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Matti Otala & "The 2 Channel Audio Power & PreAmplifier"

Wow, OK, I just listened to the best replay system I have heard! Croft Micro II MM stage feeding the Electrocompaniert is simply stunning - an extra octave of controlled bass (someone tell me what an octave is?!), and the ESL63s simply disappear. All sound is behind, in front, in the middle, or out to the sides. I felt the same about my valve hybrid monos when I first compared to my ML No. 29, this is a different level.

Listened to The Wall vinyl first, but my CD copy has such crap SQ I didn't trust it (listened to it last night). Just put Joan Armatradng, Show Some Emotion on. I'm gobsmacked!

All of this through a Lenco L75 instead of my LP12 (I kind of miss the LP12 emotional level replay quality...or did), recently installed.

So...line level better via Electrocompaniert pre, phone better via Croft. Need to either fix phono stage issues with EC unit, or modify impedance with Croft (how good would vinyl be if impedance matched?!).

On to Talk Talk, Happiness now...stunning!

Richard
 
Hi Richard,

I've attached a photo of the my latest power amp this one also has the extra transformer.

57.jpg


The input impedance of the amp is very low at only 1.8K it also DC coupled to the first transistor. Matching the power amp is key to the sound I know I've tried a few hi-end preamp's but in the end I used the EC preamp as the interface.

Your preamp is one of the last one's made, the LM723 was to feed the new phono-stage the board fitted vertical across the front. I've never seen the circuit for any of the preamp's except for my reversed engineer copy.

At the front there is a LM741 this powers the a relay for the 25-30 second delay.

The preamp output consist of a Naim like buffer stage with BC141 output transistors (with and without the heatsink's) this is the 10 ohm impedance output stage.

Sharif.
 
I have a new experemental buffer that I going to try with my modded Quad 22 preamp it based on a White's Cathode Follower.
It uses J-fet's instead of the valves this has a very low output impedance and will match the power amp.

Sharif.
 
This is the buffer I'm planning to use, it is an adaption of the "White's Cathode Follower" but uses J-fets instead.

I've not tried it with the EC power amp but the prototype looks promising.

Buffer%20Jfet.jpg


Sharif.
 
Here is the bases for the EC preamp regulated PSU.

Ignore the MURS120 diode the ones fitted to the preamp are standard 1N4004's and I've use BC547B in place of the BC413 transistors.

EC%20Preamp%20PSU.jpg


Sharif.
 
Thanks Sharif - I got a copy of the Norse Ecosse power amp service manual today, will load it up tomorrow.

Richard
 
This is the schematic for the EC preamp output stage.

EC%20Preamp%20Output%20Stage.jpg


With the volume and balance shown.

EC%20Preamp%20Output%20Stage%20with%20pots.jpg


Sharif
 
Thanks Richard for the link it look like a collection of two amplifiers the 25 Watt Class A and the later Ampwire AW100 mk 1 & 2

I have somewhere more schematics and service info for the power amp if that helps?

The 25 Watt Class Amplifier as far as I know did't change other than reducing the bias to increase the reliability of the amp.

In the first version the bias was set to give 13 watts in class A the later ones were set to give 11 watts with rest of the output running a very rich class AB.

You will know if you have an early one as the pcb will be dark brown in places due to the component heat.

Sharif
 
Hi Sharif - yes please, if you have more info, thanks. Different question though - have you seen a pre like mine with the later phono upright PCB? I'd like to know if the additional glued on electrolytics are original or not? Thanks.

I took a break of a few days as I didn't trust my ears - I'm running a Lenco L75 with DV vintage ruby instead of my LP12/ Asaka currently, and I wasn't sure if my best replay system I have heard statement was really true. Just listened again, and it does seem to be.

But I have a quandary - Naim CDI is stunning through the EC pre into matching amp, but phono stage sounds flat. croft Micro II phono stage is stunning, line stage is great, but not as good as the EC pre line stage. Neither phono stage is dealing with the cartridge, I have a head amp for my LOMCs.

I'm going to try investigate the EC pre first, try and work out why it sounds flat (hence question to Sharif about glued on caps). I'd hate to relegate the Croft, but the EC pre, matched to its amp (with low impedance), is very, very special. I just need a high performanc phono stage too...and do not want to keep croft pre as only a phono stage via its tape outs (haven't tried this, but will if I can't improve EC phono stage!).

Richard
 
OK, so I opened up the pre again tonight - looking at it, I *think* the vertically mounted board at the front is just a head amp, to amplify signals to MM levels ready for the stock MM phono stage with RIAA correction. I still don't like the bodgey looking wiring around the MM/MC switch, but before I strip the entire thing down I am going to try a LO MC (DV Karat - .2mV output) into the .35mV MC input of the EC pre.

If it doesn't sound better then I may well cross post in DIY to try and find out why - difference between line and phono inputs is massively in favour of Line level compared to the MM input on this pre.

Some better photos:

- This shows the MM (right hand pair) and MC (LH pair) inputs better, and what looks like non EC wiring from sockets to MC switch;
17105735299_2f3df3d7a1_b.jpg


- This is the whole picture of the vertically mounted "head-amp" board, the second set of shielded cables goes back to the MM/MC switch, and the board has no other connections to rest of pre except for the regulated supply from the sub-PCB's LM chip;
17084566047_367648d250_b.jpg


And then a close up of the really didgy wiring around the MM/MC switch;
17105719209_1d03b0b97f_b.jpg


To be honest, if MC sounds no better than MM input, then at least I can strip out the vertical PCB and potentially re-use it's regulated supply elsewhere in the pre.

