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Old 7th May 2012, 05:55 PM   #1
xtaljo is offline xtaljo  United Kingdom
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Default Integrated Amp as Preamp and Subwoofer amp

I am building two valve monoblock power amps to drive my speakers as I like the valve sound. I plan to use the preamp output on my Arcam A75 to drive the power amps. Is there a way of using the power output on the Arcam to power a subwoofer?

The problem is the volume control on the Arcam will determine the input level to the power amps and the subwoofer simultaneously. I will need to put a voltage divider between the preamp and power amp inputs because the sensitivity of the power amp is too high to accept the output from the preamp.

Can I use the same trick to get control of the subwoofer output ie some kind of attenuator between the power output of the Arcam amp and the subwoofer.

I realise this is far from an ideal solution but I don't really want to buy a separate subwoofer amp unless I really have to.

Any ideas/advice very welcome.
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Old 7th May 2012, 11:23 PM   #2
chrish is offline chrish  Australia
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That sounds like a reasonable solution.

If it were me, as the mono blocks sound like they are the most sensitive, I would put a volume control on them, even if it is just a trim-pot. Adjust them so that they match the sensitivity of the Arcam/sub combo. That way you only need one voltage divider (attenuator) in the signal path. Besides, once you adjust that trim pot, you won't need to touch anything and your master volume will work correctly.

Cheers,

Chris
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Old 8th May 2012, 05:58 AM   #3
chrish is offline chrish  Australia
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Further to my post this morning, if you do not have a crossover for your sub, something like this works very well Linkwitz-Riley Electronic Crossover

I am using that crossover to split my tube powered main speakers to some solid state powered woofer boxes. If you don't want to put a volume knob on the new mono blocks, the crossover mentioned in the link has a trim pot to set the sensitivity. If you don't use a crossover, the volume on the monblock can be a trim pot as it only needs to be set once, or you could mount a pot on the back without a knob right next to the RCA input.

Cheers,

Chris
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Old 8th May 2012, 06:22 AM   #4
xtaljo is offline xtaljo  United Kingdom
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Many thanks for your very helpful suggestions Chris.

Cheers,
John
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Old 8th May 2012, 04:09 PM   #5
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If I understand your original post correctly, you want to use the Arcam A75 preamp as a full range preamp to feed a tube power amp, and you want to use the power amp as a subwoofer amp, implying that only low frequencies are to be amplified. The way to do this is to use your tape monitor loop. Basically, you Y the tape monitor output so that one connection goes to your tube amp, and the other goes through a sub low pass filter which of course will need its own level control as you have pointed out, then connect that filtered signal back to your monitor input.
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