a boost, but also one that I could adjust the potentiometer on and lower the volume to 0 if I wanted to.

This circuit won't do that. At minimum, you get unity gain.

He could jumper R5, no?

[samhay]

^actually, I missed R5. At minimum, it has a gain of 2.
It's a non-inverting op-amp. Unless you pad down signal on the input or output, you will always get, at a minimum, unity gain.

Anyway, that's a rather secondary issue until the op-amp gets some power.

[moid]

It could be, or wired wrong if it is a switching kind (?)...many switch when you pull the plug out, so the battery will work.

Get alligator clip jumpers, connect your 9V directly to the power wires for testing.  CAREFUL not to reverse plus and minus or it'll be a worse problem!!! ha ha.   

Once you get power, test the power pins for + and gnd.     Then you can try an audio test again.    If that fails, re-post voltages...good luck!

OK I desoldered the old power jack and put my spare one in it's place and used crocodile clips to clamp this jack to the ground and power cables. I now have +9V going to the circuit, however with an audio test the potentiometer has no effect on audio volume.

I used the DMM on the IC and got the following values

pin1 - 4.99V
pin2 - 4.99V
pin3 - 4.5V
pin4 - 000.3mV
pin5 - 4.5V
pin6 - 4.99V
pin7 - 4.99V
pin8 - 9.13V

so from that I can infer that power is definitely getting to the chip yes? Pin 4 seems to be weird in terms of numbers compared to the others (although whether they are correct is of course something I don't know!). I noticed that on the schematic, pin 4 isn't used at all, but on the vero layout it connects to lug1 of the pot. Is this the problem?