Mid boost?

[Tdale]

I've planned to use the 70's schematics, with some alterations. But I looked at the hybrid-a chem today, and especially the mid boost.

It looks like it bypasses one cap before the treble pot.. Is that to raise the cut-off frequency?

The S2 and S3 switches are really complicated too, and I don't really understand all they do.....

Tommy

[fabiomayo]

I probably am completely out of my league answering this and
hopefully people will answer you soon.

Anyway... the boost switch make both the bass and middle
pots float out of the circuit. The treble control stays in the
circuit but not wired as a variable resistor (is that right?) and
has little if any effect on tone... Yes, the midboost does change
treble pot operational point... As you may see on the schematic,
the jazz/rock switch change the way the preamp pots operate
by adding a cap to ground from the treble and a series resistor
from the bass. Most people here don't find a use for this switch
as they leave it on the Rock position most of the time. I have
spent time with both setting and liked them both. Jazz is a little
thinner, more hi-fi and BF Fender-like IMO. Rock is gainier, fuller
and bassier. I like to have the switch but I alternate between one
on the other, never switching on the fly as I find the amp needs
to be optimized for the selected option.

Hope that helps a bit and that someone more knowledgeable chimes in...

Best of luck in your build. Keep us posted....

[jazzyjoepass]

The gain boost (preamp boost - PAB) is the one that fabiomayo's talking about.

The midboost is the one that bypasses one of the treble caps. It changes the operating point of the treble pot and boosts the mids when you bypass the cap.

[Tdale]

Makes sense.

So the gain boost bypasses the whole eq network?

Tommy

[Bob-I]

I've seen this drawn 2 ways. One parallels another cap with the treble cap to increase the total capacitance, the other has them in series to lower the value. I tried both and settled on the parallel ckt using a 330pF and .001uF. It's a pretty dramatic mid boost this way where the series ckt was more subtle.

[dogears]

Bob, if you series the .001uf with a 470pf, you get a nice circuit, that also has a very substantial midboost. 330pf ont he treble cap in normal mode. THat is what I do. An added potential benefit is having a nice OD cap for the .001. This way you get some possible effect of putting the signal through a "hifi" cap before the ceramic. Fwiw, Dumble always did it this way. I figure, why change from the real way. The real way was a .002uf and 390pf in series. THe midboost in that is way more than either of our circuits.

I've seen this drawn 2 ways. One parallels another cap with the treble cap to increase the total capacitance, the other has them in series to lower the value. I tried both and settled on the parallel ckt using a 330pF and .001uF. It's a pretty dramatic mid boost this way where the series ckt was more subtle.

[Bob-I]

Bob, if you series the .001uf with a 470pf, you get a nice circuit, that also has a very substantial midboost. 330pf ont he treble cap in normal mode. THat is what I do. An added potential benefit is having a nice OD cap for the .001. This way you get some possible effect of putting the signal through a "hifi" cap before the ceramic. Fwiw, Dumble always did it this way. I figure, why change from the real way. The real way was a .002uf and 390pf in series. THe midboost in that is way more than either of our circuits.

Now that you remind me, we talked about that before. I believe I ended up using a .0015uF cap in the final.

[Tdale]

Are we talking about the two caps that are in series, right before the treble pot?

Tommy

[fabiomayo]

Yes, with a switchable bypass. The Mid Boost...

(Look at me, all fancy answering questions LOL!)

[llemtt]

Tommy making it the real way you have to put the 2n cap on the board and the 390p on the front panel switch this has pros & cons.

BTW I prefer to put everything on the board and then I add a relay to let the midboost be footswitchable.

Teo