Peavey 400BJ

[lowell]

someone please tell me this schematic is wrong. The 5332 driver is written on the drawing as NPN, but this is a MJE253, PNP per the Peavey cross reference. CORRECT?

Been pulling my hair out haha.

[J M Fahey]

Yes, itīs drawn wrong, itīs a PNP.

Basically "all arrows should point the same way" , in this case downwards.

[Jazz P Bass]

Strange, strange, strange.

Here is the same amp, basically.
It's the 400BH.
And it has the pnp driver drawn correctly.

PV 400BH.zip

[J M Fahey]

Well, it isnīt as if Peaveyīs style is to write PNPs wrong, why would they repeat the error many times?
I guess itīs not much more than a late Friday job

[Enzo]

Just a typo.

Sometimes I discover a typo on a drawing I have looked at and used many times and never saw before. Why? Because in my mind, I know what circuits look like, and the picture on the page is just an outline for my mental image.

I used to work at a music store, big place, had a number of trucks with painted signs. Their motto was "Everything in music". One of the trucks was somehow inadvertently painted "Everythnig in music". Not sure when it was first noticed, but they decided to leave it that way. I think the store got two calls on it over the life of the truck. We tend to see what we expect rather than what is really there.

I used to tour with a big band, and one song we did was Slippin' in the Darkness, by War. Nice song. Tony the sax man intro'd that song every time, and now and then, he intro'd it as "Slippin' in the dog shit". No one EVER noticed. Same thing with a Roberta Flack tube Filling Me Softly with his Song." (We had a pretty girl singing up front) Tony would announce that one now and then as "Filling Me Softly with is Dong". And again, no one noticed. We hear what we expect.

[lowell]

Ok.... so I've been chasing my tail here. I've checked everything a million times but it's still frying the zobel resistor R113. At this point, I've had to disconnect the Bases of Q104/100 to try and locate the issue, because Q100 Vc is only -15v. With bases disconnected the Vc are +/- 43v.

Could someone please tell me what kind of Base voltages I should be seeing for those? I have -15v on Q100 and +8.8 on Q104 bases.

If I know what those should be it'll help a lot. I've tested all the diodes and replaced some of them. They test fine, but I was getting odd voltage readings across them.

Of note is that I have this running through my bulb limiter.

[Jazz P Bass]

Those base voltages sound backwards.

Q100 is on the positive rail, while Q104 is on the negative rail.
Can you post BEC voltages?

R113 is a filter of sorts for the output bases.(I would think not a zobel)

Q100 I would expect to see 1.2 volts at the base.(a diode drop would then put the emitter at 0.6, which is a good base voltage for the positive outputs)
Q104, measure across R136 (15K).

I would hope that you have the output board hooked up or you will never get valid voltage measurements.

[J M Fahey]

Just a typo.

Sometimes I discover a typo on a drawing I have looked at and used many times and never saw before. Why? Because in my mind, I know what circuits look like, and the picture on the page is just an outline for my mental image.

I used to work at a music store, big place, had a number of trucks with painted signs. Their motto was "Everything in music". One of the trucks was somehow inadvertently painted "Everythnig in music". Not sure when it was first noticed, but they decided to leave it that way. I think the store got two calls on it over the life of the truck. We tend to see what we expect rather than what is really there.

I used to tour with a big band, and one song we did was Slippin' in the Darkness, by War. Nice song. Tony the sax man intro'd that song every time, and now and then, he intro'd it as "Slippin' in the dog shit". No one EVER noticed. Same thing with a Roberta Flack tube Filling Me Softly with his Song." (We had a pretty girl singing up front) Tony would announce that one now and then as "Filling Me Softly with is Dong". And again, no one noticed. We hear what we expect.

If you read thisn *quickly*, no big deal.

If you read it slooooowwwwllllyyyyyy , you stumble:

[lowell]

I did not have the PA hooked up. Ok so that's why. So it must be that the PA Ve turns the limiters on enough so that the drivers are biased correctly. Otherwise they're biased way too hot. Correct?

So I reconnected it to take some measurements, with my bulb limiter still in circuit, and my probe slipped and shorted Q100. I now have 1 or 2 shorted output transistors. Will fix that and report back.

Those base voltages sound backwards.

Q100 is on the positive rail, while Q104 is on the negative rail.

Correct - typo.

[lowell]

Ok so the thing is all connected and running without drawing too much current. Have it direct to mains. However, some odd voltage readings but could just be my ignorance.

The main rails are symmetrical when voltage is measured in reference to junction of main filters. However, when measured to chassis ground, they are not. Q100/104 both have +/- 700mv Vbe respectively. Both +/-15v supplies are solid.

[lowell]

Q100 I would expect to see 1.2 volts at the base.(a diode drop would then put the emitter at 0.6, which is a good base voltage for the positive outputs)
Q104, measure across R136 (15K).

30v across R136
45v across R105

[Jazz P Bass]

Ok so the thing is all connected and running without drawing too much current. Have it direct to mains. However, some odd voltage readings but could just be my ignorance.

The main rails are symmetrical when voltage is measured in reference to junction of main filters. However, when measured to chassis ground, they are not. Q100/104 both have +/- 700mv Vbe respectively. Both +/-15v supplies are solid.

You have to observe the 'ground' symbols.
On Page #1: J100 & J110 show a signal ground marked Gnd 0.

The high voltage power supplies can use the mid point of the caps, yes, but to get to chassis ground, you have to have a load hooked up.

And chassis ground is 47 ohms away from signal ground.

[lowell]

Ahhhhh..... so being that the thing isn't pulling too much current, I should connect a load now. I had no idea. Odd because the driver circuitry is all symmetrical around chassis ground in the drawing.

Also, the output for this circuit is via the rails correct? The common point between the main filters is moving up and down with the signal?

[lowell]

Ok connected a load. Should I have symmetrical supplies to chassis ground or not? Does it matter? There is a slight hum through the speaker, but no big deal. The main rails to chassis ground are +/- 54/49

[Jazz P Bass]

Ok connected a load. Should I have symmetrical supplies to chassis ground or not? Does it matter? There is a slight hum through the speaker, but no big deal. The main rails to chassis ground are +/- 54/49

I don't like that difference at all.

Have you checked the Vac ripple, especially on the B- (-49Vdc)?