Dayton SPA250 Plate Amplifier repair help - diyAudio
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Old 21st June 2014, 08:49 PM   #1
nixit is offline nixit  United States
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Question Dayton SPA250 Plate Amplifier repair help

Hi,
I've been through three of the Dayton Audio SPA250 plate amplifiers over the last three years. This is my third one, and PartsExpress is no longer interested in honoring their warranty.
The failure is always the same; It starts popping. One pop here. One pop there. It can be 10 minutes between pops, or four days, and at any time of the day or night with no regard to source being active or not. Eventually, it just barely works.

I'm driving a single Dayton Audio RSS265HF-4 10" Reference HF Subwoofer 4 Ohm, sealed in a sealed enclosure, using the dedicated sub-woofer output of my Onkyo amplifier to feed the plate.

Q: If anyone has this amplifier, would you be willing to help me identify the two resistors shown in this picture? Specifically, could you open your amp and take some photos/color bands from it?

You'll notice everything is nicely charred. However, I could not find any other evidence of blown components.

Thanks greatly, in advance.
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Old 22nd June 2014, 10:16 PM   #2
SS4927 is offline SS4927  Canada
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Sorry I cant help there but your thread might get more attention here Solid State - diyAudio

PE must get a lot of complaints on those, I read so much bad talk on several sites about Daytons plates that I cancelled an order on one of their 500s. It sounds like good power is there and the built in amp eq combo is great but dependability lacks.

Last edited by SS4927; 22nd June 2014 at 10:19 PM.
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Old 22nd June 2014, 11:06 PM   #3
nixit is offline nixit  United States
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Thanks for your reply. I want to experiment, but I need to know what it was, before I decide where I want to go with it. Beats dropping another $100-130 on yet another one.
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Old 27th June 2014, 02:09 PM   #4
nixit is offline nixit  United States
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Bump. I'd really like to resolve this.
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Old 28th June 2014, 07:56 PM   #5
bonfis is offline bonfis  United States
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Default PE Plate Amp

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Originally Posted by nixit View Post
Thanks for your reply. I want to experiment, but I need to know what it was, before I decide where I want to go with it. Beats dropping another $100-130 on yet another one.
Hi Nixit-
Had the same problem with a PE amp. The board in question contains the soft limit circuit for the amp. The 2 resistors should be marked RS1 and RS2. They are dropping resistors to reduce the +-Vcc for the boards op amp to 15v. They work with 2 zeners that should be marked ZD3 and ZD4. The resistors are probably under rated at 1/2watt. If you replace them go with something larger and also check to make sure the zeners are good. See attached schematic.
Good Luck
Steve
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Old 29th June 2014, 11:06 AM   #6
bonfis is offline bonfis  United States
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Forgot to mention that you can eliminate the circuit altogether by putting in a fixed resistor in place of the one inside photoresistor U2. This resistor is in the feedback divider network and hence controls the amps gain. I think I wired mine for a gain of around 25. Not too critical since there is a gain control built into the amp.
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Old 29th June 2014, 03:14 PM   #7
TMM is offline TMM  Australia
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Damn, i was looking at buying one these amps. Still, this wouldn't put me off buying one. I'd rather buy an amp with a known failure mode than another chinese amp with unknown failure modes.

What are the main rails in this thing? I guess about 50-55V unloaded to deliver 250W into 4ohm? This gives around 0.66W dissipation on those resistors (assuming the schematic is correct that they are 2.4Kohm). I guess it's not unreasonable to them to burn out eventually - they look like 1 or 2Watt carbon resistors.

I guess if they are replaced with 10Watt resistors everything should be apples.

[following pic] has this little guy got toasty too, or is it just soot from the nearby resistor? Which resistor is it in the schematic?

Cheers,
-Tim
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Old 1st July 2014, 02:02 AM   #8
bonfis is offline bonfis  United States
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Originally Posted by TMM View Post
Damn, i was looking at buying one these amps. Still, this wouldn't put me off buying one. I'd rather buy an amp with a known failure mode than another chinese amp with unknown failure modes.

What are the main rails in this thing? I guess about 50-55V unloaded to deliver 250W into 4ohm? This gives around 0.66W dissipation on those resistors (assuming the schematic is correct that they are 2.4Kohm). I guess it's not unreasonable to them to burn out eventually - they look like 1 or 2Watt carbon resistors.

I guess if they are replaced with 10Watt resistors everything should be apples.

[following pic] has this little guy got toasty too, or is it just soot from the nearby resistor? Which resistor is it in the schematic?

Cheers,
-Tim
There were other burned components on my Amp also as well as some fried board traces. That's why I elected to circumvent the whole soft limit board as described in the previous post.
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Old 3rd July 2014, 11:31 PM   #9
nixit is offline nixit  United States
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Bonfis, Thanks so much for your reply.

Can you tell me how you bypassed the soft limit circuit at the photo resistor? Specifically, you stated "I think I wired mine for a gain of around". I don't know enough about this stuffs to understand.
- Can I eliminate the heat shrink tubing around the photo resistor?
- Does eliminating the soft limit circuit create any problems?
Anything more detailed would be wonderful.

For giggles, I went and bought another Dayton SPA250 plate amplifier. I really want to identify these blown resistors, and probably that diode as well. Otherwise, I'll work on repairing my existing plate amp. I really want it to work safely, and forever.

Do you think eliminating the ground pin off the power plug may have created a problem?

Last edited by nixit; 3rd July 2014 at 11:33 PM.
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Old 4th July 2014, 02:22 AM   #10
bonfis is offline bonfis  United States
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Originally Posted by nixit View Post
Bonfis, Thanks so much for your reply.

Can you tell me how you bypassed the soft limit circuit at the photo resistor? Specifically, you stated "I think I wired mine for a gain of around". I don't know enough about this stuffs to understand.
- Can I eliminate the heat shrink tubing around the photo resistor?
- Does eliminating the soft limit circuit create any problems?
Anything more detailed would be wonderful.

For giggles, I went and bought another Dayton SPA250 plate amplifier. I really want to identify these blown resistors, and probably that diode as well. Otherwise, I'll work on repairing my existing plate amp. I really want it to work safely, and forever.

Do you think eliminating the ground pin off the power plug may have created a problem?
Hi Nixit-
I will take a look at the specific changes I made some time this weekend and get back to you with the details. To help me help you a few questions: do you have the tools to remove and replace soldered components, can you read schematics, can you measure resistors?

I can't see any way that removing the ground pin from the line cord could cause the defect.
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