Which CROFT pre-amp?

[Marco]

Again, my previous experience of 6SN7 types is that they go microphonic in a relatively short time and therefore have to be replaced at yet more cost. I am of course referring to modern variants.

Yup, Shaun, that can happen, and I have experienced the same thing myself both with NOS and current production valves. I'm afraid it comes with the territory.

I recently bought four NOS 1950s Russian (Melz factory) 6N8S (6SN7 equivalents), which had been properly tested in the seller's professional valve tester, and he had supplied all the relevant measurements, so all seemed fine.

When I got them, they worked ok for a couple of days, and then three of them went noisy separately, all within the space of a day, producing weird 'whistling' noises through the speakers... Bear in mind that they had cost me £75 each!

I then bit the bullet and bought another three to replace the ones that were faulty, and thankfully they've been fine. I persevered because, when they're good, those valves sound utterly superb, and way better than any other similar types I've heard.

However, most folk won't have that type of patience, or the perhaps the funds to 'service' the demands of going down that road with NOS valves.

Marco.

[Wakefield Turntables]

Hmmmm old croft pre amps are quite hard to find, I managed to source an epoch in Norway .

[Marco]

It's because those who have them love them! If they were crap, then I guess they'd be in plentiful supply, second-hand

Let's also remember that they weren't exactly produced in huge quantities in the first place.

Marco.

[hifi_dave]

You need to be aware that many older Croft products weren't actually made by Glenn Croft but by his so called 'distributor'. I can't go into details but these are inferior and not worth bothering with.

Glenn has moved onto the smaller valves because, to his ears, they sound better, are quieter and more reliable. In his opinion, the amps he now makes are the best he has ever made. Certainly, back in the day when we had Croft pres using Octal valves, we did have a lot of trouble with noise and microphonics.

From my customers point of view, the Croft pre amps sound better as you move up the ladder and all offer unbeatable value for money.

[Jimbo]

Having spoken with Glenn about this in the past, primarily it was because getting good NOS 6SL7s (or 6SN7s) was expensive, and current production ones sound crap in comparison. Also, reliability wasn't consistent. As anyone who buys NOS tubes knows, you don't really know what you're getting until you plug it in and listen to it!

They might measure fine, but could still be noisy or develop faults, after even just light use when equipment is tested - and the bigger valves tend to be more 'temperamental', in that respect.

Current production ECC83s are relatively cheap, readily available, are generally reliable, and sound/perform consistently. I also believe that the circuit they use is easier and less costly to implement - all of which makes it a no-brainer decision for Glenn to use, instead of the larger octal valves, which when properly implemented, do sound better.

That said, the current range of Croft equipment still sounds superb, but in a different way... Most people just want to buy equipment fit for purpose, out of the box that sounds great, without faffing around modifying things, so the current stuff fits the bill. However, if you are prepared to go down the modification route, and seek out an old Charisma or Epoch, then the rewards (after spending a not inconsiderable sum on the necessary components) are significant.

Do remember also that Glenn will build virtually anything you want to your bespoke requirements, so if you wanted a 6SL7 or 6SN7-based preamp, designed from scratch, he'll do it for you and put it into a nice case. Obviously, however, that route will be more expensive than supplying him with a Charisma or Epoch to modify, as with the latter the core components and circuit are already in place.

Therefore, there's plenty of choice out there for anyone who wants to get a Croft preamp. Whatever you choose, you're guaranteed to end up with something rather special, which will provide significantly more 'SPPV value' than is available with designs other manufacturers are producing at many times the price!

Marco.

Thanks for that Croft insight Marco, it is what I suspected having heard about the potential microphonic problems with the larger Octal valves. It is a bit of tightrope to walk obtaining and running these valves in one of Glenns older designs and having reliable longterm performance. I am sure when they are working within specification and don,t start 'whistling' your onto something really special.

I have weighed this up myself and consider his latest 25 range certainly up to the job although I appreciate they can be bettered by older Croft designs +plenty of cash or other manufacturers costing even more spondoolies!

As always there are compromises to make but I am certainly happy with the glorious sound I get from my modified 25R. The new linestage does alow it to breath somewhat.

However regarding the OP ( Andrew), I would serious consider keeping your basic and have the linestage upraded to the RS and run a Croft RIAA R phono stage through this. This is Glenns recommendation for the best preamplification he can currently do with the new designs.

