ASTROSIM (cab simulator)

[bluebunny]

It's not set up to use phantom power.  And those output caps should mean there's no incoming DC to upset the opamps.  I bet Paul knows the right answer!

[Kevin Mitchell]

Any suggestions on where one would implant a belton reverb module into this circuit? Not sure if it's something that should come pre-cab sim or perhaps it could be injected somewhere for best performance.

I've got parts on the way to tinker a bit. I wanted to see about including reverb without making a big deal about it. Just one extra knob - using the schematic they host on their website.

[lcv]

@bluebunny
maybe those caps end up reversed biased by a PS voltage? may be I'm wrong.

[bluebunny]

You could use NP electros?  I've seen them used in a few balanced drivers.

[lcv]

That would be a good solution.

[J0K3RX]

Any suggestions on where one would implant a belton reverb module into this circuit? Not sure if it's something that should come pre-cab sim or perhaps it could be injected somewhere for best performance.

I've got parts on the way to tinker a bit. I wanted to see about including reverb without making a big deal about it. Just one extra knob - using the schematic they host on their website.

Would be a nice thing to add.. You could make it switchable easy enough pre/post. A tight slap reverb can do wonders. A compressor can also be a nice addition.

[PRR]

Phantom injection: look at the polarity of the output caps.

[samhay]

Any suggestions on where one would implant a belton reverb module into this circuit? Not sure if it's something that should come pre-cab sim or perhaps it could be injected somewhere for best performance.

I've got parts on the way to tinker a bit. I wanted to see about including reverb without making a big deal about it. Just one extra knob - using the schematic they host on their website.

I would suggest you put a reverb beforehand.
Alternatively, splice it in at the point where C22, C16 and C15 meet.

[samhay]

Phantom injection: look at the polarity of the output caps.

Indeed. Phantom power wasn't in the design brief.
However, it wouldn't hurt to make C20 and C21 NP with a max voltage > 48V as this is the only mod needed to make this tolerant of phantom power into the XLR outputs.

If you want the option to power it via phantom power into the XLR outputs then that would be a bit more work and would probably preclude the headphone output.

[Kevin Mitchell]

What would phantom power do to the XLR signal? I've been trying to look into it and get as far as powering condenser microphones.

My audio interface has the option but never thought much of it with the setup I have. Perhaps I had tried and it didn't do much for me. I remember I ran it with a dynamic mic and also line level guitar signal. Nothing beneficial happened really.

[samhay]

Phantom power on the XLR out will apply ~48V to the output side of the output caps (C20 and C21). If these are polarised capacitors as most 10u are, this will be a reverse volatage which typically leads to quite spectacular failure of the capactor.

Three options.
1. Don't apply phantom voltage to the XLR output.
2. Use non-polarised capacitors that have a voltage rating significantly greater than your phantom voltage (63V is probably ok, but 100V would be my choice).
3. Socket the capacitors and call it a feature. Fireworks mode.

[Kevin Mitchell]

Sorry my lack of understanding the use of phantom power had clouded my thoughts.

So phantom power is being brought up in terms of circuit protection of the cab sim from the 48volts. It doesn't do anything for the signal - is only used for condenser mics and would damage the circuit without precaution.

I think I've got it now. Glad I didn't blow anything up when I had the "what does this button do" moment

Thanks

[PRR]

Exactly. This unit does not use Phantom. However your low-pay helper WILL "touch that button" and send Phantom TO it, just before a critical moment. BI-polar 63+V caps are wise on nearly anything with XLR outs.

[mth5044]

Any particular reason to not have a volume control for the headphones? Someone is going to have headphones on before powering up, not realizing some volume is way too high and have a bad time. It's usually good practice to turn a piece of equipment on and turn the volume all the way down before putting headphones on.

[deadastronaut]

call it a feature. Fireworks mode.

 

yeah i had no need for phantom power....

the original schemo did have a headphones vol control,

but i paired it back, and left it as a preset...

[bool]

..
However your low-pay helper WILL "touch that button" and send Phantom TO it, just before a critical moment. BI-polar 63+V caps are wise on nearly anything with XLR outs.
...

Before digital consoles (mix-boards), "analog era" live sound guys were much more sloppy and not always sober of course. I had phantom sent to both my bass and my amp on several occasions (even on hi-profile events).

Zeners on output can help too.

[njkmonty]

couple of questions re mods?
incorporating a headphone level?  replace r22 with a pot or  r31?   or something different?

also having an aux in and level?  which could connect an external  audio source into the headphone out?  ie able to play along with a song etc?

[Ben N]

I am toying with marrying the Astrosim to a modded mixer/output section from the JamMix for external audio source input and stereo headphone outs. And maybe stick Nathan's submini FB-2 clone (board on the way; tube here & waiting) in front as a preamp. I think this would be a lot more suitable (not to mention better sounding) than the old Behringer V-amp 2 I have been using for silent practice. (This would nicely address your wish, @njkmonty.)

My order finger is getting itchy...

[DougH]

Wow, this sounds really nice!

[merlinb]

FYI I did some experiments with the headphone driver. It seems the optimum for the NE5532 is a single output resistor of 47 ohms (instead of your two resistors R25/R26). This will get you about 8mW into a 16 ohm load (i.e. 4mW per ear phone) with distortion below 0.05% until clipping. Don't use less than 47 ohms as this seems to provoke instability.