5k Hz squeal from Palmer PGA 04 and Blackstar series 1

davelittlewood

Hello there,

I've got a Palmer PGA 04 cab simulator running from a Blackstar series 1 50W head.

If I try to use the Palmer with any significant gain or volume on the amp I get a severe 5k Hz squeal in the amp.

I live in the midlands so I actually took the Series 1 back to Blackstar and they found no issues.

Anyone else had a similar issues with the Palmer?

Cheers for any help / suggestions.

Have a good New Year

Dave

(I've edited this as I screwed up and was mixing up two issues - sorry guys - I'll get my coat.....)

ecc83

'Twas ever thus Dave. Single coil pickups (and humbuckers to a much lesser extent) will always be vulnerable to hum fields from transformers * and even house wiring. Screening the cavity will not help in this instance because it is "Electro-Magnetic" hum and that goes through metal foil as easily as it does through plastic and wood.

The only solution, as you have found, it to change the orientation of the guitar and hence pickup. This is ALWAYS the most inconvenient position!

So, try turning the amps and other gear around. Put amp on its end or back and try the same with other kit. Also maximize distance.

*One of THE worst things for hum are small 'line lump' power supplies especially if they are AC-AC transformers. Keep them a good 2 mtrs from yer axe.

Dave.

Modulus_Amps

Does rotating the palmer in any direction help reduce the hum?

davelittlewood

Update:

Spent hours yesterday trying to understand the problem here and it's not really described properly by my post so sorry for the crappy post.

Guitar -> [direct cable or wireless]->G system->G system insert out to amp input->Amp output to 'Load'-> Load to G system insert return-> G system output to DI box to PA.

Even with the guitar turned down to zero and even with the wireless system off when I turn up the main output of the amp I get a high pitched squeal at about 5Kz (according to the analyser on the PA system).

If I change the presence, resonance or ISP the timbre of squeal changes slightly.

The onset of the squeal can be controlled by the pre-amp gain settings (so winding up the gain) or by the main volume or power setting on the DPR.

The squeal is on the main speaker output but it's also physical from the amp itself, sounds like it's coming from one of the transformers.

My guess is that the DPR system on the amp doesn't like being plugged into a load bank and requires a real speaker...humph

ICBM

davelittlewood said:

Spent hours yesterday trying to understand the problem here and it's not really described properly by my post so sorry for the crappy post.

Guitar -> [direct cable or wireless]->G system->G system insert out to amp input->Amp output to 'Load'-> Load to G system insert return-> G system output to DI box to PA.

Even with the guitar turned down to zero and even with the wireless system off when I turn up the main output of the amp I get a high pitched squeal at about 5Kz (according to the analyser on the PA system).

If I change the presence, resonance or ISP the timbre of squeal changes slightly.

The onset of the squeal can be controlled by the pre-amp gain settings (so winding up the gain) or by the main volume or power setting on the DPR.

The squeal is on the main speaker output but it's also physical from the amp itself, sounds like it's coming from one of the transformers.

Stop doing it. That's a sign that the amp is self-oscillating at very high power and there is a serious risk of damage. (Even with a robust amp like the Series 1 or the ID Core - it’s quite a tribute to them that they’ve survived.)

Running an amp/load setup in the loop of the G System is a very bad idea - it's the same as why you shouldn't put a distortion device in the FX loop of an amp, even the smallest amount of signal leaking back from the output to the input will be amplified enormously and is very likely to feed back, inside the equipment where you don’t necessarily hear it as you would ‘standard’ feedback via the speaker.

The reason that it’s worse with the guitar, and turning the guitar flat reduces it, is because the output transformer is under enormous stress and is radiating much more magnetic energy than normal, which is picked up by the pickups unless they’re at right angles to the field.

ecc83

Are we talking hum or a 5kHz squeal here or both? I very much doubt that it is the DPR circuit that is causing the instability since the speaker feed back to the control device is several stages of signal amplitude control and high pass filtering. DPR does not and and does not need to respond anywhere near that fast.

