PAB mode, adding bass

[Fischerman]

Here's yet another. It's similar to the one above except it connects the added cap on the other side of the .002, effectively putting the 560pF in parallel with the 390pF (and the sum of those is still in series with the .002uF when Mid-boost is OFF). My amp is a high-plate HRM with BM/Marshall power section and has no R/J or Deep switch and I also use a slightly different OD entry so maybe a little different aminal.

[IMG:757:351]http://i108.photobucket.com/albums/n4/m ... PABMod.png[/img]

[glasman]

Here is another little PAB trick.

Shunt the 22M PAB resistor between the Treble and Bass with a 0.01uf cap in series with a 470K resistor.

Still gives a really good boost and gives back a some of the bottom end. You can screw with the R and C values to get different levels of boost and rool-off. Works DYNOMITE on 70's circuits.

I developed this for a customer that a few more nuts on the bottom end when using the boost.

Gary

[Joost]

Thanks! But on my 124 schematic with skyliner update, I see two 22M resistors. One between the treble pot and the rock/jazz switch (which is also across the PAB relay) and one 22M resistor between the rock/jazz switch and the bass pot.

Which do I shunt? My goal is to fatten up the PAB and lessen the volume jump a bit, but not change anything about the clean tone or the function of the other switches. Can you tell me whether your mod works that way?

Here is another little PAB trick.

Shunt the 22M PAB resistor between the Treble and Bass with a 0.01uf cap in series with a 470K resistor.

Still gives a really good boost and gives back a some of the bottom end. You can screw with the R and C values to get different levels of boost and rool-off. Works DYNOMITE on 70's circuits.

I developed this for a customer that a few more nuts on the bottom end when using the boost.

Gary

[glasman]

Thanks! But on my 124 schematic with skyliner update, I see two 22M resistors. One between the treble pot and the rock/jazz switch (which is also across the PAB relay) and one 22M resistor between the rock/jazz switch and the bass pot.

Which do I shunt? My goal is to fatten up the PAB and lessen the volume jump a bit, but not change anything about the clean tone or the function of the other switches. Can you tell me whether your mod works that way?

Here is another little PAB trick.

Shunt the 22M PAB resistor between the Treble and Bass with a 0.01uf cap in series with a 470K resistor.

Still gives a really good boost and gives back a some of the bottom end. You can screw with the R and C values to get different levels of boost and rool-off. Works DYNOMITE on 70's circuits.

I developed this for a customer that a few more nuts on the bottom end when using the boost.

Gary

The 22M that is tied (or gets tied to) the bottom of the treble control. In normal ROCK mode, the bottom of the treble is connected to the top of the Bass control.

Gary

[glasman]

This does not effect the switch operation, only when PAB is enabled. When PAB is not enabled the parts are shorted out by the relay.

Gary

[Joost]

Great! Thanks, that's the one I would've thought. I'll give that mod a shot first, as it is easy to try out different values with alligator clips before soldering it into place.

Thanks! But on my 124 schematic with skyliner update, I see two 22M resistors. One between the treble pot and the rock/jazz switch (which is also across the PAB relay) and one 22M resistor between the rock/jazz switch and the bass pot.

Which do I shunt? My goal is to fatten up the PAB and lessen the volume jump a bit, but not change anything about the clean tone or the function of the other switches. Can you tell me whether your mod works that way?

Here is another little PAB trick.

Shunt the 22M PAB resistor between the Treble and Bass with a 0.01uf cap in series with a 470K resistor.

Still gives a really good boost and gives back a some of the bottom end. You can screw with the R and C values to get different levels of boost and rool-off. Works DYNOMITE on 70's circuits.

I developed this for a customer that a few more nuts on the bottom end when using the boost.

Gary

The 22M that is tied (or gets tied to) the bottom of the treble control. In normal ROCK mode, the bottom of the treble is connected to the top of the Bass control.

Gary

[alvarezh]

Gary, just implemented it with a switch in order to go between normal PAB and bypassed with the cap-res circuit, works real well.

BTW, is it an improper forum ethic to use the information intended for someone else? I am new in forums and I don't want to offend anyone, I am assuming that if it is publicly posted it is alright to be used by anyone. But, I could be wrong.

As you increase the resistor value you get more boost and as you increase the cap value you get more bass. Am I right?

Very thankful for the tip.

[Structo]

It is pretty much public domain if it is posted on the open forum threads.

[alvarezh]

Thank you Tom, you have just relieved me!

[glasman]

Gary, just implemented it with a switch in order to go between normal PAB and bypassed with the cap-res circuit, works real well.

BTW, is it an improper forum ethic to use the information intended for someone else? I am new in forums and I don't want to offend anyone, I am assuming that if it is publicly posted it is alright to be used by anyone. But, I could be wrong.

As you increase the resistor value you get more boost and as you increase the cap value you get more bass. Am I right?

Very thankful for the tip.

You are correct, raising the resistor controls the max boost but also raises the high pass knee frequency.

As you stated making the cap "fatter" lowers the knee frequency.

If you were to measure the response with the values I gave, you will find that you have a reasonably flat passband with about 3dB rise on the top end.

Gary

[glasman]

FWIW, anything I post can be consumed by the general public no problem. I just don't want to see it in a commercial design with someone else taking credit for the idea.

gary

[alvarezh]

Understood on all counts.

Regarding the circuit, it is fine as it is, just the right amount of bass for my needs. It looses a bit on the boost, but the loss can be pre-adjusted with the volume control, the OD controls (if it is being used) or a combination of both. No problem.

Marvelous first clip you have on your site with Scott doing his usual outstanding playing, nice "trombone" sound at the beginning.

Thanks for taking your time to clarify.

[Structo]

Here is another little PAB trick.

Shunt the 22M PAB resistor between the Treble and Bass with a 0.01uf cap in series with a 470K resistor.

Still gives a really good boost and gives back a some of the bottom end. You can screw with the R and C values to get different levels of boost and rool-off. Works DYNOMITE on 70's circuits.

I developed this for a customer that a few more nuts on the bottom end when using the boost.

Gary

Gary when you use the word "shunt" are you saying to go off of the 22M resistor with the .01 and 470K and take that to ground?
Or are you bypassing the 22M with the cap and resistor?

Thanks

[glasman]

The series pair in parallel with the 22Meg

Gary

Here is another little PAB trick.

Shunt the 22M PAB resistor between the Treble and Bass with a 0.01uf cap in series with a 470K resistor.

Still gives a really good boost and gives back a some of the bottom end. You can screw with the R and C values to get different levels of boost and rool-off. Works DYNOMITE on 70's circuits.

I developed this for a customer that a few more nuts on the bottom end when using the boost.

Gary

Gary when you use the word "shunt" are you saying to go off of the 22M resistor with the .01 and 470K and take that to ground?
Or are you bypassing the 22M with the cap and resistor?

Thanks

[Structo]

Thanks!
Perfectly clear now.