Elem Amplifier (70s, Made in England) - Information?

[gaioshin]

Hi everyone,

I came across this amp in my purchasing of several smaller combos for spares and repairs - does anybody have any background information, or technical information about it?

Despite the damage it has suffered, the components look high quality, and it would be a shame to not be able to restore this!




gaioshin

[teemuk]

Should be easily restorable. I don't see anything inside that couldn't be replaced, even with modern components.

Technical information might be impossible to acquire, except by doing it yourself. The electronics are plain and simple, no gooping, no purposedly hidden component values, no microscopic SMT parts or complex multi-layered PC boards, etc. Plain and simple. Therefore sketching a circuit diagram of the problematic parts (or even of the whole thing) should be easy though it might take a while.

This is the first time I see an ELEM amplifier or even hear about such brand. As usual, the plain logo tells very little about background of that unit. Are there any other hints that could tell who actually manufactured that unit?

[Roly]

New one on me too.

There are some signs that it has been stored in a moist environment, but that's no big deal and as teemuk says, it looks like a pretty conventional amp of the period and a very good prospect for restoration.

Given that it's fairly old and maybe hasn't been powered up in some time you should first power it up via a limiting lamp until you are sure that it is reasonably healthy and not drawing excessive current.

It looks to me like it uses a single supply rail which will be somewhere around 60 volts, the main filter cap being the big one in the clip next to the power transformer, and capacitor-coupled output which will be the 1000uF/63v beside to the heatsink.  From the small size of the power tranny and heatsink I'd guess it has an output of around 20-30 watts.

For a quick test of health measure the supply voltage on the big cap, then the voltage on the +ve end of the output coupling cap which should be close to half the supply.

[gaioshin]

Thanks teemuk and Roly for the suggestions and observations.

I have already built a dim bulb tester, and have yet to power this amp up, so will put it through that at some point in the next day or two. Fuses look fine at the moment, so that is always a good sign.

The pictures didn't really do a particularly good job of illustrating the fact that the 1000uF/63V is actually *very* loose, i.e. the solder joint has been damaged, so that would be the first fix. Similarly, on the back of the control pots, the polystyrene cap that it's on there has actually snapped off, so I will attempt to put that right too.

With regards to who manufactured the amp, the closest I actually got to discovering the original maker was the fact that the board has the term "Pro Artiste" on it. At a guess, this seems to be a rebadged and cloned Sound City amp - given that the Sound City Pro Artiste 30 is about the correct ballpark for power output, the major difference being that it was a 2x10. Even the control panel and knobs look identical to it!

As an aside, thank you to teemuk again for his generosity in terms of the downloadable book - I grabbed a copy last night and am slowing making my way though the wealth of information in there

[teemuk]

Yes, I see plenty of resemblance.

Pro Artiste 30 was introduced in the era when Sound City brand was owned by Dallas Music Industries Ltd.

However, there's very little information of these solid-state amps so it's unknown whether Dallas MI just bought them OEM from some source (that might have manufactured the same design under a dozen different names for several companies), or if Dallas MI manufactured the design itself (and then sold it OEM for several different companies, one of them which might have owned the ELEM brand).

Guys from UK who lived through the 1970's might know if there ever was something like an ELEM music shop. Quite a many music shops had their own "inhouse" brands for their products, though they neccessarily did not manufacture those products on their own.

[g1]

 There is some speculation it may be similar to Vox Escort 30 due to the Dallas Music connection.
Does the schematic match up?

[Roly]

the 1000uF/63V is actually *very* loose, i.e. the solder joint has been damaged

That may indeed be just about all that is wrong with it - I've seen amps tossed into the back shed for less.

Can't really say for the preamp, but the general layout of the power supply and output stage looks very plausible, certainly similar enough to give you a general idea.

I notice that there are two trimpots on the board but I can see only on on the Vox circuit.  One of these will be for setting the output stage idle current, most likely the one closest to the heatsink, but it's anybodies guess what the other is for; seeing the FET input on the Vox circuit it may be to tweek the FET conditions since early FET's tended to have a very wide production spread.

As always with trimpots, they shouldn't be touched until a) you have a really good idea of what they do, and b) you have a compelling reason to adjust them.

I'm not normally given to "change the caps", and you should be guided by what you find as you bring the amp up, but given their age I wouldn't be surprised if the main filter cap, and perhaps output coupling cap, are at least initially quite leaky and even if they re-form okay it might be worth at least considering renewing them with modern ones for peace of mind; but let's see how it goes with a bit of limited voltage first.

Yes, intact fuses are a hopeful sign, but still start with the lowest wattage limiting lamp you can find.

[J M Fahey]

Might have some "same era" similarities, but it's not an Escort.
The power transformer is wimpy and together with the heat sink limits power as noticed, otherwise that circuit might easily give 50+ watts.
Oh well.
The speaker is much heavier than expected in a standard 30W amp, and surprisingly in an English amp, is American made, although Dallas had some affiliations both sides of the Atlantic ant that might explain it.
The speaker frame screams late CTS/early Eminence, doubly so because of the square magnet, too sleepy now to check the "67" EIA code, so please somebody do.

[gaioshin]

Looking at the schematic for the Escort 30, with the exception of the preamp (and the fact there are fuzz controls, etc.) there are a lot of similarities indeed to it.

Double checking the actual cabinet itself, I can actually see an "D.M.I. Inspected" stamp, furthering the case for it being a Dallas Music Industries product (be it re-badged as "ELEM").

I carefully metered and checked most of the electrolytics for shorts initially, then I re-soldered the loose capacitor. Plugged it in via my dim bulb tester and flicked it on ... nothing... 

...After a brief poke and prod with a plastic paintbrush handle to quickly and very crudely check for any more loose or dry joints, there was life - but it the connection was actually temperamental at the power switch! I really should've relied on Occam's Razor more! Re-soldering the wire joins on the switch and the pilot light means that it *seems* to be working - although I am getting life from touching the jack sockets with my hands (i.e. changes in the noise levels and also responses from fiddling with the three band EQ knobs), a cable doesn't seem to yield much response, so my next point of investigation are the jack sockets themselves 

Will update a little later when I progress a bit further with it - I also spent a little bit of time trying to get rid of the excess aluminium oxidisation on the speaker, supporting bracket, fasteners, etc., but trying to do so whilst avoiding damage to any existing markings is proving quite a challenge.

[J M Fahey]

Just wipe the speaker with a rag and a few drops of kerosene.
Repeat until new rag comes out clean.
Don't worry about erasing markings, just take a picture first.