The favored standard seems to be that from the preamp to the amp, the impedance ratio should be no less than 10x with >=100x [seemingly] being most common. In the case of the BHK-250, you have an input impedance of 200K ohms (balanced). The BHK Pre [for example] shows <100 ohms output impedance. Which meets the more than “10 times”. The more the better? The BHK-300 is 100K ohms input impedance (balanced) and the BHK-600 is 200K ohms input impedance (balanced).
So taking the BHK-250, if we say “100” for the BHK Pre, this becomes a 2000x differential. Where this is going - considering a preamp who’s balanced output has an impedance of 40 ohms (lower compared to 100 but doesn’t seem like much when contrasted by 200K). Which means a 5000x differential. 2000x to 5000x is no longer a small-ish gap. Since we’re already in the 4-digit range, does that even matter? What positives or negatives would that introduce? Or is it a case of -in the overall scheme-, it really doesn’t matter? Part of the concern stems from some ‘distant recollection’ of impedance that is excessively different, may begin to act like a high pass filter - if yes, it would be an undesirable side effect. Out of curiosity, if that same preamp’s balanced output was 2K ohms or 20K ohms - would there be any impact to the resultant audio, given same ‘volume’ level of the preamp? Or does that become more of a cable length consideration?
Not sure if this is anecdotal, but have heard commentary to the effect that higher ratios (preamp->amp) may offset [some] differences in cables when it comes to sound coloration (compared to lower ratios, where cable ‘color’ may be more evident). Anyone happen to know if there’s any truth to this?
To answer the question ahead of time: “why not just go the route of the BHK Pre” - being a “regular volume surfer”, any audible ‘click’ that may be heard through the speaker or interruption in audio would be beyond agitating.
You’re way over-thinking the impedance matching question. 10X and you’re good to go.
And if you can’t live with a faint click of the BHK, there’s the Stellar Gold preamp.
Well, I have a preamp that is supposed to be seeing 50K input impedance from the power amp, but it’s actually seeing 20K. Sounds marvelous, with no discernible effect on the sound.
Thank you, thank you, thank you! Those were the responses that I was looking for. Will happily accept “over thinking it”.
Did take a brief look at the Stellar however need a minimum of 5 inputs: 2 x XLR and at least 3 RCA inputs (optimal is 4 RCA inputs + 2 XLR). The primary factor is interest in a more ‘holographic’ or ‘spotlight’ presentation of the soundstage (for lack of a better way to express it). That aside, the BHK Pre remains an absolutely awesome preamp (would strongly recommend), last experience - it just wasn’t a “for me” option. Granted, maybe with some tube rolling, different fuses?, etc. - maybe it could be, but that’s a gamble vs something that is natively closer to desired. At this juncture, rather set on pursuing another path. Who knows, maybe when a new version of the BHK pre arrives will revisit? Despite a strong personal preference for PS Audio products, there may be some things that don’t sufficiently align with preferences at that time and that’s “OK” - happy to revisit again, down the road.
Interesting, last time I listened to it - heard “clicks” (albeit faint) through the speakers and what seemed like a slight interruption in the audio output. Maybe some early(er) revision?
There are audible clicks at some point in the mid 20’s as well at 52-53 on the read-out, this is well documented.
I hear these clicks using XLR inputs. The BHK Pre is a superb preamp and a exceptional value IMO.
It has been a gem with five different power amps for me. I’m not getting rid of it soon.
Yeah, the clicks would be highly bothersome. If there weren’t clicks and could figure out tubes to create a more ‘spotlight’ soundstage - I’d absolutely purchase it, without hesitation. I would really prefer to have the BHK pre.
There is one click at 25, whenever going from less than 25 to over 25, and when going from over 25 to under 25. This is one normal click that is part of the way it was biased. The other click at 52/53 is a click that I normally don’t get to, as the volume level is loud enough before I get that high that I simply don’t reach that high a number.
But from 26 to 27 to 28 to 29 to 30, etc. I do not hear clicks with XLR connectors in the path between pre and power amps.
I also have a Conrad Johnson tube preamp. That box clicks at the preamp itself with every click of the volume button up or down. The Grimm MU2 that I am borrowing also clicks at the device itself when changing volume up and down.
-IF- it’s just those two ‘points’, then that would be more livable than what I recall. Asserting that the click issue a non-issue, anyone have a notion around tubes that lend the music towards more accuracy and a sense of ‘spotlight’ such that nuance details can be more readily picked out of the music? My previous perception was that the BHK pre was obscenely delightful when it came to musicality but recall it glossing over some of the smaller details. Starting to wonder if a different set of tubes would reign that in…
In my BHK amp, I’ve got SR Pink fuses and matched Seimens PCC88/7DJ8 that were produced in Germany (circa 1970s, IIRC). The difference from the stock tubes raised the bar for ambient detail with less coloration - as expected, but soundstage would stem from the preamp (or DAC if the preamp is notionally transparent). I’ve heard good comments about the Telefunken tubes in the BHK pre, but not sure if they would push the BHK pre closer to being ‘transparent’ in the chain. (It’s stock sound is absolutely wonderful, just not the desired end-state).
(After a good libation, I may come back around on the BHK Pre as I’d really prefer a PS Audio component in that position of the chain)
The concept to understand, is that the output is designed to drive VOLTAGE, and not CURRENT. The larger the load impedance the less the output impedance, that should be a far lower impedance, matters. Since the output isn’t a current device, it works much better driving less current. The quality of the output’s ability to sink current and voltage both is critical to good performance into varying input loads. Ideally there would be no current at all, just a pure voltage potential transfer function into the amp that takes it from there. As both ends have a resistance, there will be some current. The amplifier’s input impedance has the biggest say in the current sink. If the amps input impedance is infinity, the preamps output impedance is just the resistance the voltage transfer function is measured against at the amplifier. There is no current sink for the output to manage at all. The amps ideally drive current over voltage, the output of the preamp drives voltage over current. Just the opposite. All the high impedance stage of an amplifier should do is meausure the voltage transfer function from the pre amp, no more.
Some amp and preamp combinations aren’t compatible. So yes, it is good to watch for that. You don’t want to current limit the output. E= I*R so limit “I” and the voltage amplitude will suffer. In an ideal world we remove (theoretically) the current so it isn’t a variable.