simple question regarding HRM

[Emin7b5]

What does "HRM" mean? I've read a zillion post and can't seem to find a definition.
I've built 6 amps from scratch and want to try my hand at a D clone and this seems to be an important distinction. I'm following this site closely to try to figure out which model to attempt.
Many thanks!!!!

[chris_sanford]

What does "HRM" mean? I've read a zillion post and can't seem to find a definition.
I've built 6 amps from scratch and want to try my hand at a D clone and this seems to be an important distinction. I'm following this site closely to try to figure out which model to attempt.
Many thanks!!!!

Hot Rubber Monkey. Seriously!

It's a general term used for a circuit with a post-overdrive tone stack. Check the files section.

chris

[Emin7b5]

your kidding.
Actually thanks. It's been driving me crazy for weeks. I will dive back into the files.

Any idea which amps Stephen Bruton played through. I'm after that kind of tone. Plenty of chime and smooth, kinda non aggressive OD. Stephen doesn't seemed to be mentioned as much as others.

[Structo]

Here's a pretty good interview with Stephen.

http://www.stephenbruton.com/images/TQRNov02Bruton.pdf

He mentions owning more than one so I'm not sure what he has but given the time period you should be able to figure it out.
It also depends if he had Alexander update any of his amps to the later edition specs.

[Emin7b5]

Nice write up on Stephen. Thanks everyone for the info. This Dumble thing is vast, ain't it.

[KT66]

The official name of the post-OD stack is Hot Rubber Monkey. If you look at a schem of it ( the HRM stack ) you can see that it bears a striking resemblance the the classic Marshall tone stack. So, you can see why some might even call it a Hot Rod Marshall circuit....

In HAD's amps he used internal trimmers and had the circuit on a board mounted above the main board by securing it in the secret goo. Most cloners use stand-offs and go goo free. Some put the HRM controls on the front panel.

[bluesfendermanblues]

The official name of the post-OD stack is Hot Rubber Monkey. If you look at a schem of it ( the HRM stack ) you can see that it bears a striking resemblance the the classic Marshall tone stack. So, you can see why some might even call it a Hot Rod Marshall circuit....

In HAD's amps he used internal trimmers and had the circuit on a board mounted above the main board by securing it in the secret goo. Most cloners use stand-offs and go goo free. Some put the HRM controls on the front panel.

The HRM tonestack is actually a combination of Marshall pot values and Fender (Black face/ Silverface) architecture.

Although, in a recent Bluesmaster, I began with a 1M bass pot, like its shown in most Bluesmaster or Skyliner HRM schematics, but I ended up using a 250k instead, because you need to dial the bass in at 60K-75k range from center log to ground, so a 100k or 250k is actually more handy.

So for a Bluesmaster (HRM) I would go for 250k + 250k + 25k pots.

[martin manning]

The official name of the post-OD stack is Hot Rubber Monkey. If you look at a schem of it ( the HRM stack ) you can see that it bears a striking resemblance the the classic Marshall tone stack. So, you can see why some might even call it a Hot Rod Marshall circuit....

I have a tough time calling this tone stack architecture "Marshall," since Marshall (Ken Bran) copied it from Fender's 5F6-A. Where Fender got it is another question, but even if Fender borrowed it from somewhere he applied it to a guitar amp before Marshall did, in 1957. Here's a comparison of several incarnations of this stack showing component value and wiring changes relative to the 5F6-A in Red. Notice that the HRM stack, as understood here, uses essentially Marshall Plexi values with the mid pot wiring change.

[Structo]

Nice comparison Martin.

The schematics I have show the Bassman 5F6 and the 5F6a as having a 56k slope resistor and a .02uF bass cap.

[martin manning]

Nice comparison Martin.
The schematics I have show the Bassman 5F6 and the 5F6a as having a 56k slope resistor and a .02uF bass cap.

Thanks, Tom. You have to read the fine print (Note 1). The 5F6-A schematic floating around has those values, but gut shots of actual amps have the values I show, as does the '59 RI.

Edit: BTW, you're showing the 5F6 (not 5F6-A) in the above schematic. It has the strange NFB/Presence connection to the bottom of the Mid pot. That didn't last long, as the 5F6-A schematic is dated only a few months later.

