Cutting Some Bass on D'Lite

[greiswig]

I wonder if that's why the HRM was developed..?

Between bassy OD and the treble bleed most non-HRM amps seem to need, I've wondered the same thing. Once you spend enough time trying to deal with those two issues, you start to think about developing a dedicated tone board for just the OD side to make it easier for subsequent builds. Hmmmmmm. Or maybe "Hrmmmmm."

[Structo]

Yesterday I installed the OD entrance mod (.05uf +220K) and the .01uf mid cap and 250k mid pot.

And guess what, too thin or bright.

I put the .05uf mid cap back in and I will play it like that for a while.

Strange but I think the OD entrance mod brightened it up quite a bit.

[fullerplast]

Where I seemed to find some balance between OD and clean was in playing with the cathode bypass caps. I don't remember what I settled on, but the OD side in particular is in the 1-2uF area for both v2a ND V2b.

+1 .

When I increased the cathode bypass caps on the OTS from 1uF to 4.7uF, I found the bottom end to be a bit too heavy for my taste. OK at home, too boomy louder in a band environment. Sounds like what you may be experiencing. Also, as mentioned, you can reduce the coupling cap values as well.

[Structo]

huh, I thought the OTS came stock with 4.7uf bypass caps.

Anyway, after playing my amp some more at volume, I have concluded that the OD entrance mod really brightened the amp too much.
I had no idea that that would do that. I thought it was just to make the OD smoother.
What it did to my ears was make it sound like the presence control way up.
Like an ice pick.
I think what it's doing is shunting the bass to ground, maybe.

Anyway I am going to remove the .05uf cap and see what that does.

I had already reverted the mid cap back to .05uf but I left the 250K mid pot in.

I have 4.7uf bypass caps on all but V1b which is 10uf.

The next thing I will try is to drop the voltage to V1 which sits at around 190-195.
V2 is 205v and the PI is 291-294.

I am going to shoot for 185 on V1, 190 on V2 and try to keep V3 about the same or a touch higher.

[fullerplast]

huh, I thought the OTS came stock with 4.7uf bypass caps.
I have 4.7uf bypass caps on all but V1b which is 10uf.

The original version had 1uf. The next "dumblized" version bumped them up to the traditional 5uf. The S&M went back to lower values.

I only mentioned my experience in going from 1uF to 4.7uF because it did exactly what you described.....it got bass heavy at loud volumes.

After installing the new Prosonic OT in my D'Lite 44 (6L6) and playing for some time at a good volume it sure seems to be bass heavy. I don't think the new OT did this, I just haven't played it at a loud volume in quite some time.

[Structo]

Thanks, that may be the next direction I go. It's difficult to fine tune these amps since what you do to one area may and can affect another.

I know if I was better educated in tube amp theory it would probably be a no brainer, but it's fun to heat up the iron and see what different things do in the circuit. I've already done quite a few changes to this amp thanks to the knowledgeable people here.
Although it is a hassle to keep pulling the amp out of the cab and work in a crowded chassis.

[dogears]

Yank the 10uf on V1b. Try the 4.7uf there. You can lower the CL2 cap to a .02 then. That will remove the bass you want. Leave the pre-od net at 220K into 100K. It is not brighter than leaving the .05 in there on CL2.

Something is amiss if you describe all that extra brightness! Try setting the od trimmer to anywhere from 25K to 40K. When you mod the od network, you have to readjust the trimmer.


The 250K midpot is fine as it is just a variable resistor. No tone difference there.

The bass pot should then be jumpered since disconnecting the lugs in normal stack mode does dramitically alter the tonestack operation and may be the cause of your brightness.

Thanks, that may be the next direction I go. It's difficult to fine tune these amps since what you do to one area may and can affect another.

I know if I was better educated in tube amp theory it would probably be a no brainer, but it's fun to heat up the iron and see what different things do in the circuit. I've already done quite a few changes to this amp thanks to the knowledgeable people here.
Although it is a hassle to keep pulling the amp out of the cab and work in a crowded chassis.

[Fischerman]

Just a suggestion (since it's so easy to try) but have you tried adjusting the PI input cap? Look at the Blackface Fender values...in the .001uF range IIRC (I'm not saying to go that low though). You can get away with smaller values here than typical gain stages (I won't say 'why' for fear that I'll step in it! ). But in any case, it will affect both channels and is easy to try and it will sound a little different than some other bass-reducing mods. You might like it.

[butwhatif]

Ditto, 4.7k/.022, 220k/100k trim. The cab type and room have a considerable effect on the bass response. If the cab is on the floor the bass will manifest about 2x, in a corner on the floor--4x, on a chair in the middle of the room is where you will hear the roughly normal bass response, esp with an open back, and this is also affected by the room and it's accouterment-
I find that it's always harder to get bottom at the gig, but the gig room is always larger than my shop, and any room in my old house, so I like to tune my amp with as much bottom as I can stand. Usually there's no prob getting rid of it w/the controls, but getting more can be an issue---

[Structo]

Thanks guys you have given me some more ideas to try.

Yes I was surprised that just the OD entrance cap made such a difference as well.

I did mess with the OD trimmer after I did the mod and currently have it around 9 O'clock.
So to measure that resistance I just measure from where the 220K resistor connects to the trimmer, to ground?

[Wayne]

Hmmm... getting "bottom" at a gig - there's a joke in there somewhere, I just can't quite put it together

W

[Structo]

Ditto, 4.7k/.022, 220k/100k trim. The cab type and room have a considerable effect on the bass response. If the cab is on the floor the bass will manifest about 2x, in a corner on the floor--4x, on a chair in the middle of the room is where you will hear the roughly normal bass response, esp with an open back, and this is also affected by the room and it's accouterment-
I find that it's always harder to get bottom at the gig, but the gig room is always larger than my shop, and any room in my old house, so I like to tune my amp with as much bottom as I can stand. Usually there's no prob getting rid of it w/the controls, but getting more can be an issue---

Which .022uf cap are you referring to? The PI input?

I have the 4K7 feedback resistor.

I still have the 150K slope resistor as well.

I will also try to jumper the bass pot and have that disconnect when in PAB mode.

[Pete]

So to measure that resistance I just measure from where the 220K resistor connects to the trimmer, to ground?

Structo, you want to measure from the center (wiper) terminal of the trim pot to ground. (This measurement is used as a reference).

[Structo]

Thanks

[JamesO]

Such a helpful thread for me, too.