Do you get the squeal with the Artisan? If not and it is only with the S1 then it must I think be the Palmer load effing with the phase angle of the NFB circuit. The Artisan has no NFB.

You cannot design amplifiers that can cope with every crazy do-dad someone might bolt onto them!

As ICBM says, such instability is very likely to damage the amplifier although one would hope a fuse might blow first.

Caution! Old time PA tech about to opine! Back In The Day, when we had an amp and remote speakers an "Avo" was always hung on the line set to AC volts. Thus any standing reading could be spotted before a disaster occurred.

Dave.

ICBM

If you want to use this setup, I would try re-routing it so the amp’s power stage and the load are not in the loop.

Guitar > G-System input, G-System insert send > amp input, amp FX loop send > G-System insert return, G-System main output > amp FX return, amp speaker output > Palmer load box > DI

That puts only the amp’s preamp in the G-System loop and should be stable, I think.

davelittlewood

ecc83 said:

Are we talking hum or a 5kHz squeal here or both? I very much doubt that it is the DPR circuit that is causing the instability since the speaker feed back to the control device is several stages of signal amplitude control and high pass filtering. DPR does not and and does not need to respond anywhere near that fast.

Do you get the squeal with the Artisan? If not and it is only with the S1 then it must I think be the Palmer load effing with the phase angle of the NFB circuit. The Artisan has no NFB.

You cannot design amplifiers that can cope with every crazy do-dad someone might bolt onto them!

As ICBM says, such instability is very likely to damage the amplifier although one would hope a fuse might blow first.

Caution! Old time PA tech about to opine! Back In The Day, when we had an amp and remote speakers an "Avo" was always hung on the line set to AC volts. Thus any standing reading could be spotted before a disaster occurred.

Dave.

Dave, 

Just the 5k Hz squeal.  I tried it with just the amp and the Palmer and got the same thing (so no possibility of any feedback system through the G system) and it still does it.

The Series 1 is chock full of circuit boards (I remember an amp tech bitching about them) so there's a good chance that there's something in the amp that simply doesn't like being plugged into something like the Palmer or the Hot Plate.  Can't really complain about Blackstar here, as you say, they can't consider every possibility of how the amp might get used.

I'm just using the Emulated output from the amp at the moment and that's fine.

The Artisan is fine with the Palmer or the Hot plate but (and don't get me wrong, I love my A15H) you can't change channels on the fly

Sporky

ecc83 said:

Back In The Day, when we had an amp and remote speakers an "Avo" was always hung on the line set to AC volts. Thus any standing reading could be spotted before a disaster occurred.

Could you explain this bit in very, very simple terms please? 

ecc83

Sporky said:

ecc83 said:

Back In The Day, when we had an amp and remote speakers an "Avo" was always hung on the line set to AC volts. Thus any standing reading could be spotted before a disaster occurred.

Could you explain this bit in very, very simple terms please? 

Ah! Mayhap you are younger than I thought Mr Sporky? The "Avo 7&8" was the electronic tech's standard multimeter before digital came about (a 'lesser' make was the Taylor)

The meter had a large clear scale 0-100, 0-30 and decibels and resistance. As well as DC it contained a Copper oxide rectifier and so was a fairly high resistance, about 1k Ohms/V AC volt meter. Lowest FSD range was 2.5V.

Where you had long speaker lines and especially out doors where they could get wet they could upset the amp and cause an ultrasonic oscillation. The Avo was good up to about 30kHz IIRC and would show such a signal.

Most of the time we were using 100V speaker lines but sometimes a low Z feed was needed 50+ mtrs away in say a dressing room.

