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1
Tape Tech / Re: Otari MX-50 Track alignment
« on: February 13, 2012, 09:37:58 AM »
Hi,

From what you say you are probably playing four-track stereo tapes with a two-track playback head.

A two-track playback head with 2mm guard band between tracks in the middle of the tape (standard two-track format a la Tape Project, as opposed to wide-track two track which only has a 0.75mm guard band) will cover track 1 and track 4 of a four-track tape, with tracks 2 and 3 mostly falling in the guard band.

Since four-track stereo tapes are recorded with left and right channels on tracks 1 and 3 "going" and tracks 4 and 2 "coming" (accessible by flipping the reels over on a two-channel machine), you are hearing the left channel of the "going" stereo programme on track 1 in your left channel, and the left channel of the "coming" stereo programme on track 4 backwards in your right channel.

You need to find a machine with a four-track stereo playback head.  Consumer machines, as opposed to a pro machine like the Otari, are your best bet, since four-track stereo was the standard consumer format, with two-track more of a semi-pro or pro format.

Revox, for example, made machines in both two- and four- track formats; you need to find one in the format you want.  Some machines by other manufacturers had two playback heads, selectable by switching.

Best regards,

2
Reel to Reel Tape Machines / Re: More Revox mods
« on: June 19, 2010, 04:17:33 AM »
Hi Seth,

Re. converting the usual 3-4/4 + 7-1/2ips version of the Revox G36 to higher speed operation.

First off I don't think it's realistic, or even desirable, to aim for 15 + 30ips operation with a G36.  7-1/2 + 15ips is the target.

Next, let's look at how the factory did it.

The factory only made 7-1/2 + 15 ips available on the series 3 machines. Series 3 G36's can be spotted from the photo-electric end stop which made a different shape of head cover necessary.  There were two batches of these factory high speed machines.

For the first series, the factory substituted a motor with 8 + 4 pole windings (to get the two speeds) for the normal 12 + 6 pole motor.  That gave them 50% higher motor speed:

12 + 6 pole motor, 50Hz: 500 + 1000rpm, 60Hz: 600 + 1200rpm.
8 + 4 pole motor, 50Hz: 750 + 1500rpm, 60Hz: 900 + 1800rpm.

To get the remaining 33% speed increase (50% x 33% = 100%), they fitted a capstan shaft 33% thicker.  Obviously there were two versions of the capstan shaft for the 4 + 8 pole motor, one for 50Hz and one for 60Hz.

Since the capstan shaft was only 33% thicker, Revox made no modifications to the tape path.  The same top chassis and base casting are used and the motors have the same fixings, so the 4 + 8 pole motor and the appropriate shaft can actually be retrofitted to the normal 3-3/4 + 7-1/2ips G36.  And this can be retrofitted to the Series 2 G36 as well, if the drive couplings from the existing Series 2 motor are swapped onto the 4 + 8 pole Series 3 motor.

However, since about the early 1990's the 4+8 motor and shaft have been "unobtainium".  I actually got an invoice for these parts from F.W.O Bauch in the UK when I was a student there, total cost 180 pounds sterling which I couldn't afford at the time... life is full of regrets.

For the second batch of 7-1/2 + 15ips G36's, Revox switched back to using the same 12 + 6 pole motor as for the 3-3/4 + 7 1/2ips version.  To get the speed increase they fitted a double diameter (+ 100%) capstan shaft.  Obviously there were again two versions of this shaft, one for 50Hz and one for 60Hz.  But the 100% increase in capstan shaft diameter meant that they had to modify the chassis and the base casting to shift the motor a bit towards the VU meters to compensate; this chassis and casting had different part numbers of course.

And this is where the misunderstandings began, because people thought they could just swap the 7-1/2 + 15ips capstan shaft for the 6 + 12 pole motor into a 3-3/4 + 7-1/2ips G36 and convert it to high speed.  Naturally that wrecked the tape path geometry and with it the scrape flutter and frequency response.

If anyone is interested, I will dig out my G36 manual and post all the parts numbers for the different motors, shafts, chassis and castings.

This brings us to the question of how to make the modification today.

Any modification involving only a +100% capstan shaft is, in my opinion, not advisable, since it is impractical to correctly modify the chassis, base casting or head block to re-set the tape path and factory modified parts are of course no longer available.

We will have to proceed as Revox did with the first batch of high-speed G36's and fit a capstan shaft that is only slightly larger, and spin the motor faster.

To get a firm of precision engineers to make up a +33% capstan shaft for the G36 should not be difficult, but it will cost money.

