HRM Switching

[mlp-mx6]

OK - here's what I did on mine.

1. To have the HRM not affect the non-HRM tone you MUST disconnect the extra tone stack from ground.
2. I used a DPDT switch - one side chooses between HRM output and non-HRM output from OD2, the other side connects/disconnects the HRM stack ground.
3. PAB engaged is how you should tune/tweak the HRM tone. Also have the "low-gain network" at the entrance to OD1. I actually have a SPDT/center-off switch on my OD entrance. It can short out two different low-gain settings - 470K/47pF, or 220K, (going by memory here, I think the 2nd is 220K...) and I used a 100K trimmer w/ 4.7K between it and ground. Again, in the center-off position BOTH the resistors are in series before the 100K trimmer. I will say that I set the trimmer to my taste for non-HRM, rather than tuning for HRM. I also prefer the 470K shorted out (the highest-gain low-gain setting) for my non-HRM tone.
4. I do have "snubber caps" on my OD stages, and they are not switchable.
5. I went with the 100K OD Master control.

I'm sure this is not optimal, but I is working for me, and I really dig both the non-HRM and the HRM tones.

I would love to learn how you folks have tackled this. And how I can make my next one (or even this one) better...

Michael

[novosibir]

Could you or anybody explain, what means "HRM" and what means "PAB"?

Thanks!

Larry

[mlp-mx6]

HRM = post-OD tone stack, usually with trimmers on the circuit board
PAB = PreAmp Boost, the "lift the treble control from ground" boost

[novosibir]

Thanks for the quick response!

That the HRM means the post OD tone stack I've already noticed,
but the meaning of the three letters H-R-M I can't imagine.

Hot Rod Mod ?

Larry

[Normster]

Hot Rod Marshall or Hot Rubber Monkey...usually the latter.

[mlp-mx6]

Yeah, it's one of the dumbest names for something I've ever heard (the monkey one). And I don't think it really sounds like a Marshall either, when it is dialed in correctly. Still sounds like a Dumble.

[mlp-mx6]

So does anyone else have anything about the topic to share? Has anyone else experimented with switching these topographies?

[pullshocks]

Not sure if we are talking about the same thing but I just have a DPDT switch between the plate of stage OD2 and the 100 K OD level control. One throw has the OD tone stack in the circuit, the other has the .005 cap and 330K resistor in series as shown in the Hybrid Re A schematic.

I didn't use trimmers, the stack is on the panel. I'm hoping to get my cab done this weekend and will get some pictures up soon.

I'm still getting to know this amp but so far I find it useful to be able to get rid of some bass with the OD in use. I like to run a lot of bass for clean rhythm playing, and that can give the OD sound a bit of the dreaded fartiness

Then again, the PAB with the OD channel accomplishes more or less the same thing

[dogears]

Hi Pullshocks,

The 330k resistor in the Hybrid A is a really bad error. Dumble used from 150k to 180k. Usually 150k. Never 330k. That is dull sounding and muddy. I assume since you followed the schematics that you have a 330pf as the treble cap in the post OD stack. That is an error as well. It should be 500pf.

Also, the HRM will not work correctly into a 100k load. It is designed to have the 1M pot after it. Why not hang a 100k trimmer after the nin HRM 150k resistor. Change the 100k OD level pot to a 1M. Rewire the relay to be seperate masters..... That is what we all do.

Lastly, the pre OD network should be changed to the HRM low gain design if you want the optimal HRM tone. We relay switch two seperate pre OD nets with dedicated od trimmers.

HRM amps use no snubbers, no feedback on V1b, and the knee frequency of OD1 is up at 184hz and not the 70hz of non HRM. HRM amps use .0022 and a 350k load and not .01 and 200k load of non HRM. Once again, our switching designs take care of all the differences.

Not sure if we are talking about the same thing but I just have a DPDT switch between the plate of stage OD2 and the 100 K OD level control. One throw has the OD tone stack in the circuit, the other has the .005 cap and 330K resistor in series as shown in the Hybrid Re A schematic.

I didn't use trimmers, the stack is on the panel. I'm hoping to get my cab done this weekend and will get some pictures up soon.

I'm still getting to know this amp but so far I find it useful to be able to get rid of some bass with the OD in use. I like to run a lot of bass for clean rhythm playing, and that can give the OD sound a bit of the dreaded fartiness

Then again, the PAB with the OD channel accomplishes more or less the same thing

[pullshocks]

Interesting. I'm not sure I am totally understanding the circuit, is there a schematic showing what you describe?
I wish all that information had been around when I did the layout (I have been working on this project off & on for literally 5 years). The circuits you describe sound worthwhile, but I don't know where I'll be able to find room for the additional relays. But it sounds like they all work off the OD foot switch?

Anyway, thanks for the info. You guys are really hard core.

Mark

[skyboltone]

Hi Pullshocks,

The 330k resistor in the Hybrid A is a really bad error. Dumble used from 150k to 180k. Usually 150k. Never 330k. That is dull sounding and muddy. I assume since you followed the schematics that you have a 330pf as the treble cap in the post OD stack. That is an error as well. It should be 500pf.

Also, the HRM will not work correctly into a 100k load. It is designed to have the 1M pot after it. Why not hang a 100k trimmer after the nin HRM 150k resistor. Change the 100k OD level pot to a 1M. Rewire the relay to be seperate masters..... That is what we all do.

Lastly, the pre OD network should be changed to the HRM low gain design if you want the optimal HRM tone. We relay switch two seperate pre OD nets with dedicated od trimmers.

HRM amps use no snubbers, no feedback on V1b, and the knee frequency of OD1 is up at 184hz and not the 70hz of non HRM. HRM amps use .0022 and a 350k load and not .01 and 200k load of non HRM. Once again, our switching designs take care of all the differences.

Dogears, some of the changes you site here are reflected in the RevA1, but I still see the V1B feed back via the .47uf and the 44M ohm (!) resistor and the snubbers. Is this the non HRM correct scheme? Did HAD make an HRM amp?