Question about distortion with Dayton Audio APA150

[Pandaman617]

A friend of mine gave me this amp for free so I could tinker with it and possibly fix it. I know it’s a very cheap amp (I don’t think the Emotiva version was very good either) so I don’t plan on investing anything substantial money wise into it but am now more curious than anything else about what could be causing it’s issues. So if I connect it to a preamp in stereo mode with the low pass set at flat it sounds like it should until the gain is at a little over 1/4, at that point there mids and highs distort like crazy. If I enable the low pass and connect it to a passive sub it seems to sound fine. However I also found if I wire it as Dayton instructs you to for bridged operation no sound is output, while in bridged mode if I wire a pair of speakers like you would in two channel mode sound is than output. Any ideas?

 

[slipperybidness]

When you say you use a pre-amp, the pre-amp has it's own "volume knob", right? How do you have that set?

You may have a problem with your gain structure, driving the amp into clipping. The first thing I would say is, don't turn the amp gain above 1/4. Can you get a reasonable volume keeping the amp "attenuator" (what you called the gain knob) less than 1/4 and controlling the volume from the pre-amp? If yes, then problem solved. Note that the input sensitivity is 1V, so I bet you are driving this amp into clipping with a "hot" signal from your pre-amp.

What happens if you connect your source directly to the amp, cut the pre out of the signal chain, and control volume from the amp attenuator knob only?

Concerning bridged mode--Did you flip the switch from Stereo to Mono? Must be in the Mono setting, not just the wiring. And, in bridged mode, the red/positive wire must go to the LEFT red/positive cxn, while the black/negative must go to the RIGHT black/negative. Is that how you wired it?

 

[Pandaman617]

When you say you use a pre-amp, the pre-amp has it's own "volume knob", right? How do you have that set?

You may have a problem with your gain structure, driving the amp into clipping. The first thing I would say is, don't turn the amp gain above 1/4. Can you get a reasonable volume keeping the amp "attenuator" (what you called the gain knob) less than 1/4 and controlling the volume from the pre-amp? If yes, then problem solved. Note that the input sensitivity is 1V, so I bet you are driving this amp into clipping with a "hot" signal from your pre-amp.

What happens if you connect your source directly to the amp, cut the pre out of the signal chain, and control volume from the amp attenuator knob only?

Concerning bridged mode--Did you flip the switch from Stereo to Mono? Must be in the Mono setting, not just the wiring. And, in bridged mode, the red/positive wire must go to the LEFT red/positive cxn, while the black/negative must go to the RIGHT black/negative. Is that how you wired it?

I’ve tried the preamp at every possible volume with the same end result as well as the gain on the amp. I’ve connected sources to the amp directly with the same result, the only way I can get any sort of remotely clear sound is with the amp barely outputting any sort of volume level. I did some reading into the Emotiva & Jamo versions of this amp and it looks like it’s an issue that has been known to come up here and there. One guy replaced the caps and the gain or volume control and that seemed to work well. My caps look fine with no bulging or obvious issues but who knows.

 

[Pandaman617]

Also I did wire for mono the correct way and it doesn’t output anything with or without the bridge toggle enabled.

 

[lovinthehd]

Sounds like its broken Helpful, eh? Do your skills extend to analysis and repair of such gear, tho?

 

[highfigh]

A friend of mine gave me this amp for free so I could tinker with it and possibly fix it. I know it’s a very cheap amp (I don’t think the Emotiva version was very good either) so I don’t plan on investing anything substantial money wise into it but am now more curious than anything else about what could be causing it’s issues. So if I connect it to a preamp in stereo mode with the low pass set at flat it sounds like it should until the gain is at a little over 1/4, at that point there mids and highs distort like crazy. If I enable the low pass and connect it to a passive sub it seems to sound fine. However I also found if I wire it as Dayton instructs you to for bridged operation no sound is output, while in bridged mode if I wire a pair of speakers like you would in two channel mode sound is than output. Any ideas?

It's their version of the amp that has been sold by Jamo and others- generally a decent amp and made for distributed audio.

When you wired it for bridged operation, did you switch it to Mono? You need to do that.

 

[slipperybidness]

I’ve tried the preamp at every possible volume with the same end result as well as the gain on the amp. I’ve connected sources to the amp directly with the same result, the only way I can get any sort of remotely clear sound is with the amp barely outputting any sort of volume level. I did some reading into the Emotiva & Jamo versions of this amp and it looks like it’s an issue that has been known to come up here and there. One guy replaced the caps and the gain or volume control and that seemed to work well. My caps look fine with no bulging or obvious issues but who knows.

