Tape Project Forum

Tape Machines => Tape Tech => Topic started by: john on January 25, 2009, 03:26:49 AM

Title: Oscilloscope for RTR Alignment.
Post by: john on January 25, 2009, 03:26:49 AM
I'm considering the purchase of an oscilloscope, what are the minimum requirements for tape machine use/alignment. Analogue or digital, frequency etc. below is the spec of one that I'm considering.

Scope Description

2 independent  floating channels

Max sensitivity vertical 5V per div

Min sensitivity 5mV per div 17.5nS rise time

25MHz with 100MS/S sample rate

Trigger Edge,Normal, Single, Auto, TV

Auto measurement of frequency, peak to peak voltage, true RMS voltage, average period.

Math add, subtract, multiply, divide, one channel by the other

Would this be suitable?
Title: Re: Oscilloscope for RTR Alignment.
Post by: docb on January 25, 2009, 10:19:45 AM
Hi John,

You want to be sure to get a scope that can do X-Y display, where one channel is sent into the horizontal and the other is sent to the vertical. This will allow you to generate the Lissajous figure that will help you nail the azimuth of the playback head.
Title: Re: Oscilloscope for RTR Alignment.
Post by: john on January 25, 2009, 11:26:36 AM
Thanks Doc, I'll check that out.
Title: Re: Oscilloscope for RTR Alignment.
Post by: microstrip on February 28, 2009, 01:24:02 PM
Hi John,
If you have a good soundcard - I have Edirol UA25 - you can use the free software Soundcard Oscilloscope ( http://zeitnitz.de/Christian/Scope/Scope_en.html ) to align your machine. It has X-Y capability for Lissajous figures and an excellent signal generator with sweep options. It can also perform frequency analysis.
Title: Re: Oscilloscope for RTR Alignment.
Post by: john on February 28, 2009, 01:58:06 PM
Thanks Microstrip,
                        I will try that, it looks like it could be just the programme to use.
Title: Re: Oscilloscope for RTR Alignment.
Post by: steveidosound on February 28, 2009, 03:22:39 PM
2 considerations for scopes for troubleshooting R2R recorders.
These are not typically part of software scopes.
1. very high input sensitivity if one wants to look at the head output directly. Typically only a couple of millivolts.
2. DC blocking for high voltages - important if you go measuring around inside of a tube machine.

In addition, it is nice to have some sort of calibration so you can measure the level you are getting on the waveform as well as dual trace and X/Y lissajous patterns  for 2 channel comparisons.
Title: Re: Oscilloscope for RTR Alignment.
Post by: Ben on February 28, 2009, 07:50:20 PM
Now the optional parts ... power cord and probes are often overlooked too.
Last time I looked, inexpensive probes can be found here.
http://www.oselectronics.com/index.htm
Title: Re: Oscilloscope for RTR Alignment.
Post by: stellavox on March 13, 2009, 05:38:07 AM
I suggest looking at the little Velleman battery powered scope - I have an earlier one, it works great and it's portability is a real plus

Charles
Title: Re: Oscilloscope for RTR Alignment.
Post by: ironbut on March 13, 2009, 12:23:59 PM
Hey Charles, I was wondering about those little guys. Thanks.
Regarding software scopes, I use a program called Spectre which is $80 (for Mac). It's quite a bargain since it has tons of other meters. It's not the easiest thing to use but once you get the hang of it, it only locks up every once in a while (you have to hide it before you make any connection changes). That said, I think that if you foresee any need for doing any critical measurements (low level stuff like steveidosound was talking about) you're much better off biting the bullet and getting a real scope that you can have calibrated. A software scope (or measuring program) is only as good as the processor (analog to digital) that feeds it since the noise floor and the upper a lower frequency limits can be altered by the converters when going to digital. I think that for simply aligning your heads, you can do a reasonable job with one since you aren't going that high/low but once you get out of a set bandwidth or amplitude, you can't really trust them.
Title: Re: Oscilloscope for RTR Alignment.
Post by: miroslav on July 08, 2009, 01:32:24 PM
Glad I stumbled on this thread.

I was just lining up to get a scope...but I think I will try out the software version first.
I have real good soundcards for my DAW that will do A/D/A at 24 bit up to 96 kHz...so no worries there.

