A warning to those that use Class D amps

[Bass is the place]

Last night I had a gig in a one of those Teepee/ Marquee constructions with my Ska band. It was at the top of a field where the owner of the farm was having a party, the power source being a generator. No apparent problems, in fact a great scene for a bloody good do!

I set up my trusty Genz Benz Streamliner 900 which runs 2x Vanderkley 12 inch cabs in series.
Then powered up to find that although the amp came on (power indicator lit) I realised the protection/warm up indicator which is a blue LED wouldn't go off?! No sound! This has never happened before so the only thing that I could ascertain was my amp was knackard. Meanwhile the rest of the bands amps and PA were set up and seemingly worked ok.

Fortunately it was only a 30 minute round trip to pick up my EBS HD350 which is a fabulous amp, I just can't be bothered to lug it around anymore especially to parties where you want a quick get away as well as negotiating/ dodging pissed people!

Once set up, the EBS worked fine.

I sing in this band also and I noticed almost right away my vocal mic was distorting at a reasonably low level, ditto the guitar and keyboard back line!?

We got through the gig ok and all the punters enjoyed our set. The band collectively concluded that the power that the generator was supplying wasn't sufficient to run out amps properly.

As for my Class D Genz Benz bass amp, I figured (and i'm no technician) that a digital power amp if not supplied with enough juice is either off, or on/ 0 or 1.....with no in-between state like the regular amps with normal transformers. I'd be interested if any BCers can shed any light on this?

I tested the Genz Benz when I got home and its fine. So the moral of this story is; If I ever play in a marquee again I will be taking the EBS incase there is a generator. Indecently, unlike the guitar, keys and PA amps under the reduced power, there was no loss of quality with my EBS amp which was reassuring.
I'd be interested to learn if anyone else has encountered this situation?

[Chienmortbb]

Many class D amplifiers will have under voltage protection as the control chips do not behave reliably at very low voltages.

Class A/B Amos will operate but not put out the full power and will distort early.

If you had both, the voltage was too low ( that is way out of the 230V +\- 10% that the mains are guaranteed).

Do you know the power of the generstor?

[Chienmortbb]

Duplicate post please ignore

Edited July 1, 2017 by Chienmortbb

[gary mac]

The only time that my Genz misbehaved, was when gigging with power supplied by a generator.

[bassmayhem]

Then you will need some kind of power conditioner, that always feed the correct voltage regardless of source...

[Gareth Hughes]

Interesting. I have a similar rig. Never had any bother with my Streamliner before. However - I did have a weird one with an Acoustic Image amp that I concluded was down to dodgy power. The amp lit up, the preamp was working as there was a signal going through the DI to the soundman, but the power amp wouldn't do anything. Gig the night before with the same and next day at home, everything was fine and never any thing like that again.

[Bass is the place]

Thanks for the comments folks, I did ask the guy who was hosting the party about the generator but I couldn't get a sensible answer out of him - he was too pissed!
There is a switch on the back of the amp to change to 120v, I wonder if that would have worked?

[Dood]

[quote name='Bass is the place' timestamp='1498927375' post='3328051']
There is a switch on the back of the amp to change to 120v, I wonder if that would have worked?
[/quote]

I'm glad you didn't test the theory as that would have most certainly have cost you.

As for generators, in all my years gigging, only a few times has a venue or promoter ever known there correct specification for a generator used for live music. We've always had to get an upgrade in. So, in short, if you know the gig may include the need for a gen, make sure it is suitable before leaving for the gig because the venue sure as sh*t won't pay for damage to your gear caused by plugging it to their generator.

[Bass is the place]

Too True!

[Happy Jack]

And of course it's not just Class D.

I played the Ealing Beer Festival a few years back, using my Matamp all-valve head. At 11pm they wanted all the punters to start going home so they turned on all the floodlights. The sudden draw on the (huge) generator caused my amp to cut out instantly and it was over a minute before I could get it back up and running.

The heart of our PA was a Powersoft Digam solid state power amp which barely even noticed the interruption!

[Adrenochrome]

I remember a couple of Line 6 guitar amps that wouldn't work with the dodgy powered supplied by a generator. Not sure if it was for the same reasons.

[Count Bassy]

[quote name='bassmayhem' timestamp='1498924331' post='3328025']
Then you will need some kind of power conditioner, that always feed the correct voltage regardless of source...
[/quote]

AFIK a power conditioner can't increase a low voltage.

[M@23]

[quote name='Bass is the place' timestamp='1498920157' post='3327986']
...
[/quote]

I've had this too, I use my 'rubbish venue amp' which is an almost 20 year old Peavey combo in These situations, it's litterally indestructible I think!

Sorry to go off topic, but out of interest, how is the EBS compared to the Genz, power wise? I'm so tempted by them, but 'only' having 350w does put me off.

