Creek OBH-22 passive 'pre-amp'
Jun 26, 2013 12:07:45 GMT
Post by Deleted on Jun 26, 2013 12:07:45 GMT
System update: yet another new gadget?
I have been a fan of passive 'pre-amps' for ages now. (Oh, and I'm going to drop the use of the inverted commas now - so PLEASE don't tell me that you can't have a passive pre-amplifier; I DO know that.) While understanding something of the passive pre-amp's potential drawbacks, the simple approach they offer is attractive in that they can be cheap as well as imposing little or no character upon the signal passing through. I say can be cheap; that's true if you stick to the pot-in-a-box type rather than stepped attenuators or even transformer based designs.
I'v posted on this topic before but, to re-cap, I first tried out the passive pre approach because I had a failed Musical Fidelity B200 amp to play with. In the B200 the inputs are routed directly to the volume pot via the selector switch; the only exception being, of course, the MC/MM input which by its very nature goes first to the active RIAA equaliser stage. Because of this easy to understand layout and because I loved the casing design of the B200 I was happy to convert the old amp into a passive pre. I drilled a couple of new holes in the back plate and fitted a pair of RCA sockets which were connected to the output side of the vol pot. Simple & and effective. I bypassed the active stage of the MC/MM input too which gave me another line input and finally I upgraded the volume pot to a 50k log Alps (thanks Mike for supplying that).
The problem was, after goodness knows how many years of having to get up and down to change the volume level, I wanted it remote-controlled. I did look at buying extra circuitry to do this, but I decided the easy way was to go for a Creek OBH-22. This Creek pre-amp is beautifully put together with gold plated relays for remote input switching along with a motorised ALPS pot. HiFiWorld gave it a good review and there are plenty other recommendations too... so with a little hesitation I took the plunge.
I'll explain the basis for that little hesitation in a moment, but disappointment arrived soon after making my mind up because Creek, the miserable beggars, don't make passive pre-amps any more. So thank goodness for Ebay. I had to pay more than I would have preferred for second-hand but I still got it for a lot less than a new one would have been.
And why the hesitation? I knew that a passive pre based on a 50k log pot worked well in my system. But according to the HiFI World review the Creek OBH-22 used a 100k pot; potentially not as suitable as my 50k one. Furthermore, the HiFI World review described a worst case HF response of -1dB at 15kHz. Hmmm. But HiFi World did not say which interconnect they used, or even how long they were.
Anyway, I did buy the Creek and it's a beauty. In my system it sounds every bit as neutral as my DIY pre-amp. My interconnect between passive pre and power amp is short, the output impedances of my main sources are low(ish) too, so all is well. No hums, no buzzes, just relaxed and engaging sound. I haven't done an A-B test, and neither will I do so. I'm sure the Creek sounds superior the DIY design, probably because signal path lengths are even shorter, there is much less PCB track to traverse and the input switching is better quality.
Any sign of -1dB at 15kHz? Nope. And if high end MC cartridges can be up by as much as 6dB, and tweeters are usually all over the place in that area too.. why worry.
A seriously slick piece of kit that OBH-22.
Regards,
Derek
I have been a fan of passive 'pre-amps' for ages now. (Oh, and I'm going to drop the use of the inverted commas now - so PLEASE don't tell me that you can't have a passive pre-amplifier; I DO know that.) While understanding something of the passive pre-amp's potential drawbacks, the simple approach they offer is attractive in that they can be cheap as well as imposing little or no character upon the signal passing through. I say can be cheap; that's true if you stick to the pot-in-a-box type rather than stepped attenuators or even transformer based designs.
I'v posted on this topic before but, to re-cap, I first tried out the passive pre approach because I had a failed Musical Fidelity B200 amp to play with. In the B200 the inputs are routed directly to the volume pot via the selector switch; the only exception being, of course, the MC/MM input which by its very nature goes first to the active RIAA equaliser stage. Because of this easy to understand layout and because I loved the casing design of the B200 I was happy to convert the old amp into a passive pre. I drilled a couple of new holes in the back plate and fitted a pair of RCA sockets which were connected to the output side of the vol pot. Simple & and effective. I bypassed the active stage of the MC/MM input too which gave me another line input and finally I upgraded the volume pot to a 50k log Alps (thanks Mike for supplying that).
The problem was, after goodness knows how many years of having to get up and down to change the volume level, I wanted it remote-controlled. I did look at buying extra circuitry to do this, but I decided the easy way was to go for a Creek OBH-22. This Creek pre-amp is beautifully put together with gold plated relays for remote input switching along with a motorised ALPS pot. HiFiWorld gave it a good review and there are plenty other recommendations too... so with a little hesitation I took the plunge.
I'll explain the basis for that little hesitation in a moment, but disappointment arrived soon after making my mind up because Creek, the miserable beggars, don't make passive pre-amps any more. So thank goodness for Ebay. I had to pay more than I would have preferred for second-hand but I still got it for a lot less than a new one would have been.
And why the hesitation? I knew that a passive pre based on a 50k log pot worked well in my system. But according to the HiFI World review the Creek OBH-22 used a 100k pot; potentially not as suitable as my 50k one. Furthermore, the HiFI World review described a worst case HF response of -1dB at 15kHz. Hmmm. But HiFi World did not say which interconnect they used, or even how long they were.
Anyway, I did buy the Creek and it's a beauty. In my system it sounds every bit as neutral as my DIY pre-amp. My interconnect between passive pre and power amp is short, the output impedances of my main sources are low(ish) too, so all is well. No hums, no buzzes, just relaxed and engaging sound. I haven't done an A-B test, and neither will I do so. I'm sure the Creek sounds superior the DIY design, probably because signal path lengths are even shorter, there is much less PCB track to traverse and the input switching is better quality.
Any sign of -1dB at 15kHz? Nope. And if high end MC cartridges can be up by as much as 6dB, and tweeters are usually all over the place in that area too.. why worry.
A seriously slick piece of kit that OBH-22.
Regards,
Derek