Sylvania Exponent 4/40 Sound Issues

[old_tv_nut]

If you wired the pot correctly, you should have been able to adjust the signal level all the way from maximum to zero. Is that the result you got?
Was the distortion there even at low level?

[old_tv_nut]

L-attenuator using potiometer

Cartridge connects to Vin(1) and ground (3). Amplifier connects to wiper (2) and ground (3)

[Electronic M]

If you did it the way oldtvnut described and there is still distortion the next thing I'd try is connecting the cartridge to a different amp and checking for distortion. I'd look for a tube based device as those usually expect a ceramic cartridge on their phono input.
If distortion is still present on another amp I'd say it's the cartridge and get another one. If the distortion is gone with the same cart feeding a different amp, then the amp in the Sylvania is suspect.

Ironically I could have bought a rough one of these Sylvanias sans speakers yesterday for a buck in the WARCI swapmeet donation auction... I've got enough phonos and too little space so I passed.

[cooljer]

Guy--thanks for the quick replies. Yes, per your diagram the pot was wired correctly. The pot did the range from low to high and at all levels the distortion was the same.
Tom--I'll have to ask around for an amp that takes a ceramic input. I currently have nothing that will do that.

[cooljer]

I tried something off the cuff and was surprised by the reults. I ran the phono cable from the turntable to my ATUS AM150 mixer (magnetic phono input). Took the mixer output cables and plugged it into the AUX inputs on the Exponent. It sounded great, along with the bass and treble--no distortion. I then put the cable from the turntable straight to the AUX input on the Exponent. No distortion, but bass and treble was fair. What are your thoughts. I posted videos on YouTube with the distorted sound from the new cart and running with all Exponent internal cables. The second video shows the mixer hookup and the non-distorted sound. Y/Tube links:

https://youtu.be/_51NLbt21ho

https://youtu.be/6U6iTv3F-O4

Thanks.

[old_tv_nut]

So, the only common thing about the distorted case is going through the preamp?
Are both Left and right distorted? Or could one side of the preamp be defective?

[old_tv_nut]

http://sylvaniaexponent440.blogspot....pecifatio.html

[jr_tech]

Looks like the 25 volt supply is used by the right and left preamp stages and nothing else... is it ok?

jr

[cooljer]

Yes, distortion is on both channels. I have not pulled the electronics out yet. Would the mixer test confirm that the cartridge/needle is good and the issue could be in the amp?

[old_tv_nut]

Originally Posted by cooljer

Yes, distortion is on both channels. I have not pulled the electronics out yet. Would the mixer test confirm that the cartridge/needle is good and the issue could be in the amp?

Seems to be leading towards that, especially if it was only one side.
Anyway, the usual suspects - power supply, electrolytics (the 1 microfarads), paper caps, then resistors.

I would start by checking the 25 volt supply, then check all voltages in the preamps. If 25 volts bad, fix it first. Then if internal voltages bad, check the 1 microfarad caps, then...

[cooljer]

Checked 25 volt supply--it tested good.

[Electronic M]

I'd suspect caps, K1 and K4, the discrete resistors, and the preamp transistors in that order.

Bypassing the preamp with that external mixer pretty much confirms the preamp is at fault.

[cooljer]

Thanks Tom--I will check those out.

[zeno]

PHONO pre amp is source trouble. ( X1 & X6 )
Try C3 & C8.
Check the 25V line. There should be a lytic cap there, change it.
Without signal check the voltages on X1 & X6 be sure they are very close.
If one is leaky it could effect the "good" channel & make both bad.
Used to happen to cheapo stereos in the 70's.
Be nice if you could post schematic of power supply area also.

Zeno

[cooljer]

Zeno, I will check those out. I have attached a few Photofact sheets which cover this unit. Thanks.