Reverb or efx loop effects sound bad on Engl lead channel

[Bbender]

I have noticed that the built-in reverb in my Engl Screamer 50 changes character quite dramatically when I change channels. On the clean channel it's clear and nice, but when i change to the lead channel it gets kind of muddy, like the reverb gets overdriven, too. And I've noticed the same effect when using the effects loop too, the efx placed in the loop gets muddy on the lead channel )-: Could this be because my power tubes are bad, or is this just the the way my amp works, maybe the lead channel overdrives the power amp section too? In this case, I wonder why there's an effects loop in
the amp at all, since I guess the whole point with effects loops is that
the efx sound should be clean and stable, regardless of the amp's
settings/channels(?)
I've tried to send this question to te Engl guys, too, but they haven't
replied..

[Bbender]

Follow-up..

I just discovered something very strange: I tested the sound from the effects loop on my amp by letting my Boss RC-2 play a loop while fiddling with knobs and settings, and to my surprise, this is what I found out: The "lead presence" control on my lead channel acts as a tone control for the effects loop (and the amp's built-in reverb, too) when I'm using the lead channel..?! None of the other knobs have any effect on the sound whatsoever (except for the master volume of course), and when I turn the lead presence knob all the way up to "10", I get the exact same sound as on the clean channel. Turning the presence knob down takes away the treble, making the sound "muddier" the further down it goes. (the same goes for the on-board reverb)
But playing guitar through the amp's lead channel with the presence on 10 is NOT an option, that piercing sound might be able to cut glass or something, but it's definitely not suitable for guitar playing.. I get the best sound from the lead channel with the presence between zero and 2,5 .. Is there something wrong with my amp, or is this "normal"? (that can't be right?)

[Bbender]

Follow up..

I've read the manual, but I don't know much about amps and how they work, I'm just a guitar player who wants his amp to sound the best.. So the phrase from the manual: "lead presence defines the treble response in the poweramp stage" didn't say me anything in particular, and I didn't understand that meant I had to have this on full to get the best sound out of my reverb and FX. But now I've found out that this must be the case. So if this is how it works, it seems I have two choices then:
1: having a good lead sound and crappy rev/efx. sound (lead presence almost off), OR 2:having a good rev/efx sound but a piercing, terrible lead sound (presence on full). Anyone else think this is stupid? Do the other Engl amps (or other brands, for that matter) have this too, or is it just the Screamer?

[Enzo]

I don't know the amp, but the presence control on an amp is part of the power amp, it is not just another EQ in the tone stack. That is why it still has an effect on a signal put in through the loop return.

Your power tubes do not know which channel the preamp is set to. They cannot as a rule selectively malfuntion on one preamp channel and not the other. That is not to say the preamp cannot have odd interations with the controls.

I'd wait to see if Engl gives a response next week.

[Bbender]

So you're saying this is in fact normal for an amp with an extra presence control? But I thought the presence should be just an added extra control on top of the eq that's already passed to the poweramp section (or something like that..), not, like it seems in my case, replace the treble eq, taking away all treble from the fx loop and the built-in reverb unless it's on full?
I don't understand this. If the presence control wasn't there, would the sound of the reverb and fx loop be exactly the same then, regardless of which channel I use?

[Enzo]

I am ONLY saying that the presence control is part of the power amp, so it makes sense that it still affects the sounds even when the other controls in the preamp are all turned down.

I don't know the circuit in your amp, so I cannot comment on the interactions you are finding. It will be easier if you can come up with the schematic.

WHile we USE the presence as just another tone control, it is really part of the power amp in most cases. it is part of the NFB. SOme amps do just add another high freq EQ control, but in my mind it is not longer truly as presence, even if they label it as such.

[Bbender]

As a matter of fact I have a link to the schematics, but I understand absolutely nothing of it, but maybe you do..? Click here

[Bbender]

Maybe that link didn't work.. Here's the complete web address for the Screamer 50 Schematic:
http://schematicheaven.com/bargainbin/engle_e330_ii.pdf.

[Enzo]

OK, looking at the drawing, note the lead presence is a presence control in the negative feedback loop of the power amp, The relay switches it in and out, so on clean it does nothing. it is a presence control for the lead chanel only. Since presence controls affect how bright the sound is, I don't doubt they have an effect on the tone of whatever comes out the amp in the lead channel. That is its job. When I say it id for the lead channel only, that does not mean it only affects what is in the preamp, it affects EVERYTHING in the amp when the amp is set for lead. it is part of the power amp, so anything that goes to the power amp will be affected. That includes the effects loop and the reverb.

Turning down the presence will make any amp sound muddier. presence controls high frequencies. And the louder you play, the more effect the control has.

On the lead channel the distortion in the sound is made up of higher frequency elements, so there will be more treble in the lead than the clean, so they added the presence control to allow you to back some of that off so the amp doesn't sound too shrill.

The amp designer expects that the effects loop under normal circumstances will be sending and returning the heavily distorted preamp signal, not something clean, so they expect everything to be overly bright when it gets to the power amp, so the presence control allows you to reduce it. If you play nice music or even just plug your guitar into the effects return, set the amp to the clean channel. But that is not what it was designed for, it was designed to play guitar through from the preamp input.

The tone stack should still work regardless of what channel you select.

[Bbender]

So the presence control kind of work "backwards" then, when it's on full, it gives the full frequency response (like it would have been without the presence control), and when you back it off it works like a treble cut control? So that means that with a 2-channel amp with shared eq without this presence control, (Like the Engl Thunder, which I haven't tried) the sound from the effects loop would be exactly the same on both channels, but there might be too much treble on the lead channel (am I understanding this right)? What I don't understand is why the lead presence control isn't placed before the effects loop and poweramp section, then this problem could have been avoided..?

[Enzo]

Then it would not be a presence control anymore, it would just be another EQ control. That might be useful, but not a presence control. Yes, your description is essentially what it does.