Maker Pro
Maker Pro

Peavey XR 886, 1997, mixer amp

E

Eeyore

Jan 1, 1970
0
N_Cook said:

That is about the worst excuse for a 'heatsink' I have seen in my entire life.
It's utterly pathetic. In fact it's completely WRONG in just about every way
possible.

I have seen another that came close to being that bad but even so at least there
were a few more vanes on it (C-Audio btw). The company I was with was
considering taking the C-Audio design as a OEM product and re-branding it, but
my tests showed a heatsink temp of up to 150C with a 40C ambient on music test
signal. This was enough to cause several of the output mosfets to fail
open-circuit and I only realised that when later bench testing it and finding
asymmetrical clipping.

After declining their offer of the product I later found they'd added more
heatsinking but it was a kludge.

Just for good measure, C-Audio also exhausted the searingly hot air right over
the PSU electrolytics ! These were well known to need regular replacement which
C-Audio justified as they said they were a 'service item'.

My own designs (including one in the local venue) are known for working day in,
day out for years on end. I think the one in there is getting on for 10 years
old now and is used every night although not every night is a 'loud' band. It
has had a 'blow through' or two of the heatsinks and 2 new level pots (only one
went crackly but it's best to replace both whilst you're at it, and yes, they're
NOT pcb mounted so it's an easy job too. Compare that with a QSC RMX 2450 I also
had to do the same to (labour time approx 4:1 ratio).

I never fail to be amazed at the number of amps that illustrate that the
designers are completely incompetent when it comes to thermal management.

And don't even get me started on power transformer design !


Graham
 
E

Eeyore

Jan 1, 1970
0
N_Cook said:
The view of this amp
is upside down as the fan is at the base. So drawing air horizonatally
theough a "designed" 5/8 inch space under the amp.

Hahahahahahahaa !

What LOONIES. That's STALLING the fan blades. NO wonder putting bigger feet on
helps.

How well would a propellor aircraft fly if you put an obstruction in front of
the prop ?

Graham
 
N

N_Cook

Jan 1, 1970
0
Ron(UK) said:
I think that the worst part of that desgn IIRC is that the board is
mounted inverted with the sinks beneath, thus any heat which tried to
escape by convection has to pass through the pcb, heating the other
components. Am I correct in that assumption?

Ron


The heatsink is fitted onto the pcb that caries nothing on that area but
holds a lot of ceramic W/W seen either side on the pic, usefully, I suppose,
in the airflow.
 
N

N_Cook

Jan 1, 1970
0
Eeyore said:
I'm afraid I found the pic too unclear to be sure what I was looking at.

Is it formed from sheet aluminium ?

Graham

I was rushing around a didn't focus on the right distance.
Will have another go closer up , showing the chisel? cuts. Could not find an
image of one out there.

Often seen in Sony domestic amps of the 70s/80s TA..., STR...all convection
cooled
The cutting action must be like those butter or cheese knives/scoops that
curl the material into whirls
 
N

N_Cook

Jan 1, 1970
0
Eeyore said:
Hahahahahahahaa !

What LOONIES. That's STALLING the fan blades. NO wonder putting bigger feet on
helps.

How well would a propellor aircraft fly if you put an obstruction in front of
the prop ?

Graham

Expressing it like that highlights the flaw admirably.
 
B

BobG

Jan 1, 1970
0
That ancient Peavey transformer might be hotter (thermally! not
wattagely!) on 50hz than on 60hz, and class AB amps dissipate worst
case power at about 1/3rd max power.... its where the load line runs
right across the hyperbola on the IV curve... and if the voltage in
the club sags when the drink cooler compressor turns on, its a perfect
storm of overheat factors.
 
B

BobG

Jan 1, 1970
0
Voltages in the UK don`t generally sag much if at all
=============================================
Is that in percent or in volts? I've glanced at the power line monitor
during the end of a song and seen 105V... should be 120, but with
lights and air conditioners and everything else, 115 is more like the
nominal. So that 10% low.
 
G

gareth magennis

Jan 1, 1970
0
Ron(UK) said:
Voltages in the UK don`t generally sag much if at all

Ron


AFAIK the lowest legal voltage the electricity company can supply in the UK
is 10% down (from 240) which is 216v, the highest legal voltage is 254v,
less that 6% high. Suffice to say you won't normally get those kind of
variations at the mains intake at the venue.

I don't know how much voltage drop you might experience due to the clubs
wiring before it was deemed unsafe or illegal though.



Gareth.
 
E

Eeyore

Jan 1, 1970
0
gareth said:
"Ron(UK)" wrote


AFAIK the lowest legal voltage the electricity company can supply in the UK
is 10% down (from 240) which is 216v, the highest legal voltage is 254v,
less that 6% high.

