Simulcast too bright?

[frankenteletron]

I completed my Simulcast build and love it! The one downside to me and my rig, is that it's a bit too bright and harsh for me sometimes, even when the low-cut is OFF the top end is a bit "ice picky" to my ear. Is there a mod suggestion to roll off some of the high end? Maybe adding a treble cut knob or presence knob? Or a switch between bright and dark? Just curious.

 

[Nostradoomus]

What is your rig? Mine doesn’t get that harshness through any of my 3 amps, with a Strat. I keep my treble on basically zero though

 

[frankenteletron]

What is your rig? Mine doesn’t get that harshness through any of my 3 amps, with a Strat. I keep my treble on basically zero though

Ha! Yeah Treble on zero would help tame it

I don't mean this as a knock on the circuit. In fact it sounds great in other applications. When I find it a bit shrill I just roll down the tone knob on my guitar a bit and it definitely tames it as well. I love how I can use the low cut knob on the Simulcast, I'd just love it even more if I could tweak the highs in a similar manner as well.

I play a tele into a Greer Lightspeed, a Mach 1, tremolo, Supa Puss delay and Walrus SLO reverb into a little tube combo.

 

[benny_profane]

This circuit's topology is a little odd for me to do a thorough analysis. It'd be ideal to throw a trimmer resistor somewhere for an RC low pass filter. I haven't worked with RL filters too much, but that could also be an option. Any thoughts here?

 

[TeleCrunch]

I pulled the charge pump IC out (I socket all ICs in my builds) and that was just enough to smooth the top-end. The recommendation came from this thread https://forum.pedalpcb.com/threads/9v-simulcast.976/. I prefer the sound and slight sag with the lower voltage.

 

[frankenteletron]

I pulled the charge pump IC out (I socket all ICs in my builds) and that was just enough to smooth the top-end. The recommendation came from this thread https://forum.pedalpcb.com/threads/9v-simulcast.976/. I prefer the sound and slight sag with the lower voltage.

I'll have to try that. Thanks!

 

[Nostradoomus]

Try putting a small value (4.7nf or so) cap from output (IE lug 2 of the volume knob) to ground.

 

[benny_profane]

Try putting a small value (4.7nf or so) cap from output (IE lug 2 of the volume knob) to ground.

While that would certainly make an LPF, I'd prefer a method that involves setting it within the circuit. With that method, the LPF Fc will change with the volume level (i.e., the level becomes a variable resistor in the RC LPF circuit). I can see how it might be preferable to have the high cut be tied to output level, though.

 

[Nostradoomus]

Oh yeah so would I, it should work fine for what is needed tho. We need Chuck in here

 

[frankenteletron]

Try putting a small value (4.7nf or so) cap from output (IE lug 2 of the volume knob) to ground.

I'll try that too! Thanks!

 

[benny_profane]

I'll try that too! Thanks!

If you’re going to use that method, use an RC calculator to be sure that it’s putting the LPF at an acceptable sweep. Use 0 to 25k (i.e., the LEVEL sweep) as resistance and adjust the capacitor value as necessary.

Guitar Pedals: R-C Filter Calculator

Calculate frequency cutoff for guitar effects pedals with vacuum tubes and solid state electronics. FREE calculator.

www.muzique.com

 

[frankenteletron]

Try putting a small value (4.7nf or so) cap from output (IE lug 2 of the volume knob) to ground.

Just double checking here since I'm a cautious diy "instruction follower".

So, the closet I have is a "Vishay" 3.3nf disc cap. I also have a 2.2nf Tropical Fish one. If it'll work I'll start with the 3.3nf.

Do I literally just solder one leg to ground and the other to the pcb's middle lug pad for the volume? Or does it go between that lug and the pcb?

 

[Nostradoomus]

The pad should be fine, should be lots of room for a cap leg to fit in with the pot pin.

