Interesting findings re: caps and HRM

[Bob-I]

Last year I built a 100% ODS101HRM 100Watt Dumble. I've been fairly dissatisfied with it as it just seems too boomy and lacks definition in the low end. The neck PU of a H-H guitar was unusable as it was undefined and muddy. I tried several speakers and cabinets and decided that something has to be changed.

This week I pulled it apart and started trying things. This amp was 100% PS6 caps, tone stack to finals. I replaced the final .1uF 6PS with Xicon MPP's. It opened up slightly so I went to the next stage, the PI input caps. I also replaced these with Xicon MPPs, big difference in the lows, full and clear, little mud.

I then went to the couplers and tone stack. Nah, it lost girth so I went back to the 6PS.

Next I tweaked the HRM for the new caps. I've been noticing the 1M bass trimmer seems to work as a switch. Anything above about 50K makes no difference. I swapped it with a 250K trimmer. Now there's variation from 0 to full on and I'm able to now adjust until the lows are defined but full. I have the trimmer at about 65K now and will try it at higher volumes later.

Concluson is that the documented values are not gospel and the HAD used a variety of caps in the PI and finals for a reason.

Fun experiment.

[heisthl]

the PI input caps. I also replaced these with Xicon MPPs, big difference in the lows, full and clear, little mud.

Your amp has more than 1? or are you including the GNFB side grid cap in that statement.

[Bob-I]

the PI input caps. I also replaced these with Xicon MPPs, big difference in the lows, full and clear, little mud.

Your amp has more than 1? or are you including the GNFB side grid cap in that statement.

Yes, including the GNFB side.

[talbany]

Last year I built a 100% ODS101HRM 100Watt Dumble. I've been fairly dissatisfied with it as it just seems too boomy and lacks definition in the low end. The neck PU of a H-H guitar was unusable as it was undefined and muddy. I tried several speakers and cabinets and decided that something has to be changed.

I've run into the same problems...Mostly w/non HRM's as well....Sometimes I'll use a Mallory 150 in the clean channel .1 will help this out a bit...The PS series caps don't seem to have the consistency either... I've had several bad runs with them... In the Non HRM's if the OD side is leaning slightly more to the muddy un-focused side sometimes finding the right combination of V1/V2 12 AX's can cure the problem... Older tubes seem to be worse less focused on the low end but smoother and creamier sounding..Sometimes if you use a large plate 12ax EH or a JJ 803 in the PI can also help to keep the lows tighter on the way out..Plate voltages also play a big role in the stability of the low-end..The lower voltages 180 area gives you that nice interaction organic quality as well as a nice slow snarl..but the lower you go the looser the low-end as well..also the higher the plate resistors 220/150/180's also can help with the frequency responce of the low end.. The higher plates puts you closer to the center of the Trans.curve of the tube giving you a rounder more compressed waveform ver's the lower plates which can be more clipped and spikey causing the low end to be flabby.. Just a few things I've noticed and look at when I get an amp that comes off loose...


Tony VVT

[dobbhill]

Anybody use WIMA's??
D

[Bob-I]

I've run into the same problems...Mostly w/non HRM's as well....Sometimes I'll use a Mallory 150 in the clean channel .1 will help this out a bit...The PS series caps don't seem to have the consistency either... I've had several bad runs with them...

Me too, so I ordered a bunch more and replaced the ALL last year. I'd find it hard to believe that I'd have 2 runs bad months apart but it's possible.

In the Non HRM's if the OD side is leaning slightly more to the muddy un-focused side sometimes finding the right combination of V1/V2 12 AX's can cure the problem... Older tubes seem to be worse less focused on the low end but smoother and creamier sounding..Sometimes if you use a large plate 12ax EH or a JJ 803 in the PI can also help to keep the lows tighter on the way out..Plate voltages also play a big role in the stability of the low-end..The lower voltages 180 area gives you that nice interaction organic quality as well as a nice slow snarl..but the lower you go the looser the low-end as well..also the higher the plate resistors 220/150/180's also can help with the frequency responce of the low end.. The higher plates puts you closer to the center of the Trans.curve of the tube giving you a rounder more compressed waveform ver's the lower plates which can be more clipped and spikey causing the low end to be flabby.. Just a few things I've noticed and look at when I get an amp that comes off loose...


Tony VVT

Yes Tony, I've been through all of that with this amp. I currently have a 12AX7LPS in the PI and it seems to be the best. Keep in mind the low end isn't flabby per-se, it was just muddy like there's some low mids missing to give it definition.

[talbany]

Yes Tony, I've been through all of that with this amp. I currently have a 12AX7LPS in the PI and it seems to be the best. Keep in mind the low end isn't flabby per-se, it was just muddy like there's some low mids missing to give it definition.

