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-   -   Sugden preamp WAL AC Farnell. (https://www.vintage-radio.net/forum/showthread.php?t=176908)

wirewithgain 21st Feb 2021 8:09 pm

Sugden preamp WAL AC Farnell.
 
5 Attachment(s)
Are there any Sugden fans who might be able to shed some light on this unit?

Neat wiring, soldering and the feeling throughout of a hand assembled unit but would appreciate some more insight and background.

I think WAL stands for Wellington Acoustic Laboratories, more than that I donít know.

Would be grateful if anyone can comment on its likely sound quality.

To work as a phono preamp would it require an outboard RIAA?

What would be its best role in a system? Could it work as just a sitting box?

I havenít yet fired connected it up, are there any readings I could check with a DMM?

knobtwiddler 22nd Feb 2021 12:11 am

Re: Sugden preamp wal ac farnell
 
First thing: check earth continuity. If you have a PAT tester, that's a good idea.

Do you have a variac? I would strongly recommend switching it on by gently ramping up the voltage on one.

'Disc' input suggests that it has some kind of replay EQ in it. As to whether it's the conventional type of RIAA, you will only be able to find out either using a reverse-RIAA filter (easy to make, and probably cheap on evilbay); or using a test record (the latter won't be accurate, as you'll be measuring anomalies / resonances in the cart / stylus / preamp combination ).

If it's easy to do, you could detach the PSU from the rest of the circuitry and power the PSU on its own. You could measure its output, and you could also try powering the PCBs from a current-limiting lab PSU (while watching its output on a scope) on their own. As an early solid-state preamp, I would very much doubt if it takes more than 50mA per PCB. Be cautious with I-limiting to begin with.

Some of those yellow axial caps will need checking out. They can start to pass DC at this age. If it's easy to do without hurting the PCB, you can lift a leg and measure their R. It ought to be high: preferably in the Meg Ohm range.

It is designed to connect to some kind of control amp or level control, so you'll need to make something up to go between it and a power amp. Try it on a line input on an integrated amp first.

Before you connect it to anything, check all the inputs and outputs for DC offset. Look at them on a scope as well.

edit: This is quite likely designed for a ceramic cartridge, in which case a typical reverse RIAA won't work with it, nor will a modern cartridge. My expertise doesn't extend to ceramic carts, but there are many members here who will know how to handle it.

NB - I think it's quite elegant. I look forward to finding how it works out.

And another edit: Sugden is still going. Why not shoot them an email? I'm a fan of their work. They seem like a good company to me.

Herald1360 22nd Feb 2021 1:39 am

Re: Sugden preamp wal ac farnell
 
The yellow axial caps look like Mullard Mustards to me. I'd be surprised if they were leaky and even more surprised if they were leaky enough to matter in a relatively low impedance solid state circuit.

stacman 22nd Feb 2021 6:56 am

Re: Sugden preamp wal ac farnell
 
Unusual unit with it having a microphone input as well as disc and tape, the microphone has left and right too, the case with the outward facing wings for screwing down to hold it in situ, maybe used in an educational, theatrical or something similar setting.

Lucien Nunes 22nd Feb 2021 9:05 am

Re: Sugden preamp wal ac farnell
 
Anyone got a Farnell catalogue of that era? I don't know when the company changed from A.C. Farnell to Farnell Electronic Components or whatever it became next. Might it have been a special commission for Alan Farnell?

The Erie / Hunts electrolytic cap is interesting in having a date code of YYA = 009. It must be a YMM code rather than WWY as there is no week 00, and if it has Erie branding it's late enough to be YMM anyway. That puts it at September 1970, which tallies with the only Philips / Mullard code I can see in the pics B0S which is April-June 1970. Perhaps you can read others. As per Herald1960 it is most unlikely there is anything wrong with mustards.

Craig Sawyers 22nd Feb 2021 9:44 am

Re: Sugden preamp wal ac farnell
 
The mullard mustards are polyester dielectric and very unlikely to be a problem. The axial electrolytic caps could do with checking, particularly since the superb construction unit is over half a century old (eek!)

