lowering the presence

[Rod]

Hi, everyone.

I think that my Marshall dsl 15h, has to much presence, what components do i have to change in the attached schematic to lower the presence, or cut some more harsh trebles?

[Enzo]

First thing I would change is the speaker. Connect the chassis to some other speakers for a listen.

Also, be fair to yourself and post the whole schematic. Too much of something a particular control can adjust out doesn't mean the congtrol is source of the problem.

[Rod]

QUOTE=Enzo;462225]First thing I would change is the speaker. Connect the chassis to some other speakers for a listen.

Also, be fair to yourself and post the whole schematic. Too much of something a particular control can adjust out doesn't mean the congtrol is source of the problem.[/QUOTE]

HI Enzo,

I think that the speakers are ok, i have other amps and dont sound so harsh trough the same speaker.

[J M Fahey]

Just set the Presence knob to 0.

And if possible, use it loud.

99% of people who complain about way too bright unusable amplifiers are using them at too low volume, often bedroom levels, and, of course, alone; most "famous" amps are worktools for Pro Musicians (that´s why you chose a Marshall to begin with, you saw them countless times on stage) , and they are equalized for that use ... at blasting levels, together with other instruments and amplifiers, often in poor acoustics large rooms, and by a LOUD drummer, that´s why they are usually equalized with a piercing, cutting sound .
Now you use it at home and sound is annoying ... but that´s the amp true sound, it´s not "a defect".

EDIT: just checked the official demo:

Yes, biting nasty sound ... it´s a High Gain Marshall !!!!

Editing the Edit (EDIT squared? ) : at the end of the video the speaker is seen through the back grill, it´s about the cheapest 12" Celestion available (G12E60).
As Enzo suggested, many speakers will sound better there.
If possible, a Celestion V30, Creamback, 12T75, G30H , Hot 100, any of the "good" Celestions will work fine.
If too expensive, get an Eminence: Governor, 1258, etc.

[Chuck H]

"less presence"??? Like Juan mentioned, the presence control is adjustable. So it shouldn't need to be modified at the circuit level to get less. Simply turn it down. If there is still too much presence with the control at zero then it's not the presence control causing the harshness. Unless there is some aesthetic missing for you with the control at zero and so the knob must be adjusted to some visually pleasing level and you want the amp to have less presence at that setting? That's not as silly as it sounds actually. As a designer I have to fuss with the aesthetics of knob settings. That is, if I designed an amp with a presence control and the amp only sounded good with the control at zero I would indeed modify the circuit or remove that control from the design. As a player though you should simply turn the knob to zero if that's what sounds best to you. Take heart... I read that Malcolm and Angus play with the presence on their Marshalls at zero.

The circuit looks to have many top end filters which would cut HF either for tonal or stability reasons. Has the amp been modified before? If not then perhaps there's nothing wrong with it, you just don't like it. Since you do have other amps why chase tone on the one you don't like?

[Justin Thomas]

I think Juan has a point with the "LOUD!" theme, too. Being a 20W tube amp, this thing was made to be able to complement a "reasonable" drummer...
Also being a 20 W tube amp, maybe there's some other issue at hand causing the obnoxious presence... maintenance?
And, have you tried the amp through different speakers, and not just different speakers with this amp?

Justin

[Jazz P Bass]

Nobody asked but is the issue obvious on both the Clean & the Dirty channels?

[Enzo]

The speaker may have nothing at all wrong with it, but it may not agree with THIS amp. Other amos are not this one. Speakers do not have a simple impedance, their response curve is a bunch of peaks and valleys. A different speaker may well work better with this amp, it is simple enough to just try other speakers with it. If it sounds harsh through every kind of speaker you try, then we have room to work on it, but you might be surprised.

The speaker is THE single most effective way to change the tone of an amp.

And where is this amp sitting as you play it? A lot of speakers "beam" their sound straight out, and that is where it is most piercing. Off to the side, it is more mellow. In fact they sell "Beam Blockers" to mount in front of speakers to break up this laser beam of sound.

[Mick Bailey]

Hate to be a party pooper, but the schematic has come from Marshall's Imagebank and should not be posted unless the OP has written agreement from Marshall to do so.

[Dave H]

Just set the Presence knob to 0.

The knob goes to 0 but the circuit doesn't

[Justin Thomas]

Then maybe it should go to -1. That's one LESS, innit?


Justin

[Chuck H]

The knob goes to 0 but the circuit doesn't

Actually, the circuit goes to lower than zero for the highest frequencies and not quite to zero for the upper mids/low HF. Notice that the feedback series resistor is bypassed by a 22n cap.

[pdf64]

Actually, the circuit goes to lower than zero for the highest frequencies and not quite to zero for the upper mids/low HF. Notice that the feedback series resistor is bypassed by a 220n cap.

I think you may be looking at the switchable bass boost R93//C69? The regular series feedback resistor R91 is 22k unbypassed, so there's no HF rolloff in the feedback network in the normal mode.
But the minimum gain of an ideal non-inverting amp is 1 anyway

[Chuck H]

Ah. Yes. That's the bass boost series resistor. But the 22n bypassing some resistance (and increasing NFB for the HF) is still always in circuit a little. Just like the 100n in series with a 10k parallel load is. I won't be doing any math to confirm the issue or any actual level of the affect, but that's how it looks to me.

[Gaz]

I don't anyone mentioned this, but you could change the presence pot to 25K. At 10K, there will be some presence boost even at "0" on the dial. That said, sounds like the OP is talking about general 'presence', and not actual Presence, and other posters are right in that a speaker change is probably the most effective and simple change - that's what I would do.