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PostPosted: Sun Mar 12, 2017 11:19 am 
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I am looking for a quality high input impedance ss power amp to be driven by a passive preamp. I'm looking at the quad 405 but I was wandering if anyone has found any good quality modern amps that are a good match for passive pres?


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PostPosted: Sun Mar 12, 2017 12:34 pm 
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What is the output impedance of the passive pre?


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PostPosted: Sun Mar 12, 2017 12:51 pm 
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It's zero at max volume but probably somewhere around 100 ohm at average volumes.


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PostPosted: Sun Mar 12, 2017 2:06 pm 
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A hundred ohms output impedance for a preamp is actually quite low, even for an active preamp. My active preamps have up to 300 ohms output impedance and I drive 10 kOhm input power amps with no issues.

If your figure is accurate, I don't see you having an issue with most any power amp, at least impedance-wise. And that includes pro amps, which typically have a 10 kOhm impedance.

The issue may be the gain of the power amp, since it will have to supply the gain that the preamp does not supply.

The Quad 405 is a good choice because it has high gain: 36 dB, if I remember correctly. Most of the pro amps I use have 32 dB gain, also fairly high. I can recommend the Lab-Gruppen IPD2400 and the Yamaha P7000S. Both have fans, but those of the first are not audible at further away than 1 foot and in the case of the second, well the fans have actually never turned on, although like many audiophile amps the case gets warm.

I mention these amps because they are not expensive and because I find their audio quality comparable to many consumer models at two and three times their price. I'm sure there are many other viable options—again, if your preamp does really have an output impedance of only 100 ohms.


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PostPosted: Sun Mar 12, 2017 2:14 pm 
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Quote:
It's zero at max volume but probably somewhere around 100 ohm at average volumes.


That cannot be correct. What passive are you using.?

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PostPosted: Sun Mar 12, 2017 4:17 pm 
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My mistake, you're right, I misread. The tape out is 100 ohm. The buffered out is 250 ohm. The passive out is not listed, it just says zero at full volume and varies with volume.

The model is a McCormack tlc-1, user manual is here
http://www.mccormackaudio.com/manuals/tlc1man.PDF


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PostPosted: Sun Mar 12, 2017 4:23 pm 
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Yes, you need a high gain amp to compensate for no preamp gain.
The only purpose of passive preamp would be extra connectivity.
Try professional JBL MPX600, you may not need a preamp after all when you compare quality with and without, unless you run Phono input.
But then, there are turntables with pre-amplification already built-in, for use with Line inputs.
Pioneer PL-12D II comes to mind, some versions, at least.


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PostPosted: Sun Mar 19, 2017 9:01 pm 
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I use a Plinius amp with a TVC line stage. 47K and up to 38 dB gain, using balanced XLR.


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PostPosted: Mon Mar 20, 2017 2:01 am 
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I used Bryston amps with a TLC and I had no problems.


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PostPosted: Mon Mar 20, 2017 2:10 am 
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malthuse wrote:
I am looking for a quality high input impedance ss power amp to be driven by a passive preamp. I'm looking at the quad 405 but I was wandering if anyone has found any good quality modern amps that are a good match for passive pres?


Its the parasitic capacitance in the input stage of an amp that requires the current.

Look for amps that have jFET's or tubes in the input stage - these have low capacitance.

Amps with bi polar transistors in the first stage can be more difficult to drive.

.


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PostPosted: Mon Mar 20, 2017 2:27 am 
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I have an older Jeff Rowland amp which has user adjustable input impedance settings, maybe the new ones do to?

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Collecting vintage tube Pilot (Pilotone) HiFi gear.


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