My entry into the world of Croft

[Qwin]

http://www.jkwynn.co.uk//Project_Images/Micro25/micro_01.jpg

I decided to simplify my Vinyl set up and return to moving magnet/Iron cartridges.
I also required a Pre Amp that would work with my Proton Power Amp + Yamaha NS1000M speakers and I fancied trying valves for the first time, it's all change round here.
I acquired this used Micro 25 Croft Pre Amplifier with built in Phono Stage. For the few that have not come across these, Glen Croft virtually hand builds these amplifiers and is flexible about the spec to match your needs. This one has a single volume control and reduced gain, exactly what I was going to ask Glen to build for me, so I was very lucky indeed to find a used item of the exact specification I wanted.




http://www.jkwynn.co.uk//Project_Images/Micro25/micro_02.jpg

Everything is standard Micro 25 on the back panel.
Internally the volume control is an Alps Blue Stereo Pot and the Line stage gain is set at 0dB. This is the build spec Glen used when he produced this particular unit from new.
The reduced gain equates to inputs of 3mV on the Phono stage and 0.5V on the Line stage for an output of 0.5V
The only line stage input I use is from my DAC, which outputs 2V, so no gain is required there anyway, as my Proton Power Amp only requires 1V to achieve full output.
My normal reasonably loud listening level is with a quarter turn of the volume and at half a turn is VERY loud, I don't think I could listen to that level for long in my smallish room. The volume pot is smooth and gives a nice gradual change, as for hiss or background noise, the unit seems very quite and works well with the other items in my system.

One thing to note: this series of Croft gear reverses phase, this is ok if you use Croft for both Pre and Power because phase is corrected by the second unit. If you only use one, either Pre or Power and your other amp does not reverse Phase you hit a problem. It's not as bad as it sounds, you just have to swap the speaker leads round at one end, either at the amp or at the speaker which ever is easier to get to, but only at one end, connect Red lead to - and Black lead to + and its sorted (both speakers). Even though a couple of people had told me this in the past, I forgot and was initially disappointed in the sound produced. Once I swapped the connections I was more than happy, the out of phase sound when listening through my Celestion 66's had flattened dynamics and the tweeter sounded very slightly distorted.

I just read RichB's thread in here and see the same thing about reverse phase beeing pointed out, still better to get it out there.

[Jimbo]

Nice one Ken, glad you find the Croft pre is working for you. Plenty of opportunity to tweak and fettle. :eyebrows:

Just try this cheap one I did this weekend -pop it on some oak cones and have a listen ;)

[mik_rik]

Got a lot of Ecc types ,if you want to do some rolling at any time [once you get to know it's house sound] Don't know if you have any already, but the offer is there --- Mick [ ps used old stock and different types , no burn in time required ]

[Qwin]

James - still getting used to the sound, only connected the Yamaha speakers half an hour ago, Celestions have now gone.
My rack is full, so my Power amp is sat on the floor, some work needed to sort this, but I note what you say about the Wood cones.

Mick - Thanks for the offer, as you know I am new to valves. My unit runs ECC83 in the Phono stage and are marked as JJ ECC83S Edicron 2213.
The Line stage is ECC82 and it just says Ei (Yugoslavia). I will just listen to what I have for now but being a used unit I have no idea how old the valves are or how much use they have had.

[Halfway Tree]

Looks like you are really ringing in the changes there Ken! Be careful - you might find yourself getting hooked on this valve stuff! :)

It's taken me 20 odd years to finally have a system without valves and although I'm not using any of my valve gear at the moment I'm not parting with any of it either... so I'm not really cured! :lol:

Gordon

[Qwin]

Hi Gordon

Yes its all change - by the time I'm finished there will only be my turntable/arm from the original set up.

I desperately need to recap the Yamaha speakers, I can't judge the Croft amp properly (or anything else) till that is done, last of the caps ordered so won't be too long.

I am liking the Croft but need to work out if the zero gain in mine compromises the sound in any way over the standard. It is a valve change from EEC83 (mu 100) to an EEC82 (mu 19) on the line stage. I have read that the feedback resistor values may also have been adjusted, it was said that you get a better sound if the amp is driving and giving some gain, wouldn't know whether this is true or not as I am a complete novice on these things. I need to pull mine out and have a look at what has been changed from stock and do nothing else for now.

Got my ticket for the 29th by the way.

[Halfway Tree]

Yes, me too. Looks like there's some interesting kit so should be a good day. My satnav always manages to get me lost (even though it's been updated), but we'll get there eventually!

I've just taken some photos of my LX521s so I'll get my system pics updated here, too.

Gordon

[Haselsh1]

I owned a Croft pre/power back in 2009 and have to admit that it was one of the best sounding amplifiers I had ever heard. In fact, even to date, I have not heard better for that kind of money. The level of detail it uncovered was truly astonishing and then I added the power amp...! I love them so much that I am at this very moment purchasing another preamp to use with my Rotel monoblocks. I take heed of your warning about polarity.

[The Black Adder]

Yep, the polarity trick is something that goes unknown for some...

[mik_rik]

Hi Ken ,what caps are you going to use ,plenty of room in there to put some nice Russian teflon .or some pio types

[Qwin]

Hi Mick

I was refering to the Yamaha speakers x-over caps.

