Ampeg PB800 part

[BassSpinner]

Hey, hello, I was wondering if you can help me. I have this part from a Portabass amp, that was tested in two more PB800. This particular piece, when the amp gets a little warm, starts to make crackling sounds. Do you know if there's a part number or name? Or where I can get it?

 

[popcat]

That appears to be the power amp itself (class-D), which the 2003 manual refers to as Micro Dynamic Technology (MDT).

 

[BogeyBass]

Doesn't seem to have much ability to get rid of heat. Sounds like heat is it's enemy.
If it's still working, I couldn't tell you if it's gonna be the same issue with a " new" unit.

Looks like a lost cause, or the issue is with the actual thermal design of the amp. Not sure if it's more a cooling issue with your fan. Or just a poor design.
Class D crackle smackle

How to improve thermal issues in what seems a potted case is beyond me. Does that case open and can you see components tied to the case for cooling.
Might be more a thermal compound that needs to be replaced. Or vent the unit better.

I've searched like mad and cannot find a schematic or parts. Was hoping it's not proprietary part. But possibly a module from another manufacturer.

 

[beans-on-toast]

Here are the schematics.

[Invalid or Expired Link Removed]

You are looking at the modulator board. It can’t be fixed, if it indeed has an issue, and you won’t find a replacement. Ampeg bought this part from an undisclosed third party. Check that the connectors are mating well to the posts, that there is no oxidation.

 

[BogeyBass]

Looks like they used same pcb for PA use so you mind find a dead pa and steal the modulator.

Looks like 2 revisions from posted schematic. Could be more.
One resistor change for the limiter/ over current sense circuit. R33
Maybe check your board. Doubt it's the issue. There is jumpers for the limiter on the analog side going to modulator pin 1 . One is for bass the other PA. Look at your jumpers.
Hell try the pa jumper at this point

I'm sure you've checked the modulator power pins for 15 volts. No over voltage/undervoltage

You got crakles with higher heat, who knows. Needs more cooling. Potting the modulator seems dumb. Must be protecting the amazing crackle technology lol

For all you know it's just a international rectifier chip. Gooped inside a overheating potted case. Put a mini fan on the modulator worst comes to worse. You'd think they tied to the metal side of the potted case for cooling

 

[agedhorse]

Potting assemblies like modulators is commonly done to improve the stability by using thermally conductive potting compound. This helps insure that the components thermally track each other more uniformly.

Does a known good modulator from one of the other units solve the problem?

Some Ampeg service centers may have these parts still available as old service stock, I would consider calling around to see.

 

[Calebmundy]

I have an ampeg PF800 that I couldn't rely on for gigs-it would cut out once it started getting warm pretty consistently. I can't use it, and I don't feel like I can sell it as a working unit. If that doesn't sound like the problem you're trying to fix, I would be happy to sell it to you for crazy cheap for the parts. I'll re-up my supporting membership to sell it through Talkbass, if that sounds helpful.

 

[Bass 45]

I have an ampeg PF800 that I couldn't rely on for gigs-it would cut out once it started getting warm pretty consistently. I can't use it, and I don't feel like I can sell it as a working unit. If that doesn't sound like the problem you're trying to fix, I would be happy to sell it to you for crazy cheap for the parts. I'll re-up my supporting membership to sell it through Talkbass, if that sounds helpful.

The op has a PB800 from the mid 2000’s. Different amp

 

[popcat]

As Beans pointed out, not much you can do with the module except clean the pins or look for a replacement. There *could* be a tin-whisker issue with the connector pins where they grow dendrites that can cause intermittent shorting, so inspect inside the female pins on the module as best as you can. But, it is most likely an internal component breaking down with heat.

Or, do a google search for Jeff Baker and ask him.

 

[agedhorse]

As Beans pointed out, not much you can do with the module except clean the pins or look for a replacement. There *could* be a tin-whisker issue with the connector pins where they grow dendrites that can cause intermittent shorting, so inspect inside the female pins on the module as best as you can. But, it is most likely an internal component breaking down with heat.

Or, do a google search for Jeff Baker and ask him.

The PB-800 was pre lead free solder for SLM so there's not going to be any tin whiskering.

In fact, even for lead feee solders, it's VERY uncommon because of the typical pcb design rule geometries used in bass amp products, and the solder alloys and processes used.

 

[popcat]

It's not about the solder, it is the plating on the connectors.

 

[BassSpinner]

Hey, hello, my dear friends, I will check every post. I was wondering about the part in the picture, if any of you guys had the part number. I took it out and put it in several PB 800's that were working without problems, and as soon as I connected this particular part the other amps and started to do the crackling sound after about 4 minutes. That is why I asked for this part in particular. Mr. Calebmundy, if you do not mind, send me the value of the parts or the whole thing to see if I can purchase it from you. Thanks to everybody and keep on playing, be safe.

 

[agedhorse]

It's not about the solder, it is the plating on the connectors.

The pitch on virtually every tin plated connector that is used in the audio industry is WAY too large to be a problem with whiskering IME. We don't use fine pitch connectors, at least not in the analog MI amps side of things.