PV 12L and SS Power Amp Question

[2sixR]

I just acquired a PV12 preamp and have heard talk about impedance matching tube preamps with SS amps... I'm a newbie with this stuff... my power amp is a B&K ST-2140 which has an input impedance of 33.2 k ohms... any CJ owners know if these two amps will work together, or do I need to look for another power amp... speakers are KEF 105.1's if that matters in any way... thanks in advance.

[admin]

2sixR,

Welcome to the site, great to have you. I am also a PV12 owner. I think you'll find the PV12 rather forgiving with compatibility and you should have no problems with matching it with a SS amp.

[Ian Millar]

SS power amps typically have an input impedance in the order of what you quote, whereas valve power amps are typically around 100K. Your PV12 doesn't care either way. Just use basic low capacitance interconnects such as Blue Jeans LC-1 and you'll be laughing. The speakers don't affect it. The "talk" that you refer to would be typical intenet nonsense.

[hukkfinn]

The rule of thumb I've heard is that you want at least a 10X difference. Take this with a grain of salt. So, if the preamp has output impedance of 1K ohms, the rule of thumb is, you want the input impedance of the power amp to be at least 10K ohms. Most solid state power amps have input impedance high enough that you never have to worry (50K ohms or 100K ohms). Tubed power amps are even higher (200K, 250K....) so with them you REALLY don't have to worry.

However many people in this hobby consider the 10X concept too lenient / not good enough. With a preamp that has 1K output impedance, they would insist on the power amp having at least 50K or higher input impedance. Or, if the power amp had 10K input impedance, they would insist on very large output coupling capacitors in the preamp. Your PV12 has 2.0uF output coupling capacitor values, so with 33K input impedance, you might be "on the line" in the view of these more conservative audiophiles.

The V-Caps capacitor website has a calculator that you can play with. If you plug in 33,000 ohms for your B&K (on the right side of the page) and 2Hz as your ideal bass frequency (which they basically tell you to use, if you read the whole page) it shows that you want preamp output coupling capacitors with at least 2.4 uF. The PV12's 2uF output coupling capacitors are still probably fine, because the 2hz they tell you to plug in is very conservative. But let us know if you notice problems with lacking bass.

The V-Caps calculator: http://www.v-cap.com/coupling-capacitor-calculator.php

EDIT: I just bought another PV-12 stock unit and found 2.0uF in the output couplers, so I updated this post accordingly.

-Hukk

[joeinid]

Great info Hukk. Thanks!