Aragon 8008ST runs hot right side with certain speaker wire @4ohm

[siackerz]

My Aragon 8008ST has had trouble with the right channel, specifically with heat and on 4ohm speaker (runs fine 8ohm speaker). At one point it was rebuilt and had the output transistors on the right side replaced. After this rebuild it was still running hot on the right side. I had the same shop check the bias and they said it was something on my end.

I did some troubleshooting and tried changing the speaker wire from my Straight Wire Rhapsody 3s to something generic. It went back to normal temps on 4ohm speaker. Using that same Straight Wire cable on 8ohm speaker results in normal temps. I also found changing it to the slightly lower Straight Wire Monster S had the right side still heat up but slightly less than the other straight wire cable.

This doesn't happen if I use the same speaker wire on other amplifiers (tested on 4004 mk1)

Speaker wire tested with:
Straight Wire Rhapsody 3 Spade
Straight Wire Monster Spade
RCA generic speaker wire 12awg?

TLDR: With the certain speaker wire, the amp works perfectly fine on an 8ohm load, but with a 4ohm load the right side heats up a lot. Changing speaker wire to something generic makes it run normal temps on a 4ohm load.

Any ideas on why this happens?

 

[chazix]

Any ideas on why this happens?

The case certainly seems to scream for a check whether the amp is oscillating. Got an oscilloscope, or a friend with one?

Welcome to AK, BTW.

 

[egellings]

My Aragon 8008ST has had trouble with the right channel, specifically with heat and on 4ohm speaker (runs fine 8ohm speaker). At one point it was rebuilt and had the output transistors on the right side replaced. After this rebuild it was still running hot on the right side. I had the same shop check the bias and they said it was something on my end.

I did some troubleshooting and tried changing the speaker wire from my Straight Wire Rhapsody 3s to something generic. It went back to normal temps on 4ohm speaker. Using that same Straight Wire cable on 8ohm speaker results in normal temps. I also found changing it to the slightly lower Straight Wire Monster S had the right side still heat up but slightly less than the other straight wire cable.

This doesn't happen if I use the same speaker wire on other amplifiers (tested on 4004 mk1)

Speaker wire tested with:
Straight Wire Rhapsody 3 Spade
Straight Wire Monster Spade
RCA generic speaker wire 12awg?

TLDR: With the certain speaker wire, the amp works perfectly fine on an 8ohm load, but with a 4ohm load the right side heats up a lot. Changing speaker wire to something generic makes it run normal temps on a 4ohm load.

Any ideas on why this happens?

It could be that the amplifier is marginally stable and may break into oscillation under certain conditions.

 

[damacman]

The speaker wire may be high in capacitance... IE - Polk Cobra Cables ...

 

[siackerz]

The case certainly seems to scream for a check whether the amp is oscillating. Got an oscilloscope, or a friend with one?

Welcome to AK, BTW.

I do not have/know anyone with an oscilloscope. Is it bad to keep the amplifier running as is? or should I look into it?

 

[PF Sound]

I do not have/know anyone with an oscilloscope. Is it bad to keep the amplifier running as is? or should I look into it?

At least run it without the cable that's causing the issue. Some of those boutique cables try to add capacitance/inductance/whatever to color the sound. In this case your amp may be teetering on the edge of an issue & the cable is doing just enough to exacerbate it.

 

[chazix]

Is it bad to keep the amplifier running as is?

I think it's definitely bad to run it with any output hookup that makes it run hot.

It's sorta, kinda, probably OK to run it with hookups that don't provoke the problem. For sure it would be better to ascertain whether it's an oscillation stability problem, and correct the problem if so. But that is a seriously tricky challenge - pretty much impossible, if the symptoms don't show up at the service shop. Wish I had a more positive outlook, but that's how it looks to me at this point.

 

[Blue Shadow]

I do not have/know anyone with an oscilloscope. Is it bad to keep the amplifier running as is? or should I look into it?

That was your opportunity to say “Anyone in my area with a scope that might be able to help me out? “ Heck you might have an aker a few miles away that could scope it for you. I got a scope but would need to twist dials to fine any oscillation. Still learning what buttons to push, too.