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Author Topic: Technics RS1520  (Read 3534 times)

Offline mossfred

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Technics RS1520
« on: December 08, 2010, 03:19:27 PM »
I now have a 1520 to replace my 1500 because of the ability to set up for tapes without going into the machine.
My 1500 will produce a flat frequency response to 19khtz @7.5ips the 1520 will go flat to 10k then drops of sharply. Any adjustment to the bias or eq will extend the response to 16khz but with a 7db lift between 2khz to 12khz or worse, and it sounds nasty. I have tried all the headblocks i have including a new 4 track record but they all produce similar results. Is there something that i dont know or understand that is causing this problem
or must there be an electronic fault. The problem is affecting both channels.
Fred

Offline mikkelbreiler

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Re: Technics RS1520
« Reply #1 on: January 20, 2011, 05:15:41 AM »
My 1500 will produce a flat frequency response to 19khtz @7.5ips the 1520 will go flat to 10k then drops of sharply. Any adjustment to the bias or eq will extend the response to 16khz but with a 7db lift between 2khz to 12khz or worse, and it sounds nasty. I have tried all the headblocks i have including a new 4 track record but they all produce similar results. Is there something that i dont know or understand that is causing this problem
or must there be an electronic fault. The problem is affecting both channels.
Fred
My first suspect is the BIAS circuit as it happens on both channels at the same time.

Normally I'd trace the signals past switches and cables to see if the deterioration happens at a certain location on a pcb or at a component which is then replaced. But with two channels acting up simultaneously I'd start with stuff that can affect both channels right off, or you are perhaps having both channels fail on the same components in both channels.
Repro of source is identical to source itself right? It is only the signal off the tape that is bad?

Is a tape just recorded on this deck ok playing on the other deck? If yes, then recording (and BIAS) is ok and you're looking at something in the repro path.

If you have not noticed any differences when playing back a tape made on the 1500, then I'd suspect the BIAS.

-Mikkel

Offline mossfred

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Re: Technics RS1520
« Reply #2 on: January 20, 2011, 12:24:44 PM »
Hi Mikkel,

It seems that the eq circuit may be the problem as moving the lever does nothing and as i understand it on this machine there different settings of eq for each speed selected and this does not seem to be happening either!

Fred

Offline xcortes

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Re: Technics RS1520
« Reply #3 on: January 20, 2011, 03:41:07 PM »
The eq lever is only for recording
Xavier Cortes

Offline ironbut

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Re: Technics RS1520
« Reply #4 on: January 20, 2011, 09:20:33 PM »
Hey Fred,

You should probably give us a little more detail if you want something other than generic answers.
In particular, you should be more specific. For instance, you should explain the procedures you're followed when measuring the freq. response.

Do you have a good test tape? If not, you should get one. Otherwise, it's hard to figure out whether the issue is on the recording side of things or the playback.
If you get a test tape, you can also check the head alignment. No amount of bias or eq can overcome heads which aren't aligned. You mentioned that you have a new 4 track record head but just because it's new, doesn't mean that it's adjusted correctly.
There are many adjustments other than the head alignment on both of your machines. Almost all of them can cause high frequency issues and are (for the most part) getting the tape to travel across the heads correctly.
Stuff like tape tension, pinch roller pressure and keeping the tape from being pushed against either side of all  the guides/tensioners effects high frequency response.

If the 1520 is new to you, I'd suggest that before you start to change anything, you need to go through and service all the mechanical elements. One of them is more than likely, the problem.
steve koto
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Offline mossfred

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Re: Technics RS1520
« Reply #5 on: January 21, 2011, 05:38:51 AM »
It is not a mechanical issue, the machine will playback perfectly confirming playback head alignment and there is no difference other than 1 or 2 db between the three headblocks i have tried, incidently they perform perfectly on my other machines, the tape tension is good and it is travelling as it should visually and it it plays ok. I am aware the eq control is on the record side and it does not function apart from that, i dont know how to give any further detail!!!
Fred