Condor Cab Sim volume issue

[pedalbuild]

I build a Condor Cab sim to use directly into headphones. It works and sounds fine, except that the volume does practically nothing until it spikes to near max volume when the volume pot is almost all the way up. I made a small graph to illustrate it below.



I used a 2n5458 instead of a J201 (couldn't source it) and chose two 4588 for the opamp's.

It's still usable but it is kind of annoying so I would like to fix it if possible.

Also the max volume is on the low side with single coils, any (easy) way to increase the output volume a bit?

Schematic:

[PRR]

> I used a 2n5458 instead of a J201 (couldn't source it)

That's not remotely a replacement. EDIT -sorry, brain fart.

Your Volume pot: you are sure it is 10K?

[Rob Strand]

> I used a 2n5458 instead of a J201 (couldn't source it)

That's not remotely a replacement.

With a 2N5458,  it looks like the 100k bias trimpot is going to be impossible to set.   The drain resistor needs to be around 2k to 3k ohm so that trimpot needs to be 5k or 10k.   You could try putting a 4.7k resistor across the 100k trimpot.  I'm assuming real 2N5458's not Ebay weird stuff.

I'm assuming you mean the volume pot and not the gain pot.      If the device you are driving has a low impedance then the volume control will act weird like that.

[Rob Strand]

That's not remotely a replacement. EDIT -sorry, brain fart.

I was agreeing with you.  It doesn't look like a great replacement to me.  A bearable  one maybe.

[pedalbuild]

> I used a 2n5458 instead of a J201 (couldn't source it)

That's not remotely a replacement.

With a 2N5458,  it looks like the 100k bias trimpot is going to be impossible to set.   The drain resistor needs to be around 2k to 3k ohm so that trimpot needs to be 5k or 10k.   You could try putting a 4.7k resistor across the 100k trimpot.  I'm assuming real 2N5458's not Ebay weird stuff.

I'm assuming you mean the volume pot and not the gain pot.      If the device you are driving has a low impedance then the volume control will act weird like that.

Thanks,  I'll try adding a resistor to the trimpot.

I got the 2N5458 from Tayda, so I'm assuming they're legit.

Headphone impedance is 80 ohms.

About the transistor, I couldn't easily source any of the obvious replacements for a J201 either. So instead I just soldered in sockets and gave the 2N5458 a shot. Is it likely the 2N5458 is causing any other issues besides volume?

[antonis]

Is it likely the 2N5458 is causing any other issues besides volume?

If it can't be properly biased (Drain at about power supply mid-point) it can cause distortion (asymmetrical clipping) for Drain signal amplitude higher than the lower headroom..
e.g. for Drain set at 7V and Q1 stage gain of 10 say, any negative waveform of greater than 200mV amplitude will be distorted..

[composition4]

Is the volume pot a 10k log pot, and not accidentally linear?

[pedalbuild]

I added a 4.7k resistor to the 100k trimpot, which worked well. It's significantly louder now. The issue with the volume only being audible with the pot almost all the way up remains the same.

Is the volume pot a 10k log pot, and not accidentally linear?

I double checked just now, it is a 10k log as should be.

[merlinb]

Headphone impedance is 80 ohms.

Do you mean you plugged your headphones right into the output of the Condor? I don't think the circuit is really capable of driving heaphones directly...

[PRR]

Do you mean you plugged your headphones right into the output of the Condor?

He says right in the first line "Condor Cab sim to use directly into headphones" and we all (until Merlin) missed it. (I was side-tracked by the 2N part I thot was a BJT.)

Yes, that's the curve of a 80r load on a 10k pot. So working as expected on an unexpected load.

[pedalbuild]

Headphone impedance is 80 ohms.

Do you mean you plugged your headphones right into the output of the Condor? I don't think the circuit is really capable of driving heaphones directly...

Wasn't sure whether it would, but aside from the taper it works well, I'm quite happy with it.

[Rob Strand]

Wasn't sure whether it would, but aside from the taper it works well, I'm quite happy with it.

There's no good place to move the volume control without the volume control affecting the speaker sim filters.
A few other things follow from the driving the headphones,
- it stresses out the opamp
- the cap C14 could cause low-end roll-off because it is too small.

A slight improvement would be to put a resistor between the volume pot wiper and the output terminal.   Try 220R, 470R, 1k.
A higher value will reduce the opamp stress and will make the volume control work a *bit* better.   The side-effect is it reduces
the output level but only when driving headphones.   Play with resistor so the level is good without clipping.

Ideally the condor circuit should feed into a headphone amp.   Then there's no problem at all.