With my couple of R2R decks...they've been babied and have seen only light to moderate use...so I was not too concerned that the heads had gone out of physical alignment...and they have no visible wear at this point.
That said...I figured it was time to put the decks up on a scope, especially my new Otari BIII which came by UPS, and they tend to bounce things!
I figure I can at least check the physical alignment...and if it comes up good...then I know my electronic calibration will be accurate.

I don't think I would have too much other use for a hardware scope...so maybe the software will be just the thing for me!

Title: Re: Oscilloscope for RTR Alignment.
Post by: docb on July 08, 2009, 02:29:02 PM
Quote
(for Mac). It's quite a bargain since it has tons of other meters. It's not the easiest thing to use but once you get the hang of it, it only locks up every once in a while

What?! "Mac" and "locks up" in the same paragraph?! Tell me it ain't so. Only PCs have these problems. I know, 'cause a Mac guy told me so - while he was trying to figure out why he couldn't mirror his old Mac laptop HD onto his new Mac laptop.
Title: Re: Oscilloscope for RTR Alignment.
Post by: ironbut on July 08, 2009, 03:48:37 PM
Yeah yeah,..
Actually it's a little user error'ish. My tendency is to want to open up a whole bunch of cool looking meters all in one window so it looks kinda "Foo'ish". With this software it just doesn't fly. Also, if you open app's and switch routing while the meters are going,.. freezo!
They've been saying a new version is right around the corner but in the meantime, I'm just methodical in it's use.
Hey, what do want for $80?
Title: Re: Oscilloscope for RTR Alignment.
Post by: xcortes on July 08, 2009, 04:15:17 PM
Hey Steve: I knew it was you
Title: Re: Oscilloscope for RTR Alignment.
Post by: miroslav on July 08, 2009, 05:04:25 PM

I have real good soundcards for my DAW that will do A/D/A at 24 bit up to 96 kHz...so no worries there.

I spoke too soon.

The software scope doens't work with 24 bit cards. :-(

I have an old 16bit card...not sure if I want to mess with my DAW just to install an old sound card because of the scope.
Title: "Software scopes" - BE CAREFUL!!!
Post by: stellavox on July 09, 2009, 05:39:08 AM
I have nothing against software scopes but PLEASE keep in mind that you are using inputs and outputs to your soundcard that were "designed" to see signal levels from headphones/speakers and microphones.

You go using your PC as a piece of test equipment and you could inadvertently inject who-knows-what into it.  IF you do this please think about PROTECTING the I/O ports somehow.  I haven't done any research on this but someone probably has - like using back-to-back zeners from "hot to ground" to limit the voltages - and maybe even a micro fuse in series with the "hot" leads!  Hopefully there are I/O specs somewhere in your Soundcard literature - if not, ask.

Charles 
Title: Re: Oscilloscope for RTR Alignment.
Post by: ironbut on July 09, 2009, 10:10:22 AM
Hi Charles,

I posted a link to some probes for sale on eBay that are made to protect the soundcard while using 'scope software. I'm sure it's pretty easy to make one too but these were only about $20 and come with all the adapters you might need. Like I said, I don't seem to be able to find that thread at the moment but I think it was listed under "soundcard probes" on eBay.

As I've said before, if you plan to use this for anything other than just aligning your heads, bit the bullet and buy the real thing. Spending a few hundred on an old scope that is more than you'll ever need is a lot better than replacing a laptop!
Title: Re: "Software scopes" - BE CAREFUL!!!
Post by: miroslav on July 09, 2009, 10:36:18 AM
I have nothing against software scopes but PLEASE keep in mind that you are using inputs and outputs to your soundcard that were "designed" to see signal levels from headphones/speakers and microphones.

You go using your PC as a piece of test equipment and you could inadvertently inject who-knows-what into it.  IF you do this please think about PROTECTING the I/O ports somehow.  I haven't done any research on this but someone probably has - like using back-to-back zeners from "hot to ground" to limit the voltages - and maybe even a micro fuse in series with the "hot" leads!  Hopefully there are I/O specs somewhere in your Soundcard literature - if not, ask.

Charles 

Appart from the issue I mentioned in my previous post where the software scope didn't like my 24 bit converters...I wouldn't think there's any real concern...if you have decent soundcards/converters.

