How did HAD tame the bass?

greiswig · Post by **greiswig** » Wed Aug 17, 2011 3:03 pm

...or did he? I don't ever recall seeing anything like a .02uF, let alone a .0047uF in series with the other coupler going into the OD section in one of the original Dumbles. Were these amps just really bassy? Or did he have some way of aligning the crystal lattices such that the bass rolled off?

bepone · Post by **bepone** » Wed Aug 17, 2011 3:58 pm

maybe is the key in specially selected output transformer, which can-t play low notes? i built several dumbles 183, everyone with different material (i played with caps manufacturer like WIMA. PHILIPS, VISHAY.. but values exactly like on 183 schem).

Output Trafos were also different (i played with toroidal, certain custom wound trafos etc etc) and i found that in two of my builds i had bass problems (too much). But others 183 amps were excellent. So, something maybe with the OT i suppose.

I did not search for fault in other two amps with known methods> i cut bass in OD channel with smaler capacitor in series with OD trimmer, put 47 to 27nF cap to output tubes, bass pot reduced to 250kA, bass pot resistor made smaller from 10K to 3K3..

greiswig · Post by **greiswig** » Wed Aug 17, 2011 4:42 pm

Maybe this issue was partly what made him move toward the HRM builds?

CHIP · Post by **CHIP** » Thu Aug 18, 2011 2:37 am

I don't have a bass problem with my #183, if anything I find myself turning the treb pot to about 9 o'clock.
I used a Mercury Mag. OT.

Luthierwnc · Post by **Luthierwnc** » Thu Aug 18, 2011 9:15 pm

I've had trouble with the OD being too woofy on low-plate builds. I came up with this schematic to try on the next amp. I think it will work but who knows. This is identical to the dual master schematics here on AGA except for the series cap going to the OD entrance. I don't think it will pop but will leave room for a 4m7 or 10m bleed resistor if it does. If I thought this out right, I've got the usual .05uf feeding the clean but .025uf into the OD. The second cap can be seasoned to taste.

Comments invited, Skip

ToneMerc · Post by **ToneMerc** » Thu Aug 18, 2011 9:26 pm

Luthierwnc wrote:I've had trouble with the OD being too woofy on low-plate builds.

Comments invited, Skip

Skip, my thoughts on the low plates is to maybe drop the PI couplers from .1 to .068.

TM

greiswig · Post by **greiswig** » Thu Aug 18, 2011 9:42 pm

ToneMerc wrote:
Luthierwnc wrote:I've had trouble with the OD being too woofy on low-plate builds.

Comments invited, Skip
Skip, my thoughts on the low plates is to maybe drop the PI couplers from .1 to .068.

TM

I played with that a bit, but then you lose something on the clean side as well, which I really like on the low plate amp. I went back to the higher value on the PI. It's just the OD that is problematic.

Luthierwnc · Post by **Luthierwnc** » Thu Aug 18, 2011 11:12 pm

I was going to go 100k on V1 and 220k/150k on the OD. That said, I always buy an assortment of RN resistors and metal film K resistors when I order the little parts.

What I'm mostly trying to do is not drive the OD so hard. Go back a couple months and there is a thread I started on having a dedicated low-plate clean and dedicated two-tube OD -- each dialed in separately. The switching and relays got cumbersome.

When I give myself time to think about a mod that is a little off the reservation, it falls into one of two categories:

a) it would be great to have both choices on the fly or
b) I don't know which I'd like better but once I know, I'll only use that one.

If it is the latter, it is better to just swap components rather than have unnecessary gizmos. FWIW, sh

jelle · Post by **jelle** » Fri Aug 19, 2011 12:33 am

Luthierwnc wrote:I've had trouble with the OD being too woofy on low-plate builds. I came up with this schematic to try on the next amp. I think it will work but who knows. This is identical to the dual master schematics here on AGA except for the series cap going to the OD entrance. I don't think it will pop but will leave room for a 4m7 or 10m bleed resistor if it does. If I thought this out right, I've got the usual .05uf feeding the clean but .025uf into the OD. The second cap can be seasoned to taste.

Comments invited, Skip

you sure this is wired correctly? The cl mv is grounded where?

Luthierwnc · Post by **Luthierwnc** » Fri Aug 19, 2011 2:06 am

In the normally-closed position (bottom throws on the diagram) the tail of the clean master pot goes to one pole and is grounded at the throw. When the OD is engaged, the clean master grounds through the OD entrance. That is important because if you use the bright cap, it has a lot of extra resistance to keep from shunting highs to ground -- even if the clean master is cranked.

I got the basic circuit from a 2nd/3rd generation dual master schematic posted by Gary. There is also a "2nd gen hybrid" layout diagram that uses the same design. The series cap that allows the clean channel to use the full .05 coupler but decreases the capacitance for the OD is my idea -- but certainly can't be original. I think it will work but haven't tried it yet.

You can look up both original diagrams. If you can't find them, send me a PM with your email address and I'll send them. I can't send files through PM, though. I'm on double-secret probation for file-size violations -- no clue why.

Just let me know if this doesn't make sense and I'll try again. Skip

glasman · Post by **glasman** » Fri Aug 19, 2011 1:29 pm

I did the exact same thing in my original Super Overdrive amps. I used a .022uf || 4M7 resistor before the 220K resistor. Work nicely and you can tweak the .022uf to taste.

Worked on an original SOD yesterday and I had forgot how nice that sounds.

The first person that told me of this trick was Gil Ayan several years ago.

Gary

Luthierwnc wrote: I got the basic circuit from a 2nd/3rd generation dual master schematic posted by Gary. There is also a "2nd gen hybrid" layout diagram that uses the same design. The series cap that allows the clean channel to use the full .05 coupler but decreases the capacitance for the OD is my idea -- but certainly can't be original. I think it will work but haven't tried it yet.

angelodp · Post by **angelodp** » Wed Dec 28, 2011 2:14 am

Gary on that OD mod did you prefer the .022w4m7 // mode vs the .02uf w/ 10m to ground. Did you ever have it switchable?

Ange

glasman · Post by **glasman** » Wed Dec 28, 2011 1:29 pm

angelodp wrote:Gary on that OD mod did you prefer the .022w4m7 // mode vs the .02uf w/ 10m to ground. Did you ever have it switchable?

Ange

Never made it switchable, but it might be a usable trick depending on the type of guitars being used.

Gary

Max · Post by **Max** » Wed Dec 28, 2011 3:18 pm

As I'm not sure what you are talking about: Is there perhaps a clip in the "Dumble reference thread" https://tubeamparchive.com/viewtopic.php?t=11906 that can be used to demonstrate this "too much bass" problem you are talking about?

Cheers,

Max

glasman · Post by **glasman** » Thu Dec 29, 2011 12:48 pm

Max wrote:As I'm not sure what you are talking about: Is there perhaps a clip in the "Dumble reference thread" https://tubeamparchive.com/viewtopic.php?t=11906 that can be used to demonstrate this "too much bass" problem you are talking about?

Cheers,

Max

The discussion was talking about too much bass in the OD tone and how to shape it out a little.

A .02 uf (in parallel with a 4.7M to remove clicks) before the input trimmer (220K -> 100K trim) removes a bit of the bass and works well when you like to use the neck pickup for overdrive.

Not a standard thing that Dumble incorporated, but a nice tuning aid.

Gary

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