HRM clean channel...how's yours?

[massygt6]

Well, I'm asking this because while I'm very satisfied of the OD channel, the clean seems a bit dull and "closed" and bass heavy.
The non-HRM I had before had a very pretty clean channel, shimmering, almost Twin like...
Any hint to improve it?
I was thinking to try the local feedback on V1, and also, I'd like to experiment with value of the slope resistor(previous non hrm had a 180k), and finally to bring back the bright cap on the clean master.
To trim some bass, could be useful to bring the bass cap to 0,0047uf?

[benoit]

Well, I'm asking this because while I'm very satisfied of the OD channel, the clean seems a bit dull and "closed" and bass heavy.
The non-HRM I had before had a very pretty clean channel, shimmering, almost Twin like...
Any hint to improve it?
I was thinking to try the local feedback on V1, and also, I'd like to experiment with value of the slope resistor(previous non hrm had a 180k), and finally to bring back the bright cap on the clean master.
To trim some bass, could be useful to bring the bass cap to 0,0047uf?

FWIW, the stock ODS-101-HRM circuit produces some very nice cleans for me, thought I've only built one.

Edit: Probably worth noting that mine's a 6L6 HRM.

[massygt6]

For sure the clean on mine are nice, but absolutely not as nice as my previous non HRM amp...
I was wondering if is normal that the HRM has a clean channel a bit more sterile than the non HRM...
I would define it as a little "boxy".

[greiswig]

Doesn't the HRM circuit only come into play when OD is engaged? If so, that eliminates whether it's an HRM or not from the equation.

I've done one thing on my non-HRM to make the cleans better to my ear. The bright switch is only on on the clean channel, and it has three positions: off, 60pF and 120pF. The 60pF is almost always on. The other thing I've thought about doing is making the LNFB switchable so that it is only on when the OD is engaged. To me, cleans sound a little richer without it, but the OD does not sound as good without.

HTH,

[benoit]

Doesn't the HRM circuit only come into play when OD is engaged? If so, that eliminates whether it's an HRM or not from the equation.

I've done one thing on my non-HRM to make the cleans better to my ear. The bright switch is only on on the clean channel, and it has three positions: off, 60pF and 120pF. The 60pF is almost always on. The other thing I've thought about doing is making the LNFB switchable so that it is only on when the OD is engaged. To me, cleans sound a little richer without it, but the OD does not sound as good without.

HTH,

Actually, funny you should mention the LNFB - HRMs don't have any.

[massygt6]

Doesn't the HRM circuit only come into play when OD is engaged? If so, that eliminates whether it's an HRM or not from the equation.

Yes, "HRM" refers to the amp type...yes the second tonestack is operative only in OD mode...
But from non HRM to HRM, something changes...the values of the plate resistors, for example...

[Tonegeek]

There is a long thread on AG about plate resistors that might give you a clue to the clean sounds. My HRM clean channel is not where I want it to be either and I really think it has to do with the gain and bias point and to some extent the tone stack values/types. I have managed to get the eq where I want it (at least for single coil guitars) by using a 100k slope and 250pf treble cap, but it just sounds kind of Hi-Fi. To me a "clean" channel is a misnomer. The HRM really does have a clean channel, too damned clean IHO. What I want from a clean channel is warmth, and sweetness and that involves some distortion. (I can get this somewhat by switching to OD and using really mild settings on the drive control, but it is not quite the same as say an old Fender). Lowering the plate resistor to 100k and shifting the bias point will cause the stage to produce more distortion (in the stage itself). Cap and resistor types play a part as well. Where it gets tricky is that if you mess with the front end of your HRM, it will change the OD channel as well and that's the rub. This has been discussed a lot on AG.

I tried an experiment a while back where I tapped off the normal channel of my wonderful sounding '64 bassman (right off the plate of the recovery triode for the tone stack). I ran this signal into the FX return (built in Dumblelator) on my HRM. So I have got the Bassman pre-amp feeding the output of my HRM. The tone sounded just as good as the Bassman itself. I thought well maybe its the tube in the Bassman. Nope, swapped tubes and it still sounded great. I am convinced it is the way the tube is configured for bias and gain, and maybe a bit of the aged components (or thier type) in the Bassman tone stack.