You may be able to "jumper" across a gain pot to effectively remove that from the circuit. Do you know if the gain knob on the amp is a pot? If you do this, that would be the same as if the knob were at full blast, so you would need the pre-amp to start turned down completely, then creep up the volume on the pre.

Be sure you know what you are doing! I believe the pot should have an input, an output and a common. So you would jumper the input directly to the output. If you jumper the input to ground.....you may fry your preamp.

 

[Pandaman617]

You may be able to "jumper" across a gain pot to effectively remove that from the circuit. Do you know if the gain knob on the amp is a pot? If you do this, that would be the same as if the knob were at full blast, so you would need the pre-amp to start turned down completely, then creep up the volume on the pre.

Be sure you know what you are doing! I believe the pot should have an input, an output and a common. So you would jumper the input directly to the output. If you jumper the input to ground.....you may fry your preamp.

Jumpered it and it worked!!! Thanks so much for your help man! I know it’s not an amazing amp but my mom wanted a two channel small system for her bedroom and I had this amp, a NAD preamp, a pair of Mirage Omnisats and a Mirage Omni S8 sub laying around so this really made her and my day!

 

[slipperybidness]

Jumpered it and it worked!!! Thanks so much for your help man! I know it’s not an amazing amp but my mom wanted a two channel small system for her bedroom and I had this amp, a NAD preamp, a pair of Mirage Omnisats and a Mirage Omni S8 sub laying around so this really made her and my day!

So, are you just gonna leave it permanently jumpered, and control volume with the pre?

Glad I could help! Glad you would actually follow advice! Too many people ask for help, but never follow through.

If it were me, I may be inclined to find a replacement pot to remove that one and solder a new one in. But hey, working is working, if it don't look pretty, nobody will see it unless they open it up.

EDIT-- It may be worth hitting that pot with a good shot of DeoxIt (contact cleaner). Usually that is more for a "scratchy volume control", but it is possible a good shot of DeoxIt will resolve the issue.

 

[Pandaman617]

So, are you just gonna leave it permanently jumpered, and control volume with the pre?

Glad I could help! Glad you would actually follow advice! Too many people ask for help, but never follow through.

If it were me, I may be inclined to find a replacement pot to remove that one and solder a new one in. But hey, working is working, if it don't look pretty, nobody will see it unless they open it up.

EDIT-- It may be worth hitting that pot with a good shot of DeoxIt (contact cleaner). Usually that is more for a "scratchy volume control", but it is possible a good shot of DeoxIt will resolve the issue.

I deoxed it before I tried anything. I actually just ordered a replacement pot this morning. I really appreciate all of your help! This forum is literally the only website I trust in terms of audio advice. I used to belong to AudioKarma until one of their members responded to a post I made with a 6 paragraph summary of why upgrading speakers & subs is a waste until you get and I quote “Cable elevators, Audioquest or similar cables (the ones he mentioned were around $5,000 from what I recall and he didn’t like me telling him my 12/4 OFC KnuKonceptz wire that’s $1.85/ft sounds identical) isolation pads for ALL of my equipment, etc” they really drink the Kool-Aid over there

 

[slipperybidness]

I deoxed it before I tried anything. I actually just ordered a replacement pot this morning. I really appreciate all of your help! This forum is literally the only website I trust in terms of audio advice. I used to belong to AudioKarma until one of their members responded to a post I made with a 6 paragraph summary of why upgrading speakers & subs is a waste until you get and I quote “Cable elevators, Audioquest or similar cables (the ones he mentioned were around $5,000 from what I recall and he didn’t like me telling him my 12/4 OFC KnuKonceptz wire that’s $1.85/ft sounds identical) isolation pads for ALL of my equipment, etc” they really drink the Kool-Aid over there

Yup, there are a lot of nut-jobs out there!

At one time, I was working towards a cert as an electronics tech, a few more classes and a test would get me there. To be fair, that is a step back from my job as a chemist.....but modern chemistry really marries classic chemistry and electronics (advanced instrumentation) anyway. I have no problem tearing apart a $1M piece of gear! I "probably" won't break anything worse than it already was.....probably

I have several vendors that say, "you are one of the few customers we would send the parts to let you make this repair"

TLSguy is the real electronics guru around this site.