Studer A807 replay frequency response query - UK Vintage Radio Repair and Restoration Discussion Forum

jascha · 28th Dec 2015, 11:10 am

Hi everyone,

I came across an odd experience recently when checking the azimuth of one of my Studer A807s with a test tape and am asking for some understanding please as to what is going on and what could be the problem and a possible easy fix.I wanted to check the azimuth of my machine which I do roughly once a year and upon playing the 10Khz tone and viewing the result on a scope, the azimuth was fine however on one of the channels I got a ghostly display of the waveform shifted by 180 degrees I would imagine together with the actual waveform on the display. It only showed up on the RH channel and am wondering why I'm not getting just a clean waveform. The fact that I used a copy of a test tape made on brand new Studers at the time surely is not the reason as otherwise it would do it on both channels?

The machine performs flawlessly but could this be the case that some caps are playing up somewhere? Is it advisable to recap the whole machine/s at this day and age? I think the softwares on them are from 88/90 era.
Thanks for any advice. If I need to post an image of the scope image I am happy to try and upload this when I get back home in a couple of days.

Cheers

cmjones01 · 28th Dec 2015, 11:24 am

That sounds more like scope trouble to me. I can't think of any possible fault with a tape recorder which would cause the output to occasionally swap phase. Try adjusting the trigger level control on your scope and I'm pretty sure the ghost will disappear.

Chris

jascha · 28th Dec 2015, 11:37 am

Hi Chris,

Thanks for response. maybe I should have made myself better understood by stressing that the original waveform doesn't disappear. It stays fixed however next to it there is an extra waveform displayed shifted and dimmer. Cannot though remember if it does it on all frequencies. I need to test this tape on my other studer to rule out the test tape and also maybe sway headblocks too and see if problem shifts. Please in the meantime I would appreciate any other thoughts

Cheers

Michael Maurice · 28th Dec 2015, 12:31 pm

I concur with Chris, this is probably due to a mis-setting on the scope, try altering the trigger levels

jascha · 28th Dec 2015, 12:58 pm

I shall have another try and adjust the scope trigger and see how it goes. In the meantime any advice on any thoughts of recapping audio boards at some point ? Or is it the case of if it ain't broken don't fix it?

Cheers again

julie_m · 28th Dec 2015, 1:21 pm

If it's an analogue 'scope, the screen could be being refreshed fast enough for you not to notice the odd "missing" screenful when the trace appears in the wrong place due to false triggering.

jascha · 28th Dec 2015, 2:03 pm

Aha, it sounds like a triggering situation then. Glad about that. My scope is an analogue Tektronic 453?

Thanks

28th Dec 2015, 11:10 am	#1
jascha Hexode Join Date: Nov 2005 Location: Kent, UK. Posts: 332	Studer A807 replay frequency response query Hi everyone, I came across an odd experience recently when checking the azimuth of one of my Studer A807s with a test tape and am asking for some understanding please as to what is going on and what could be the problem and a possible easy fix.I wanted to check the azimuth of my machine which I do roughly once a year and upon playing the 10Khz tone and viewing the result on a scope, the azimuth was fine however on one of the channels I got a ghostly display of the waveform shifted by 180 degrees I would imagine together with the actual waveform on the display. It only showed up on the RH channel and am wondering why I'm not getting just a clean waveform. The fact that I used a copy of a test tape made on brand new Studers at the time surely is not the reason as otherwise it would do it on both channels? The machine performs flawlessly but could this be the case that some caps are playing up somewhere? Is it advisable to recap the whole machine/s at this day and age? I think the softwares on them are from 88/90 era. Thanks for any advice. If I need to post an image of the scope image I am happy to try and upload this when I get back home in a couple of days. Cheers

28th Dec 2015, 11:24 am	#2
cmjones01 Nonode Join Date: Oct 2008 Location: Warsaw, Poland and Cambridge, UK Posts: 2,681	Re: Studer A807 replay frequency response query That sounds more like scope trouble to me. I can't think of any possible fault with a tape recorder which would cause the output to occasionally swap phase. Try adjusting the trigger level control on your scope and I'm pretty sure the ghost will disappear. Chris __________________ What's going on in the workshop? http://martin-jones.com/ Last edited by cmjones01; 28th Dec 2015 at 11:25 am. Reason: typo

28th Dec 2015, 11:37 am	#3
jascha Hexode Join Date: Nov 2005 Location: Kent, UK. Posts: 332	Re: Studer A807 replay frequency response query Hi Chris, Thanks for response. maybe I should have made myself better understood by stressing that the original waveform doesn't disappear. It stays fixed however next to it there is an extra waveform displayed shifted and dimmer. Cannot though remember if it does it on all frequencies. I need to test this tape on my other studer to rule out the test tape and also maybe sway headblocks too and see if problem shifts. Please in the meantime I would appreciate any other thoughts Cheers

28th Dec 2015, 12:31 pm	#4
Michael Maurice Moderator Join Date: Feb 2006 Location: Wembley, Middlesex Posts: 7,225	Re: Studer A807 replay frequency response query I concur with Chris, this is probably due to a mis-setting on the scope, try altering the trigger levels __________________ Forum Moderator http://www.michaelmauricerepairs.co.uk/

28th Dec 2015, 12:58 pm	#5
jascha Hexode Join Date: Nov 2005 Location: Kent, UK. Posts: 332	Re: Studer A807 replay frequency response query I shall have another try and adjust the scope trigger and see how it goes. In the meantime any advice on any thoughts of recapping audio boards at some point ? Or is it the case of if it ain't broken don't fix it? Cheers again

28th Dec 2015, 1:21 pm	#6
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: Studer A807 replay frequency response query If it's an analogue 'scope, the screen could be being refreshed fast enough for you not to notice the odd "missing" screenful when the trace appears in the wrong place due to false triggering. __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

28th Dec 2015, 2:03 pm	#7
jascha Hexode Join Date: Nov 2005 Location: Kent, UK. Posts: 332	Re: Studer A807 replay frequency response query Aha, it sounds like a triggering situation then. Glad about that. My scope is an analogue Tektronic 453? Thanks