Studer B67 Mk2, calibration. Uneven bass 80Hz-> Ideas? - UK Vintage Radio Repair and Restoration Discussion Forum

backstreets · 24th May 2017, 11:02 am

Hi guys!

I had my B67 break down on me, I restored it 6 years ago and did recap the electrolytics on most pcb cards, but left rec and repro cards. One channel suddenly dropped 20dB in level and started behaving weird overall. Ended up with recapping both channels rec and repro cards as well as swapped ICs on those. All good and I've got a nice and clean signal again.

One thing though that's been bothering me even before the break down is uneven bass response. I had the analyzer going yesterday but forgot to take a screencap of it. Attached you'll find a picture though where I've drawn roughly on top of a downloaded pic of my analyzer. (PLEASE NOTE only the handdrawn red line, the rest of the analyzer doesn't make sense in this matter as it's a downloaded pic)

When calibrating it's good down to 100hz and with the test tape I'll get that nice and even between the channel but then below that it sways out to the right on the analyzer (thus stronger on the right channel). Same thing kind of happens in the top end. All good at 5khz even at 10k it's okay and then it goes off balance between the channels. I'm not at my studio for a couple of days now but from memory bass is a little right-heavy and high treble is left heavy.

The repro cards calibrate fine, so it has to be something with the rec cards I assume without having too much of an electronics background. Any ideas on what's causing this and how to fix it?

Much appreciated!
-L

TIMTAPE · 24th May 2017, 12:30 pm

Do you know that at the higher speeds of 15 and 30ips, bass response is generally lumpy due to "head bump"? You will not get nearly as smooth a response as further up the range.

Here's a link to some graphs showing head bump on various machines:
http://www.endino.com/graphs/

I would test and align each channel on its own, one at a time. The interchannel balance I would do after that as a final check.

Similarly the problems in bass response and treble response are two separate issues. Treat one problem at a time and you'll make steadier progress.

mitajohn · 24th May 2017, 3:27 pm

As per B67 mk2 SM in section 6 there is a detailed calibration guide.

24th May 2017, 11:02 am	#1
backstreets Retired Dormant Member Join Date: Feb 2011 Location: Helsinki, Finland Posts: 22	Studer B67 Mk2, calibration. Uneven bass 80Hz-> Ideas? Hi guys! I had my B67 break down on me, I restored it 6 years ago and did recap the electrolytics on most pcb cards, but left rec and repro cards. One channel suddenly dropped 20dB in level and started behaving weird overall. Ended up with recapping both channels rec and repro cards as well as swapped ICs on those. All good and I've got a nice and clean signal again. One thing though that's been bothering me even before the break down is uneven bass response. I had the analyzer going yesterday but forgot to take a screencap of it. Attached you'll find a picture though where I've drawn roughly on top of a downloaded pic of my analyzer. (PLEASE NOTE only the handdrawn red line, the rest of the analyzer doesn't make sense in this matter as it's a downloaded pic) When calibrating it's good down to 100hz and with the test tape I'll get that nice and even between the channel but then below that it sways out to the right on the analyzer (thus stronger on the right channel). Same thing kind of happens in the top end. All good at 5khz even at 10k it's okay and then it goes off balance between the channels. I'm not at my studio for a couple of days now but from memory bass is a little right-heavy and high treble is left heavy. The repro cards calibrate fine, so it has to be something with the rec cards I assume without having too much of an electronics background. Any ideas on what's causing this and how to fix it? Much appreciated! -L Attached Thumbnails

24th May 2017, 12:30 pm	#2
TIMTAPE Octode Join Date: Jul 2006 Location: Perth, Western Australia Posts: 1,969	Re: Studer B67 Mk2, calibration. Uneven bass 80Hz-> Ideas? Do you know that at the higher speeds of 15 and 30ips, bass response is generally lumpy due to "head bump"? You will not get nearly as smooth a response as further up the range. Here's a link to some graphs showing head bump on various machines: http://www.endino.com/graphs/ I would test and align each channel on its own, one at a time. The interchannel balance I would do after that as a final check. Similarly the problems in bass response and treble response are two separate issues. Treat one problem at a time and you'll make steadier progress.

24th May 2017, 3:27 pm	#3
mitajohn Pentode Join Date: Sep 2005 Location: Athens, Greece Posts: 197	Re: Studer B67 Mk2, calibration. Uneven bass 80Hz-> Ideas? As per B67 mk2 SM in section 6 there is a detailed calibration guide. __________________ Regards, John