To spin the motor 50% faster, we only need to supply it with a frequency 50% higher, since it is a synchronous motor.  We can use an electronic power supply as used for upgrading synchronous motors for turntables.  There are a number of boards or kits available to do this.  And since the frequency will be electronically controlled, the mains frequency of either 50 or 60Hz will not affect the speed.  We will only need one version of the capstan shaft, and our modified G36 will be "internationalised", needing only a switch to set the capacitors for the reel motors to move between 50Hz and 60Hz regions.

I have two G36's and you, Seth also have two.  Any firm we can get to make the +33% shafts for us will probably charge less per shaft for a batch of four shafts than for a one-off but it is still not likely to be cheap.

This is not likely to be a beer-money project, but there are several things in its favour:

- Secondhand prices for professional tape machines with all-valve (all-tube for you transatlantic fellows) record and playback circuits are much higher than for later solid-state machines and parts for such machines tend to be expensive and hard to find.
- The G36 is a simple, rugged, reliable, long lasting and easy to maintain design of good quality.  There is reasonable availability of spares and a plentiful supply of used machines.
- And, of course, a 7-1/2 + 15ips G36 is by definition a Tape Project playback machine.  They came with IEC eq as standard; NAB was offered on the 60Hz machines only.

I would be very interested to hear from other G36 owners / users who could be interested in a 7-1/2 + 15ips conversion done as above.

3
Reel to Reel Tape Machines / Re: Otari MX5050 newbie questions
« on: April 14, 2010, 01:47:21 AM »
Greetings,

My Otari 50-50 has been sitting for 3 or 4 years. Play back is great and the 15 ips works great and is ON SPEED.

However, 7 1/2 just sits dead as a doornail. I can hardly turn the capstain can hardly be turned by hand.

I don't know about Otari, but similar problems with Revox (high speed OK, low speed - capstan is stuck, especially after the machine has been sitting unused for some time) are usually due to capstan shaft lubrication issues (lubricant dried out or congealed).

The higher motor torque at the high speed setting overcomes the stiction and gets the capstan going.  Lower motor torque at the low speed setting can't overcome the stiction and the capstan remains stuck.  The fact that you can't turn the capstan by hand seems to confirm this diagnosis.

Straightforward disassembly, cleaning and relubrication of the capstan shaft and bearing should cure it.

Best regards.

4
Tape Tech / Re: REVOX A77 ALIGNMENT QUESTION
« on: March 18, 2010, 03:50:34 PM »
Hi,

That could have been one of my posts you read about the B77 alignment.  I use 468 tape (previously Agfa, then BASF, then EMTEC and now RMGI) and set a reference level of 355nW/m on the B77 Mk.II, which is 3dB higher than the 250 recommended by Revox.  I also set my meters to read 0dB at reference level, whereas Revox recommend a "ballistic lead" of 7 dB if I recall correctly.  So my setup is a total of 10dB "hotter" than the recommended Revox setup.

I reckon that about half of that 10dB difference is accounted for by the difference between 468 and the typical 1970's consumer tape, and the other half by the use I put the machine to.  I record mostly chamber music and small acoustic ensembles without percussion, so there's not a lot of high frequency or transient energy there to cause overload problems and I can run the tape hotter to get lower noise.

Whatever blank tape and whatever reference level you choose at whatever tape speed, you can quickly see if you can make a bias adjustment at that level on that tape at that speed.  Record 1kHz at your reference level, and set the bias for maximum output off tape.  Then switch to 10kHz at the same recording level and set the bias for maximum output off tape, before increasing bias to reduce the output level off tape to the prescribed 10kHz drop-off.  If you can't find a 10kHz maximum that is fairly close to the 1kHz maximum, then the tape is saturating and you need to use a lower level for the bias adjustments.  You can double check this once the HF record equalisation has been set, after setting the bias.  Tweaking the bias for a maximum again, after setting the HF EQ, should give a maximum at 10kHz which is higher than the maximum at 1kHz, dialling in the prescribed overbias will restore flat response.

Using 468 in the B77 at 15ips and at 7 1/2ips, I could get a 10kHz maximum close to the 1kHz maximum at my reference level which is 10dB higher than Revox' recommendation.  I wouldn't think you'd choose a higher reference level than that, so I would think you should be OK to carry out your bias alignment at any reference level you choose.  And if you're in any doubt as to the dynamic capabilities of an A77 with 468 tape, find a copy of the the famous audiophile favourite recording "La Spagna, Siglos XV - XVI - XVII" on the BIS label, made in 1979 or thereabouts - I think the CD is still available.  BIS used an A77 at 15ips with 468 tape to capture that, and anyone who's heard it can vouch for the dynamics and the frequency range.

