DSJR
01-06-2009, 09:11
Following on from my comments on the Linn fanbois thread, Marco's asked me to post a few thoughts and questions in this room, to see if anyone's had a similar experience.
I bought a Croft Super-Micro 4 "PP" preamp last year. I'd owned one many years ago, which was stolen from the friend who'd bought it and I was very lucky to get this one. Not being flush with funds, I was very pleased with a couple of 5841A's in the line amp stage, which all but removed a trace of "thickness" on these inputs. I've been using this preamp in recent times to drive the bridged Crown D 60's (25K input impedance) to very good effect. My very preamp is described here by its original owner, although Glenn fitted 500K pots rather than 1M ones -
http://www.soton.ac.uk/~apm3/diyaudio/Croft_preamps.html
This post concerns the phono input. I've been using a collection of MM cartridges with no ill effects whatsoever, my favourite ADC's and Sonus Blue sounding great, although a NOS B&O SP12 I had high hopes for sounded dull as ditchwater despite tracking as well as a typical Shure. In recent times, I've been given a motley collection of cartridges, including a couple of MC's - Ortofon MC10 II and MC30 Super, as well as a pair of Ortofon T-5 SUT's. I've also dug out a Stilton (?) OC9 and a Supex 900E with still good tips.
Firstly, the gain via the T5's does seem a little higher with all but the Supex, and I was noticing some distortion on loud compressed bits, not like mistracking, but a sort of resonant edge, which sounds a a bit like a worn stylus (the MC10 and 30 are new/as new). The Supex is too sucked out in balance for the similarly voiced BC2's, but was better in this respect. before totally condemming the deck, I swapped back to the AVI ss pre I have with inbuilt phono stage and the problem totally disappeared, the MC30 Super working well with the AVI's rather safe and "contained" sounding phono stage.
Sorry to turn this into an essay, but I really want to use the Croft pre for now. Apart from this "problem," the sonics are great, the line stage doing full justice to CD and radio and the basic sound on phono being superbly open and spacious.
The yellow coupling caps added by the first owner (see pics) have been removed on Glenn's insistance, the mains filter network was removed and the big blue supply caps were replaced with smaller Dubilier ones, again on Glenn's advice.
Is this the T5's not being beefy enough - or are they overloading the Croft's phono stage at very high frequencies, or the non-named ECC83's getting old? Maybe the supply valves are tiring, although there's no hiss at normal LP playing volumes and no hum whatsoever. money really is tight, but could stretch to some good but standard ECC83's. I suspect that better used SUT's would cost heavily now. This phono stage design always worked fine with a Decca and they're hardly shy up top :D
Finally, the thing ought to go to Glenn for further fettling (he has offered, bless him :)), but it's going to cost a bit (less than a Naim preamp service though.....;)) and as the pre sounds so good otherwise I was hoping for a cheap (ish) fix by changing valves or investigating a different step-up (I had a Lentek battery one, as well as an ortofon MCA76 for years but sold them twenty or more years ago).
I bought a Croft Super-Micro 4 "PP" preamp last year. I'd owned one many years ago, which was stolen from the friend who'd bought it and I was very lucky to get this one. Not being flush with funds, I was very pleased with a couple of 5841A's in the line amp stage, which all but removed a trace of "thickness" on these inputs. I've been using this preamp in recent times to drive the bridged Crown D 60's (25K input impedance) to very good effect. My very preamp is described here by its original owner, although Glenn fitted 500K pots rather than 1M ones -
http://www.soton.ac.uk/~apm3/diyaudio/Croft_preamps.html
This post concerns the phono input. I've been using a collection of MM cartridges with no ill effects whatsoever, my favourite ADC's and Sonus Blue sounding great, although a NOS B&O SP12 I had high hopes for sounded dull as ditchwater despite tracking as well as a typical Shure. In recent times, I've been given a motley collection of cartridges, including a couple of MC's - Ortofon MC10 II and MC30 Super, as well as a pair of Ortofon T-5 SUT's. I've also dug out a Stilton (?) OC9 and a Supex 900E with still good tips.
Firstly, the gain via the T5's does seem a little higher with all but the Supex, and I was noticing some distortion on loud compressed bits, not like mistracking, but a sort of resonant edge, which sounds a a bit like a worn stylus (the MC10 and 30 are new/as new). The Supex is too sucked out in balance for the similarly voiced BC2's, but was better in this respect. before totally condemming the deck, I swapped back to the AVI ss pre I have with inbuilt phono stage and the problem totally disappeared, the MC30 Super working well with the AVI's rather safe and "contained" sounding phono stage.
Sorry to turn this into an essay, but I really want to use the Croft pre for now. Apart from this "problem," the sonics are great, the line stage doing full justice to CD and radio and the basic sound on phono being superbly open and spacious.
The yellow coupling caps added by the first owner (see pics) have been removed on Glenn's insistance, the mains filter network was removed and the big blue supply caps were replaced with smaller Dubilier ones, again on Glenn's advice.
Is this the T5's not being beefy enough - or are they overloading the Croft's phono stage at very high frequencies, or the non-named ECC83's getting old? Maybe the supply valves are tiring, although there's no hiss at normal LP playing volumes and no hum whatsoever. money really is tight, but could stretch to some good but standard ECC83's. I suspect that better used SUT's would cost heavily now. This phono stage design always worked fine with a Decca and they're hardly shy up top :D
Finally, the thing ought to go to Glenn for further fettling (he has offered, bless him :)), but it's going to cost a bit (less than a Naim preamp service though.....;)) and as the pre sounds so good otherwise I was hoping for a cheap (ish) fix by changing valves or investigating a different step-up (I had a Lentek battery one, as well as an ortofon MCA76 for years but sold them twenty or more years ago).