The Presence Control

Hootsmon

On Marshall amps....what is this tone knob all about?

ICBM

It controls the amount of high frequency negative feedback (NFB) in the power amp.

Presence 0 - full NFB on all frequencies, smoother sound.

Presence 10 - no NFB on highs, giving a more dynamic and spiky sounding treble which cuts through a mix really well, ie ‘presence’.

It becomes more effective at higher volume.

Hootsmon

ta 

nikolas7333

Next question : what about the presence control on Mesa Rectifiers? My understanding is that Modern mode turns off the NF in the power amp, so what's the presence control controlling?

RandallFlagg

nikolas7333 said:

Next question : what about the presence control on Mesa Rectifiers? My understanding is that Modern mode turns off the NF in the power amp, so what's the presence control controlling?

I don't know about Rectifiers but on my Mark V 35 Xtreme mode switches out the NF and the presence control seems to do very little if anything at all when in that mode.

ICBM

nikolas7333 said:

Next question : what about the presence control on Mesa Rectifiers? My understanding is that Modern mode turns off the NF in the power amp, so what's the presence control controlling?

When Modern mode is on it becomes simply an overall tone control shunting highs to ground when the control is set low, after the tone stack.

As RandallFlagg says, on the models with Extreme mode it simply turns it off entirely. (And on the ones with a Raw mode, I think.)

nikolas7333

Thanks for the explanation.

ecc83

As is often the case in the guitar amp world, a word that means something else to everybody in the studio and hi fi world has been "purloined"!!

On a mixer, "presence" is a control that boosts or cuts the upper mid frequencies, say 3-5kHz but is in fact usually called "mid eq" and has variable turnover effs.  The rest of the spectrum is unaffected.

The NFB presence control that ICBM so ably explained works over the whole upper spectrum from say 3kHz. Since a guitar speaker has falling output past ~5kHz and next to buggerall by 10kHz the moniker is perhaps justified!

Dave.

JayGee

I have to admit I’ve generally been a bit flummoxed by these (along with the companion “resonance” control which is presumably buggering around with the NFB in a similar manner at lower frequencies) and on my Blackstar Series One I’ve settled for parking them around the 12-o-clock position when dialling in the channel eqs at rehearsal to get a sound/tone which works for me and then using them as a sort of global eq to sort out room related issues (like booming bass from being stuck in corners or spiky treble from loads of mirrors on the wall) at gigs.

Might have to play around a bit more...

57Deluxe

ICBM said:

It controls the amount of high frequency negative feedback (NFB) in the power amp.

Presence 0 - full NFB on all frequencies, smoother sound.

Presence 10 - no NFB on highs, giving a more dynamic and spiky sounding treble which cuts through a mix really well, ie ‘presence’.

It becomes more effective at higher volume.

yeah but to me it just sounds like  < M o r e   W d i t h >

ecc83

JayGee said:

I have to admit I’ve generally been a bit flummoxed by these (along with the companion “resonance” control which is presumably buggering around with the NFB in a similar manner at lower frequencies) and on my Blackstar Series One I’ve settled for parking them around the 12-o-clock position when dialling in the channel eqs at rehearsal to get a sound/tone which works for me and then using them as a sort of global eq to sort out room related issues (like booming bass from being stuck in corners or spiky treble from loads of mirrors on the wall) at gigs.

Might have to play around a bit more...

FYI on the 104 it changes the response at 50Hz by about 14dB and about 10dB at 100Hz, past 100Hz it has little to no effect.

I would aver that 100Hz is beyond the range of many guitar speakers and standard guitars so, unless you have a 4x12 closed box loaded with 55Hz Greenbacks the control is going to be subtle!

Dave.

ICBM

Not at all - it’s where the thump and punch comes from. It’s a very effective control. The frequency response of a guitar speaker might roll off by many dB down there but it doesn’t mean it’s irrelevant at all - just watch the cones move when you play palm-muted power chords, and you can see it’s important well down into the few Hz range, regardless of cab type. (Although a closed cab does show it more.)

On the ID series these two controls are far more effective than the normal EQ.

ecc83

ICBM said:

Not at all - it’s where the thump and punch comes from. It’s a very effective control. The frequency response of a guitar speaker might roll off by many dB down there but it doesn’t mean it’s irrelevant at all - just watch the cones move when you play palm-muted power chords, and you can see it’s important well down into the few Hz range, regardless of cab type. (Although a closed cab does show it more.)

On the ID series these two controls are far more effective than the normal EQ.

