Suhr Riot + 2 Band Baxandall issues

[juan_felt]

Hi! I hope you are all doing great!

I successfully built a Riot clone using the following schematic:



Then, I wanted to change the tone control so i removed the Tone Pot (C10K) and the C8 (0,022uF) Cap, and added the Baxandall from a BB Preamp using the following schematic (the Baxandall is placed where the Tone pot was):



I used the VEE from the Riot to feed VB of the Baxandall (IC pin 5).
The Treble knob seems to work properly, but the Bass one changes the sound making it sound as if it was improperly biased.

The Baxandall's IC voltages are:
1) 8.44
2) 1.22
3) 1.35
4) 0
5) 4.5
6) 1.9 to 4.5 depending on the bass knob position
7) 4.7 to 8.3 also depending on the bass knob position.
9

Are this voltages correct? Am I messing things up by placing the baxandall there without changing/adding/eliminating any components?

Thanks!!

[GibsonGM]

Hi Juan,

Are you measuring the IC pins from upper left, down, to the right and up?  Like a horse shoe?

Your voltages seem really off!  If you are using a TL072 I would expect to see 9V on pin 8....4 is ok...pin 5 ok so you are probably using the 2nd half of the opamp....6 & 7, something is not right in here.   So, go back thru the R's and C's around the opamp to see if something is shorting, connected to power somehow...some mistake.  Sounds like it might be around that bass knob, some DC there you are changing with pot setting...

You have kept C10, blocking cap, right?

You should tie the unused pins off to ensure they are not doing anything odd.  (output to inverting input...noninverting input to ground)

Almost done, keep at it!

[marcelomd]

Hi,

I did that to a Guvnor a few weeks ago. Works great. You inserted the Bax in place of the tone knob, right? Did you put a coupling cap between the Baxandall input node and the diodes? There is a path to ground there and might be misbiasing the whole thing via R17.

[PRR]

> i removed the Tone Pot (C10K) and the C8 (0,022uF) Cap, and added the Baxandall

Anything with more than one wire, draw it out!!

At least my tiny brain can't keep things straight.



OK, see the DC path from the center-biased Bax down through the LEDs to Zero volts? That DC leak exactly matches your symptoms. You need a DC-block cap.

[juan_felt]

Hi,

I did that to a Guvnor a few weeks ago. Works great. You inserted the Bax in place of the tone knob, right? Did you put a coupling cap between the Baxandall input node and the diodes? There is a path to ground there and might be misbiasing the whole thing via R17.

> i removed the Tone Pot (C10K) and the C8 (0,022uF) Cap, and added the Baxandall

Anything with more than one wire, draw it out!!

At least my tiny brain can't keep things straight.



OK, see the DC path from the center-biased Bax down through the LEDs to Zero volts? That DC leak exactly matches your symptoms. You need a DC-block cap.

Thanks a lot, I tried using the Cap and it works great!
Now I have to figure out the massive hum, but I assume that it is due to the protoboard.

Thanks!!

PS: Thanks PRR for the drawing, lesson learnt... I'll draw more, it makes a lot more sense.

[juan_felt]

> i removed the Tone Pot (C10K) and the C8 (0,022uF) Cap, and added the Baxandall

Anything with more than one wire, draw it out!!

At least my tiny brain can't keep things straight.



OK, see the DC path from the center-biased Bax down through the LEDs to Zero volts? That DC leak exactly matches your symptoms. You need a DC-block cap.

Again, thanks for the reply.
Now, I have another question regarding Vref. In the Riot's schematic it uses the opamp (to keep it more accurate?) after the voltage divider. Can I use a "standard 2 resistor" voltage divider, and use the remaining opamp for the baxandall?

Thanks!!!

[PRR]

Make C8 100uFd or 200uFd, then recycle that opamp.

[juan_felt]

Make C8 100uFd or 200uFd, then recycle that opamp.

Thanks! May I ask why is this..? Sorry for all the questions, I'm trying to understand why things happen...

Thaaaaanks

[marcelomd]

Now, I have another question regarding Vref. In the Riot's schematic it uses the opamp (to keep it more accurate?) after the voltage divider. Can I use a "standard 2 resistor" voltage divider, and use the remaining opamp for the baxandall?

Yes, you can. I guess they had a spare opamp and they used it for Vref.

Just use a larger value for C8 so Vref is stable.

[GibsonGM]

Yes!  I find it very hard to believe that you would need such stability for Vref that you would need a buffer attached to it     

Like Marcelo says, a nice-sized C8 will give you a reservoir, and then no need to worry.  100u, 220u...seem to be good values.

[juan_felt]

Yes!  I find it very hard to believe that you would need such stability for Vref that you would need a buffer attached to it     

Like Marcelo says, a nice-sized C8 will give you a reservoir, and then no need to worry.  100u, 220u...seem to be good values.

Now, I have another question regarding Vref. In the Riot's schematic it uses the opamp (to keep it more accurate?) after the voltage divider. Can I use a "standard 2 resistor" voltage divider, and use the remaining opamp for the baxandall?

Yes, you can. I guess they had a spare opamp and they used it for Vref.

Just use a larger value for C8 so Vref is stable.

Thanks for all the replies, help and patience!

Cheers 

[marcelomd]

Hi,
Just found something you might be interested. A pedalpcb.com version of JHS Angry Charlie, which is a Guvnor/Riot/etc variant with baxandall: http://www.pedalpcb.com/product/angrycharles/

It is always good to see how others do similar stuff.