Pacer 100: slightly distorted, slightly low output?

This forum is for talking about all kinds of Peavey guitar amplifiers.
Post Reply
janah
New Member
Posts: 4
Joined: Wed Nov 30, 2022 1:47 pm

Pacer 100: slightly distorted, slightly low output?

Post by janah » Wed Nov 30, 2022 2:05 pm

Curious if someone here may have some insight? I have never worked on a SS amplifier with an interstage xfmer, so I wanted to pick the hivemind before going further..

https://www.audioservicemanuals.com/p/p ... schematics Here is the schematic for easy reference.

The amplifier has been recapped (recently), output transistors test good (but were swapped for good measure, anyway). Both rails test at a nominal -36/+36 respectively. Cone rattle has been ruled out. The .68 and 1k 5w resistors in the output stage don't appear to have drifted (trying to rule out under/overbiasing). I have another Pacer 100 in working order, and this one's output measured ~15% lower. In addition to being distorted, the output will also "drop out" at low volume, and spring reverb tails get cut off (think: underbiased fuzz pedal).

I think that's all I got.. Maybe one of you folks can supply me with that "a-ha" bit of info I need before I start down the wrong path.

Thanks!

rogue777
Member
Posts: 301
Joined: Mon Sep 14, 2009 7:07 pm

Re: Pacer 100: slightly distorted, slightly low output?

Post by rogue777 » Wed Nov 30, 2022 11:15 pm

Check the 2/35 caps. That is 2ufd at 35Vdc. A forum member mentioned they could be high failure items.

User avatar
Pappy B
Member
Posts: 762
Joined: Sun Jan 31, 2016 2:30 pm

Re: Pacer 100: slightly distorted, slightly low output?

Post by Pappy B » Thu Dec 01, 2022 10:05 am

Double check the polarity of any parts recently installed. Try unplugging the reverb wires from the tank and see if it changes anything.
The more I learn the more I realize how much I don't know.

janah
New Member
Posts: 4
Joined: Wed Nov 30, 2022 1:47 pm

Re: Pacer 100: slightly distorted, slightly low output?

Post by janah » Thu Dec 01, 2022 1:13 pm

rogue777 wrote:
Wed Nov 30, 2022 11:15 pm
Check the 2/35 caps. That is 2ufd at 35Vdc. A forum member mentioned they could be high failure items.
Thanks, this is exactly the kind of knowledge I came in search of! Interestingly, the leg of the 2/35 cap that connects to the drain of the JFET had a solder joint that failed entirely. Putting pressure on the cap to momentarily restore the connection helped a great deal, and I'm sure this was it, though they will be replaced for good measure. Time to inspect each and every solder point now, I suppose.Thanks again

User avatar
Pappy B
Member
Posts: 762
Joined: Sun Jan 31, 2016 2:30 pm

Re: Pacer 100: slightly distorted, slightly low output?

Post by Pappy B » Thu Dec 01, 2022 8:09 pm

While you have your chassis pulled, It would be a good idea to to use some contact cleaner spray on the pots, switches, jacks and any pull apart connectors to include the reverb pan connectors if you haven't done so yet.

The Pacer is a great amp and well worth fixing.
The more I learn the more I realize how much I don't know.

janah
New Member
Posts: 4
Joined: Wed Nov 30, 2022 1:47 pm

Re: Pacer 100: slightly distorted, slightly low output?

Post by janah » Fri Dec 02, 2022 11:11 am

Thanks for the suggestions. Unfortunately, replacing that capacitor did not solve the issue completely, but it did improve significantly. I imagine more of those 2.2uf caps are on their way out, or another component has drifted. More than good enough to use, anyway.

And yes, the Pacer is a fantastic amp, which is why I have two; both with the original squareback eminence. I don't see or hear much about them, which i find weird. Not nearly as much as something like the special 130, bandits, etc. Those who know, know, I s'pose.

related, but does anyone know the function of the interstage transformer? peavey part number is DC-298. are replacements available? would like to rule out a potential faulty xfmer, also.

User avatar
Pappy B
Member
Posts: 762
Joined: Sun Jan 31, 2016 2:30 pm

Re: Pacer 100: slightly distorted, slightly low output?

Post by Pappy B » Sat Dec 03, 2022 10:03 am

If you still have any original electrolytic capacitors that haven't been replaced it would be a good idea to do so. Even if you don't hear a difference it will improve performance. That amp is old enough to have caps that are out of spec, if not completely failed.

I would be surprised if the transformer is bad. Peavey used good transformers.
The more I learn the more I realize how much I don't know.

User avatar
The Guitar
Member
Posts: 44
Joined: Fri Oct 01, 2010 10:54 pm
Location: IN

Re: Pacer 100: slightly distorted, slightly low output?

Post by The Guitar » Mon Dec 05, 2022 10:17 am

Keeping an eye on this as my Studio Pro 50 is in the same boat.

janah
New Member
Posts: 4
Joined: Wed Nov 30, 2022 1:47 pm

Re: Pacer 100: slightly distorted, slightly low output?

Post by janah » Mon Dec 05, 2022 4:10 pm

The Guitar wrote:
Mon Dec 05, 2022 10:17 am
Keeping an eye on this as my Studio Pro 50 is in the same boat.
i don’t think there will be many similarities between these amps. the pacer is a fully transistorized amp while the SP50 uses op-amps and is overall a bit more complex.

User avatar
Pappy B
Member
Posts: 762
Joined: Sun Jan 31, 2016 2:30 pm

Re: Pacer 100: slightly distorted, slightly low output?

Post by Pappy B » Mon Dec 05, 2022 4:34 pm

I would say that a Studio Pro 50 is also old enough to have out of spec or failing capacitors.

Personally, I think this amp is easier to work on than the Pacer. The opamps are easy to replace if one is bad and when you replace an Opamp you have changed out a whole circuit, not just one transistor or other part.

Try cleaning the pots, jacks, switches and connections with contact cleaner spray and one at a time lift out the Opamps, clean the legs and sockets then reinstall them. Make sure you get them oriented correctly. Snap a good picture before you start.
The more I learn the more I realize how much I don't know.

Post Reply