Good luck and best regards,


5
I have no experience of Otari machines but my guess as to what a "reference fluxivity" switch would do is:

- Change the meter calibration so that the reference setting - say 0VU for a VU meter - reflects the reference fluxivity on the tape, both for recording and playback.
- Change playback gain so that the output reference level is the same for tapes recorded at different reference fluxivities.

Best regards,

6
General Discussion / Re: new to group - future Revox A-77 owner !
« on: April 06, 2009, 07:43:21 PM »
Hi,

Welcome to the world of open-reel tape, i am sure you will discover a new world of quality analogue sound recording and reproduction.

I acknowledge what Steve and Mark have pointed out about the virtues of machines of more professional design than a Revox, but there are several good things about Revoxes too.

First and foremost, what you have discovered already:  many were bought as a prized possession by music lovers or audiophiles of in the old days and, since the primary media were LP records and FM broadcasts - and, later, CD's - many of these machines ended up being used very seldom.  Since they were engineered to be very rugged, most domestic users' usage patterns hardly put a dent in them.  Professional machines, however, were bought to be used and the best one can hope for is to find a properly maintained example - a barely used one would be a rare find.

Re. tape hiss: on Revoxes, the reference level set at a conservative 250nW/m, with plenty of "lead" to allow for the VU meters' ballistic characteristics.  On my B77 Mk.II with IEC equalisation at 15ips and SM468 tape, same as used by the Tape Project, I have arrived at a setting of 355nW/m - that's 3dB above 250 - and _no_ ballistic compensation which adds another few dB (I don't recall offhand how much was recommended by Revox).  I use this for making live recordings that are more likely to overload the machine than taping off LP's and have noticed no problems with distortion or saturation of the highs (but please note I record acoustic instruments).  I have had similar good results also with copying LP's at both 15 and 7 1/2ips.  The reason Revox used such a conservative setting was, I suppose, that they allowed for domestic tapes of much lower performance than the professional SM468, which was available back in the day but was largely unknown to home users, and they would also have allowed a margin for user error.  So you are looking at, say, 6dB or more improvement in signal to noise ratio just from re-setting the reference level and VU meters to take advantage of pro-grade tape.   The B77 electronics seem to have more than adequate headroom for this adjustment, I haven't had an A77 but I don't suppose its electronics would differ widely in available headroom from those of the B77.

About conversion to two-track format, all you need to do is change the heads and possibly a few components in the bias oscillator as well.  I don't have an A77 manual.  But I have done conversions on B77's and A700's, given the heads the conversion is easy.  It depends if you want the two-track format.  If the machine needs the heads replaced I would convert it to two track.  But four track has its advantages too, especially when copying LP's where four track at 7 1/2ips is more than adequate quality for most LP's.  Tape is expensive, four track gives you double the time but the heads have to be very carefully aligned to avoid "dead channel" crosstalk.

The other good thing is that the wearing parts are available and reasonably priced, and there are very few of them in each machine... it's a very simple transport.

By the way, when copying from LP's, monitor on headphones with your speakers silent.  The absence of acoustic feedback to your turntable improves its performance to the extent that you may notice better performance from your copy tape when playing back from loudspeakers than when playing back from the turntable over loudspeakers.  I've posted before in this forum about this in a thread about copying LP's.  A Revox is good enough to show that difference even with high quality turntables, in my experience.

If you have any questions don't hesitate to post or PM me.

With best regards,

7
General Discussion / Re: For sale - SM468 pancakes with splices
« on: March 21, 2009, 11:55:57 AM »
Hi Steve,

Hey George, speaking of 7" reels, I guess RMGI stopped making the 7" low torque reels a while back. I was wondering if you knew of a source for them?

A quick Google search yielded the website of a company called  Elmar Plastics.  They seem to make these.  As you can see from the web page, they offer 7" reels with 4" centres and apparently they'll sell you a carton of 200 at 65 cents each ex works...  So depending on how many of them you use per month, I guess 130 bucks plus shipping should see you sorted out for a while...

With best regards,

8
General Discussion / Re: For sale - SM468 pancakes with splices
« on: March 21, 2009, 04:53:56 AM »
Thanks for the pointers Larry.  I understand very well that a splice made quickly to simply store some blank tape would need to be re-made carefully before an important recording is made on the tape.

In any case since we use the Nagra IV-S TC for location recording, we wind the tape down to 7" reels for location work and then edit everything back together onto 10 1/2" reels in the studio.  Once these pancakes are wound down to 7" reels there'd be either one splice or no splices per 7" reel.

