La Petite Boite

[Chuck D. Bones]

Here are some technical details of the Dirty Sanchez to Complex OD transformation that I posted in Build Reports.

Because the ref des are different between the two circuits, we'll refer to the Complex OD Build Docs.
All of the capacitors are the same except...
C9 is 220pF vs 120pF.
C14 is new. If installed, it has to be patched in parallel with R20.
The complex has two more power supply bypass caps (C102 & C105). Nice, but not req'd.
C100 is 100uF on the Sanchez, 47uF on the Complex. Either value works. Since more is better here, I went with 100uF.

All diodes are the same between the two units. I subbed 1N4004 for D1 & D3 to smooth out the clipping a little. I learned that trick from HamishR; he learned it from J. Rockett. Credit where credit is due.

All opamps are the same.

Resistors, here's when it gets fun.
I always use my own value for the LED resistor (R107, 22K) because the Aqua LEDs I use are Sofa King bright.
R20 is 2.2K on the Sanchez, 47K on the Complex.
I jumpered R25 and R26 on the Sanchez board, and omitted the TIGHT switch. No other jumpers!
The Sanchez's trimpot takes the place of R16 on the Complex.

All pots are the same, except...
There's no STRUCT switch on the Sanchez and I didn't feel the need for one. It sets the GAIN range on the Complex. I made the GAIN pot A500K, which is a compromise between the two positions of the STRUCT switch. If you like to use only the top end of the GAIN range, then go with B500K or B1M.
I subbed B100K for the MID pot. It has a better feel than A100K.

The same game could be played on the Brown Betty or Thermionic Deluxe boards, just keep track of the ref des because they are not all the same. I was very very careful and managed to have it work the first time I powered it up. It could have easily gone the other way.

 

[Chuck D. Bones]

By Request: the TIGHT control explained.

Most of the Friedman AIAB pedals contain a TIGHT control. The purpose of the TIGHT control is to roll-off some of the bass and lower mids before the 1st distortion stage. Cutting the bass prior to the distortion stage(s) reduces muddiness when paying chords.

Let's look at the BE-OD (Thermionic). C3, R7 & the TIGHT pot form a high-pass filter.

The corner freq is 1 / (2*π*C3+(R3+TIGHT))

When TIGHT is at zero, R3+TIGHT = 104.7K. That makes the corner freq 150Hz. When TIGHT is at 10, R3+TIGHT = 4.7K. Then the corner freq is 3.4KHz. Here's a plot of the tight control's freq response for TIGHT = 0 (light green) thru 10 (dark red).

 

[Danbieranowski]

By Request: the TIGHT control explained.

Most of the Friedman AIAB pedals contain a TIGHT control. The purpose of the TIGHT control is to roll-off some of the bass and lower mids before the 1st distortion stage. Cutting the bass prior to the distortion stage(s) reduces muddiness when paying chords.

Let's look at the BE-OD (Thermionic). C3, R7 & the TIGHT pot form a high-pass filter.
View attachment 27490
The corner freq is 1 / (2*π*C3+(R3+TIGHT))

When TIGHT is at zero, R3+TIGHT = 104.7K. That makes the corner freq 150Hz. When TIGHT is at 10, R3+TIGHT = 4.7K. Then the corner freq is 3.4KHz. Here's a plot of the tight control's freq response for TIGHT = 0 (light green) thru 10 (dark red).

View attachment 27492

Any reason/advice as to why the tight control wouldn't be placed just before entering the IC? Or is it a '6 in one/half dozen in the other' situation?

 

[fig]

By Request: the TIGHT control explained.

Most of the Friedman AIAB pedals contain a TIGHT control. The purpose of the TIGHT control is to roll-off some of the bass and lower mids before the 1st distortion stage. Cutting the bass prior to the distortion stage(s) reduces muddiness when paying chords.

Let's look at the BE-OD (Thermionic). C3, R7 & the TIGHT pot form a high-pass filter.
View attachment 27490
The corner freq is 1 / (2*π*C3+(R3+TIGHT))

When TIGHT is at zero, R3+TIGHT = 104.7K. That makes the corner freq 150Hz. When TIGHT is at 10, R3+TIGHT = 4.7K. Then the corner freq is 3.4KHz. Here's a plot of the tight control's freq response for TIGHT = 0 (light green) thru 10 (dark red).

View attachment 27492

Let me know when you‘ve started explaining.

 

[Chuck D. Bones]

Look at the full schematic, the TIGHT circuit is between two opamps. For the TIGHT circuit to work properly, it needs a low-impedance source (IC1.1 in the example above), and a high-impedance load (IC1.2, not shown in the example above). If we put the TIGHT control right at the input, it would load down the guitar and produce undesireable side-effects.

 

[Danbieranowski]

Look at the full schematic, the TIGHT circuit is between two opamps. For the TIGHT circuit to work properly, it needs a low-impedance source (IC1.1 in the example above), and a high-impedance load (IC1.2, not shown in the example above). If we put the TIGHT control right at the input, it would load down the guitar and produce undesireable side-effects.

Ah so it's that pesky impedance. Thanks sir!

 

[Chuck D. Bones]

It's always about impedance.