How hot does your plate amp run?

[bossman]

Does your plate amp run hot? The entire plate on my Yung SD500 amp is pretty hot (almost hot enough to be uncomfortable to hold your hand on it). I am not even pushing it hard - this is just using it at a low listening volume.
Just wondering if this is normal operation or is there something wrong. I thought the plate amps were supposed to be very efficient.

[Ryan A]

Mine runs relatively cool. It's only the 200 watt model though.

Is it located in an enclosed space or can it get airflow? What kind of load is it running?

[byacey]

Two things will cause heating at low power levels, RF oscillation or over bias on the output transistors. I would suspect the bias first.

[67baja]

My yung 500 also runs hot as you described as well. No problems with it but it is hot to the touch.

[bossman]

I cut out the back of my TV stand and mounted it to the back of it (should be equivalent airflow to mounting it in a subwoofer box). The amp is hot even at idle (I found this out because it didn't go to sleep mode after I turned off the receiver and left for an hour - the light was still green and the plate was hot). I only have a single Table Tuba connected to it so I am sure I am not overloading it.

byacey, what would cause the overbias? Poor design, or defective components?

67Baja - does your amp auto turn off feature work? How long before it goes to sleep if it's working?


I guess this is seems to be normal operation if 67Bajas runs hot also. Anyone else with a hot running plate amp? This is my first plate amp and I found it strange that it would be so hot with minimal power output. The heat this thing is generating I would expect if I had it pounding for 30 mins+.
This amp is advertised as being cool running and having excellent efficiency.
http://www.parts-express.com/yung-sd500 ... t--301-512

[Ryan A]

Just FYI the auto shutoff on mine works fine. Guessing it takes about 10-15 minutes.

I wonder if there's some type of constant signal going through the inputs. After it's on , you might try disconnecting the inputs and see if it will auto shutoff after a while.

[byacey]

Bias is a small idling current flow through the output transistors. It's purpose is eliminate crossover distortion by keeping the transistors always conducting slightly at idle with perhaps 20 to 50 ma of current. If the bias is too high the transistors get hot because they are idling with a higher current than necessary.

On discrete amps of any reasonable quality this is adjustable with an internal control. I've seen some Hi-Fi amps that ran hot as a toaster, having the power output stages contained in a block module, basically a large integrated circuit. In these the bias is set internally and is not adjustable. These are basically engineered to cook itself and the surrounding components to death over time.

I'm not very familiar with any plate amps as I haven't worked on any more recent than 25 years ago, so I can't say if it might be adjustable or not.

DC offset could be another potential cause of heating. Measure DC voltage between the + and - speaker output terminals on the amp with the amp on and the speakers disconnected. Ideally this should be zero with no signal input, but up to 5mv one way or the other isn't uncommon on a properly functioning amp.

[67baja]

My amp goes into sleep mode after about 15 minutes, but there is a loud thump through the sub when it goes to sleep.

[bossman]

Ok the amp now shuts off after some time. The only thing I changed was to plug it into a different power outlet (I moved it to the same one that the receiver is plugged in to -it was previously plugged in to one on an adjacent wall since I didn't have enough outlets available). The amp is still running hot when its on, but at least it now shuts off. Maybe there was an issue with the power on 2 different circuits causing a signal as Ryan suggested.

byacey - I measured the DC offset as you suggested and it is 3mV. I don't see any type of adjustments on this amp. I don't think its designed to be tweaked or repaired - probably just a low cost unit.