Revox b790 troubleshooting

[Oscarshock]

Basically the technician who gave service to my turntable said that it is difficult and complex to address this problem and he said this will not have significant impact to the performance of the turntable so I should content with it as long as it actually develops into a issue in the future. Nonetheless I still want to gather more opinions from your guys about it and even better if you can explain what the cause is.

Here is the description : When I press the start buttom, a pump in the end of the tonearm should control the speed of dropping so that the stylus is going down gently. Whereas in my case, the stylus looks like just failing down quickly without anything is pulling it back and hold on when it touch the vinyl surface. So it sounds like a sudden drop and likewise there is also sudden up. When I press the button again, the stylus is pulling aways from the vinyl suddenly and it is so quick that it even shakes a bit on the hang on position.

By the way, there is also a problem of suspension. So basically if the lid clump the base tight and I close it down while the platter is turning, a scratching sound appeared inside the turntable, it sounds like a metal scratching sound. The technician told there is nothing to worry about either if I close the lid slow. However I found out something strange, the sound won't appear now no matter how fast I close the lid if I didn't clump the base and the lid that much tight. What I meant by clumping tight is that the lid doesn't slide down deep into the back holding position for it.

I wonder if any revox owner familiar with this problem and how difficult it is to deal with. Thank you for any advice.

 

[borchee]

Which damper is in there, bellows/accordion or cylinder-piston?



The latter has a tiny hole in the botom of the cylinder. By turning it, the hole gets covered (fully, partially, not at all) by the bracket it's clamped (or screwed) onto, thus regulating airflow (lowering and rising speed).

Bellows is more challenging.

Don't understand what you mean with the second issue. Susspension of the subchassis can be adjusted from underneath - it shouldn't touch (lean against) the base. Transport-screws must be loose.

 

[Oscarshock]

Hi I am not sure I understand what you meant by the way also sorry for my by wording. Therefore I shot a video for demonstration

As you can see the stylus bumps a little bit when it raise. The lid problem is less worrisome to me so let's focus on this stylus problem first.

 

[borchee]

Yeah...bellows. Not much you can do easily to adjust speed.

Your arm is set to descend to low.

Set the stylus/arm lowering depth according to manual. The adjustment screw also stabilises the arm while travelling up/down - it has no effect on playback...if not set to high, that is.

 

[Oscarshock]

So do you suggest me to adjust the height higher or lower in this case to stablize it? And the bumby of the stylus when going up is because the arm is set too low? is that what you mean? My technician said it could be the case that a component is miss.

 

[borchee]

1) Take the record off
2) Swing the tonearm into play position
3) Drive the arm/stylus to above the inner ridge of the mat...towards left...to the spindle
4) Power the TT off and stopp the platter, or wait it does so
5) Turn the screw in, so it raises the arm
6) Lower the arm by pushing on the square lifting rod
7) Adjust the stylus height/depth with the screw so that it just barely touches the ridge of the mat and then lift it a smudge. Done.

The procedure is described in the manual...it just suggests to lower the arm while platter/mat is spinning and check for "acoustic signal" - stylus touching the mat. You can do that, but I was always reluctant to go this way.

 

[Oscarshock]

I have done this myself following the manual before but what is the square rod? I thought the up and down of the arm is controlled totally by turning CCW and CW to the screw on the top.

 

[borchee]

I thought the up and down of the arm is controlled totally by turning CCW and CW to the screw on the top.

Yes, the screw controls how far down the arm/stylus can travel. Set it as I told you.

Lifting rod...its square (crosssection)...it lifts the arm via a spring (pull-magnet gets released and the spring takes action).

 

[Oscarshock]

Thank you. I got what you mean now.