When recording live on location with two machines, there's no avoiding splices and little choice as to where to make them when transitioning from one machine to the other, besides allowing for a sufficient overlap so that a good spot can be chosen.   But with a 7" reel of 468 only lasting 15 minutes at 15ips, there's only so much overlap you can allow for.   You would be surprised how many of the "Golden Age" recordings considered to be audiophile milestones today were made in precisely this manner - Decca's 1955 Keilberth Ring cycle, for instance.  When listening to that, I don't think I can hear where they made the splices.  I can't hear most of mine either, even on headphones.  I have got to be quite good at it...  The trick is to use a good splicing block, a sharp single-sided razor blade, and to demagnetise the blade before use.

I still haven't heard from the Project about shipping the pancakes to Cyprus...

Best regards,

9
Tape Tech / Re: Self contained tape repro unit
« on: March 20, 2009, 09:38:59 AM »
This would be an interesting upgrade for the battery-powered Nagra IV-S we're using, though measurements indicate it's the line output amp and not the playback preamp-equaliser that's the weakness.

Could you post more details about how it can be powered?  The Nagras can supply -12V unregulated or -10V regulated battery power, with the positive pole earthed to the chassis.

10
General Discussion / Re: For sale - SM468 pancakes with splices
« on: March 20, 2009, 03:40:46 AM »
Have emailed the address given above requesting a quote on the shipping charges for one box of 20 pancakes to my address below but have had no reply.  Have they sold out?

In case they're still available I'd consider having two boxes.

Best regards,

11
General Discussion / Re: REVOX G-36 REPRO QUESTION
« on: February 09, 2009, 08:20:43 AM »
Hi Mark,

I am posting this question to be answered by the G-36 gurus we have available on this forum.  I have a G-36 with mechanical/electrical issues (with power off, you can push the FF, RW, Play buttons and they will detent, as soon as the power is turned on, they will not detent).  Anyway, I was thinking of removing the tube repro electronics

Seems a pity to trash a G-36 and gut the electronics out of it for what seems to be a minor problem.  Also, the reproduce electronics in a G-36 are a very small circuit using three ECC83/12AX7 tubes.  The circuit draws just a few milliamps of B+ at a couple of hundred volts, and needs less than one amp of 12.6V DC on the heaters, it would be very easy to build from scratch.  This is like scrapping a vintage car to get the seats out of it...

If your G-36 is a Series III, your fault could simply be a problem with the photoelectric end stop device.  Look on the right hand tape guides, if the large one has a hole through it to let the light from a small light bulb through, and the small one has a photocell in it, then it is a Series III.

Otherwise it could simply be a minor problem with the switches that control the detent-cancelling relay.  It's probably a problem that doesn't even need parts replacement to solve.

PM me if you have any questions,

With best regards,

12
Raw Tape / Re: NAB Reels and Flanges
« on: January 30, 2009, 05:10:19 AM »
Besides usually having thicker flanges and, therefore, usually needing a different reel turntable adjustment, plastic reels have another disadvantage.

Their hubs usually have slots in them for threading the tape.  The way the slot is molded into the plastic can sometimes leave an indentation in the first few layers of tape wound on them, which in my experience causes measurable dropouts (though I'm not sure I can hear them).

Recorded tape shouldn't ever be stored as pancakes.  The tape pancakes sold on flangeless NAB hubs are meant for people who throw a lot of tape away, like editing studios and broadcasting stations.  Buying tape as pancakes on flangeless NAB hubs saves them money and space - no leftover empty reels everywhere.  They just take the flanges and screws from an empty metal NAB reel, assemble them onto the NAB hub of the new tape pancake, toss the empty tape hub in a basket full of them somewhere - or in the bin - and off they go.  In Europe those professionals often use the AEG-style hub and single flange, which also makes the tape more accessible for editing work, but also more vulnerable.  But I don't think you can get tape on AEG-style hubs any more, even if you wanted to go that way.

13
Suggestion Box / Re: Classical Music Subscription Series
« on: January 30, 2009, 02:50:50 AM »
I really want the four titles that have already been done, but I don't want the other two titles that I would have to pay for to get them with a selective subscription.  So for me, I would love to have all the present classical titles that have already been released, and future titles, like those in series two, put into a separate classical series. 

No, I am not suggesting an "alternate pricing structure".  I have no problems with the price of the subscriptions; I think the prices for both series are fair and reasonable - this is an incredible undertaking.  I am only asking about the possibility of a separate classical music series.

David, I fully second your position.

I would be interested to know how many others would sign up for an all-classical series. We have been talking about splitting it off; we have some ideas for how we could do a serious classical program over a couple of years. What's holding us back is just the feeling that there wouldn't be enough subscribers to make it feasible. 

