can a preamp influence how hot a power amp gets?

[mufster]

I am not sure if I am imagining it, but when using my hitachi hca-6500 preamp with my hma-6500 power amp i did not notice my power amp getting very hot. However, I swapped the preamp for the preamp output of my Kenwood KA-1100D and since I did, it feels like the power amp is hotter but I am still playing it at the same volume level. Not the volume knob setting as the Kenwood is quite powerful, but the volume level I can pick up using my ears as the gauge. The volume on the hitachi would be at about a quarter of the full. The volume on the Kenwood would be about a tenth of full.

So can two different preamps make the power amp run hotter than one another?

Paul

 

[petehall347]

the hotter one might have more bass .

 

[mhardy6647]

... or perhaps there is some DC offset from the preamp that is causing the amplifier to work overtime (which is sort of the same as the previous response... but a tad more pathological).

Check the preamp for DC offset at its outputs if you have a DMM (and the inclination).

 

[g..v]

There should be no difference. One preamp may have a different taper in the volume control, or just produce a higher output voltage, but the real test would be to have a accurate way to measure the actual power output of the power amp. Anything else is speculation. Close only counts in horse shoes and hand grenades.

The class of amplifier may be an indication of how hot it may run.

 

[slow_jazz]

Shouldn't make a difference.

 

[whoaru99]

By ear isn't a good way to judge something like this.

3dB difference, which is twice (or half) the power, is just a small change in apparent volume.

 

[Pio1980]

... or perhaps there is some DC offset from the preamp that is causing the amplifier to work overtime (which is sort of the same as the previous response... but a tad more pathological).

Check the preamp for DC offset at its outputs if you have a DMM (and the inclination).

This.

Also, knob position will be determined by gain of the pre vs source level and perception of the listener at the time.

Sent from my SM-N900V using Tapatalk

 

[whoaru99]

I saw some mention of a direct/capacitor input switch.

If set on "direct", wouldn't changing to "capacitor" either confirm or refute DC offset from the preamp?

If already set on "capacitor", is DC offset from a preamp still a factor of consideration (for the symptom)?

 

[Billy Dio]

The pre-out voltages might be drastically different, and I'll bet the older unit has a weaker output. It's no different than car audio head units that typically have adjustable gain for sub outs in addition to the amplifier having it's own gain. If amplifier gain is at say 2v, and you crank the head unit's gain up as far as it'll go, the amp will get louder quicker and probably clip the sub before the head unit powered speakers get even moderately loud, whereas if you set the head unit's gain low, the amplifier's sound will be able to scale better with the rest of system and won't be driven as hard.

In your case, I suspect the Kenwood has a much stronger volt pre-out and thus is driving the amp board harder, quicker, (and maybe S/N ratio is a factor). This is one of those scenarios where having a selectable input sensitivity would be beneficial i.e. .775, 1.0, 1.5V

Also, if one pre-amp produces sound in a non-selectable fixed range like midrange and overly colors it (looks like the 6500 only has Bass and Treble pots) or it's fixed setting is the equivalent of having 1khz at a +setting vs. one that leaves it flat, it might sound louder at lower volume position vs. the other that might need more gain to sound the same. If you are really worried about it, suppose you could add a resistor or something (someone correct me if that's not possible).

 

[JoeESP9]

Capacitor coupled outputs can't pass DC. Neither can transformer coupled outputs.

 

[mufster]

Thanks for all the responses, of which I admit some went over my head. I have the power amp switch set to Condenser coupling. I think I will swap it back to the hitachi preamp as this is the matching pre. I am concerned with the heat.

Thanks again.

Paul

 

[JoeESP9]

Condenser (capacitive) coupling means there is a roll-off in the extreme low end. This is because capacitors have a limitation with the lowest frequency they will pass. They will not pass DC regardless of value. The value of the coupling capacitor is chosen so that the roll off is below any audio frequency (>20Hz).

So, if you are experiencing excessive heat in your power amp it can't be DC from the preamp that's causing it. Capacitive coupling assures this.

 

[mhardy6647]

Condenser coupling will block any DC from reaching the power amplifier (as long as the coupling "condensers" aren't shorted).

 

[JRhoBurton]

It might be possible that one preamp is oscillating at ultrasonic frequencies. Probably not, if it's bad enough to create much heat, it would probably have fried your tweeters.