The test signals coming from the the deck's outputs are typical Line level signals/voltages, +4dBm to +16dBm...which should work with OK with most soundcards made these days.
Title: Re: Oscilloscope for RTR Alignment.
Post by: microstrip on July 10, 2009, 01:32:02 PM
I prefer to use an USB audio adapter to avoid damaging the computer if something goes wrong. The EMU tracker PRE (192khz 24 bit) has high impedance inputs with 1Mohm. This is the standard impedance of most oscilloscope inputs and can be used with a normal 10X oscilloscope probe giving an attenuation of 10, extending its range to 20V RMS. I bought some 1/4 phono to RCA and RCA to BNC adapters and connect the probes directly to the  HiZ input.
Title: Re: Oscilloscope for RTR Alignment.
Post by: miroslav on July 11, 2009, 11:33:00 AM
Just found this FREE audio analysis software tool that looks to be just the ticket of anyone not wishing to go the hardware oscilloscope route.

Visual Analyzer

http://www.sillanumsoft.org/

I will be installing the latest version (VA 2009HR) later today on my DAW, and will post back how well it works, but I already installed and earlier version (8.xx) on my XP laptop without issues, and it looks very good so far.
Title: Re: Oscilloscope for RTR Alignment.
Post by: docb on July 11, 2009, 01:35:45 PM
From their webpage:

Quote
Frequency compensation: one can create/edit a custom frequency response and  add it to the spectrum analyzer spectrum ;

Oooh, that could be a really nice feature for measuring eq curve response...sounds like a very worthwhile piece of software.

Speaking of test equipment for alignment,  I just picked up a Sound Technology 1510A last night that powers up and passes the self test - for a whopping $75. Can you say "screamin' deal?" Thanks to Ed Fallon for spotting it on Craigslist!
Title: Re: Oscilloscope for RTR Alignment.
Post by: miroslav on July 11, 2009, 08:29:05 PM
I'm sure for fulltime bench work, a real good piece of hardware is the ticket, and you don't have to deal with the soundcards or PC...etc.
But since I have the DAW right next to the R2R decks and mixer in my studio...the software version is a good choice for me.

I installed it and tried it out tonight for my Otari R2R alignment?and it works great!
Ran smooth-n-steady, and never crashed, except one time when I clicked on a couple of options while also trying to open a couple of its windows in fast succession while I was running a calibration on the software?s input.
That was a bit much on my part! ;-D
Plus?I never restarted the PC after I installed, though it didn?t ask for it.
But once I restarted, then the software was better at quickly recognizing my soundcards since I have 24 channels of A/D/A split up as 12 input and 12 output pairs?plus the same number of digital I/O channels?so it?s no wonder the software was a bit confused at first.

Anyway?works like a charm for doing the azimuth, plus there are quite a few other analysis tools built in, so it has many more uses.

Not bad for FREE software?though I will donate some $$$ to the guy via PayPal.
He put some serious work into this and it has value for me.
Title: Re: Oscilloscope for RTR Alignment.
Post by: ironbut on July 11, 2009, 10:50:25 PM

Speaking of test equipment for alignment,  I just picked up a Sound Technology 1510A last night that powers up and passes the self test - for a whopping $75. Can you say "screamin' deal?" Thanks to Ed Fallon for spotting it on Craigslist!

You dog!
I'd love to get my hands on one. I can't believe you found a working one for $75 bucks!
Title: Re: Oscilloscope for RTR Alignment.
Post by: docb on July 12, 2009, 11:33:13 AM
The guy I got it from had bought an auction lot of gear. He had some sort of budget scope, a CRT tester, a couple of ancient analyzers, mostly kind of useless stuff. Makes me wonder what it was that was in the original lot that made him buy it.
Title: Re: Oscilloscope for RTR Alignment.
Post by: Studer Fool on July 13, 2009, 08:54:15 AM
Indeed, "SCREAM'IN DEAL" Dan!  A Sound Technolody ST1510A for $75!

What options if any did it come with? 
What software level is it at? 

I suspect you have a later software level if you passed the seft test, as with earlier versions it was important to set the output level before running self test, where as with the later versions this was worked around so that the self test would pass w/o setting the output level (or you knew this already??).

By the way, our own Charles King (Stellavox) would appear to have amassed some experience with these devices!