Re the Series Ones being "crammed with PCBs"? Yes they are a complex amp but really only differ from many others in respect of the (unique?) DPR circuitry. There is a front PCB which carries the solid state low voltage signals with tone stacks, channel switching and 'pre conditioning' to feed the middle PCB which has triodes for OD sounds and the PI. Despite what the knockers say, some 90% of the pre amp OD effect is done by the triodes.

I cannot be dead sure about this but I would say the Series Ones are pretty reliable judging by the almost total lack of evidence to the contrary in this and other forums? I will agree that tackling a S One without a schematic would be a daunting task for a service man. Personally I would like to see schematics readily available to everyone. They used to be but the likes of Behringer put the kybosh on that!

None of the above will cause instability as discussed here. The amps do use a modest amount of negative feedback and various models use this for "resonance" control. I strongly suspect the Palmer is a bloody awful load 'power factor' and it is quite possible that it upsets other amplifiers as well? Most 30W and below valve amps do not use any NFB but most higher power amps do.

Got interrupted BTW by son's arrival.

Dave.

ICBM

davelittlewood said:

The Artisan is fine with the Palmer or the Hot plate but (and don't get me wrong, I love my A15H) you can't change channels on the fly

This does sound like a phase angle issue with the load causing trouble with the amp’s negative feedback loop - that surprises me, I haven’t found it a problem with a Hotplate or even a Marshall Powerbrake, which is even more inductive, although I don’t think I’ve ever worked on a Series 1. (And I don’t have a Palmer.)

Even so, I would still avoid putting a power amp in the loop of the G-System - or any other arrangement where there’s a possibility of internal feedback - it’s just asking for trouble, even if it’s not the main problem here. If a preamp or an effect unit goes into self-oscillation it’s usually just annoying, if a power amp does it it’s very likely to cause damage. Luckily it appears this amp is tough… there are many others which wouldn’t fare so well.

ecc83 said:

Most 30W and below valve amps do not use any NFB but most higher power amps do.

Interestingly almost all Fender amps right down to the 5W Champ have NFB - the 5E3 Deluxe famously doesn’t, but is a rare exception.

The Mesa amps with a ‘Modern’ (very oddly named!) or ‘Extreme’ (better…) mode which turns off the NFB are also prone to oscillation, in fact they’re unstable with no load even with no signal, as is the old Vox AC50 which has no NFB.

ecc83

I WAS going to say "most Fender amps use some NFB" IC but thought I had waffled on enough! Just looked in my Dave Funk Big Book and yes, non-NFB Fenders are very rare.

Not surprised many other amps can go unstable! I find their 'rat's nest' construction very disturbing to my technical sensibilities!

Just one of the advantages of PCB amp construction is that if the fekker isn't stable in the pro-prod model you HAVE to fix it before you can sell it! Rat's nests are a wing and a prayer.

Now, the last thing I want to do is upset Blackstar but I will mention that a few, very early examples of the Artisan 15 and 30 suffered "parasitic oscillation" when tone and volume pots were in certain, not max, positions. Could be tricky to fix (lead dressing) but if anyone has an old amp with the problem drop me a PM.

Dave.

Sporky

ecc83 said:

Sporky said:

ecc83 said:

Back In The Day, when we had an amp and remote speakers an "Avo" was always hung on the line set to AC volts. Thus any standing reading could be spotted before a disaster occurred.

Could you explain this bit in very, very simple terms please? 

Ah! Mayhap you are younger than I thought Mr Sporky? The "Avo 7&8" was the electronic tech's standard multimeter before digital came about (a 'lesser' make was the Taylor)

Thank you! I think those do perhaps pre-date me, all makes sense now. 

davelittlewood

Hmmm.  OK - brought the amp home (was in a separate building) and did do some more experimentationings.

I now think it's the G system that is either toast or crap...

G system->Insert send->Amp -> Palmer.  = 5kHz squeal. (No guitar plugged in, no return to the G system from the Palmer)

Guitar->Amp->Palmer  = Amp cranked up and no squeal at all.