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Tim7099

Member
Joined
Dec 23, 2021
Messages
19
Location
Swanage, UK
Hello one and all, as a long time collector of records I recently got into quad by chance of picking up an EMI SQ1500 decoder very cheaply and, as I had plenty of spare equipment and a few SQ records, I decided to set up a four channel system to see what I had been missing since having zero cash back in the heyday of quad in the mid 70s.

Since that first foray I decided to delve a little deeper and now have a reasonable set up that handles SQ, QS and CD-4 although I am generally disappointed with the later due to the well known issues of record wear and tear and I have an odd problem with one of my decoders and although this is probably not the place to do so would also like to pose my first question, if that is acceptable.

I am currently using a Pioneer QD-240 decoder for my CD-4 records which works OK but I also have a JVC 4-DD5 which has a rather odd issue that someone might also have come across. Basically, it has no front – rear separation. Using the JVC adjustment record, the Radar beacon lights as it should but adjustment to the separation pots just increases or decreases level on the channel being adjusted. Both front and rear stay at a similar read out as the level goes up and down (as viewed on the VU meters of my Sony SQ decoder). When I originally bought the decoder it seemed to work, at least as far as the left channel is concerned, but it soon became obvious that something was wrong. The carrier adjustment tone also cannot be heard.

I’m not at all familiar with demodulators of any kind but like most of us that value our vintage equipment am perfectly capable of exchanging components and using a multi meter/scope if need be. I’m really just asking for suggestions as to where to start looking, I assume a semi conductor has decided to fail or partially fail but I suppose it could be any one of a number of things that have decided to call it a day after almost 5 decades, NOS or not.

If anyone has any ideas or can suggest the way to proceed I would be grateful.


May I wish you all a Merry Christmas and a Happy New Year.

Kind regards
Tim
 

Tim7099

Member
Joined
Dec 23, 2021
Messages
19
Location
Swanage, UK
Just a foot note to my original post (that I had forgotten about) the problem with the CD4 decoder was traced to a defective transistor. This I found rather odd as it measured OK on my component tester but, when in circuit, voltages were out of kilter with those shown on the circuit diagram and also with it's opposite number on the other channel. Two new transistors and all was well. but it does go to show that you can't always rely on your cheap Chinese test equipment!
 

Sonik Wiz

👂 500 MPH EARS 👂
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May 30, 2005
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Kansas City
Just a foot note to my original post (that I had forgotten about) the problem with the CD4 decoder was traced to a defective transistor. This I found rather odd as it measured OK on my component tester but, when in circuit, voltages were out of kilter with those shown on the circuit diagram and also with it's opposite number on the other channel. Two new transistors and all was well. but it does go to show that you can't always rely on your cheap Chinese test equipment!
Thanks for the update. Glad to see you're still stickin' around! Seems your quite the CD-4 fan. But I've never heard of an EMI SQ1500 decoder before. I should look into it.

And, isn't Swanage where Basil Fawlty is supposed to be from?
 

Tim7099

Member
Joined
Dec 23, 2021
Messages
19
Location
Swanage, UK
Hi Sonik,

Thanks for your interest, yes I'm still here, quiet on the whole but still around. First of all Basil Fawlty, the series was set in a holiday resort called Torquay, which is on the same stretch of coast as Swanage but around a 100 miles further West, so still pretty local by your standards :) As for Basil Himself, he might have been supposed to have come from Swanage in the series, I'm afraid I don't know, but the whole thing was quite amusing in it's own way don't you think?

