Sansui QSD-1 Modification Question

[Wagonmaster_91]

I scored a good deal on a Sansui QSD-1 that I think the seller thought was dead. I didn't really need it since I already have one in my system, but the deal was too good to pass up (you how that is...). Turned out it only had a blown internal fuse (it was a .5V instead of the required 1V) and a broken power toggle switch.

I know the QRX receivers and the QSD-2 and QSD-1000 have blend resisters (both of the ones I own have this modification) but I could not remember if the QSD-1 also used blend resisters. If so, I can't remember if the one in my system has been modified and it would be a real chore to remove it just to find out. I have been searching the QQ and web for info, but everything I find refers to the QRX and QSD-2 units. Since the QSD-1 splits the frequencies into high, medium and low for processing with separate boards for each, maybe it does not use blends. Anyone know?

I have pdf service manuals for the QSD-1 (and QRX-9001) and have been trying to compare the two, knowing the mod for the QSD-2 and 9001. If the QSD-1 does have blends, I'm guessing one of them is on the F-2466 Phase Shifter board at R06. (That's just a guess ...)

Any info is appreciated. Thanks!

 

[Wagonmaster_91]

OK, I found a thread where the blend resistors were discussed.
https://www.quadraphonicquad.com/forums/showthread.php?1554-Sansui-Vario-Matrix-Blend-Resistors
(I even replied to it years ago.)


It does appear that the QSD-1 also has blend resistors, but in the thread QuadBob won't say which ones they are. (QB was probably trying to entice more quadies to unknowingly part with their money and equipment rather than keeping them from messing with their Sansui units. But I digress...) The boards in the QSD-1 and QSD-2 are not the same, so if any of you have info on the QSD-1, please share it. Thanks.

 

[bigbillquad]

Hi. Wagonmaster_91

I got my QSD-2 4 or 5 years ago totally recapped & recalibrated plus the holy grail done.
From Jim Showker he repairs Quad Sansui gear he was or is still a member of QQ & he will try to help people how has a problems, you can get his email address from his web site ( www.qrxrestore.com ) I highly recommend him & I`m sure he will help.

OK, I found a thread where the blend resistors were discussed.
https://www.quadraphonicquad.com/forums/showthread.php?1554-Sansui-Vario-Matrix-Blend-Resistors
(I even replied to it years ago.)


It does appear that the QSD-1 also has blend resistors, but in the thread QuadBob won't say which ones they are. (QB was probably trying to entice more quadies to unknowingly part with their money and equipment rather than keeping them from messing with their Sansui units. But I digress...) The boards in the QSD-1 and QSD-2 are not the same, so if any of you have info on the QSD-1, please share it. Thanks.

 

[Wagonmaster_91]

Thanks. I emailed Jim, but got no response.

 

[bigbillquad]

Hi. Wagonmaster

I have not kept in touch with Jim in a view years now so I don't now way he has not got in touch with you he might be busy or ?? or family matters. from memory on his web site he has a ph. number you might try if you live in the US.

I just now the work he has done for me in the past has all ways been first rate. he went out of his way to find a cheap courier to keep price down and he substantially packed the QRX 8001 he totally restored for me, for the trip to New Zealand were I live.
Bill...

Thanks. I emailed Jim, but got no response.

 

[par4ken]

I scored a good deal on a Sansui QSD-1 that I think the seller thought was dead. I didn't really need it since I already have one in my system, but the deal was too good to pass up (you how that is...). Turned out it only had a blown internal fuse (it was a .5V instead of the required 1V) and a broken power toggle switch.

I know the QRX receivers and the QSD-2 and QSD-1000 have blend resisters (both of the ones I own have this modification) but I could not remember if the QSD-1 also used blend resisters. If so, I can't remember if the one in my system has been modified and it would be a real chore to remove it just to find out. I have been searching the QQ and web for info, but everything I find refers to the QRX and QSD-2 units. Since the QSD-1 splits the frequencies into high, medium and low for processing with separate boards for each, maybe it does not use blends. Anyone know?

I have pdf service manuals for the QSD-1 (and QRX-9001) and have been trying to compare the two, knowing the mod for the QSD-2 and 9001. If the QSD-1 does have blends, I'm guessing one of them is on the F-2466 Phase Shifter board at R06. (That's just a guess ...)

Any info is appreciated. Thanks!

Reviving an old thread as I'm currently working on my QSD-1. The main problem was dirty switch contacts and noisy output pot. DeOxit cleaned things up nicely.

Yes on the QSD-1 (F-2466 Phase Shifter Board) the resistors are R05 (front blend)and R06 (back blend) both are 39K.

On the QSD-2 (board 2087) they are R39 (front blend) and R40 (back blend) both 100K. Also on (board 2088 is R601 220K) blending the input signals.

On the Photolume they are R53 150K (front blend) and R66 100K (back blend).

 

[Sonik Wiz]

Reviving an old thread as I'm currently working on my QSD-1. The main problem was dirty switch contacts and noisy output pot. DeOxit cleaned things up nicely.

Yes on the QSD-1 (F-2466 Phase Shifter Board) the resistors are R05 (front blend)and R06 (back blend) both are 39K.

On the QSD-2 (board 2087) they are R39 (front blend) and R40 (back blend) both 100K. Also on (board 2088 is R601 220K) blending the input signals.

On the Photolume they are R53 150K (front blend) and R66 100K (back blend).

Do the output blend resistors have matching values? Just wondering since I noticed differences on the Hall & Synth resistors on different units. On the three QS decoders I've bothered to check (QSD1, 2, Photolume) the synthesizer mode resistors all had different values. But they were a bit shy of -7.7 dB opposite phase blend, closer to -10dB. Me thinks that was due to reciognition that stereo material will already have somne out of phase action & better not to over do it.