[Bass is the place]

[quote name='M@23' timestamp='1498948720' post='3328237']


I've had this too, I use my 'rubbish venue amp' which is an almost 20 year old Peavey combo in These situations, it's litterally indestructible I think!

Sorry to go off topic, but out of interest, how is the EBS compared to the Genz, power wise? I'm so tempted by them, but 'only' having 350w does put me off.
[/quote]

The EBS 350 isn't as loud as as the Streamliner, but it still packs a punch. It's definitely louder than the SWR SM400 which I used to own which was rated at 500w when run in bridged mode.

[kev b]

Its not only class D amps that play up, my band plays a couple of venues where there is a issue with the power supply. The ancient keyboards (4) use 9volt phone charger type power supplies and I use my 1970s HH solid state head for bass.

At various points during the set my bass will sound horribly distorted but one keyboard in particular will fail altogether, just producing a clicking noise.

We put this down to a voltage drop caused by the long extension leads and demand from the fryers and other equipment in the venue, the cure is not easy to find.

I dont look forward to playing one of these gigs as our sound is always compromised, the place was rewired last year but we use the same setup elsewhere and never have a problem.

[Chienmortbb]

[quote name='Count Bassy' timestamp='1498935694' post='3328142']
AFIK a power conditioner can't increase a low voltage.
[/quote]True a waste of money if you ask me.

[Chienmortbb]

[quote name='kev b' timestamp='1499036735' post='3328789']
Its not only class D amps that play up, my band plays a couple of venues where there is a issue with the power supply. The ancient keyboards (4) use 9volt phone charger type power supplies and I use my 1970s HH solid state head for bass.

At various points during the set my bass will sound horribly distorted but one keyboard in particular will fail altogether, just producing a clicking noise.

We put this down to a voltage drop caused by the long extension leads and demand from the fryers and other equipment in the venue, the cure is not easy to find.

I dont look forward to playing one of these gigs as our sound is always compromised, the place was rewired last year but we use the same setup elsewhere and never have a problem.
[/quote]If the voltage goes down so does your headroom and distortion will start earlier. Incidentally I have two HH bass amps and no valve amp watt is equal to an HH watt (tin hat on).

[markstuk]

[quote name='Chienmortbb' timestamp='1499086245' post='3329031']
True a waste of money if you ask me.
[/quote]

You could bring along a UPS - however I suspect this might offset the lightweight Class D loveliness :-)

[Treb]

In class D the D does not denote digital. Just saying.

[Ghost_Bass]

Well... i would rather not play at all than give poor, distorted, fart sounds to the audience. If it can't sound good it shouldn't sound at all, kudos to class-D for that!

[oo.viper.oo]

In class D the D does not denote digital. Just saying.

This is true, "Class D" is a "D" simply because "D" follows "C".  Edited June 12, 2018 by oo.viper.oo
Removed nonsense about quantisation

[Count Bassy]

[quote name='oo.viper.oo' timestamp='1499150016' post='3329461']
This is true, "Class D" is a "D" simply because "D" follows "C". But it doesn't change the fact that it uses quantization and PWM modulation so it is "kind of" digital. Just not not the same kind as your average digital calculator.
[/quote]
So where did "Class H" come from?

And I agree with your other point. Class D is digital in that the output has two states, on or off. However there have been very long threads regarding this before, so best not open that particular can of worms again!

Edited July 11, 2017 by Count Bassy

[DBerriff]

I had a similar problem with a Genz Benz Shuttle a couple of years ago. In my case the amp would suddenly cut out for minutes at a time. The head lights were on and everything looked ok, but no output. The PA and guitar amps continued to work. It turned out that one of the caterer's fridges was overloading the generator, possibly because it was sat on wet grass (!).

It does seem that Class D can suddenly stop working where Class A/B just degrades. I have stuck with Class D though as it is the best match for my requirements.

[deepbass5]

I have had many generator related gear issues, i have documented here in various threads in the past so will spare you the detail

Basically generators if they are overloaded, the frequency will dip. Larger sets e.g. Fair grounds you may have noticed the set cough when additional load comes on, you may see a puff of black smoke from the exhaust as the AVR linked to the engine tries to correct the speed to keep the frequency stable. If the set that your venue hires is too small or set up with Freq too low Your gears transformers will experience higher current get hot so your protection circuit may shut it down.

An example -Quote
The lower the operating frequency the more flux lines that are generated. Operating a transformer at 50Hz generates 20% more flux lines than at 60Hz. As the number of flux lines approaches the magnetic material’s limit, the heat in both the transformer’s core and its coil wires increases, and under certain circumstances, unpredictably so. This can result in a transformer that exceeds safe temperature levels. Therefore, a transformer designed to run at 50Hz will simply run cooler at 60Hz. But one designed only for 60Hz may overheat if subjected to 50Hz.

[JapanAxe]

The technical term for what the OP has described is a 'brown out' - really!