[KT66]

Bluesfendermanblues wrote

The HRM tonestack is actually a combination of Marshall pot values and Fender (Black face/ Silverface) architecture.

No, actually it's not. It's a dead copy of the Marshall tonestack found the 1987 (plexi ), 2204, etc. The OP wanted to know what HRM means, and that's what it means - at least according to Funk, Heisthl, Bob-I, etc :

https://tubeamparchive.com/viewtopic.ph ... d+marshall

https://tubeamparchive.com/viewtopic.ph ... l&start=15

Martin Manning wrote

I have a tough time calling this tone stack architecture "Marshall," since Marshall (Ken Bran) copied it from Fender's 5F6-A.

I don't know why you would have trouble with that since in your own post you state that the HRM stack is the plexi stack except for the slight mid pot difference which is wired as a variable resistor anyway. I think we all know the Marshall/tweed bassman story, but does this mean that every discussion of an FMV style stack has to have a footnote as to its origins ? In that case I suppose its time to split hairs some more and mention the Western Electric origins of the architecture.

So, in summary : Rubber Monkey % = 0 ; Marshall style stack = yes

[martin manning]

I don't know why you would have trouble with that since in your own post you state that the HRM stack is the plexi stack except for the slight mid pot difference which is wired as a variable resistor anyway. I think we all know the Marshall/tweed bassman story, but does this mean that every discussion of an FMV style stack has to have a footnote as to its origins? In that case I suppose its time to split hairs some more and mention the Western Electric origins of the architecture.

I've heard it mentioned that Fender used circuits developed by Western Electric before, but I have never seen anything specific... do you know of any references?

That aside, I don't think this is in any way splitting hairs. I acknowledged above that Fender probably didn't invent this network, but he applied it to a guitar amp first, and Marshall/Bran copied it from him. In my opinion it is simply more correct to refer to it as a Fender tone stack. Marshall and Dumble are truly standing on the shoulders of a giant here.

[KT66]

Martin Manning wrote

I've heard it mentioned that Fender used circuits developed by Western Electric before, but I have never seen anything specific... do you know of any references?

The most specific reference that I could find is from Gerald Weber's A Desktop Reference of Hip Vintage Guitar Amps on page 55 where he states " Contrary to popular belief, Leo Fender did not design the Bassman circuit. The circuit was actually patented by AT&T and Western Electric in 1948 and later licensed to Fender Electric Instrument company."

Although, this is admittedly rather vague as to which specific Bassman circuit was licensed and still leaves in question the origins of the so called FMV ( Fender Marshall Vox) tone stack. If you accept that terminology to mean that that type of tonestack is common to all 3 types of amps in its popular FMV nickname ( and you very well may not, and I can see why, as the Vox stack has a fixed mid resistor and the bass pot grounding "error" : http://members.optusnet.com.au/~glen325/topboost.html then I guess we should call it the GFMV stack because Gibson first used it in the GA-77 and GA70 in 1954 - predating the 5F6-A by 4 years.

All this I feel is moot, because the subject of this stupid thread is supposed to be : "Simple question regarding HRM". I gave a simple answer, but for some strange reason a number of familiar contributors to this forum felt it necessary to point out the origins of the plexi tone stack. As I stated before, I think we all know that already, what's the point of stating it? Is this tonestack footnote brought up every time the Skyline is mentioned ? Are we supposed to mention Lee De Forest in every tube discussion to make sure that the appropriate "Giants" get there due ?

I didn't give the circuit it's name, HAD did. He used the Marshall plexi stack as a post overdrive tone shaping circuit, and called it the HRM.

I apologize to anybody who has wasted there time reading this crap, I promise not to bump it up again.

[Dr d]

Just getting back to the HRM values, I started with a 500k bass pot in my recent Bluesmaster build and felt the OD was lacking something. I then changed it up to 1Meg and ,wow, what a difference. Still set @ 75K, but had more depth and character in its tone. I am not sure it is as simple as just using the nearest value needed for adjustment. When in doubt I always trust that HAD had a good reason for chooseing the values he does. Just my opinion, of course.

[CircuitButcher]

Dr d, you're correct.

When the variance to stated value of components is considered, it's not surprising that some tweeking is required, especially when one's ears are involved - just trust them, they're yours.

Thanks Ryan, for staying on topic & keeping it simple.

Thanks Martin, for the tonestack table comparison.