Peavey Tour Series 450 Bass Amp

welcome to my nightmare,

keep it simple?  not this box, surface mount chips and obscure power transistors,

weird flying rails power supply,

how about the popular Triac crowbar on the output circuit?

throw in some input jacks with 5,000 contacts,

relays never fail, so may as well add a few more bones to the stew pot,

what else can i whine about, .... give me time, ill figure out something else,  ;D

it does have a nice toroidal pwr trans, hope it don't break cuz we can't rewind that,

power output, has a fan which did not stop the heatsink grease from melting,

schematic for output section,

filter caps in the power supply are tied to a floating center tap,


here is a thread with other tortured souls, it has the full schematic,

http://music-electronics-forum.com/t34497/

Nice the way they faced the fins into the wall so they don't get a chill from the fan.

good catch on the fins!


front board needs that fan panel to come out as the pot shafts don't clear the sheet metal, but we got er out,

signal tracing now, pin 1 U1, pin 7 U1, pin 1 U2.....  4550 op amps,

luckily front board opamps are thru hole,

notice the weird dual opamps in between the EQ sliders, kind of slick,

noticed that when the voltmeter was put on pin 2 on the U2 opamp, the sound from the signal generator gradually got louder,

this usually means that the volt meter is completing a resistive path to ground, which means that something is going on with the components around the input circuit,

supply rails are good, +/- 15 , 

turn the power off and measure ohms from pin 2 to ground,  infinite!

we found the problem,  broken resistor? no,

check the schemo, see that there is a tone pot in the input circuit,

poking around the pot we find a broken leg! (see screw driver)

suck the solder out and put in some 22 ga braided wire,


find that another pot leg is broke, so we fix two compound fractures and add some solder to all the other pot legs to beef them up a little, 450 watts of bass will rattle parts so we don't want another break down,

here is the part of the circuit that was causing the problem,


broken pot leg (red),  ground path broken (green)

How does the air flow out of the power amp section?

From the pictures it look like air comes in from the side the amp section. then looks like it might have positive pressure area for the power amp section.
When the top is on does the air flow out down the fin side of the heatsinks and exit at a slot at the PCB metal wall area?  I can not tell from the pictures.

here is a shot of the assembled amp, looks like intake vents on sides and exit vents on the back, but not room above or below the heat sinks inside for any major airflow,

this amp does sound nice with bass, kind of a warm MOSFET sound, octave divider is pretty horrid sounding but you don't have to use that,

somebody probably dropped it on the bass knob which broke the legs, knobs need to be recessed on git amps so tired people don't break anything,

no failed components so a pretty dependable amp if you don't drop it,

and the speaker jacks (green things) are pretty cool,

CJ said:

schematic for output section,

filter caps in the power supply are tied to a floating center tap,

Click to expand...

That is well after my time but that amp topology is what is called a "driven rail" a very inexpensive amp topology because the front end can run off modest op amp voltages. I've seen these widely used in fixed install amps and value applications.

Using two transformer windings in parallel is not typical but i suspect that is a transformer from another product being repurposed. The fact that the power board is not fully populated (room for more power devices) suggest more mixed use.

here is a thread with other tortured souls, it has the full schematic,

http://music-electronics-forum.com/t34497/

Click to expand...

Don't feel tortured because the speaker connects to the PS common instead of the drivers , it really is a pretty simple low tech amp, widely used and cheap.

We called those tall right angle leg pots "spider pots" and they were tooled to work with .950" high panel to PCB spacing so vertical 1/4" jacks could fit into  the same PCBs.

I wouldn't worry too much about the heat sink orientation, back in the day we had some good heat sink designers (one of my patents at Peavey was related to heat sinks). While none of my personal thermal design crew are still there (AFAIK my other two co-inventors on the heat sink patent are now retired. ).

JR

thanks JR!

cool to have inside info!

yes, there is room for 2 more power transistors which make it a 700 Series amp,

this amp does not seem to get very hot even when cranked, so that fan and heat sink seem to be doing just fine,

spider pots , can't wait to tell the owner>
"yeah dude, it was just a broken spider pot "    ???