Cutterhead SX-74 problems!

[StanSimon]

Hi, guys! I have a problem, need help. I must say - I'm new, many still do not understand. I have two cutterheads SX-74 with mirrored problems. One cutterhead has the sibilants in the left channel, the other in the right channel. Everything seen in the photos. What are the ways to solve the problem? Is it possible to swap coils from one cutterhead to another? If so, can it be done independently? Or need to rewind all the coils to have the correct DC resistance (Ohm 4,7)? I would be grateful for any hint.

heads_freq_test.jpg

[opcode66]

Do not attempt to disassemble! Unless you know how. Don't.

Where are you located? We can connect you with a lathe tech.

I think you are measureing the dc resistance of the feedback coils. The drive coils will measure 4.7 Ohms. The pins for the drive coils are in the same location as the feedback on the opposite side of the connector lengthwise. You measured the pins at one end. Now measure the ones at the other end.

It seems to me that your head was rewound at one point. The feedback coil values are very widely ranged which means they weren't wound very accurately. Anyway, it sounds to me like you have a calibration issue. The coils can have some variance to them that is adjusted and accounted for in calibration. Have you calibrated your amp rack recently? The calibration would be for one head specifically. Swapping heads would require recalibration.

[StanSimon]

Unfortunately I'm on another continent. I'm sorry, I didn't know how to measure. Now I did as you said. Cutterhead No. 729 has a resistance of 4.8&3.9 Ohm: https://youtu.be/p9qUXEEQqxc, cutterhead No. 653 has to 4.9&4.9 Ohm: https://youtu.be/0NGts3HUwAU
About calibration: I think it was done a very long time. You mean this?

CalibrationInstructions.jpg

If so, I think I don't have all equipment in the rack for this operation. Here you can see all that I have: https://youtu.be/vtzfU0DtMNs
Maybe there's an alternative way?

[jjgolden]

Here's a video from Chris Muth's site. (thanks Chris!)

http://www.taloowa.com/SX74.html

You can click on the blue highlighted links for video and step by step PDF instructions on how to calibrate drive and feedback levels in the SAL74 / SX 74 combo.
Read the instructions a thousand times, then if you feel up to it, you can give it a go. You may want to consult directly
with Chris or someone else who can walk you through it to avoid damage to the head.

JJG

[StanSimon]

Thank you so much, colleagues. I will try...

[opcode66]

Any accurate 1k and 5k tone source and a callibrated VU meter, a test tone record, and a tonearm on your lathe is all you need. The calibration process is easy. Totally required. I think this will resolve your issues. However it should be noted that the calibration is specific to one head. If you swap out heads, you must recalibrate.

You heads have been rewound. It seems to me that both heads were repaired at some point. All four drive coils are not Neumann spec. If anyone can roll the coiks correctly, they can nail the 4.7 Ohm value. Check my latest dev video. I'm making 4.7 ohm coils on plastic bobbins. If I can do that in on plastic, why are these not 4.7 with accurate metal parts? I wonder who did the repairs....

[StanSimon]

Any accurate 1k and 5k tone source and a callibrated VU meter, a test tone record, and a tonearm on your lathe is all you need. The calibration process is easy. Totally required. I think this will resolve your issues. However it should be noted that the calibration is specific to one head. If you swap out heads, you must recalibrate.

You heads have been rewound. It seems to me that both heads were repaired at some point. All four drive coils are not Neumann spec. If anyone can roll the coiks correctly, they can nail the 4.7 Ohm value. Check my latest dev video. I'm making 4.7 ohm coils on plastic bobbins. If I can do that in on plastic, why are these not 4.7 with accurate metal parts? I wonder who did the repairs....

One head was rewound by someone in the US. The second was already like this when we bought it. Yes,I saw your video on YouTube. Your response to my comment led me here, thank you. In my country there are no specialists who can rewind. There is one who could, but he doesn't know how to disassemble the SX and don't know what thickness wire should be. And the head repair in another country, with delivery to both locations is very expensive for me now. And I learned... About a year ago came spec. from Europe and did the calibration head No. 653, but it still had the sibilants in the left channel. So that might be another cause, but first I'll do the calibration.

[opcode66]

The enameled wire for the drive coils is flat. It is impossible to purchase to the exact specification. You have to make your own like I do.

Oh, that is you... Hey! Welcome.

[StanSimon]

Do you mean I must to buy a round wire and flatten it? Another misunderstanding in the disassembly is the piston rods that are glued? How to remove? And what kind of glue can be used after?

[opcode66]

Why would you even attempt to take an SX cutterhead apart? Leave it to the experts. If you don't have some required items, you can't make the flattened wire accurately. Yes, you buy round and flatten it. But, there is more to it than that.

Don't disassemble your cutterhead. There are folks in Europe who can do repairs. People here can direct to the right folks. Flo can help for sure. But, there are others.

[StanSimon]

Maybe I want to become an expert))) just kidding. Of course I'm not going to risk it. It's just a new theme for me, all want to understand. Florian promises already 3rd month, but does not arrive for some reason.

[StanSimon]

Nothing has changed after calibration of both cutterheads. Still sibilants, where the high resistance of the feedback coils.

[mossboss]

Check out Roberto at cutter head repairs in Bologna. Italy
Best

[Greg Reierson]

I had a strange distortion on my SX74. Chris Muth found something loose and fixed it. Could be similar. Very hard to diagnose in the field without the right equipment.

[StanSimon]

Do not attempt to disassemble! Unless you know how. Don't.

Hi. I did it. Moved the coil from one head to another. Now I have a head where the two coils with 4.9 and about 90 Ohms. Replaced the chips and capacity in sal74. Calibrated already 1000 times in various ways. Frequency response feedback is close to linear. Still I can't cut the music at the proper volume level without distortion. Maximum output level on the 20 minutes lacquer is -8dBfs. If more appear distortion at 10 kHz. It remains to think that the accelerate limiter guilty. Is there such a thing? I found a lot of tuning stuff on the Board. It may also need to be calibrated somehow? I found nothing about it in neuman's documentation.

[leo gonzalez]

bypass the bsb and run test...


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[StanSimon]

bypass the bsb and run test...

What is bsb?

[leo gonzalez]

correction,

dont do anything until you have someone that knows helping you.

[opcode66]

I agree with Leo. Wait until a professional can assist.

But, to answer. BSB's are Acceleration Limiters (High Frequency Limiters) for cutterhead protection. Your rack might not have them.

[StanSimon]

I agree with Leo. Wait until a professional can assist.

But, to answer. BSB's are Acceleration Limiters (High Frequency Limiters) for cutterhead protection. Your rack might not have them.

I have them. I wrote about them:

........ It remains to think that the acceleration limiters guilty. Is there such a thing? I found a lot of tuning stuff on the Board. It may also need to be calibrated somehow? I found nothing about it in neuman's documentation.