to HRM or not

[chris_sanford]

I'll let you know when I try it!

Well, dude, hurry! Some of us are waiting to hear from you before we start our next amp, you know?

Gil

Yeah... it takes like what, 2 minutes to swap those four connections? C'mon.

chris

[Pete]

Right, I guess what I was saying is there is no way of knowing from the pic posted that the stage is unused, right? So can I just take your word for it?

Also, the V2 tube looks to have the first triode grounded out by the shielded cable. My guess is no trimmer or the trimmer is now a pot on the front. 3 stages and not 4. Carlton likes it clean. The 68K grid is useless since the triode is not operational. All in my opinion.....

I don't see anything grounded out by shielded cable, what am I missing? thanks

I think what Scott meant was that the shielded cable (connecting to the OD 'level' control) provides a ground *reference* for the grid of the unused tube section. Since it looks like the plate and cathode are still connected, one would need that connection to avoid damaging the tube.

HTH,

chris

[chris_sanford]

Right, I guess what I was saying is there is no way of knowing from the pic posted that the stage is unused, right? So can I just take your word for it?

Don't take my word for it, I am only speculating!!! I suspect that it's a three stage deal because 1) Larry doesn't use that much gain these days, 2) because I tried the circuit both ways and felt that the 3 stage version sounded great.. less compressed (yet with plenty of sustain) than the standard 4 stage HRM circuit, and 3) because placing the TS between the gain stages makes it extremely hard to dial in a good sound, since the EQ has more to say about what frequencies are overdriven by the following stage. YMMV, of course.

chris

[fabiomayo]

Don't take my word for it, I am only speculating!!! I suspect that it's a three stage deal because 1) Larry doesn't use that much gain these days, 2) because I tried the circuit both ways and felt that the 3 stage version sounded great.. less compressed (yet with plenty of sustain) than the standard 4 stage HRM circuit, and 3) because placing the TS between the gain stages makes it extremely hard to dial in a good sound, since the EQ has more to say about what frequencies are overdriven by the following stage. YMMV, of course.

chris

Can you share a few tips, chris? I mean, the signal goes from the trimpot directly to the OD2 triode through the grid resistor (taking the .002uF/100k/drive pot out of the circuit) or does it go through the .0022uF coupling cap and drive pot? I'm curious.
Any ideas on plate and cathode resistors and cathode bypass caps in the triode left?

[chris_sanford]

Can you share a few tips, chris? I mean, the signal goes from the trimpot directly to the OD2 triode through the grid resistor (taking the .002uF/100k/drive pot out of the circuit)

That's the way I would do it, yes.

It's my feeling that with the HRM 'platform' you have to use a fairly high load for the input to the OD network, since the 1M master control is always in parallel with it.... so, I believe that the standard HRM input circuit (or something very similar) is probably used on the 'LC' amp, although with a fixed resistive divider instead of a trimmer. This kind of makes sense, from the standpoint that with a 3 stage OD you must run the clean preamp hotter to get the amp to sing... so think about the amp's input volume control (and maybe a boost pedal) as your pre-od trimmer.

Any ideas on plate and cathode resistors and cathode bypass caps in the triode left?

For plates, the only data-point I have is 150k/120k/220k/150k... bias them to taste, maybe a little hotter (current-wise) up front, and cooler towards the back. For bypass, 4.7uf or 5ufs all the way across.

HTH,

chris

[fabiomayo]

Thanks, chris.

I'll certainly try that.

[Funkalicousgroove]

Jeez Chris and Gil!! It'll take a bit longer since my bench amp isn't HRM yet!

Do we know for sure that the amp has separate masters?

[dogears]

Fwiw, the last HRM I played and was inside, had 220/150 on both tubes! Sounded really good.......

[chris_sanford]

Do we know for sure that the amp has separate masters?

I think so. The channel-switch relay has been replaced, and it looks like the normal HRM configuration as far as how the wires are attached to the pcb (unless I'm missing something).

chris

[fabiomayo]

Fwiw, the last HRM I played and was inside, had 220/150 on both tubes! Sounded really good.......

thanks!

[Pete]

placing the TS between the gain stages makes it extremely hard to dial in a good sound, since the EQ has more to say about what frequencies are overdriven by the following stage. YMMV, of course.

It occurred to me that the tone stack values of caps/trimmers could be more Fender like than Marshall like which could sound better for this application (4 stage) or player ... just guessin'

[pman]

[quote="Funkalicousgroove"]In my experience the standard 80's style amp is far more forgiving, and has quite a bit more compressed overdrive. It's no where near the compression of say a Boogie, but still has alot more than the HRM.

I personally prefer the HRM, with that circuit you get 4 really distinct tones: Clean, boosted clean, non-boost OD, Boost OD

hi guys, new guy to this forum. this explanation is the exact opposite of what i was told by joe at two rock. to summarize , post od=more marshall, more compressed, pre od= more articulate, less compressed. how can there be such differing views? inquiring minds want to know!

[chris_sanford]

hi guys, new guy to this forum. this explanation is the exact opposite of what i was told by joe at two rock. to summarize , post od=more marshall, more compressed, pre od= more articulate, less compressed. how can there be such differing views? inquiring minds want to know!

Well a lot depends on how you set the post-od tone stack.. turn the mid control down and the amp can sound somewhat compressed, however I've played a couple of real HRM Dumbles, and the weren't compressed at all, in fact, quite the opposite. You have to take the entire circuit into account, and sometimes a single part (such as a small bypass cap on a master volume control) can totally change the feel of the amp.

Now I do agree with Joe re: the HRM being a more Marshall sounding circuit, but again, it depends. There are lots of HRM variants out there, and some sound more 'Marshally' than others.

chris

[pman]

Well a lot depends on how you set the post-od tone stack.. turn the mid control down and the amp can sound somewhat compressed, however I've played a couple of real HRM Dumbles, and the weren't compressed at all, in fact, quite the opposite. You have to take the entire circuit into account, and sometimes a single part (such as a small bypass cap on a master volume control) can totally change the feel of the amp.

Now I do agree with Joe re: the HRM being a more Marshall sounding circuit, but again, it depends. There are lots of HRM variants out there, and some sound more 'Marshally' than others.

chris[/quote]
so, i guess the old adage, you can't generalise is appropriate.

[heisthl]

hi guys, new guy to this forum. this explanation is the exact opposite of what i was told by joe at two rock. to summarize , post od=more marshall, more compressed, pre od= more articulate, less compressed. how can there be such differing views? inquiring minds want to know!

so, i guess the old adage, you can't generalise is appropriate.

I can generalize, I've built a few of both now based on the schematics found on this forum and IME the properly tweaked non-HRM has more sustain on overdriven notes because it's more distorted. The HRM still has plenty of sustain but sings differently and never sounds as distorted. Both amps have the same amount of "compression" if you use the same powersupply and plate/cathode values. My definition of compression is note bloom. My definition of sustain is how long a note hangs with minimal or no vibrato to keep it alive. My definition of distortion as it relates to the Dclone is overdriven tube character but none of the clipping diode(fuzz face) sound.
If I could have only one it would be non-HRM. There is no substitute for the high you get when every note can sustain forever - it really is the "talent in a box" sound and if you play like I do you need all the help you can get....