No plans as yet to touch the Croft amp parts though the tube rolling sounds interesting.........

What have you got in the way of ECC83 (pairs needed) and ECC82 (single)?

[mik_rik]

Hi Ken Ecc83 are mostly used Mullards,some Brimars ,Matsushita's and afew other makes,same with Ecc82's .12bh7 are G.E branded as Hammond ,Brimar and a few other types ,welcome to try.I have a couple of JJ TESLA Ecc83 which I really like,nice big sounding valve ,current production I think,can always give them a try-- Mick

[Qwin]

Hi Mick

My line stage 82 is an Ei and that sounds really good, very clean, better than the phono stage which has 2x JJ ecc83s's which sound dull/smeard in comparison.
I would be interested in trying some you mentioned, the Mullard and Brimmer 83's and the GE 82 for instance.
Let me get my speakers sorted and I will get back to you.
Just about to start measuring the caps and pair up the closest combinations.:eyebrows:

[mik_rik]

The G.E 's are 12bh7 , an Ecc82 equivalent but with a higher current draw, but should be ok with a decent p/s in the Croft [ignore if you already knew all this ]-- Mick

[Qwin]

Mick - Nope didn't know that about the 12bh7 - I'm still on page one of the valves for dummies manual.:D

[The Black Adder]

I'm reading 'Valves are Witchcraft' - it's a good read.

I've really no idea how valves actually work (apart from how the internals fit together)... But then I don't really need to, at the moment anyway. :)

[Jimbo]

Mick - Nope didn't know that about the 12bh7 - I'm still on page one of the valves for dummies manual.:D

Hi Ken,

I would be interested to know how the Croft sounds with your Yammys, I think my mate is selling a pair so just curious.
Best get the linestage modified in the Croft to use 12BH7A. Not sure if you can find out how to do this yourself or ask Glenn, he may tell you.

[Qwin]

James - If the circuit needs modifying then thats a step too far. I will just be doing simple tube rolling.

Glen seems to have changed the way the line stage is wired, it looks different to other pictures of stock internals I have looked at.

Maybe its set up as a cathode follower? Not really sure what that is but its something I read about in conjunction with ECC82 used with zero gain, so maybe its not just component values but the type of circuit that has been changed. Whatever it is it seems to work well, so I will leave it alone.

[Jimbo]

James - If the circuit needs modifying then thats a step too far. I will just be doing simple tube rolling.

Glen seems to have changed the way the line stage is wired, it looks different to other pictures of stock internals I have looked at.

Maybe its set up as a cathode follower? Not really sure what that is but its something I read about in conjunction with ECC82 used with zero gain, so maybe its not just component values but the type of circuit that has been changed. Whatever it is it seems to work well, so I will leave it alone.

Hi Ken,

you are correct - the circuit needs changing to accept 12BH7A

[RichB]

Mine appears to have become a white noise generator... plugged it into the system last night and it sounded like a radio between stations....

I'm prepared to accept that positioning may have a role in all of this and its currently far from optimal but looks like I'll be spending my weekend getting to the bottom of it:scratch:

[Jimbo]

Mine appears to have become a white noise generator... plugged it into the system last night and it sounded like a radio between stations....

I'm prepared to accept that positioning may have a role in all of this and its currently far from optimal but looks like I'll be spending my weekend getting to the bottom of it:scratch:

Bad news Rich, something gone horribly wrong there?:(

[RichB]

Bad news Rich, something gone horribly wrong there?:(

Yep, I just seem to lurch from one problem to another with the system at the moment. At its core, i.e. the passive and the monos all is good but the sources are all doing my head in. I'm about a hair away from flogging them all and the vinyl/CDs, building a top notch quiet music server and being done with the ruddy lot of it.

[Firebottle]

Rich just remove and reinsert the valves in their sockets to be sure you haven't got dirty connection on one of the pins.

:) Alan

[mik_rik]

Hi Rich sorry to hi-jack the thread but tap the valves gently whilst playing with a pen or whatever [observe all safety precautions:D] if it "rings" then it's gone microphonic[ecc 88's are very prone to that ,ecc82and 83 not so much]Good luck --Mick

[Qwin]

There isn't a ground lift on The Croft Pre's.

Mine doesn't seem to need one and runs very quite.

The routing of your leads, Grounding and positioning of the unit is as good a place to start as any Rich.

Hope you get it sorted easily.

[mik_rik]

Rich ,is there any provision to fit screening cans on the valves? [preamp valves usually are screened]If the bases are "skirted and the cans are missing then the valves can easily pick up stray rf..Don't worry -if it's gone wrong it can be put right.

[RichB]

Thanks for the suggestions, I've just returned home a bit half cut after a liquid lunch with the Mrs. Best not start faffing now but I want some choons:lol:

The whole system comes apart tomorrow and goes back but by bit with careful attention paid to the cables until I find the source of this. It ain't the power amps as they're making sweet music fed from the squeezebox so I can only guess one of the sources is affecting the pre or mains in some way.

Mick n Alan, I'll try those suggestions if the rearrange don't work.

[The Black Adder]

Glenn put a switched earth lift on my pre... great addition.

[Tarzan]

Glenn put a switched earth lift on my pre... great addition.

What is that then Jo?:)