-cdw
Title: Re: Oscilloscope for RTR Alignment.
Post by: ironbut on July 13, 2009, 09:40:05 AM
Speaking of tape test equipment, has anyone ever seen an Altair T2DS? As far as I can tell, they dwell in the land of unicorns and the "perfect date"!
Title: Re: Oscilloscope for RTR Alignment.
Post by: jcmusic on July 13, 2009, 11:15:54 AM
Speaking of tape test equipment, has anyone ever seen an Altair T2DS? As far as I can tell, they dwell in the land of unicorns and the "perfect date"!
Please describe the perfect date!!! I must have missed something way back when!!! LOL!!!

Jay
Title: Re: Oscilloscope for RTR Alignment.
Post by: microstrip on July 13, 2009, 01:00:08 PM
Apologies for a naive question, but only recently I entered the RTR kingdom with a subscription of the Tapeproject.
I went trough several sites about wow, flutter and scrappe flutter and can now understand what they are. I looked at the specifications of several instruments at Dave Manquen site and Jay McKnight papers. My question now is: what can be measured with these old dedicated instruments that can not be done using a good 24bit 192 kHz USB soundcard with, for example, Spectraplus v5.0 software?
I have been playing with with the demo version and an USB EMU Tracker pre and the specifications are great for RTR tests.
Title: Re: Oscilloscope for RTR Alignment.
Post by: ironbut on July 13, 2009, 05:32:02 PM
It's more of a difference in levels of detail that these instruments can measure. They're both purpose built measurement devices that are more for repairs and pretty extreme tweaking in the case of the Altair. The Sound Tech. would have found a home with someone who might have done studio machine maintenance where getting something done fast and correctly would have been paramount (a recorder down during an expensive session just isn't an option). Having a one box solution would save tons of time.
Any purpose built measurement device avoids the particular noise spectrum that obscures what it's trying to measure too. It's left to concentrate on the range of measurements that are meaningful.
Title: Re: Oscilloscope for RTR Alignment.
Post by: 1audio on August 28, 2009, 11:01:45 PM
I have an ST1510 and the closest to an Altair in the broader market a Mincom wideband flutter analyzer. For working on tape machines these have lots of benefits over a PC program with the special functions for optimizing bias and tape motion analysis. You can analyze wideband flutter with an fft analyzer but its hard. To get down to 1/2 Hz you need a very large sample and plenty of processing time, and you are looking at close in sidebands of the carrier. The dedicated machinery gets the info much more quickly.

For a scope for this work and one that will be harder to inadvertently damage I would suggest a Tek 5000 series scope from eBay like this http://cgi.ebay.com/Tektronix-5115-Storage-Oscilloscope_W0QQitemZ330354826888QQcmdZViewItemQQptZBI_Oscilloscopes?hash=item4ceaae9e88&_trksid=p3286.c0.m14#ht_500wt_1166 (http://cgi.ebay.com/Tektronix-5115-Storage-Oscilloscope_W0QQitemZ330354826888QQcmdZViewItemQQptZBI_Oscilloscopes?hash=item4ceaae9e88&_trksid=p3286.c0.m14#ht_500wt_1166) . They can be had for peanuts and the plug in options are endless and cheaper still. Digital scopes have appeal BUT your into analog recording aren't you (or you would not be here) and analog scopes are much better for seeing what comes out of a tape machine that a digital scope. Tape isn't really stable and a digital scope will average the signal making it harder to see.
Title: Re: Oscilloscope for RTR Alignment.
Post by: ironbut on August 29, 2009, 12:17:26 PM
Thanks 1audio (btw we use our real names here). Most of the measurements that I'm interested in making is the flutter in the transport/tape path (at least that's been my focus for a while). I assume that something like a Mincom will use an MRL flutter/speed test tape?