Ah! Well! If we are talking "out of band" signals IC then I stand corrected! I only had a bit of a "fiddle" at modest volumes with an S1 and could not tell a lot of diff' even though it met the specc'.

I was really responding to the guy that did not find the control all that effective?

YOU gigtists!!

Dave.

ICBM

ecc83 said:

Ah! Well! If we are talking "out of band" signals IC then I stand corrected! I only had a bit of a "fiddle" at modest volumes with an S1 and could not tell a lot of diff' even though it met the specc'.

It's definitely that 'feel' thing - the resonance control really opens up the amp and makes it 'breathe'. Totally non-scientific language I know . Without any disrespect to you or the designers at Blackstar at all, I think it's a big part of what Blackstar get wrong about their amps - too tight and controlled.

My starting point for any of the Blackstar amps with a resonance control is to turn it up FULL and only back it off if the low-end is just too boomy - presence less so, but it still needs to be above halfway. It's actually much more useful to have both controls than simply turning off the NFB entirely - I had to modify a friend's Mesa because it was so undamped in the 'Modern' mode (no NFB) that the speaker would resonate after a staccato note and make an odd booming 'reverb' noise. I added a pot to reintroduce just enough to stop it without taking away the loose sound he wanted.

ecc83

Cannot recall IC, have you tried an Artisan 15 or 30? They have no NFB at all a la AC30.

Dave.

ICBM

ecc83 said:

Cannot recall IC, have you tried an Artisan 15 or 30? They have no NFB at all a la AC30.

I've tried an Artisan 30 - still didn't like it. Even without NFB it seemed very stiff compared to an AC30, as well as the typical darker voicing I don't like. The V30s won't have helped...

JayGee

ecc83 said:

ICBM said:

Not at all - it’s where the thump and punch comes from. It’s a very effective control. The frequency response of a guitar speaker might roll off by many dB down there but it doesn’t mean it’s irrelevant at all - just watch the cones move when you play palm-muted power chords, and you can see it’s important well down into the few Hz range, regardless of cab type. (Although a closed cab does show it more.)

On the ID series these two controls are far more effective than the normal EQ.

Ah! Well! If we are talking "out of band" signals IC then I stand corrected! I only had a bit of a "fiddle" at modest volumes with an S1 and could not tell a lot of diff' even though it met the specc'.

I was really responding to the guy that did not find the control all that effective?

YOU gigtists!!

Oh, it’s effective alright, and I actually find it very useful as a global control for reigning things in in “boomy” rooms or on the odd occasion I’ve used my amp with a different cab. Likewise the presence control to take out spikyness (there’s a particular place we played a couple of times where just about every vertical surface was covered in mirrors and unless you had a lot of people in there everything sounded excruciatingly “bright” - backing off the presence a bit helped a lot there) or add a bit of sparkle when a room fills up with soft, squishy bodies after soundcheck. For that kind of quick “global tweak” I found them much more convenient than mucking around with 2 sets of channel eq mid gig

It’s just that I’ve occasionally often wondered wether I was using them “correctly” (whatever that means - I’m very much an “if it works for you it’s right” kind of guy when it comes to this stuff) and/or whether I was missing out on any of the amps potential ability/range/vocabulary by not experimenting beyond that simple “global eq” model...

ecc83

Just out of interest IC, what value are the main smoothing caps in an AC30?

Dave.

DJH83004

Hi Dave not to jump in on the thread, but have a Copper top on the bench at the mo, they have 16u / 16u across the choke, 8u supplying the bright/normal inputs and 32u supplying the Vib/trem input and modulator / oscillator. 

ICBM

As DJH said the old ones were very lightly filtered, a mixture of 16 and 32uF and even an 8 in the preamp. By the late 70s they had gone up to slightly larger values (33s and 50s I think, off the top of my head) and solid-state rectifiers so they're a bit tighter but still sound 'Voxy'.

The recent Custom Classic uses switchable main filtering, either 22uF ('vintage') or 44uF ('modern') with a valve rectifier, 10uFs in the preamp, and sounds good, but the current Custom model uses 47 before the choke and 100 after, with a solid-state rectifier... and to me, sounds too stiff and flat.

The AC30 circuit does seem to be much more sensitive to filtering than some others - the switchable 22/44uF on the CC model is very easily audible. I've noticed much less change when increasing the old 32uFs to 50s in Marshalls.

ecc83

Right well the Artisans are 47 and 47mfd across a choke and 10 or possibly 22s downstream for the pre amp. Will check.

Dave.