Lost the distortion on an Orange Crush 15R.

[bclemons]

Is the guitar volume all the way up?
Does the first Gain pot affect the signal at all?

Yes, and yes.

[DrGonz78]

To me what you describe sounds like an intermittent problem since the clipping kicked on for moment. Try chop sticking the components and tapping on the board to see if you can trigger the possible intermittent problem.However, it still could be something else but first I would rule out bad solder joints all throughout the clippings stage of the circuit. A signal tracer might prove to be valuable in a situation like this one.

[olddawg]

I just powered it on to test the effect of the gain pot again and the clipping came on for just a minute, and then was gone again. The regular gain pot seems to be working fine and the overdrive level pot (when the switch is engaged) provides a significant volume boost when turned up, regardless of the regular gain pot position. Maybe the diodes aren't getting to ground properly? The soldering looks good on the diodes.

Or the pot is broken internally or disconnected somehow. Easy enough to check the pot and it's connections. It is common for a pot to be banged and damaged internally, the casing separated, the wiper bent, the lugs disconnected, etc.

[Jazz P Bass]

I have been bitten more than once by an intermittant pot.

The only way to actually measure one for breaks is out of circuit.

[bclemons]

No result from chopsticking. I'll fire it up again tomorrow.

[TimmyP1955]

Here's how I think it works - someone please correct me:

The pot is in parallel with R112, and the pot is wired such that when CCW its value is 100K, and when CW it is 0.

So when the Overdrive pot is CCW, R112 is in parallel with 100k.

As the pot is turned up, the value of the pot decreases, so the value of R112//Pot decreases, which increases the gain of IC101.

Additionally, as the gain pot is turned CW and approaches 0 Ohms, the switch end of the diodes gets closer to ground. As this happens the signal voltage than can be developed across the series combination of the diodes + the pot decreases as the diodes start to clamp the signal.

[eschertron]

Here's how I think it works - someone please correct me:

The pot is in parallel with R112, and the pot is wired such that when CCW its value is 100K, and when CW it is 0.

So when the Overdrive pot is CCW, R112 is in parallel with 100k.

As the pot is turned up, the value of the pot decreases, so the value of R112//Pot decreases, which increases the gain of IC101.

Additionally, as the gain pot is turned CW and approaches 0 Ohms, the switch end of the diodes gets closer to ground. As this happens the signal voltage than can be developed across the series combination of the diodes + the pot decreases as the diodes start to clamp the signal.

Clever! I was trying to figure the diodes as part of the negative feedback, but I see now that the pot and R112 are basically doing double duty; in the NFB loop with R108 (It think it says 108!), and then after the op amp dividing the signal with the diodes, just as you said.

Looking at it that way, I'd expect when the amp goes from fizzy to non-fizzy there'd either be A) a loss of perceived volume because the pot or the switch went open and the 'boost' function shut off, or B) a jump in perceived volume because the diode network went open and there's still a gain increase but no actual clipping.

@bclemons: when the clipping came and went, was there a clear change in volume? Which way?

[52 Bill]

I just powered it on to test the effect of the gain pot again and the clipping came on for just a minute, and then was gone again. The regular gain pot seems to be working fine and the overdrive level pot (when the switch is engaged) provides a significant volume boost when turned up, regardless of the regular gain pot position. Maybe the diodes aren't getting to ground properly? The soldering looks good on the diodes.

You may be looking at this in the wrong way, it isn't a channel switching amp with a clean and dirty setting. It is a single channel amp that can be set up to distort.

Turn the overdrive control all the way up to 10, as this is where the diodes are fully engaged and the stage gain is highest. Now use the gain control to set the amount of distortion and the master volume to set the overall level. Doing this, can you get a good distortion sound?

[bclemons]

You may be looking at this in the wrong way, it isn't a channel switching amp with a clean and dirty setting. It is a single channel amp that can be set up to distort.

Turn the overdrive control all the way up to 10, as this is where the diodes are fully engaged and the stage gain is highest. Now use the gain control to set the amount of distortion and the master volume to set the overall level. Doing this, can you get a good distortion sound?

Well, you helped me figure this out by suggesting I was looking at it the wrong way. I knew what you described should be how to engage the clipping and adjust it. I looked at the controls and they seemed a little ambiguous (see attached pic of control panel), so checked the manual online and the controls for this thing are unlike any amp I've ever had (And I've had a lot). I was doing it wrong. Even though it says "Master" right above the knob, I was reading it as "Gain" like it said underneath it. I guess they were labeling the whole section of 3 knobs as the "Gain" section. The "Volume" knob on the far right controls the amount of gain driving the clipping section (it says "gain" on the schematic, go figure). I had it in my head that the 3 knobs were the "Master" section like on a Marshall that has Reverb and Volume under the "Master" section. I feel like a goob now. I had the knob labeled "Volume" turned down too low to drive the clipping circuit, and when it was being intermittent, it was too loud and I had turned that knob down to quiet it down. Thanks for your efforts, gentlemen.

[The Dude]

I wouldn't say it's entirely your fault. That has to be the most confusing labeling of gain structure I've seen on an amp. They couldn't have f'd it up more if they tried.

[eschertron]

I wouldn't say it's entirely your fault. That has to be the most confusing labeling of gain structure I've seen on an amp. They couldn't have f'd it up more if they tried.

In fact, there are a few discussion threads here that have poked fun at the labeling (and especially the wordless pictograph labeling) that Orange has used. They fooled you once, so shame on them

[Jazz P Bass]

Cool ending.

[bclemons]

Here's how I think it works - someone please correct me:

The pot is in parallel with R112, and the pot is wired such that when CCW its value is 100K, and when CW it is 0.

So when the Overdrive pot is CCW, R112 is in parallel with 100k.

As the pot is turned up, the value of the pot decreases, so the value of R112//Pot decreases, which increases the gain of IC101.

Additionally, as the gain pot is turned CW and approaches 0 Ohms, the switch end of the diodes gets closer to ground. As this happens the signal voltage than can be developed across the series combination of the diodes + the pot decreases as the diodes start to clamp the signal.

So, if I put some diodes with a higher forward voltage (like LED's) in place of the IN4148's, the increased negative feedback produced will prevent a volume jump, like I would get from the same modification to a clipping circuit that connected the diodes to ground?

[eschertron]

So, if I put some diodes with a higher forward voltage (like LED's) in place of the IN4148's, the increased negative feedback produced will prevent a volume jump, like I would get from the same modification to a clipping circuit that connected the diodes to ground?

I think it would get louder before clipping.