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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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fsmithjack OP
712 posts
 
Thanks guys 

Darn I was all set with the BAT until I read this: 

The BAT's input impedance measured a high 220k ohms, and its output impedance at 1kHz was 414 ohms from both sets of output jacks. This figure rose slightly to 422 ohms at 20kHz, which is a negligible change. At 20Hz, however, the source impedance was a very high 4.6k ohms, which suggests undersized output coupling capacitors, even with the Six-Pak option, which I assume was fitted to the review sample. Care should be taken when mating the VK-500SE with power amplifiers that have an input impedance of less than 10k ohms. The voltage-divider action of its high source impedance at low frequencies and the power amp's input impedance will roll off the low bass.
Read more at https://www.stereophile.com/content/balanced-audio-technology-vk-50se-line-preamplifier-measurements...

One of the guys above smartly stated he thinks the Pass is 30k input impedance - so that is better but still everyone says must be careful with tube preamps and the input impedance specs are great unil 20k.  i just don't want the BAT's bass to roll off. I mean 20k is low so I don't want to go crazy over the numbers but i also want to be smart and set it up properly. Do you think the BAT could be ok? 
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fsmithjack OP
712 posts
 
I prob should have shared a bit more of the article.

Into the Linn Klimax 500, for example, which has a low load impedance of 7.7k ohms, the BAT's response at 20Hz will be down 1.8dB compared with the level at 1kHz. That Jonathan still found the combination to sound fine is presumably due to this being outweighed by other, positive aspects of the BAT's sound.

This rolloff at low frequencies can be seen in fig.1, where the lower pair of traces was made into a 600 ohm load, which is typical of some professional amplifiers and is a switchable option on the Jeff Rowland designs. Into a more typical 100k load (top traces), the LF response is flat down to the 10Hz lower limit of the graph. At the other end of the audio band, the output is -0.3dB at 20kHz, with slightly more audio-band rolloff into the low load. Channel separation was better than 80dB below the mid-treble, but with a rise in crosstalk to -67dB (L-R) and -76dB (R-L), due to capacitive coupling between channels. This will be subjectively inconsequential.


Read more at https://www.stereophile.com/content/balanced-audio-technology-vk-50se-line-preamplifier-measurements...

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kalali
1,977 posts
 
What about an Atma-sphere MP-3 preamp? Output impedance 250ohm from 2Hz-400KHz. No idea how much they go for new or used but just wanted to throw it in the mix.
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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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