Hill DX 3000 low power

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I have recently purchased 2 Hill DX 3000 as part of a collection.
The amps were sold as defective.
I have had them apart and checked everything through from the toroid to the transistors.
At the moment the everything seems ok, i mean ive checked the transistors individually and none of them are showing short.

Originally i also believed there was a problem as the amps would trip the breaker i was on when turned on.
But when reading the manual it was obvious that i was just using a 16 amp breaker when i should have been using a 32.

So one of the amps so far fires up without error. As i am using a processor i have removed and bridged the volume pots on the front so that now input volume is controlled from the processor.

But before this i built myself a dummy load from two 1500w resistors that i ordered, although they were only available in 12r so my dummy load is 6r (which im sure is fine as the amp is rated for 2,4,8 ohm loading, also the resistors are very good at keeping their rating).

SO upon loading the amp with a 45hz sinewave at just under clipping, i measure the output voltage with the 6r load to be approx 48v. so correct me if im wrong but, 48/6=8x48=384va

Now this at a 6r load doesnt seem to be up to the rated power of 550w into 8ohm (i expect a higher power for a lower impedance).

So finally my question is......if everything checks out ok on the amp and it doesnt error......why am i getting such lower power outputs, is there something im missing about the transistors, maybe they are damaged i just dont know how to tell.

Any help from this point would be great, i really would love to get these amps up and running as they would run my system perfectly, and well yes they are big and heavy but i like old school stuff. Lots of capacitance, nice big toroid and sturdy cases. Worst case scenario i swap put the amps for some newer types and keep the rest.

Some links to previous work on a similar amp and spec sheet.
hill audio�@DX3000
Download your HILL AUDIO DX3000 user guide or user manual

Thanks for reading
Joined 2010
Paid Member
Just a couple of quesions about your tests:
You say that you measure 48V output and this is just below clipping. Is this a peak voltage reading on a scope or the RMS or Average reading of a DMM?

What tells you that the amplifier clips at only 48V? The power output rating would seem to be about 720W per channel into 6R, so it would need to output around 65V RMS to achieve that.

Could it be that the clipping indicator or the management circuits are part of the problem(s) that caused it to be labelled "defective", assuming you have adequate input level to meet the spec. requirement.
Follow up

So the tests were done using a DMM

I measured 48v on the output when hooked up to the 6 ohm load
i say it is near clipping as the input gain was turned up untill it registered just under the red clip light on the front of the panel.

My osc is down atm so will check again when it is up

but i stiil somehow think the voltage output is too low
Joined 2010
Paid Member
You could be right about your measurement. A typical DMM detects average (simple rectified) AC which assumes a sinusoidal waveform and should read correctly for a 45 Hz signal.

To check that the measurement is unaffected by frequency input, you could use a higher test frequency like 150 Hz and remeasure. You have to consider that something is wrong with the sensing of the clipping level indicator or the measurement method to give an error as large as 30%. An oscilloscope indicates peak levels and this would be a better instrument to check the indication of clipping level. Clipping levels are sensed relative to the rail voltages, so if the rails are say, +/- 95VDC, you might expect clipping to commence at 88V - around 65V RMS output which might even be OK, depending on the actual design. Test the rail voltages to be certain they maintain the ability to supply power for the specified output level. The input level for full power from each channel is clearly specified as 1.55V. What do you measure at the onset of clipping?

The clip sensing appears to be via the circuits around IC1/101 where there is a conventional rectifier bridge and LED for each channel. As this is operational, it seems unlikely there is any problem that is similar in both channels - assuming you tested both channels with the same result.

Bear in mind that if the problems were minor and any DIY could repair it, it is hard to imagine that the amplifiers would be sold off as "defective".
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