The EMI SQ 1500 is a bit of a mystery to me as well. I know that it was sold as an accessory to the EMI 1515 amplifier in the early/mid 1970's but I can find no literature, apart from the handbook that came with it and an entry in a HiFi Year book that I have from around 1974 to support it ,and, somewhere out there is a scan of an advert in a magazine too. I suppose that it probably didn't sell well, what quad stuff did? Appearance wise it looks very similar to the Tate 8, same control layout etc. I'm not suggesting that the SQ1500 is a re-badged Tate 8 - but it could be, the price was very similar too. I have put it back into service recently as I have found that the "suck out" that sometimes afflicts the Sony 2020 can be rather annoying. There is none of that with the EMI and, as would be expected, not much separation either. Sounds nice though, within it's limitations. You might be amused to hear that EMI claimed 60dB of separation for the front channels and 20dB for the rears but there is no mention of front/back separation :)

I am a late comer to quad, it was always well beyond my pocket when it was around back in the day. CD4 strikes me as a love/hate relationship, when the software is unworn it's great but when wear dominates it sounds dreadful, easily as bad as the jarring, grating overload sound that can plague digital recordings, quite horrible in my view. Sadly, in the UK ,Quadradiscs tend to be pricy ( they all do!) so I don't have many. Luck of the draw whether they sound OK or not. I have a couple of Tomita discs that sound quite awful but a Japanese pressing of Cosmos which is perfectly fine. Go figure I suppose.

Stay safe
Tim
 

par4ken

2K Club - QQ Super Nova
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The separation specifications would be correct. The front is limited by the decoders electronics the rear more by the accuracy of the phase shift network. Back in the day 20 dB was considered to be perfect separation (voltage difference of 10 to 1). Most phono cartridges only gave 20dB separation. Front to back separation would be only 3db.

Logic decoders like the Sony 2020 use a bit of blend across the rear channels, reducing separation to 12 or 15 dB. IMHO that blend is very audible. Blend is used there to improve Cf to Cb separation, without it there is no centre separation at all. Logic action can cause annoying pumping if it is not set up properly.

For years I used the Audionics 106A, which did not use logic but had an accurate 6 pole phase network. I believe that the board was actually imported from England and sold there under a different name. Audionics didn't like the logic circuits that were available at the time but promised to make logic available when it was perfected. We had to wait until the late seventies to get "Tate DES" in the Space and Image Composer!
 

esimms86

1K Club - QQ Shooting Star
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Just a foot note to my original post (that I had forgotten about) the problem with the CD4 decoder was traced to a defective transistor. This I found rather odd as it measured OK on my component tester but, when in circuit, voltages were out of kilter with those shown on the circuit diagram and also with it's opposite number on the other channel. Two new transistors and all was well. but it does go to show that you can't always rely on your cheap Chinese test equipment!
Sorry to hear that your transistor was Fawlty(maybe the clue was in the Manuel?); anyway; glad to hear that everything’s working now. And I do hope that you somehow got in on @edisonbaggins’s CD-4 blowout.
 

Tim7099

Member
Joined
Dec 23, 2021
Messages
19
Location
Swanage, UK
The separation specifications would be correct. The front is limited by the decoders electronics the rear more by the accuracy of the phase shift network. Back in the day 20 dB was considered to be perfect separation (voltage difference of 10 to 1). Most phono cartridges only gave 20dB separation. Front to back separation would be only 3db.

Logic decoders like the Sony 2020 use a bit of blend across the rear channels, reducing separation to 12 or 15 dB. IMHO that blend is very audible. Blend is used there to improve Cf to Cb separation, without it there is no centre separation at all. Logic action can cause annoying pumping if it is not set up properly.

For years I used the Audionics 106A, which did not use logic but had an accurate 6 pole phase network. I believe that the board was actually imported from England and sold there under a different name. Audionics didn't like the logic circuits that were available at the time but promised to make logic available when it was perfected. We had to wait until the late seventies to get "Tate DES" in the Space and Image Composer!
I would imagine that a 3dB front - rear separation wouldn't have been much to boast about, which probably explains the the lack of this item of data in the specifications. It's amazing that such a figure is even remotely sufficient but history says otherwise. Incidentally the pumping or "suck out" out as I call it usually seems worse on the rear left in the Sony SQ2020 so my guess is it probably in need of a service, not that I feel like giving it a go to be honest :)
 
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