Quad question

[kevzep]

Thanks tcdriver,

I will get low capacitance cables when I replace them - does what I describe sound like it may be resolved by replacing the cables?

Is the cartridge a CD4 approved cart? This is the other thing often overlooked....

 

[patwalsh]

Yes - specs seems to line up correctly and before I bought it from LPGear.com, they confirmed it is. taking their word for it may be a mistake, they are out to make a sale.. But I do believe it is.

 

[kevzep]

Yes - specs seems to line up correctly and before I bought it from LPGear.com, they confirmed it is. taking their word for it may be a mistake, they are out to make a sale.. But I do believe it is.

I wonder if its worth buying a JVC CD4 cart if you don't have any success with the cables?

 

[tcdriver]

Thanks tcdriver,

I will get low capacitance cables when I replace them - does what I describe sound like it may be resolved by replacing the cables?

If there is too much capacitance, the high-frequency carrier and modulated signals will not be properly delivered to the demodulator in your Sansui. Based on your description of the problems you are having with detecting the carrier, I believe that it is highly likely that the problem is too much capacitance. Reducing the capacitance should resolve the problem.

During the quadraphonic era many, but not all, turntables were sold with low capacitance wiring in the tonearm and the supplied interconnects were also low capacitance. Again, you need for the sum total capacitance for the combination tonearm wiring and interconnects to be less than 100pF. Replacing the interconnects with low capacitance cable is only part of the solution, if the tonearm wiring capacitance is high. You need to know the total capacitance.

 

[kevzep]

If there is too much capacitance, the high-frequency carrier and modulated signals will not be properly delivered to the demodulator in your Sansui. Based on your description of the problems you are having with detecting the carrier, I believe that it is highly likely that the problem is too much capacitance. Reducing the capacitance should resolve the problem.

During the quadraphonic era many, but not all, turntables were sold with low capacitance wiring in the tonearm and the supplied interconnects were also low capacitance. Again, you need for the sum total capacitance for the combination tonearm wiring and interconnects to be less than 100pF. Replacing the interconnects with low capacitance cable is only part of the solution, if the tonearm wiring capacitance is high. You need to know the total capacitance.

Actually yes this is a very relevant and good point and probably the best place to start.

 

[Macdude]

I realize this thread is a year old, but it has some great info regarding the variomatrix system. I have the 7001 model. I've gone through every board on it as well as repaired the CD-4 demodulator. I've attempted to perform the "holy grail" alignment of the QS boards, however, I can't get it quite right. The separation appears fine but there is notable pumping in the rear channels whenever a signal is in front-center. For instance, when the vocals start, the rear channels pump quite notably. Once the vocals stop, the pumping stops. The alignment doesn't quite follow the same results as the instructions for me either. VR3 and 4 adjust the right front/rear and left front/rear separation as per the inctructions, however, VR1 and VR2 simply act as volume controls. "Low and Equal" doesn't fully apply. How low is low? I adjusted them to about 11 oclock, which is as low as the signal gets before the trimmer loses effect. The enlongated instructions on the QRX Restore site says to listen to a stereo signal in QS mode while monitoring the front channels. Doing this, adjusting VR4 should cause the stereo separation to collapse down to near mono. This never happens for me. VR4 has zero effect when trying this.

I've replaced one of the HA1327 ICs, as I couldn't make any adjustments when I started working on the receiver. Supply is set dead on at 25VDC. I have swapped in the other ICs as well but haven't had any change. Caps are new, blend resistors are removed. Trimmers were all removed, checked and tested fine. I almost need someone intimately familiar with this adjustment to walk me through it. Maybe someone with the same LPs as I have can take a listen and tell me if what I'm hearing is normal.