Like you've indicated, software just doesn't cut it when it comes to making these tiny measurements. The AD converter has to be extremely quiet and the higher fequencies become less and less accurate too. When it comes right down to it, I just don't know whether to believe the measurements. I have no problem with doing basic playback head adjustments but outside of that, the software meters aren't well suited to analog signals.
Title: Re: Oscilloscope for RTR Alignment.
Post by: microstrip on August 29, 2009, 03:57:34 PM
Although I can accept that a dedicated instrument is easier to use and faster, you have to consider that it can need calibration and service, something not easy to get nowadays and can be very expensive to get- sometimes an order of magnitude higher than purchase price.
I went through the excellent papers of Dale Manken at manquen.net, and after understanding the basics of his excellent paper on the ALTAIR T2DS I could emulate some of the measurements with a 24 bit 192 KHz sound card and appropriate software. Recently I have sorted some old and recent made pinch rollers to came to the conclusion that no recent one in my possession  surpasses in wow and flutter the original old Revox?s, although they look nicer! As soon as I go through the bearing tests I will post them to this forum - Arian suggestion for Revox was 100% accurate.
Do not forget that modern PC?s can perform very fast FFT?s with 131072 samples at 96kHz sampling rate with  .732 Hz resolution, more than adequate for this purpose.
All we have to do now is asking Doc to issue a 10 minutes reference tape at 15?recorded at 12.5 KHz in his excellent machines to make the measurements of scrape flutter much easier and more reliable. 
Title: Re: Oscilloscope for RTR Alignment.
Post by: ironbut on August 29, 2009, 05:32:32 PM
Recently I have sorted some old and recent made pinch rollers to came to the conclusion that no recent one in my possession  surpasses in wow and flutter the original old Revox?s, although they look nicer!


Hey, that's exactly what I came up with a while back.
The original rollers on my Technics are tapered so the contact surface is only about 1/16th of an inch on either side of the tape width (that's just a guestimate, it could be smaller). I believe the difference in performance is due to the amount of tape stretch that the deformation of the roller surface causes as it pushes  against the capstan. The wider (larger) contact patch of a new, more compliant or physically wider roller is in more intimate contact with the capstan surface around the tape or before and after the primary contact area. I believe that because the roller has a different diameter outside of the primary contact area, the capstan tries to rotate the roller surface at differing rates forcing the tape to either slip or stretch. Either way this causes speed irregularities which mimic the classic "stick/slip" of scrape flutter.
In a perfect world, a dual capstan/roller system might minimize this but in reality, it might be simply changing this from "stick/slip" to "slack/tight" which might also effect tension and tape/head contact too.
It seems that the amount of tape path friction could also have a part in this mechanism. The head profiles (contact area) and condition or any other guides seems to distribute the amount of tension at any given point differently and whether it's stick slip or slack, this tension determines where in the tape path these irregularities in speed are compensated.

Of course all these things are probably secondary to things like capstan surface finish and tape surfaces but, for the most part those are things that are design considerations and not really in our control to change.
That doesn't stop me from making home spun theories like the one I just outlined.

BTW For those who don't know better, these and many things I post here are the results of way too much time on my hands and a miss spent youth!
Title: Re: Oscilloscope for RTR Alignment.
Post by: 1audio on August 30, 2009, 09:34:09 PM
I should have a signature below. I use the 1audio in many audio boards for consistency.

I just tried a close in measurement of a 1 KHz oscillator with an FFT running at 131K points and 96 KHz sampling. 10 averages didnt take long (but averaging might remove the flutter artifacts??) The frequenct resolution is there, I can see an artifact from something 20 Hz from the 1 KHz tone at -80 dB. It brings up lots of questions I have about digital systems since it should not be there. I'll dig out the analog spectrum analyzer and see if I can find it in the source (an analog oscillator). However its not easy to see from this if its a frequency modulation of the carrier or a tone from something else. I'll dig out the Mincom and see if it sees anything.

If you have lots of time you could look at the "violin string" resonance of the unsupported tape with an optical system. You might learn something. Fixing it would be the challenge. Dale Manquen suggests that above 12 KHz the tape itself damps the vibrations but below a lot can happen.

I have had to put in my own calibration resources. the ST1510 is a real pain to work on but seems to be very stable once its running. The Mincom also is very stable, self calibrating and seems to be built to run forever. Mine is at least 30 years old. Its an IRIG version with a lot of different carrier frequencies. But only the first few are useful.

The 3M design was based on stretching the tape with a stepped capstan and pinch rollers. It seemed to work very well. Some hate the design on philosophical grounds. I hope to have mine up by CES and I can get a better fix on it by then.

