Impedance matching

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Glory_Morris
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Impedance matching

Post by Glory_Morris » Tue Feb 01, 2005 11:58 am

Here's the situation...I have a Traynor YGM-3 amp which produces only about 15-20 watts with an 8ohm extension output. I need to amplify this for live shows to about 100watts. I know, I could always just buy another amp, but this amp sounds really REALLY good.

I've found a couple power amps that would do the trick, like the ART SLA-1 100watt amp. Its input impedance is 22kohm. Should I just put a resistor on the head's extension output to match the input impedance of the power amp? Or is there some other solution? Should I even bother? Thanks in advance.

puffpastry
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Re: Impedance matching

Post by puffpastry » Tue Feb 01, 2005 12:52 pm

Should I just put a resistor on the head's extension output to match the input impedance of the power amp?
I'm not 100% sure that I understand the question--are you wanting to run out of the 8-ohm output into another power amp?
If so, the answer is no--because you're dealing with more than just impedance between devices here, you're also dealing with a power stage.

Obviously the best scenario would be to utilize some sort of line output. As you may realize, though, the sound of your amp has a great deal to do with the output stage, so you might miss out on some of the characteristic that you want. Assuming that this is a tube amp, the output transformer helps generate a great deal of the character that you associate with it (this is especially true in older models).

I don't know if this helps...

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Glory_Morris
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Re: Impedance matching

Post by Glory_Morris » Tue Feb 01, 2005 1:11 pm

I suppose some clarification is in order:

Its only a 15watt tube amp, made in '73. The originals were combo amps (speaker built in) but this one appears to be modified. the serial number on this amp matches a combo, buts its in a Traynor reverd head unit. So it looks like a normal Head, no speaker. Looks like it was gutted and outfitted in this new shell. Anyway, it needs an extension cab to be used. At 15watts, it can't compare to the rythm guitarist's 80 watt tube amp. It would be easy I suppose to just get another head, but I want to use this one. So, I figured I could use a Power Amp of some sort to amplify the output of the head to compete better at say 80-100watts. I found such a power amp (ART's SLA-1 Studio Linear Amplifier) but its input is 22k ohms. The extension output on the head is 8ohms. So I assume I need to match the impedance somehow, and I guess I need to do this without replacing the transformer. I thought maybe a simple resistor on the extension output would do this, but I'm not sure.

The basic problem is this: I need this head to be louder. I need it to compete with 80watt amps, if possible. I don't know if I should even be using a Power Amp. Maybe there's some way to modify the head itself to be louder...I dunno. Short of mic'ing the thing, I would think there'd be a solution.

In all reality I guess to make this amp 2x as loud we'd have to bump the power to 150watts. If the rythm guitarist is only at 5 or 6 on his volume knob, then he's probably only pushing 50 or 60 of the available 80 watts (guessing) and my 15watt amp should compete ok with that, at full volume. But, at full volume all the time I would think I'd be replacing tubes like a madman. Since I've already blown 3 tubes.

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Re: Impedance matching

Post by puffpastry » Tue Feb 01, 2005 2:33 pm

Hmm...
I think the safest, most cost-effective solution is going to involve mic'ing the cabinet.

I think I understand the direction you're pointing to with this, though--you want to use a resistor as a power soak, and then, instead of running the output of the power soak into the 8-ohm load, you want to run it into the input of another power amp--correct?

You know, I personally don't care for power soaks--I think they tend to weigh down the amplifier's tone, and they're resistive loads, not reactive (like a speaker). That's merely an aside, though.

What about using something like a THD Hotplate? I think those are reactive loads, and behave more like a speaker does in terms of loading.
I can't think of any reason off the top of my head why that wouldn't work...
(I could be wrong, though--it wouldn't be the first time. I would get a second opinion just to be sure.)

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Re: Impedance matching

Post by KennyLusk » Tue Feb 01, 2005 3:09 pm


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