Cheers, Richard
 
I wonder if the MM stage has been setup for a non-typical cart with regards to loading and capacitance? It might be worth trying to figure out what it's doing in that respect as getting it wrong for a given cart can be a real deal-breaker IME. As an example I considered the phono stage in my Quad 34 to be truly dreadful with my 2M Black until Rob went at it, afterwards I preferred it to £1300 worth of EAR 834P!
 
Yes, thanks Tony, something weird going on;

So, I needed the EC power amp to power the pre I thought and check voltages - I never got that far, but while checking the pre I reconnect my Mark Levinson power amp to the croft to listen to tunes while I work. It sounded great, different but good.

So when I reconnected EC power and pre into circuit the first thing I did was listen to line level from the Naim CDI - better, much better, than Croft and ML. I then switch on Lenco turntable, select phono input in EC pre...no sound. Forgotten the MC switch on back (I'm now running DV karat into MC input of EC pre, no more McKinnie head-amp), turn volume back down, push MC switch, turn volume back up - hugely distorted sound. Switch back to line input for CD, also distorted. Switch of pre & turn back on - 20 second delay - still distorted. Feel power amp heat sinks - they've cooled down!

Switched everything off, took a pee & opened a bottle of red. Quick sip and turn everything back on - line level fine. Try MC input again - fine! Switch from MC to MM to try and identify a faulty switch...no problem. Back on MC, wow this sounds better!

On second side of Joan's Show Some Emotion so far, Blue Nile up next (same as line source test, sorry), and the I then I think some early Pink Floyd.

Stunning - I can live with this! Does that mean my 2 McKinnie (John Curl Vendetta head amp clones) head amps and beloved Croft Micro are surplus to requirements? Not sure yet - but feck this sounds good :)
 
So, results so far are that someone has fecked about with MM input on my pre :) I try and find out why...but no rush when MC input sounds this good with LO MC!
 
I have never seen the MC head amp board before so can't make any comments about the glue around the capacitors.

I've not try the EC phonostage for a long while from what I remember it never sounded dull and life less.
The MM phonostage had a very similar sound as the rest of the preamp it did have a small amount of hiss at high levels.

This is the MM phonostage schematic for my preamp the switch on the back of mine changes the sensitivity from 3.5mV to 1.2mV

EC%20MM%20phonostage.jpg


Just a thought the capacitor on the MM phonostage the one in the feedback, if they have aged will give a sound as you described.
In my circuit there is a 1000uF 16V, 220uF 16V and a 1uF 25V you could try changing them.

Sharif
 
Thanks Sharif - I think the stock MM stage is ok, I've gone through a few albums now direct with a low output MC into the MC and it sounds great. I think Tony is right, someone has messed about with MM stage loading settings - MC input had a bit of graininess in upper mid frequencies initially, but even that is starting to get better. What is stunning is how it deals with bass - currently listening to The Cure, In the Forest - upper frequencies still not as good as Croft, but bass imaging more than makes up for it.

Basically, a sympathetic service is pending the this EC pre and power - they are a stunning combination, why did anyone want anything more in the 1970's? :)

I need to confirm after a few days of listening, but the sound I now have is the best I have a heard I think. All for chf 170!

Me very happy, Richard
 
Hi Richard when you do the your service could you post some photos of the top and bottom of the MC head-amp I would be interested in reverse engineering it.

Sharif.
 
Hi Shariff - yes, of course, the least I can do. It maybe a while though, I want to live with it as is for a few weeks, and then swap my LP12 back into the main system.

I guess it won't be until I have all the caps that I will hack off the glue bodge job either - and a large part of cct is hidden with it in place.

As it stands currently, the EC phono stage is competing with a McKinnie RO III (John Curl Vendetta clone) head amp, feeding a Croft phono stage. Both have a rather good reputation, and to my ears sounded better than anything I had heard before.

Extended listening (post honeymoon phase :)) reveals the upper mid graininess as a major negative, but bass imaging is still stunning. Given how hot it runs (pre as well as power, those poor little BCs with heat sinks are being hammered!), I'm hopeful a recap will help. I have a lot of tants in mine too - not so sure about swapping these, probably start with just electrolytics. Any thoughts anyone?

One interesting point - this combination is stunning when sitting in front of it, but listening from elsewhere in house just seems to reveal all the negative points. Weird, wonder why.

Richard
 
Hmmm - swapped L75 back to the LP12 a week ago, and the EC pre/power back to McKinnie/Croft pre/DIY mono blocks 2 nights ago. I'm really not clear what the EC kit did better yet, but my normal system is so much more enjoyable. But why, reading above I was impressed with the EC kit? CD had perhaps more presence with the EC, but imaging much better with my normal kit, and it just makes me laugh or smile constantly listening to it.

Not sure what to do now - I'm now living in a small apartment since separating from my wife last year, and do not have the space to hoard kit anymore. I I refurbish the EC pre/power, or try and sell as original and let new owner refurb?

Richard
 
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