It won't be based on 240V any more because we're officially (on paper) 230V.
Maybe 230 +/- 10% but that's just an EU standard - it's NEVER as low as that.

Suffice to say you won't normally get those kind of
variations at the mains intake at the venue.

I don't know how much voltage drop you might experience due to the clubs
wiring before it was deemed unsafe or illegal though.

Never seen any worth talking about. Have you ?

Graham
 
G

gareth magennis

Jan 1, 1970
0
Eeyore said:
It won't be based on 240V any more because we're officially (on paper)
230V.
Maybe 230 +/- 10% but that's just an EU standard - it's NEVER as low as
that.


On paper maybe, but in practice its still pretty much 240v.


Never seen any worth talking about. Have you ?

Graham


No, I put that down to good wiring regulations.

(I remember when I was in a function band and we used to play the Forces
bases in Germany with dodgy old 220v domestic-at-best wiring. We only had
about a 3K system but often had to carefully switch the amps on one at a
time to stop the breakers tripping, then all the house lights and all the
gears' illumination would dim in time to the kick drum. Frightening really.
None of my keyboards ever crashed though.)

So what would be the maximum voltage drop you might expect from a non
overloaded mains system?




Gareth.
 
E

Eeyore

Jan 1, 1970
0
gareth said:
So what would be the maximum voltage drop you might expect from a non
overloaded mains system?

Crikey. I know where I'd test with a highish power PA rig, the local venue that
has some 5kW ? or so of amps but last year I had a separate 32A circuit run in
just for the amp rack so I doubt it would be more than a few volts.

Graham
 
G

gareth magennis

Jan 1, 1970
0
Eeyore said:
Crikey. I know where I'd test with a highish power PA rig, the local venue
that
has some 5kW ? or so of amps but last year I had a separate 32A circuit
run in
just for the amp rack so I doubt it would be more than a few volts.

Graham


I was just curious, knowing nothing really about wiring regulations.

If the regulations require heavier cable for longer runs to prevent voltage
drop, then is there some kind of formula with voltage drop limits? Or can
you just run a very long cable (in a large building) capable of carrying the
current required and have to live with the voltage drop. Or is any voltage
drop just a few volts as you suspect, so the point is mute.

Kind of thing.



Gareth.
 
E

Eeyore

Jan 1, 1970
0
gareth said:
"Eeyore" wrote



I was just curious, knowing nothing really about wiring regulations.

If the regulations require heavier cable for longer runs to prevent voltage
drop, then is there some kind of formula with voltage drop limits? Or can
you just run a very long cable (in a large building) capable of carrying the
current required and have to live with the voltage drop. Or is any voltage
drop just a few volts as you suspect, so the point is mute.

Well, a 'spur' rated at 32A requires 6mm2 cable. You could calculate a voltage
drop along that based on resistance data. There is AFAIK no limit on length
aside from practical limitations ! I don't know how the incoming feed from the
electric company to the breaker box might drop with load though.

Graham
 
J

Jamie

Jan 1, 1970
0
Eeyore said:
gareth magennis wrote:




Well, a 'spur' rated at 32A requires 6mm2 cable. You could calculate a voltage
drop along that based on resistance data. There is AFAIK no limit on length
aside from practical limitations ! I don't know how the incoming feed from the
electric company to the breaker box might drop with load though.

Graham
In the US, it's no less than 5% drop from the source to the load at full
load.. conductor must be rated to supply a min of 95%.

for example, 10 awg = 0.999/M or 3.28/kg ohms

of course, all conductors are based from copper, copper being 100% of
the scale. All others are based from that.
etc..


http://webpages.charter.net/jamie_5"
 
T

Tim Phipps

Jan 1, 1970
0
gareth said:
I was just curious, knowing nothing really about wiring regulations.

If the regulations require heavier cable for longer runs to prevent voltage
drop, then is there some kind of formula with voltage drop limits? Or can
you just run a very long cable (in a large building) capable of carrying the
current required and have to live with the voltage drop. Or is any voltage
drop just a few volts as you suspect, so the point is mute.

Kind of thing.



Gareth.

I haven't looked it up properly but in the design of fixed installations
you are not supposed to have more than a 4% voltage drop from the point
of supply. So whilst 6mm cable will easily carry >32A, once you go over
a certain length you would need to go up to 10mm to comply with the regs.

http://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html
 
G

gareth magennis

Jan 1, 1970
0
Tim Phipps said:
I haven't looked it up properly but in the design of fixed installations
you are not supposed to have more than a 4% voltage drop from the point of
supply. So whilst 6mm cable will easily carry >32A, once you go over a
certain length you would need to go up to 10mm to comply with the regs.

http://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html


Thanks. Then from my calculations the maximum legal drop for any
installation should be 13.6% from 240v - 207v and a bit, not including
your own power distro.


Gareth.
 
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