This Week on the Breadboard - ROG Azabache

[Chuck D. Bones]

Try removing the cab sim at the end and see if that sounds even better to you.

 

[Jawacan]

Try removing the cab sim at the end and see if that sounds even better to you.

I did try that before the experiment with the tone control and it sounded better but perhaps a little on the mellow side (everything sounds mellow compared to a stock Azabache maybe). Maybe I’ll try that again, after all this is what breadboarding is about

 

[Jawacan]

@Chuck D. Bones what is Q5 doing? Is it just at buffer or is it amplifying things (it’s tapped from the emitter so that tells me it’s a buffer…?)

 

[Chuck D. Bones]

It's a unity gain buffer. The low output impedance is necessary to drive the cab sim at the end. The feedback via the 1nF cap turns the Q5 buffer into a Sallen-Key 2nd-order low-pass filter.

 

[eh là bas ma]

I am about to start building the Azabache.

If I understand correctly, a presence knob after Q4 would be useful, and a toggleswitch, allowing to turn on or off the cab sim, would be interesting too.

2 questions, if I may :

Another place for a treble cut control is right after Q4. Disconnect the 47K and 100K from the 1nF and 39K and insert a B250K pot between the 100K + 47K and the 1nF + 39K.

Do I need a capacitor between the middle lug and ground, like in Jawacan's exemple, reply #14 ? If so, what value ?

Where should I put the cab sim switch ? At the intersection of Q4, 20k trim and 47k resistor ? On the schematics, does the cab sim section starts right after Q4 ?

 

[Chuck D. Bones]

A picture is worth 1K words.

2 questions, if I may :

That's actually 4 questions.

Do I need a capacitor between the middle lug and ground, like in Jawacan's exemple, reply #14 ? If so, what value ?

1. No. See pic above.

Where should I put the cab sim switch ?

2. Try using a SPST switch to short out the 22nF cap. See if that works.

At the intersection of Q4, 20k trim and 47k resistor ?

3. No.

On the schematics, does the cab sim section starts right after Q4 ?

4. IMO the cab sim is everything between the 220nF cap and the VOLUME control. The stuff between Q4 and A5 is a filter that simulates a tube amp's output transformer. Sure, there is some overlap between the two filters, but for simplicity, let's call the stuff after Q5 the cab sim.

 

[eh là bas ma]

Everything is clear now, thank you very much !

I can't wait to build my first Run Of Groove circuit.

"Chaumière où du foyer étincelait la flamme,
Toit que le pèlerin aimait à voir fumer;
Objets inanimés, avez-vous donc une âme
Qui s’attache à notre âme et la force d’aimer ?"

Lamartine, Milly ou la terre natale, 1826

 

[eh là bas ma]

Hello !

So I tried to add both mod on my build tonight, and no luck on the cabsim toggleswitch. I may have done something wrong.

All pots are backwards, of course... I will cut them off right now, and handwire them correctly.

Here are some pics :


When the 22n cap (C18) is switched off, there is a big loss of volume. Did I wire it correctly ? Maybe I should connect the remaining switch's lug to ground ?

For the Presence control, it is working and I am sure it will be very useful, thanks !

 

[Chuck D. Bones]

I see what you did wrong with the toggle switch. The switch is supposed to short out C18. Remove the orange lead from C18. Solder that lead of C18 to the switch lug with the green wire on it. Now solder the orange wire to the other lug that has C18 connected to it. In other words, connect C18 to pins 2 and 3 on the switch. Connect green to pin 2 (where it is now) and orange to pin 3. Nothing connects to pin 1 of the switch.

Did you not check the board layout (pot orientation) before placing the order? I suspect that what happened is that you did not account for the pots mounting on the opposite side of the board from all of the other components. You're not the first one to do that.

What's the deal with the trimpots? Why is there exposed metal on them?

 

[eh là bas ma]

I see what you did wrong with the toggle switch. The switch is supposed to short out C18. Remove the orange lead from C18. Solder that lead of C18 to the switch lug with the green wire on it. Now solder the orange wire to the other lug that has C18 connected to it. In other words, connect C18 to pins 2 and 3 on the switch. Connect green to pin 2 (where it is now) and orange to pin 3. Nothing connects to pin 1 of the switch.

Argh... I am realizing i mixed up C10 and C18.... I will do as you kindly suggested and report.

What's the deal with the trimpots? Why is there exposed metal on them?

? I don't know. They were supplied by musikding. I didn't have any trouble to bias all transistors. I guess they are unusual ?

 

[Chuck D. Bones]

Unusual to say the least. They looked like that when you received them?

Can you post your schematic so we can all see the ref des?

 

[eh là bas ma]

Yes they did. There was some surprises in the order though : ten J201 instead of 5 (with an "F" as brand logo) and all through hole. First time i touch a J201 through hole in my life...I shed a few tears of pure joy...I found also a couple of extra toggleswitches, more than necessary. It was a full kit, so I suppose they prepared the kit a long time ago. TH Custom Effects 03/2014 is written on the pcb.

 

[eh là bas ma]

Thank you so much !

I think I managed to fix everything. The cabsim toggle has an interesting and noticeable effect.

Edit : I made a mistake on C10 again, it's supposed to be 220n...


I'll carry on with the building process, drilling two more holes and give some nice artwork to the enclosure...No idea about it so far...

I wonder which colors can highlight the Fender sound singularities ?

 

[Chuck D. Bones]

Edit : I made a mistake on C10 again, it's supposed to be 220n...

100nF, 220nF, will make no difference.

 

[eh là bas ma]

Try using a SPST switch to short out the 22nF cap. See if that works.

Quik update : For the Cabsim toggleswitch, shorting the 22n at C18 cuts a lot of low frequencies. I thought it wouldn't be as useful on my build as the opposite alternative : adding some low frequencies.

I soldered an extra 47n cap on the switch, to be able to toggle between 22n and 47n, and I am pleased with the result, it gives a bit more low ends to the signal, more dark colors. The signal is not really thicker but deeper, i'd say. I guess I'll mostly use the 47n setting in the future.