There was a process for resurfacing capstans with a satin finish that improved the grip and was supposed to reduce the flutter. That may all be lost art today.
Title: Re: Oscilloscope for RTR Alignment.
Post by: ironbut on August 31, 2009, 11:09:20 AM
Hey Demian,
Yeah, the 3M machines don't get a lot of respect. I suspect that some of that is the whole parts availability thing but the stepped capstan isoloop does seem to stir up some debate. I came close to picking up a 4 track M79 a while back but just didn't have the room. Really interesting machines but a love/hate item it would seem.

I seem to recall it was the MM1200 that had problems with the capstan becoming polished and the tape slipping after a while. I read that some owners have taken to using emery paper to give them grip. That sounds pretty scary to me! I would think that a good machine shop (especially the ones that work on aircraft engines who work to insane tolerances) would be able to resurface a capstan with just a tiny bit better grip.
Title: Re: Oscilloscope for RTR Alignment.
Post by: 1audio on August 31, 2009, 12:19:10 PM
Keith Johnson first turned me on to the capstan refinishing thing. There was a shop in the Bay Area that resurfaced the capstan motors for the Ampex AG350's. It was some sort of bead blast finish. Rule 1 on AG350s, use the Bodine motors. The Ashland motors had design problems that limited their performance. Something about fields or heat, I don't remember what.

Keith also didn't like the stepped capstan. When I built up a 3M M23 for Reference Recordings (25 years ago now) he insisted that the pinch rollers be replaced with flat ones to defeat the differential drive. I'm not going to argue even though I'm not convinced. I would love to build a Steven's clone and ditch the pinch rollers completely. Or a machine like this: http://www.labguysworld.com/ChesterNewell_2.htm (http://www.labguysworld.com/ChesterNewell_2.htm) with no loop. But I have a real world to deal with.

If I get the 3M running well I'll invest in Manquen's servo upgrade for the drive.
Title: Re: Oscilloscope for RTR Alignment.
Post by: ironbut on August 31, 2009, 02:40:42 PM
Yep, of all the machines out there, I'd love to get my hands on a Stephens. I believe that John Stephens started out modifying 3M M23's until the parent company stopped selling them to him (I wonder why? yuk yuk). His machines are still considered by many to have been the best sounding of any multi track although I believe he produced a 1/2" 2 track.

For any of those who've never heard of them, here's a link to a Stephens brochure;

http://www.dvq.com/hifi/images/stephens.pdf
Title: Re: Oscilloscope for RTR Alignment.
Post by: microstrip on August 31, 2009, 05:21:21 PM
My A700 has a capstan shaft with a highly polished surface, the A77, B77 and PR99 have a satin finish.
I can not remember anymore where I read it, but I had the idea that as the A700 is a constant tension transport, the best performance could be attained with a polished capstan.
MDIPrecisionMotorWorks can redo a capstan with a ceramic sleeving for around 175 usd.
Title: Re: Oscilloscope for RTR Alignment.
Post by: ironbut on August 31, 2009, 08:42:51 PM
Yeah, Fred Thal once told me that tape machines were designed as systems and changing things without taking the rest of the system into account will quite often degrade performance. I'm sure that Revox didn't spend the extra money to have that capstan polished for no reason so I'm sure you're right about the constant tension designs (it's the same on my Technics which is constant tension too).

I always wondered if continued design development had continued if they might have adopted pneumatics like on the big main frame computers at the time. That would have taken a total redesign of almost the entire transport/tape path. Maybe there are other reasons why it wouldn't have worked since video tape development continued and I don't believe they ever adopted pneumatics.
Title: Re: Oscilloscope for RTR Alignment.
Post by: 1audio on September 01, 2009, 12:49:40 AM
I worked on those big tape drives briefly. There is no way they could be economical enough for use in anything but a mainframe. They were very complex. The vacuum columns were not for smooth drive, they were to permit reading and writing tape record by record. They could start and stop in a millisecond. The vacuum capstans had voice coil valves behing them to switch between air and vacuum. The columns had opto sensors to control the reel motors, which would push tape in and pull it out. Flutter was not a big issue.
Title: Re: Oscilloscope for RTR Alignment.
Post by: c1ferrari on November 21, 2009, 09:53:55 PM
Utterly OT: ironbut (post 8/31/09) - thanks for the pdf...that cover is alright!!  1audio (8/31/09) - thanks for the link...loved it!  -Sam
Title: Re: Oscilloscope for RTR Alignment.
Post by: ofajen on December 31, 2009, 01:20:49 PM
Keith Johnson first turned me on to the capstan refinishing thing. There was a shop in the Bay Area that resurfaced the capstan motors for the Ampex AG350's. It was some sort of bead blast finish. Rule 1 on AG350s, use the Bodine motors. The Ashland motors had design problems that limited their performance. Something about fields or heat, I don't remember what.

