GGG ITS8 help

[Govmnt_Lacky]

Where did you source your LEDs from? Are they Red diffused? 5 or 3mm?

[Phoenix60]

From SmallBear. 3mm red diffused.  LED T-1

[Govmnt_Lacky]

Just noticed that you have yet to post up some voltage readings from the IC (4558 I presume)

Can you do that?

[Phoenix60]

Yes 4558

1  4.5v
2  4.59
3  4.5
4  0
5  4.5
6  4.5
7  4.5
8  9.06

[antonis]

More than perfect..!!
(congratulations on your DMM impedance, also..)

[EBK]

Do you happen to have another op amp you could swap in?

[Phoenix60]

Yes I think I do,  I'll report back

[Phoenix60]

I did have another one to swap out and same thing.  Cannot see the LEDS glowing and lifted position and LED position sound the same to me.  Might've noticed a small volume difference between the two, but honestly at this point I think my ears are playing tricks on me. 

[EBK]

Have we tested those LEDs out of the circuit?

[Phoenix60]

Yes they're working

[EBK]

So, to summarize:

DC voltages at the IC look fine. 
LEDs work.
Si diodes exhibit expected clipping.
Op amp probably is working fine.
Switch is working (Si diodes plugged in where the LEDs are supposed to go work as expected).

So, it looks like something is either attenuating the input more than expected, or something is reducing the gain of the op amp.

Likely culprits would be:

Bad solder joints?  There were plenty of "ball" joints on the underside of your board.  Perhaps reflow everything. Edit: Not quite "ball" joints.  Looks like a bit too much solder instead.  BUT, if excess solder were used on an otherwise properly heated joint, I'd expect more would have shown on the topside of the board.

Wrong component?  As near as I could tell, the resistors looked like they were the correct nominal values.  Maybe a misplaced capacitor?

Bad component?  Could the ceramic cap in the feedback loop be too leaky?  (I don't even know if that is something that happens with small ceramics).

If you happen to have an oscilloscope, now would be the time to mention it.   

[Govmnt_Lacky]

Been recently bit by this so, might be worth a quick look....

Are you 100% positive you are using an ON-OFF-ON toggle for the clipping options? Could it be an ON-ON-ON?

[iainpunk]

Could the ceramic cap in the feedback loop be too leaky?  (I don't even know if that is something that happens with small ceramics).

no they don't. AFAIK only polarized caps actually leak DC, and old rotten paper-in-oil caps as well

cheers, Iain

[Phoenix60]

First of all, thanks everyone for sticking with me on this...


EBK your summary is spot on, and no, I don't have an oscilloscope

Lacky I'm using the switch General Guitar Gadgets provided, I don't know how to test it.  Just trying to understand, did you ask that because you're thinking it may be actually clipping with the LEDS in both positions?

The only issue I recall is when I first soldered C11, I shorted that to R15 because they're pretty close together.  I powered the board up and I noticed that and re-soldered that joint.  Remember also, I had a short because I had D5 in backwards.  I removed that.

[Govmnt_Lacky]

Lacky I'm using the switch General Guitar Gadgets provided, I don't know how to test it.  Just trying to understand, did you ask that because you're thinking it may be actually clipping with the LEDS in both positions?

I asked because ON-ON-ON switches work totally different than ON-OFF-ON switches and could cause problems like you are seeing.

On one side of the toggle switch you should be able to see it stamped with ON-OFF-ON (in the silver part of the casing)

[Phoenix60]

OK thanks.  I checked, mine says on off on.

[Govmnt_Lacky]

Switch is working (Si diodes plugged in where the LEDs are supposed to go work as expected).

Here is what is peculiar to me....

If the diodes work fine in place of the LEDs (and the switch is verified as working correctly as indicated before) then the only thing(s) that can be causing the issues are:

- The LEDs are being installed incorrectly
- One or both of the LEDs are bad


Other than that, I do not see anything else it could be 

EDIT: Unless any of the "C" pads on the PCB are shorted to any other pads on the board -OR- if the associated wiring and/or toggle points are shorted.

[Phoenix60]

I know.... Double checked LEDS, they're good and installed correctly (opposite of each other).

Next step I'll pull the board and check for shorts on the pads.

BTW, in changing op amps I found I liked the LF353P better than the 4558.  Seems dirtier to my ear.