ASTROSIM (cab simulator)

[njkmonty]

merlins mustache!!

[njkmonty]

so you mean replace both r25 and 26 with 47 r?
or replace both r25 and r26 with 47r and connect both left and right outputs together?

[merlinb]

or replace both r25 and r26 with 47r and connect both left and right outputs together?

Yes just one resistor, both outputs tied together.
Or I suppose you could just replace the two resistors with 100R each, with much the same result.

[njkmonty]

or use each halves of the ic ?  or no real benefit

[merlinb]

or use each halves of the ic ?  or no real benefit

Well, you'll get more power if you use one half of the IC for each ear...

[njkmonty]

so ill try both on breadboard  , so just duplicate both when using both halves of chip

[samhay]

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.

That's interesting. I guess that headphones are built with sufficient tolerances such that you will get a fairly balanced output. Do you get noticably better peformance than with 2 100R resitors?

[Marcos - Munky]

I still didn't got the headphone out on my build working. I'll give a try on the 47r, maybe I get lucky

[njkmonty]

after playing around with tda2822 chips and different other values and chips, i ended up with the following which i
stuck onto the end section of my cab sim.
surprisingly the simple Ne5532 sounded great by my ears so i gave up on the more component intensive alternative designs!

i tried up to 100k volume pot but found the 1kb gave me a better range and more control

[Ben N]

Finally getting around to this, using Rob's board. Is this supposed to take board mounted 9mm pots, or offboard? Or, forget "supposed to"--did anyone build this and do it one way or t'other?
Also, I'm guessing the vintage/modern switch could be a SPST switching a 51k in parallel with the 100k, if that's what you have handy.

[deadastronaut]

Hi Ben, no, it uses offboard 16mm....

Uses 3 way on on on 

And a spdt 2 way...

[Ben N]

Thanks, Rob, I guessed as much on the pots and ordered . As for the switch, I think I was unclear: what I meant was that you can accomplish the same thing as the On-On (should you wish to) by wiring the 100k across the switch (i.e. always in-circuit) and just switch a 51k on/off with a SPST in parallel with it, since 100k || 51k = ~34k, and you have a 33k there as the Modern setting.

[Kevin Mitchell]

you can accomplish the same thing as the On-On (should you wish to) by wiring the 100k across the switch (i.e. always in-circuit) and just switch a 51k on/off with a SPST in parallel with it, since 100k || 51k = ~34k, and you have a 33k there as the Modern setting.

Sounds about right to me 

-KM

[jonny.reckless]

This is the best sounding all analog speaker simulation I have heard. It beats the "emulated" output on my Blackstar HT20 MkII, Peavey Classic 20MH and Sansamp. It's better than some convolution / IR based cab sims I have seen.

It must have taken you ages to tune. Do you have a sweep of the frequency response? There's a lot going on in the feedback loop of that op-amp 

[suryabeep]

Hi everyone,
I built this astro sim with only a headphone output and I tacked an aux mixer onto the front end so that I could play along with my music. However, it does not work. When I plug in my headphones I can hear a hum (like when there's a cable with a free end plugged into an amp) and I can hear when I tap on the input jack, but I cannot hear any guitar signal from the headphone output. Audio probing shows the guitar signal to end at pin 2 of IC1. I also hear a *very* loud high pitched buzz when I probe Pin 2 of the Air potentiometer.

Here is the schematic I'm using:


My voltages: (taken without a guitar, aux, or headphones plugged in)
IC 1
Pin 1 - 8.17
Pin 2 - 3.9
Pin 3 - 4.35
Pin 4 - 0
Pin 5 - 4.351
Pin 6 - 4.354
Pin 7 - 4.41
Pin 8 - 8.73

IC 2
Pin 1 - 8.25
Pin 2 - 0.20
Pin 3 - 0.33
Pin 4 - 0
Pin 5 - 4.283
Pin 6 - 4.34
Pin 7 - 4.29
Pin 8 - 8.73

Images of the board:




Am I making some noob mistake in the mixer stage? I'm not 100% sure if simply tacking it on was a good move.

[PRR]

> Here is the schematic I'm using:

IC1A has _no_ feedback. It gives infinite gain and no DC centering.

Go back and look at mixer circuits, find the difference.

[suryabeep]

Spot on PRR, thank you! Man, I can't believe I made such a dumb mistake.
I fixed it by soldering a 100k resistor from pin 1 to pin 2 on the bottom of the board. Now the circuit works like a charm.

It sounds really good! I really like the vintage/modern switch.

[deadastronaut]

Cool,  yeah the vintage mod is nice for bluesy and tight metal stuff... 

I use mine all the time now...

[deadastronaut]

forgot to post these....here is a slimmed down version on the same pcb.

just no phones, or xlr.

[vigilante397]

Love the artwork, slick work as always Rob