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PLEASE match Advice Pass Labs X350.5 (20k) to Hovland HP-100 (2500ohms) Miss-match ???

GUYS / GALS NEED YOUR HELP PLEASE!

A friend said this preamp is outstanding and will sound great with Pass Labs amps and to not get caught up in the specs but the measurements say different.

Pass Labs X350.5 amplifier with input Impedance 30k ohms Balanced or 20k ohms Single ended* 
(*source Pass Labs Manual)  

Hovland HP-100 source impedance 2500ohms* 
(*source Stereophile) 

Guys / Gals, can I used my Pass Labs X350.5 amp with Hovland HP-100 preamp? Has anyone used Pass amps with Hovland pre's. I will be using Magico S5 Speakers and Bricasti M1SE DAC but want it to sound the best it can. Should I just stick with the Aesthetix Calypso pre I was leaning toward before my gut said to go for the Hovland HP-100

Hovland HP-100 Preamplifier: * Output impedance: approximately 2500 ohms or according to Atkinson, Hovland HP-100 (2500ohms) its source impedance was high at 2.4k ohms, rising to 4.3k ohms at 20Hz. The partnering power amplifier would best have an input impedance of at least 47k ohms if the bass is not to sound lean*. The Pass Labs doesn't meet the x10 requirement it is supposed to but it is sort of close when looking at it. What do you guys think? I am not sure what to do but you guys will know what to do?

Stereophile: Its input impedance was a usefully high 100k ohms in the midrange and bass, with just a small reduction to a still-high 86k ohms at 20kHz. Despite the claim that the HP-100 uses a cathode follower output stage, its source impedance was high at 2.4k ohms, rising to 4.3k ohms at 20Hz. The partnering power amplifier would best have an input impedance of at least 47k ohms if the bass is not to sound lean.

Read more at https://www.stereophile.com/content/hovland-hp-100-preamplifier-measurements#YZXZfGLbbL2COkLR.99 https://www.stereophile.com/content/hovland-hp-100-preamplifier-measurements#YZXZfGLbbL2COkLR.99
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almarg
9,670 posts
 
Jmcgrogan2 10-8-2017
I believe that you have those two numbers reversed. The way I read it on the Pass Labs website:
Input Impedance (SE & BAL Kohms) 30/20.

The way that reads to me is that the Input impedance is 30Kohms for SE, and 20Kohms for BAL.
John, I’ve noticed that apparent anomaly in the specs of the Pass .5 amps in the past, and I’m pretty certain it is a mistake in the specs, and what was intended was 20K single-ended/30K balanced.

All of the Pass .5 amps are spec’d the way you stated, but John Atkinson measured the input impedance of the XA30.5 as 20K single-ended/29K balanced. Also, the fact that the .5 amps require a jumper between pins 1 and 3 of the XLR connector when the RCA input is used would seem to indicate that the same input stage is being used for both inputs, with one of its two "legs" being grounded when the RCA input is used, and the balanced input impedance (representing the sum of the impedances between each leg and ground) should therefore be higher than the unbalanced input impedance.

Best regards,
-- Al


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kalali
1,977 posts
 
A constant 250 ohm impedance across the entire frequency range into a downstream 30K ohm impedance should be okay, don't you think? I thought the major swings in the impedance are to
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almarg
9,670 posts
 
Fsmithjack, re the BAT VK-50SE (the reference in JA’s measurement writeup to VK-500SE appears to be an error), given my previous comment you would have a balanced output impedance of 4.6K at 20 Hz driving a balanced input impedance of 30K (or perhaps 29K), which is a ratio of a bit more than 6. You would also have a very wide variation in output impedance over the frequency range (from 414 ohms to 4.6K). Not ideal, and personally I wouldn’t risk introducing a compromise like that.

The Atma-Sphere preamp that was suggested would certainly be fine in terms of impedance compatibility (Ralph’s designs do not have capacitively coupled outputs), but I don’t know if it would provide the warmish sonic character you appear to be looking for.

Regards,
-- Al

jperry
2,444 posts
 
OP,

Reading through this thread it seems that you are reading reviews, listening to advice from others, and looking at specs for components.

My suggestion is that you call Reno HiFi. They have new, used and demo product from Pass. They allow you to demo, and return if not satisfied. Get a Pass preamp and try it in your system.

I don't own any Pass (I have an Aesthetix preamp and amp), but you already have the Pass amp, so I would recommend trying a Pass preamp.

Good luck with your search.

Jim Perry
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