Ampeg BA300-210

[ubxf]

I just got one of those amps and the preamp works but not the power amp. I'm going to look at it further in the coming days but wanted to see if anyone here worked on one of those and might have some tips or advice.

 

[ubxf]

After a quick look around i found that one of the speaker leads became unplugged. After re attaching it now i have sound. Unfortunately the sound is low volume and distorted.

 

[emrr]

Can’t see the pdf in my phone but i recall it being very common for Ampeg with insert jacks to have jack failures that would separate preamp from power amp. Always worth making the loop with a patch cable to be sure, if there is an insert loop.

 

[ubxf]

Thanks Doug, good call. unfortunately i still have the same problem.

 

[mjrippe]

Wow, what a beast!  I see tubes with +300v, Class D output amps, vactrol compression, THAT 1606 output driver, and a whole lot more.  Break it into parts.  Check PSU voltages first, note the thermal protection and voltage guidelines on page 3 if you lose sound again.  Then check output of the preamp, balanced line out, insert send, etc. to see if signal is clean at each stage.

Good luck and be careful, there is a lot packed in there!

 

[ubxf]

yes the preamp is fine i get clean sound out of the line out. I'm going to check the speakers first in case they are blown, then i'll follow your advice and go step by step checking voltages. What is lamp1 and lamp2 in the crossover ?

 

[abbey road d enfer]

What is lamp1 and lamp2 in the crossover ?

These are protection lamps. Connected in series with the drivers, their resistance increases in case of overload, so they absorb most of the juice.

 

[ubxf]

Thanks Abbey, so they are like a light bulb limiter . I was reading that their role is to protect the high frequency driver. Right now all i'm hearing is sound mostly from the tweeter so they might be ok.

 

[ubxf]

So the speakers are fine and the amp is almost dead but not quite because when i crank it all the way up i hear the sound through all speakers. I will follow the schematic and check voltages.

 

[ubxf]

power supply

 

[ubxf]

power amp

 

[Tubetec]

Ive worked on a few of the smaller BA series , all else being well suspect the protect circuit , the smarter the protection got the more prone it is itself to weird failure modes, the vactrols themselves are the first suspects to check. Your going to have a few seconds delay before the relay connects the speaker after power up , if it doesnt click in suspect the protect circuit. Sounds like your amp is doing the business only its driving an O/C load .

 

[ubxf]

Great thank you i'll check the vactrols and the whole protect circuit

 

[CJ]

resize pic so i can get more than 1 square inch of chassis on my notebook,

poke around that preamp tube with a meter,

i worked on a similar nightmare a while back, maybe something relevant here>

https://groupdiy.com/index.php?topic=58157.0

it can't be any worse than the Soundcaft Gigrac 600 i am working on now,

 

[ubxf]

Thanks CJ i read your thread and learned a lot. I measured the voltages at J8 on the power supply and got +30V -30V and +18V on the proper pins.So i guess the power supply is ok.
One thing i don't understand on the schematic is the voltages at J1 how does the voltage go from 30V to 42V. I have to troubleshoot the amp pcb but i'm not quite sure where to look first. Should i change Q1,Q2,Q3,Q4. When you said check the vactrol do you mean U5 (VTL5C4)

 

[ubxf]

I couldn't figure out how to fix the amp but since the preamp works well i thought of swapping the amp board for this one
https://www.parts-express.com/ICEpower-200ASC-Class-D-Audio-Amplifier-with-Power-Supply-Module-1-x-200W-326-208
I still have to get the measurements to make sure it will fit inside the chassis