Craig

G6ONEDave 22nd Feb 2021 11:30 am

Re: Sugden preamp WAL AC Farnell.
 
A.C. Farnell were based in Sheffield, where as Farnell Electronic Components were based in Leeds and were totally seperate companies, although they were set up by members of the same Farnell family. A.C. Farnell were more into brown goods and service spares, I used to buy PL519 and PY500A from them, as their valves were g'teed and seemed to be of a higher quality than a lot of others at the time. I think that A.C. Farnell ceased trading a lot of years back. Farnell Electronic Components did and still do mainly electronic components.

The preamp of the OP was probably built for factory usuage to supply music and announcements over the 'in house' entertainment system for the factory workers. It may also have been used in warehouses, larger offices and shops for similar purposes.
Dave

knobtwiddler 22nd Feb 2021 11:40 am

Re: Sugden preamp wal ac farnell
 
Quote:

Originally Posted by Herald1360 (Post 1344849)
The yellow axial caps look like Mullard Mustards to me. I'd be surprised if they were leaky and even more surprised if they were leaky enough to matter in a relatively low impedance solid state circuit.

I did think that they could be the much-fabled Mustard caps (desirable in much vintage audio), but I have seen similar looking caps go virtually short in valve gear, so automatically leaned on the side of caution.

Craig makes a good point re: electrolytics. More reason to use a variac when turning it on, unless you plan to shotgun re-cap them (which could irk some around here!).

I haven't encountered a ceramic cart since my age was in single figures. Am I right in thinking it most likely is for ceramic?

Craig Sawyers 22nd Feb 2021 11:49 am

Re: Sugden preamp WAL AC Farnell.
 
Well there are two polystyrene capacitors in there of clearly different value. So I suspect that it *might* have RIAA correction - implying it equally *might* be moving magnet and not ceramic.

Without tracing the circuit, or measuring its frequency response it is difficult to be certain

Craig

knobtwiddler 22nd Feb 2021 11:51 am

Re: Sugden preamp WAL AC Farnell.
 
The gain will be different for ceramic, right? They are a lot louder than the typical 4mV from a MM. I think you are probably right, though. You can make a fairly effective RIAA with 2 caps.

barrymagrec 22nd Feb 2021 11:59 am

Re: Sugden preamp WAL AC Farnell.
 
Quote:

Originally Posted by G6ONEDave (Post 1344909)
The preamp of the OP was probably built for factory usuage to supply music and announcements over the 'in house' entertainment system for the factory workers. It may also have been used in warehouses, larger offices and shops for similar purposes.
Dave


I think that is quite probable.

No tone controls, Jack sockets on the front, no Tuner input wouldn`t be a great spec for a domestic Hi Fi pre amp, even in the sixties.

stacman 22nd Feb 2021 12:40 pm

Re: Sugden preamp WAL AC Farnell.
 
I thought they were jack sockets, but looking closely, they look more like phono type, top row of sockets, the far right one, you can see a gap around the edge through fascia, and the shadowing of said socket.

duncanlowe 22nd Feb 2021 12:54 pm

Re: Sugden preamp WAL AC Farnell.
 
1 Attachment(s)
It seems WAL is Wellington Acoustic Laboratories. Seems to be for music / PA rather than home as others have suggested.

wirewithgain 22nd Feb 2021 1:37 pm

Re: Sugden preamp WAL AC Farnell.
 
What a superb forum! Just excellent.
Thanks to everyone who's contributed so far.
I now know a great deal more than I did yesterday..
Further contributions of course welcome.

Craig Sawyers 22nd Feb 2021 2:17 pm

Re: Sugden preamp WAL AC Farnell.
 