 

[par4ken]

The Hall and Synth resistors are, Hall 12K (in series with a 10 μF capacitor and Synth is 18K. I haven't checked exactly how much blend they produce but I rather like the sound of the Synth mode as it is. Still thinking about numerous mods that I might want to try but for now I've put the unit back in the rack to do some more listening.

 

[par4ken]

I was working on my QSD-1, I had to clean the switch contacts as they were becoming intermittent. Liberal use of DeoxIT fixed that problem. previously I had replaced many of the electrolytic capacitors with film types. This go around I added polystyrene (.01μF) bypass capacitors shunting the larger polyester coupling capacitors. The final output used 1μF coupling capacitors, I replaced them with 10μF (the very same capacitors that I used in my S&IC). Now my two super decoders contain the same output capacitors. That change improved the bass response of the QSD-1 so there is no difference tone wise between the two. The S&IC is still a bit cleaner sounding but the gap has closed significantly.

I decided to reinstall the blend resistors to see if I could notice a difference. Well I can't say for sure subjectively, front to back separation is still excellent and I don't notice less left to right separation. For a real test a switch could be installed so that you could switch them in and out to see what difference it makes. I think that what I'm getting at is that if you leave the blend resistors in it's no big deal. People used to consider 20dB to be perfect separation. That is a ten to one voltage difference and corresponds to the separation of most phono cartridges. So is 30dB or more really necessary?

So for now my QSD-1 is back in my audio rack expanding stereo to four channel via the synthesize mode. The effect still blows me away after all these years.

 

[Sonik Wiz]

I think that what I'm getting at is that if you leave the blend resistors in it's no big deal. People used to consider 20dB to be perfect separation. That is a ten to one voltage difference and corresponds to the separation of most phono cartridges. So is 30dB or more really necessary?

Good luck on the continuing QSD-1 project & also good question.
I agree that manufacturers would strive for 20>25 dB separation as that was the norm for phono carts & put it on par for stereo. But of course phono carts had varying separation depending on frequency. I can see someone in marketing saying "hey look at that! Right about 2.5kHz we have 25dB separation. Lets put that on the spec list."

And so it probably went with all sorts of varied surround decoding from the 70's. Nobody listed separation vs frequency except for the Sansui QSD-1. Indeed with a left front QS input it is only a few dB down to left back & a few more to right back at 50 Hz or less. It improves at 500Hz & left back is down -20dB from there & up& right back is -40dB & creeps up a bit from there.

A center front signal like wise has very poor separation at the lowest frequncies but for the most is -20dB in the rear chs.

I'm mentioning all of this stuff because the final output circuit in Sansui Vario-Matrix decoders is more than a simple left/right blend resistor. More specifically is -30dB separation better than 20? The Ambisonic NRDC tests say only 12dB amplitude seperation is needed for distinct directional localization. Chucky goes a step further & sez a person can not hear more than 12dB seperation. I would disagree with that depending on several factors. Of course the Surround Master has sep specs exceeding anything of Sansui's & no output blending by frequency or otherwise. I think that is one factor to the exceptional soundfield the SM creates. I can't answer if you can hear the difference between 20 & 30 dB on the QSD-1 but if the blend resistors can't be pinned down as having a real benefit then I'd say perform an ohmage vasectomy.

 

[par4ken]

My thought is that the blend resistors might make the decode action bit smoother, pure speculation I can't say for sure without a-b listening tests. You would have to listen while switching it in and out. It's just my observation that it may not be such a big deal whether you remove them or just leave them in, the separation is high anyway.

I'm sure that with 12dB of separation that you would have no trouble in discerning a sounds direction, but that doesn't mean that that's all you really need. Checking the speciation's of the Sony QSD-2020 and 2050 shows 14dB separation between Lb and Rb , that amount of fixed blend is very audible, audibly pulling the back speakers much closer together!

 

[LB-V]

Technically speaking, I have no business in the conversation...but I like the QSD-1 with blend resistors....what that unit accomplishes as original is amazing to me. I switch between the QSD-1 and SM pretty regularly in a/b for fun, and I'm always amazed how good the old Sansui ranks against the SM. Never really quite as good, but always giving it a run for the money and very close, very enjoyable. Anyway, I prefer having the resistors remain. I have a 9001 without them, but its had intermittent problems, so its been down for a while. Its probably all in my head, but I think it is a bit smoother with them as @par4ken mentioned. Maybe its the tri-band vs. single or maybe my tinnitus is worse now, or better...

 

[Colin London]

I have a working Sansui Pre Amp C-55
you can plug your electric guitar into it.

 

[M-D-Z]

I have a working Sansui Pre Amp C-55
you can plug your electric guitar into it.

No idea, but if you can not, then grab an old Sansui AX-7.

 

[Colin London]

No idea, but if you can not, then grab an old Sansui AX-7.

It is Plugged into my Pioneer 8.1 Modern Amp
Left and Right Audio in.

I bought it in 1980, I think
The C-55 Sansui Pre Amp is special
as it has a Slide Fader so it has double the switches.
If I use the Record Player (Rare)
it goes through the C-55.

If I record through it
on one of my CD Recorders
I can increase the Bass and Treble

And Recording on a Audio CD-R while moving the Fader over for another CD player
gives me a great mixer.

Having Mic or Electric Guitar in - is so clever.

HiFi now needs to do a Pre Amp like this Sansui


In USA some are selling the C-55 on Ebay.