 

[frankenteletron]

The pad should be fine, should be lots of room for a cap leg to fit in with the pot pin.

thanks! I'll post the result later tonight. appreciate it!

 

[phi1]

Like Benny said, putting it on the volume lug 2 would make the tone change with volume.

I’d suggest experimenting with putting the cap in parallel with R15. This essentially puts in on the output of the fuzz circuit (before the transformer and volume pot) to ground. You can roughly calculate the cutoff frequency using R14 and whatever cap you use. For example, 4.7nF would give about 2.2kHz cutoff frequency. I say ‘roughly calculate’ because there may be other impedances from the transistors, but in any case you can decide by ear what cap you want to use.

To test I’d hook a wire onto the leg of R15 that connects to R14. Connect that wire to the cap. Connect the other end of the cap to ground.

 

[frankenteletron]

Like Benny said, putting it on the volume lug 2 would make the tone change with volume.

I’d suggest experimenting with putting the cap in parallel with R15. This essentially puts in on the output of the fuzz circuit (before the transformer and volume pot) to ground. You can roughly calculate the cutoff frequency using R14 and whatever cap you use. For example, 4.7nF would give about 2.2kHz cutoff frequency. I say ‘roughly calculate’ because there may be other impedances from the transistors, but in any case you can decide by ear what cap you want to use.

To test I’d hook a wire onto the leg of R15 that connects to R14. Connect that wire to the cap. Connect the other end of the cap to ground.

Hey thanks! I followed Nostradoomus's suggestion and the 3.3nf cap and it helped a little bit. That said, I'll try your method as well. I'd like to tame it even more than this. Thanks again!

 

[benny_profane]

Hey thanks! I followed Nostradoomus's suggestion and the 3.3nf cap and it helped a little bit. That said, I'll try your method as well. I'd like to tame it even more than this. Thanks again!

The 3n3 is rather small. Your LPF Fc is going to be really high with that. If you want to use that method, going below 4n7 won’t give you dramatic results.

 

[frankenteletron]

So I used a 10nf cap, one leg to the middle lug of volume pot on the pcb and the other to ground. MAN! That really did the trick. At least for me and my ears! I totally love the sweep of the low-cut now and can find so many more usable sounds in my setup now. Nothing shrill at all and I love the different shades across the whole sweep of the Low cut knob. With the low cut all the way counter clock wise it is still thick and juicy and all the way clock wise has so much chime without being shrill at all. I'm mostly using the medium gain toggle setting and the gain around 2 o clock. Volume around noon. Thanks for all the feedback and yay for mods!

 

[benny_profane]

I think what I’m looking for here is a complementary control to the ‘Low Cut’ for a ‘High Cut’.

Can anyone explain how the ‘Low Cut’ is working?

I the suggestion @phi1 made above. Though, I’m not sure how the transformer affects things and if there’s a possible RL filter being formed there.

 

[phi1]

I haven’t seen that type of control before, but here’s my take on what’s probably going on.

The low cut seems to be affecting the bias of Q2 for different frequencies. Higher frequencies bias to Vcc through C5. With low cut turned ccw, low frequencies also bias to Vcc, through C9. With low cut turned cw, the low frequencies bias to a lower Voltage (stepped down by R9 and the pot in parallel).

Without using inductors, I don’t see an easy equivalent way to affect the bias of high frequencies with a pot.

If I were implementing a high cut knob, I’d probably run a cap and pot together in series, parallel with R15. Basically like my previous mod suggestion, but the pot would control how much the cap bleeds highs. Or, replace R14 with a 10kB pot and 4k7 resistor in series (pot first, lug3 to C11 and lug1 to the 4k7 R). Then take a cap to ground from lug2. This way the pot controls the cut off frequency of the filter (like the rockett animal). 15k between C11 and the transformer would be maintained regardless of the pot position.

Plenty of options, keep in mind I haven’t tried this circuit, just going off bits of theory picked up along the way.