Paul, perhaps one way it could be done is the following:  Once there are ten classical titles in the catalogue, offer those ten at the same price as a charter subscription, which is also ten titles.  I would get on board for that.  How does that sound to you?

14
General Discussion / Re: ANYONE MADE 15 ips 2 TRACK COPIES OF LPs?
« on: January 19, 2009, 04:13:56 AM »
Hi Steve,

Really interesting thread guys.
I always dreamed of having an isolation booth to put my turntable in but until the advent of standalone phono stages that wasn't really practical. Now I could see that have a phono stage with balanced outputs could get the table far enough away so that any mechanical feedback would be eliminated.

Myself, I sit as far away from the speakers as possible.  I have the turntable and preamp close to me, and the power amp or amps close to the speakers.  In my experience, the long interconnect between the preamp and power amp does not degrade quality, but having the turntable and preamp as far away from the speakers as possible on one hand, and having as short a speaker cable as possible on the other, makes for a significant improvement.

At line level, and at the kind of cable length we're talking about here - enough to get across a room - unbalanced inputs and outputs are OK.  Balanced interfaces do offer advantages, but having unbalanced interfaces wouldn't stop me from running long interconnects in my room - in fact that's what I do, I have seven metres between my preamp and power amp and everything is unbalanced.

You do need to watch the output impedance, though.  Anything below 1k is OK to drive up to twenty metres (sixty feet) of cable of 100pF/m capacitance (30pF/foot) and get a -3dB bandwidth of 80kHz.  An increase of cable length, or of output impedance, or of cable capacitance per unit length, decreases the bandwidth proportionally.

If you want the advantages of balanced interfaces, I hold that you can get most of them by driving a balanced input from a single-ended output if they are interfaced properly.  The other way around - balanced output into single-ended input - does also get you some of the advantages, but not nearly as many as when driving a balanced input from a properly interfaced single-ended output.  Of course, driving a balanced input from a balanced source is the optimum in terms of interfacing, but the balancing at the source end of things is the icing on the cake, and not the cake itself, especially at line level, in my humble opinion.

So it's not actually necessary to upgrade all your sources to balanced outputs to reap most of the advantages.  I consider that the most bang for the buck when going for balanced interfaces is a preamp with balanced inputs - that will give most of the advantages of balanced interfaces with all your sources, single-ended or balanced.  Also a power amp with balanced inputs will get you most of the advantages of balanced interfaces when driven by any preamp.  I consider balanced outputs from the sources to be the last priority.

So I suggest that, if you're interested in balanced interfaces, having balanced outputs from your phono stage is lower in priority than having balanced inputs on your preamp or whatever else the phono stage will be feeding.

Best regards,

15
General Discussion / Re: ANYONE MADE 15 ips 2 TRACK COPIES OF LPs?
« on: January 17, 2009, 09:35:40 AM »
Hi Mike,


[...] the acoustic feedback problem George mentioned does not effect my Rockport Sirius III turntable. it is a limitation of some tt's, not a format flaw.

[...]

btw George; i also have a Garrard 301 in a custom plinth; i am not surprised that it is somewhat affected by acoustic and floor sourced feedback. i love the Garrard none-the-less, it makes great music.

anyway; my personal perspective is why worry about making a copy; you cannot improve the original Lp by copying it, you can only make it less or different.


Great looking Garrard 301 and plinth!  Who made it for you?  I had mine made up by a local carpenter to my own design.  It's in two parts, the top part on which the turntable and arm are mounted is isolated by three squash balls that do a pretty good job in killing off structure-borne vibration.

If you have a tape machine that can record and play back at 15ips, why not try an experiment with your Rockport turntable?  Record an LP onto open reel at 15ips while monitoring on headphones.  Then play back the recording on your speakers and compare to the LP playback from your turntable, again on the speakers.  I think you will find the results interesting.

It does seem to me that the complete isolation from the loudspeakers afforded by the copying process can't be matched by any amount of turntable design or engineering.  Even if complete mechanical isolation is achieved, the arm and cartridge will always be affected by the airborne sound waves, unless the turntable is placed in a separate, soundproof room.  Of course, with a really high-end turntable like your Rockport, the difference might be so small as to make the degradation from making the tape copy more significant.  Thinking about this another way, it's a different way of assessing how good a turntable setup is...  Try it and let us all know.

I do concede that copying to 15ips tape is an expensive and inconvenient method of listening to LP's, though, even if it does give a copy that is much more durable than the original.  In my case, it's only really worth it in the case of the mega-rare and expensive La Spagna LP that I had the good luck to borrow and copy.

With best regards,

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