I have also tried reconfiguring the first preamp tube in my HRM for lower plates and it did sound better on clean. I got the best results by lowering just the first triode to 100k and the cathode to 1.5k (Fender!). Unfortunately it sounded worse in OD. Others have had a similar experience.

[greiswig]

Actually, funny you should mention the LNFB - HRMs don't have any.

Hah! That might be it. Okay, without LNFB, the cleans are less compressed, seem to have a bit more harmonic content, and a little more raw overall. I kind of like that. But with LNFB in place, it has its own character that is also nice. Maybe that's what the OP is looking for.

[Funkalicousgroove]

Ummm, HRM refers to "Hot Rubber Monkey" whch is ONLY the Post OD tonestack Overdrive section. If your Clean side is too Bassy Perhaps you've wired something incorrectly, it is my experience in the amps I've built that the amps with no LNFB have a much chimier and open clean sound. the Correct slope for any skyline EQ is 150K. You can always try different Plate values, the lower the value the Brighter the sound.

[benoit]

Ummm, HRM refers to "Hot Rubber Monkey" whch is ONLY the Post OD tonestack Overdrive section.

Isn't it true though (and I'm asking this becuase you are the guy to ask) that the LNFB was generally present in non-HRMs and not present in HRMs? I haven't experimented to see how much this does or doesn't effect the cleans, but am just curious.

[massygt6]

Ummm, HRM refers to "Hot Rubber Monkey" whch is ONLY the Post OD tonestack Overdrive section. If your Clean side is too Bassy Perhaps you've wired something incorrectly, it is my experience in the amps I've built that the amps with no LNFB have a much chimier and open clean sound. the Correct slope for any skyline EQ is 150K. You can always try different Plate values, the lower the value the Brighter the sound.

That's ok Brandon, HRM vs non-HRM on a "first level" is intended just to identify the amp, and if we go into technical details, HRM is the second tone stack...
Well, maybe I've not used the best words to describe it, is not only bass heavy, has some chime and brilliance, but I need to set the bass pot on 9-10 o'clock max, or the bass become really too much, and I get no balance with the OD channel.
On a strat type guitar is nice, but on the PRS, is too bass heavy...
The clean master has no bright cap...I should give it a try...15 to 47 Pf should be in the ballpark, I guess...

[massygt6]

I have also tried reconfiguring the first preamp tube in my HRM for lower plates and it did sound better on clean. I got the best results by lowering just the first triode to 100k and the cathode to 1.5k (Fender!). Unfortunately it sounded worse in OD. Others have had a similar experience.

That's an interesting point, as I'm thinking to reduce the first plate resistor from 220k to 180k and see if could be a good compromise between clean richness and OD smoothness.
I forgto to mention, and that's A BIG POINT, that my B+ is approx 405v-410v and around 180V on the preamp tubes nodes.
Yes, this is a low value, but I can assure you that the OD tone is somewhat magical...smooth, creamy and deep...lot of overtones and bloom, no flub at all and the volume is bloody massive...the bias is a bit low...with the pot to the max is set to 35mA...with a B+ of 405v I coould pump in a little more...but the amp sounds really gorgeous in OD...

[benoit]

Well, maybe I've not used the best words to describe it, is not only bass heavy, has some chime and brilliance, but I need to set the bass pot on 9-10 o'clock max, or the bass become really too much, and I get no balance with the OD channel.

What sort of speakers are you using? Even on a 1x15 using a guitar wiht humbuckers I did not find my amp too bassy. I usually leave the bass control at noon. Maybe something is wired funny?

[massygt6]

I get the same result on 3 different cabs and 3 different speakers

1) mesa 2x12 recto cab with v30 (sounds great with myHRM)
2) A.D. 2x12 semi open back with Eminence Governor
3) Self made 1x12 with Eminence V12Legend

I'm noodling with the amp now and I can't stop to play the OD channel with the PAB on...hard rock tone, fat, juicy and tight in the low end...this amp is a gain machine...but the clean is so so

[Tonegeek]

In case there is a misunderstanding when I mentioned bias, I was only referring to the the bias on the pre-amp tubes (set by the cathode resistor, mostly).

If we are going to start talking bass content then it might be helpful to post a schematic. There are so many places where the bass is affected (coupling, bypass caps, and speaker as Ben pointed out). FWIW my amp sounds the best with the bass around 9 oclock. This was true even before I changed my slope to 100k. I have read other posts where the poster had a similar experience, so your bass setting seems normal to me.