Cool Bob...Yeah I wasn't saying changing caps was the wrong thing don't get me wrong...If I stepped on you in any way that as not my intent...You just hit on one of my sore spots with these amps(Especially Non HRM's) and am surprised the subject is rarely discussed here... Maybe it's me and some people accept it for what it is..I suspect this is one of the reasons why Dumble went to the HRM...Got tired of tweaking...Boom put in the stack tweak it up out the door!!The best overall sounding caps I heard in these amps is the old Phillips/Mullard Mustard caps... Even if they are used in the OD only Great mids focused lows..... Zoso's are advertised as the old mustard replacments and are a nice sounding open smooth cap... The Xicon MPP's are closer to the mustards IMHO...


Tony VVT

_________________

[Bob-I]

Maybe it's me and some people accept it for what it is..I suspect this is one of the reasons why Dumble went to the HRM...Got tired of tweaking...Boom put in the stack tweak it up out the door!!The best overall sounding caps I heard in these amps is the old Phillips/Mullard Mustard caps... Even if they are used in the OD only Great mids focused lows..... Zoso's are advertised as the old mustard replacments and are a nice sounding open smooth cap... The Xicon MPP's are closer to the mustards IMHO...


Tony VVT

_________________

Interesting thoughts. I've never thought of MPP's as comparable to Mustards, but I've never compared them either. I've tried Mallory 150's as couplers with some pretty bland results.

[talbany]

Interesting thoughts. I've never thought of MPP's as comparable to Mustards

Bob

Yeah!! I was mainly referring to the MPP's sharing more similarities
to the Mustards than the Zoso's..Most noticeable being the lively zing cut through everything chime the mustards are famous for...

I've tried Mallory 150's as couplers with some pretty bland results.

Same here!! They are kind of cool in the clean stack .1 Bass cap only.. To me kind of softens the bass...
EJ does this in his Twin's...


Tony VVT

[jelle]

WIMAs rock!

[erwin_ve]

WIMAs rock!

What type?

[benoit]

Last year I built a 100% ODS101HRM 100Watt Dumble. I've been fairly dissatisfied with it as it just seems too boomy and lacks definition in the low end. The neck PU of a H-H guitar was unusable as it was undefined and muddy. I tried several speakers and cabinets and decided that something has to be changed.

Bob, it's funny you should have that experience with your ODS101. Are you running 6L6s or EL34s? My 100% ODS101HRM 100W is really really nice with well defined clear low end on every speaker cab I've tried (open and closed back 2x12s, closed 4x12s) except a junky old closed back 1x15, and even then, only the OD sucked, cleans were lovely. I used all 6PS series caps as well. I wonder if there's a goofy component in your amp, or perhaps a happy accident in mine.

Ben

[heisthl]

I wondered that too, too bad you don't know if it was a preamp or Phase Inverter/output section causing the issue.

[Bob-I]

Bob, it's funny you should have that experience with your ODS101. Are you running 6L6s or EL34s? My 100% ODS101HRM 100W is really really nice with well defined clear low end on every speaker cab I've tried (open and closed back 2x12s, closed 4x12s) except a junky old closed back 1x15, and even then, only the OD sucked, cleans were lovely. I used all 6PS series caps as well. I wonder if there's a goofy component in your amp, or perhaps a happy accident in mine.

Ben

I'm running 6L6's right now, Chinese 6L6's . I've tried EL-34's KT-77's and 3 6L6 sets and I like these best. I have an EH12AX7 in V1, JJ gold pin ECC83 in V2 and Sovtek 12AX7LPS in V3. I don't like spending a ton of money on NOS and I don't think these amps need it anyway.

My thought is the inconsistency of the 6PS caps caused the mud. I've found the MPP's to be consistent and even the direction doesn't seem to matter when the 6PS can be pretty dramatic at times. The HRM mod is nice as well because it removes the oversensitivity to little tweaks. Much smoother now.

Since I posted this I made 2 more changes. I replaced the 390pF treble cap with a 330pF and I like the shimmer it gives. I also replaced the bright switch with a 3 way, middle off, down 120pF and up another 120pF in series with the first for 240pF. Very cool.

My speakers of choice is either an EVM12L original, recently reconed, in a Boogafunk thiele cab, or a pair of WGS Veteran 30 and Brittish Lead 80 in an open back 2x12.

[heisthl]

I also replaced the bright switch with a 3 way, middle off, down 120pF and up another 120pF in series with the first for 240pF. Very cool.

Must be the new math - I can't get 240pf when I series 2 120pf caps.