Keith also didn't like the stepped capstan. When I built up a 3M M23 for Reference Recordings (25 years ago now) he insisted that the pinch rollers be replaced with flat ones to defeat the differential drive. I'm not going to argue even though I'm not convinced. I would love to build a Steven's clone and ditch the pinch rollers completely. Or a machine like this: http://www.labguysworld.com/ChesterNewell_2.htm (http://www.labguysworld.com/ChesterNewell_2.htm) with no loop. But I have a real world to deal with.

If I get the 3M running well I'll invest in Manquen's servo upgrade for the drive.

You might get a kick out of this.  This is my M-23 that I finally got up and going this summer.  A rack mount transport that I suspect came from a film sync machine and two electronics channels I got from JRF's machine, all housed in a little console I put together.  Once I sold my M-79 2-track, the M-23 restoration became more urgent.

http://i203.photobucket.com/albums/aa115/ofajen/IMG_8196.jpg

BTW, will Dale actually sell you the servo upgrade for the M-23 drive?  He's helped me a ton over the years in keeping my other 3Ms going and in getting this M-23 together, but when I asked about the servo upgrade, he said he'd got most of them back (mainly from the Rochester School of Music) and didn't want to sell any more because he didn't want to be responsible for supporting them.

Cheers,

Otto
Title: Re: Oscilloscope for RTR Alignment.
Post by: ofajen on January 08, 2010, 09:02:31 AM
Yep, of all the machines out there, I'd love to get my hands on a Stephens. I believe that John Stephens started out modifying 3M M23's until the parent company stopped selling them to him (I wonder why? yuk yuk). His machines are still considered by many to have been the best sounding of any multi track although I believe he produced a 1/2" 2 track.

For any of those who've never heard of them, here's a link to a Stephens brochure;

http://www.dvq.com/hifi/images/stephens.pdf

I'm working on picking up a certain Stephens 2" 16-track machine some time this year.  We've agreed on a price, but the seller is in no hurry, which is just as well, since it seems to be taking me a long time to get the funds together.  The most compelling feature for me is actually the portability of the machine.  The guts (transport/meter panel/PSU) weigh a total of about 65 pounds and work nicely in two portable cases.

Cheers,

Otto
Title: Re: Oscilloscope for RTR Alignment.
Post by: ironbut on January 08, 2010, 01:25:26 PM
That's a beautiful M23 Otto! Fantastic work there.

Perhaps you could give us a little detail regarding the servo upgrade you mentioned.

I seem to remember that Dale was working on a way to do away with the stepped capstan also.
Title: Re: Oscilloscope for RTR Alignment.
Post by: ofajen on January 08, 2010, 03:05:24 PM
That's a beautiful M23 Otto! Fantastic work there.

Perhaps you could give us a little detail regarding the servo upgrade you mentioned.

I seem to remember that Dale was working on a way to do away with the stepped capstan also.

I just sent him an email to ask if he still has the kits and if he will sell them.

Here's the link:

http://www.manquen.net/audio/index.php?page=4

Cheers,

Otto
Title: Re: Oscilloscope for RTR Alignment.
Post by: ofajen on January 08, 2010, 04:55:00 PM
I remembered correctly.  Dale says he will no longer sell the direct-drive servo kits for the 3M transport because he doesn't want to have to support them.  Too bad.

Cheers,

Otto

That's a beautiful M23 Otto! Fantastic work there.

Perhaps you could give us a little detail regarding the servo upgrade you mentioned.

I seem to remember that Dale was working on a way to do away with the stepped capstan also.

I just sent him an email to ask if he still has the kits and if he will sell them.

Here's the link:

http://www.manquen.net/audio/index.php?page=4

Cheers,

Otto