View Full Version : Croft phono stage woes?

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 -


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).

Spectral Morn
01-06-2009, 10:08
Hi Dave

The Ortofon T5's were a nice cheap entry into using MC carts into a MM stage but they were a fairly crude thing and best upgraded from whenever funds allowed. I have an Ortofon T2000 SUT which I got with my Ortofon mc2000 mk2 as I too at the time only had a valve MM stage (in my Audio Innovations Series 500 amplifier) to use. But it was only when I picked up a S/H Head SUT that I realized how crude the T2000 was as well, compared to the Head.

I think the problem you describe is very much one of input overload i.e to much gain with some of your MC cartridges....and this will show up exactly where you are hearing it on dynamic peaks or overly loud recordings. I must admit that I have never heard of a SUT with switchable gain, only loading (does such a beast exist?). Probably the only way to sort this would be some very high quality resistors in adapter plugs to allow reduction of gain (but only by very small amounts). You might also find that different tonearm cables might help as well, as some are harder to drive than others, this assuming you can switch cables.

I am aware that none of these suggestions are cheap but I fear that to solve this issue you will have to spend a little money.

I have always found my Lyra Clavis cart to be prone to these sorts of issues. Not enough gain...slightly to much etc. In fact the only time it did work properly was when I had it through the Head into the AI 500's MM stage. However the sound quality I get now is much better overall. I guess there are always awkward carts and the Lyra Clavis is one in my experience so far.

Ask Guy Sargent of Pure Sound about his new SUT...it will be a good one...if its fully compatible with your carts and phono stage ?

Regards D S D L

PS it could however just be faulty....

01-06-2009, 11:14
You say the phono section is fine with MM, which would indicate the problem is not with the Croft, but as Neil says, with the SUT.

Anyone know the step up ratio of the T5's and the maximum permissible input level for the Croft?

With that info it should be easy to work out if it's an overload problem.

The Grand Wazoo
01-06-2009, 16:29
Anyone know the step up ratio of the T5's and the maximum permissible input level for the Croft?

Hi Mike,

I'm fairly sure the T5's ratio is/was 1:20 - for 26dB gain.

01-06-2009, 17:14
Thanks for input so far.

The trannies are actually Sony HA-T10's, which were made for Sony by Ortofon and supposedly identical to the T5. I've downloaded a "manual" from Vinyl-Engine and yes, the gain is 26db (20x step-up ratio).

The Head was/is superb as I remember and Tim also used to supply my good mate HiFi dave with cheaper little trannies that can be built into a box for a lower cost option (as soon as they started to sell in quantity, the price to Dave sky-rocketed as I recall...).

The thing is, using the current deck, I like what the OC9 and MC30 Super do with the LP's I've played, their bright freshness suiting the Bc2's better than the Supex, which took a lot of messing about with spacers (yuch!) in the headslide to work properly.



01-06-2009, 17:24
I think it's more likely to be the (crappy) T5's overloading than the Croft as we never had any such problems in the past and it doesn't occur when you use MM. To confirm, when you next visit, bring the Croft and we'll try a selection of step up x'mers.:ner:

02-06-2009, 08:54
I'll have a hatch full of suspect "goodies." with me. Hope you have a strong back :D