Help Needed Power Amp lacks punch


I just got a used supposedly high power Adcom GFA-5500. Had it run in for a few days and found that this amp has got very weak bass punch. No unusual noise or hum. Got everything but bass punch. Asked the dealer he said it's because the amp is not powered for a few months and it needs time to charge up those hugh capacitors. Asked a technician and he told me it could be a faulty capacitor or maybe also a transitor fault.
I don't know who is right and I hope that someone can give me some advise here.

I would like to know
1. how does faulty cap sounds like?
2. how does faulty transitor sounds like?
3. how long must it takes for a cap to charge up? and can that result in weak bass like lack og power?

Please help. Thanks.
rainchild

Showing 3 responses by sean

In case you didn't know it, you have a Mosfet amp. As a general rule, most Mosfet amps have less "slam" or "impact" than a well designed Bipolar unit. Mind you, not all Mosfet amps are "weak" on bass output, but they do tend to sound softer and more rounded. Part of this is why people say that they tend to sound "more tube-like" than Bipolar's along with a few other reasons.

If you haven't already been doing so, leave the amp powered up 24/7 for a couple of days. I've found that this tends to even out their tonal balance much better / faster than powering them up and using them as needed. If the amp hasn't been run in a long period of time, 48 - 72 hours of continuous power will get you most of the way there. After that, the unit will be pretty much as good as it gets within about two weeks or so. Mind you, these are just my sonic observations, so take them for what they are worth. Sean
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Kgveteran: The 555's were bipolar amps, hence my comments above.

Sugarbrie: While your basic suggestions are good ( heavier gauge cord directly into the wall ), "dirty" AC typically sounds "fuller" than clean AC on the bottom end and harder / grittier as frequency rises. The increased warmth has to do with all of the harmonic distortion of the 60 Hz AC signal itself being further amplified through-out the chain. Cleaning up the incoming AC and then minimizing the ringing that takes place in the equipment itself via replacing slow rectification devices tends to lean the sound out a bit.

Rainchild: If my suggestions above don't give you what you want, you might want to think about modifying your amp. That is, if you like it enough to want to keep it. These amps were notorious for starving the earlier stages of amplification when dynamic swings or sustained high level spl's were taking place. There are several different approaches that one can take to rectify this situation with the two most common being to add massive amounts of filter capacitance and / or install a regulator circuit. You can find the circuit boards for the regulators at this link that i've provided for Audio Xpress aka "Old Colony Sound Labs". Sean
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Big power helps, but the quality of the power is more important. I have seen 75 wpc amps absolutely stomp 250 wpc amps in terms of "punch" and ability to drive difficult loads. As such, i would avoid all makes / models that you mentioned short of the Plinius. Sean
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