[walpurgis]

Hmmmm old croft pre amps are quite hard to find, I managed to source an epoch in Norway .

I tried an Epoch in my system. Can't say I was particularly struck. Both my existing pre-amps were better.

[Marco]

Hi Jim,

Yup, undoubtedly good advice there for Andy. There is definitely a distinct sonic difference between, say, a 6SL7 and an ECC83; 'night and day', actually. It's rather like comparing a 300b with a KT88...

Like you say, it's definitely 'the luck of the draw' with NOS valves of any description. However, to put it into perspective, in nearly eight years of owning and using my modded C-X daily, on average for 5-6 hours per day, I've had about three faulty valves, despite having bought (probably 100s of different 6SL7s) over that timescale.

In that respect, experience suggests that 6SL7s, used as signal valves in a preamp, appear to be more reliable than 6SN7s, used as driver valves in a power amp (the Russian ones I mentioned earlier being a case in point) - I guess because in the former application the valves aren't being driven as hard, or perhaps 6SL7s are generally more reliable? I don't know.

All I know is that in the many years I've owned my modded Charisma-X, it's provided trouble-free use, other than the odd valve going down, which really comes as part of the territory of owning valve equipment. Therefore, the *real* picture here is that it's not 'the norm' for the larger octal valves to go tits up (it's far more likely that they'll be great and last for years, as in general they were built to much higher standards than current production ones), but you can get faulty ones.

Therefore, the choices are there for those interested in owning Croft equipment to take the route that best suits them

Marco.

[Firebottle]

.... producing weird 'whistling' noises through the speakers....

Marco, the valves themselves may not be at fault here. What you describe could be a sign of instability, with the valves oscillating at a very high frequency. This often sounds like weird whistling in the audio band which is why I suspect this.

I don't know the exact circuit of your Charisma but it is possible that a simple cure may be available. 'Grid stopper' resistors are usually fitted to prevent this problem so I would get Duncan or Anthony to check if your pre is fitted with them, or if present what value they are. They don't affect the audio performance in any way.

Worth a check surely with your investment in the particular valves?

[Marco]

I tried an Epoch in my system. Can't say I was particularly struck. Both my existing pre-amps were better.

That's the whole point, Geoff. The stock ones aren't that good, which is why they need modifying. What they have got going for them though, is an excellent (point-to-point wired) circuit, designed to be used with great sounding output valves (6SL7s).

In order to 'unlock' that greatness, however, the original electrolytic coupling and PSU caps need replaced with quality modern polypropylene (or teflon) types, and the carbon-based volume pots replaced with quality stepped attenuators. Fitting an 'over-specced' off-board PSU also helps, with separate regulation for the line-level and phono stage, as does changing the amp from valve rectification (via the use of a 6080 tube), to solid-state MOSFET rectification.

Do all of the above, with an Epoch or Charisma (and Glenn will carry out the work for you, if necessary), and you've got a seriously killer valve preamp!

All in, it'll cost around £1500 to have the above mods done, which when added to the cost of a second-hand Epoch or Charisma (say £700), comes to under £2.5k. And I'd put said preamp up against ANY other valve preamps on the market, at any price, and expect it to compete very favourably with them!

I've compared my own modded Croft against £15k preamps, and it's often outperformed them, or certainly not disgraced itself. Therefore *that* is the whole point of going down the modification route with a Croft: to obtain the highest possible SPPV. It just depends if you can be arsed with all the faff, or merely want something simple that's 'plug & play'!

Marco.

[Marco]

Marco, the valves themselves may not be at fault here. What you describe could be a sign of instability, with the valves oscillating at a very high frequency. This often sounds like weird whistling in the audio band which is why I suspect this.

I don't know the exact circuit of your Charisma but it is possible that a simple cure may be available. 'Grid stopper' resistors are usually fitted to prevent this problem so I would get Duncan or Anthony to check if your pre is fitted with them, or if present what value they are. They don't affect the audio performance in any way.

Worth a check surely with your investment in the particular valves?

Hi Alan,

Thanks for that advice, mate. It's appreciated, but I've already had the amp checked out (as you've suggested), and all is fine. Simply swapping out the faulty valves, for different ones, cured the problem instantly

Marco.