Looking at what I can see of the board, it looks like this could be based on the Bailey three transistor design, which appeared in December 1966 WW. This had the innovation of feeding the frequency selective feedback from an emitter follower rather than the two transistor gain cell. (In addition, one of those transistors looks like a Ferranti E-line, now made by Diodes Inc. One of the secrets of low voltage noise designs are the E-line devices)

https://worldradiohistory.com/UK/Wir...ld-1966-12.pdf

It was further improved byWalker WW May 1972

https://worldradiohistory.com/UK/Wir...ld-1972-05.pdf

But that post-dates the OP's unit.

Craig

Lucien Nunes 22nd Feb 2021 2:28 pm

Re: Sugden preamp WAL AC Farnell.
 
Quote:

A.C. Farnell were based in Sheffield, where as Farnell Electronic Components were based in Leeds and were totally seperate companies
Thanks for the clarification, I had an incorrect recollection that one became part of the other.

Quote:

The preamp of the OP was probably built for factory usuage to supply music and announcements over the 'in house' entertainment system for the factory workers. It may also have been used in warehouses, larger offices and shops for similar purposes.
In those applications I would have expected a mono output, even with stereo inputs, separate preset gain controls, and balanced input at least for the mic(s). While its purpose might well have been within a commercial installation, perhaps one more along the lines of demonstration or testing of audio equipment?

Radio Wrangler 22nd Feb 2021 2:51 pm

Re: Sugden preamp WAL AC Farnell.
 
Quote:

Originally Posted by Craig Sawyers (Post 1344976)
(In addition, one of those transistors looks like a Ferranti E-line, now made by Diodes Inc. One of the secrets of low voltage noise designs are the E-line devices)

To most users, Ferranti had evolved some quite outstanding transistors with particularly good current handling for their package size. Thismade them great for motor control... EG switching to drive stepper motors and bridges for switching direction of DC brushed motors.

This was done by designing in excellent current sharing mechanisms and low base-spreading resistance.

Coincidentally, this also made them rather good for low noise capabilities in low impedance environments. It took a while for this to be recognised, but it's real.

Low noise people designing dynamic microphone inputs eventually found that Rohm made a range of low spreading resistance transistors for the motor drive market, and that these parts were about the best for their work. Of course, Rohm obsoleted them when they saw the motor market drop off as it changed to MOSFETs and IGBTs.

Who'd have thought that tough motor drive transistors would have a sideline in the most delicate applications?

David

Craig Sawyers 22nd Feb 2021 3:06 pm

Re: Sugden preamp WAL AC Farnell.
 
The other characteristic is low Vce(sat). I have measured 6mV on some of the current E-line devices even at a few mA Ic. Of course this is a needed characteristic for applications like stepper-motor drive. There is a definite correlation between Vce(sat) and en.

The rbb' of some of the E-line devices has been measured (HH Ed 3) at sub 2-ohms with very low 1/f noise corner, better even than the legendary and long obsolete Rohm parts.

Diodes Inc have now recognised the low noise performance of their E-line devices, and list as one of the applications low noise audio.

The disadvantage is of course high capacitance, because of the extended (interdigitaged) junction area.

Craig

Craig Sawyers 22nd Feb 2021 3:18 pm

Re: Sugden preamp WAL AC Farnell.
 
Just found my measurements. Cobo is in the range 60-100pF at 10V Vce, which means that they really need to be cascoded, or used common base.

Craig

ajgriff 22nd Feb 2021 3:22 pm

Re: Sugden preamp WAL AC Farnell.
 
Quote:

Originally Posted by Lucien Nunes (Post 1344979)
Quote:

A.C. Farnell were based in Sheffield, where as Farnell Electronic Components were based in Leeds and were totally seperate companies
Thanks for the clarification, I had an incorrect recollection that one became part of the other.

The history of Farnell is really quite complicated and I've always thought that A C Farnell was originally based in Leeds. This potted history is interesting:

https://advanceproductservices.co.uk...s/our-history/

Not hard to imagine that there could have been a business relationship between Sugden and Farnell in view of their close geographic proximity. Worth noting too that R E Sugden was very much focused on good quality audio equpment.

Alan


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