Peavey CS-800 Power Amp

[CJ]

let's try to get down with an 800 watter, classic Peavey, they still make upgraded versions of this,

weighs a ton, don't drop it on your foot, this one is well worn, probably been on the road, supposed to be a "professional" amp,  which means it can stay on 24-7 and not blow up,

real simple up front, a couple of micro click pots and were ready to go,

 

[CJ]

large chunk-o-iron, the lights go dim for a second during pwr up,

a transformer like that could cause a house fire, so they have a "suicide" Triac circuit in there, when DC is detected on the outputs, a triac shorts the pwr supply which blows the fuse, then the triac has to be replaced. otherwise voice coils turn red and paper ignition is a reality,

common complaints seem to be Ch. B works fine but Ch. A is weak or dead,

fixes include pwr transistors and driver components, even bad resistors sometimes,

has a fan and wind tunnel full of dust and brown recluse spiders,

next hassle is figuring out how to take it apart,

 

[CJ]

driver board,

 

[JohnRoberts]

Yup  that was the last model before they went 2 ohm, so 250W@8 400W@4... 

the really old school CS800 was 4U high and even heavier.

JR

 

[CJ]

a back panel with choices, hi, lo, in, out, crosovers, xlr, transformers, 1/4 inch and binding posts in case you want to do some heli-arc welding in between sets,

 

[CJ]

JR is talkin about this guy>

smart deal having the vol controls recessed, especially with an amp this heavy,

 

[CJ]

this guy runs NPN-PNP outputs, non of that Quasi junk here, 

Jack Sondermeyer might be the designer,

here is a link to a parts list for a lot of Peavey solid state stuff,

http://www.ampix.org/albums/userpics/10003/PV_Semi_Cross_Ref.pdf

p/n info for the output pairs>

 

[CJ]

link to quasi  schemo>

https://dl.dropboxusercontent.com/u/8335881/CS800.pdf


for this complimentary amp>

 

[JohnRoberts]

this guy runs NPN-PNP outputs, non of that Quasi junk here, 

Yes, we specified our own house number power transistors from Motorola. We bought a lot of TO-3s from them.  You will notice that the class A bias for the output stage is set by some double diodes. For that to work reliably in large scale production the power devices also need to be well managed for forward Vbe. If you ever repair one, do not casually substitute some other power devices, or you may need to tweak the class A bias and there is not trimpot. Peavey did not believe in trimpots.  ;D ;D

Jack Sondermeyer might be the designer,

More than might be, Jack was hired away from RCA by Hartley to help make the power amps more bulletproof and he pretty much succeeded IMO.

here is a link to a parts list for a lot of Peavey solid state stuff,

http://www.ampix.org/albums/userpics/10003/PV_Semi_Cross_Ref.pdf

p/n info for the output pairs>

Some other iconic design features of that power amp is the DDT clip limiter.  The top left corner op amp is the input buffer and immediately below it is an OTA shunt to quickly drop level when clipping is detected.  That OTA was another house part number graded by the manufacturer for low control feed through, you don't want a limiter to be all thumpy.

This model also shows the high damping factor, low output Z circuitry that uses additional feedback to reduce output impedance. It was very difficult to measure damping factor for these amps because the output Z was dominated by output connector contact resistance.

There is separate input board not shown that should have a balanced op amp input. I had to arm wrestle Jack to add that into the CS800S .  Note this schematic is for the "800S" so this version was 2u high and had the switching power supply. IIRC it weighed < 25# Other wise the amp itself is pretty similar to earlier CS800X so this schematic will have higher current output to support 2 ohm loads (different current limiting values) than the pictured 4 ohm CS800.

JR

PS: There are a few patents listed in the top right corner, I suspect one is for the DDT clip limiter, and another is the special low output Z circuit, I don't remember any more in that one,  My angled heat sink patent was after this model so used in later series. 

 

[ricardo]

I particularly like the serious (18dB/8ve) supersonic filtering.

No concessions to deaf Golden Pinnae here.  ;D

 

[JohnRoberts]

I particularly like the serious (18dB/8ve) supersonic filtering.

No concessions to deaf Golden Pinnae here.  ;D

It might even be this amp but I recall one bass artist using one in his personal bass rig and complaining that it kept cutting out. It turns out he was tripping the DC speaker protection circuitry. We had to dial that back a little for him,  8)

JR

PS: For some reason bass players really liked the DPC class D amp, for bass rigs. Perhaps the 1u and light weight.

PPS: While not on anybody's hifi list the CS800 was a mature design with very low noise and distortion.

 

[mjrippe]

A friend who has done club audio install/maintenance told me about visiting a bar in Texas with an all-Peavey sound system.  The clip lights on the amps were blinking in time with the music all night long but neither amps nor speakers failed the whole time he was there.  Sounded pretty lousy, but he wasn't there on business

 

[CJ]

thanks John for all the cool info! 

this thing came apart a lot easier than esxpected,

no wires to unsolder, the back panel is the first to come of with all the I/O stuff,

 

[CJ]

looks like a trip to the garage for the shop vac,

 

[CJ]

no offset screwdrivers required, no rivets to drill,

just a few power wires to remove from that blue board at upper right and out comes the main assy,

 

[CJ]

back of the mother board, heavy traces required for the high currents involved,

good board material and tinned traces,

 

[CJ]

just two ribbon cable connectors to remove and the wind tunnel comes off with the driver boards,

 

[CJ]

so far, all of the pwr transistors check good, there are 20 of them and they are all soldered to the main board, we are going to R&R each one to clean and check them and apply fresh grease,

 

[JohnRoberts]

A friend who has done club audio install/maintenance told me about visiting a bar in Texas with an all-Peavey sound system.  The clip lights on the amps were blinking in time with the music all night long but neither amps nor speakers failed the whole time he was there.  Sounded pretty lousy, but he wasn't there on business

I won't speculate on what your friend was hearing but DDT was pretty well dialed in after 20 years for transparent limiting (fast attack and fast release). I was very disappointed by several single blind (I knew which was which)  listening tests where people actually preferred the sound of letting the amps clip.  : : : Clipped was louder and had more snap on the clipped bass. It bothered me, but not the peeps in the seats. 

JR

 

[ricardo]

The clip lights on the amps were blinking in time with the music all night long but neither amps nor speakers failed the whole time he was there.

Many live sound guys and ALL DJs think that's what the lights are for  ;D

So forget peak hold etc.  They just gotta keep time wid da music ... and wats da point wid different coloured lights if they don't all get a chance to shine.