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Topics - stellavox

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31
General Discussion / RMAF
« on: October 06, 2009, 09:04:49 AM »
O my God, where to begin.

What a great time but I blinked and it is gone; except for the memories.  LOTS of great sound; which you can undoubtedly read about in the ?press? and blogs.  And a very little bit of reel tape. 

J-Corder was there with more 1500?s in one place than at anywhere else in time ?cept back at the Technics factory.  Beautiful refinishing jobs ? hope they sold a few.

I only found one exhibit with a recorder in residence.  I believe it was a local Denver dealer Audio Unlimited, with a modified 1500 playing Project tapes.  Outside the door I found Paul S. who had just delivered a demo Jimmy Smith Project tape ("The Sermon" ? TP20).  Went back in and listened.  Oh my ? Lee Morgan and his trumpet were there.  I can understand why Paul indicated that he is ?very happy? with that and the Staples Singers release.  Can?t wait to get my own.

Brought my Stellavox and went around to a few rooms to ?audition? a few tapes including the Project Arnold Overtures.  When allowed, it proved to be a mixed blessing as the ?front end and medium? exposed problems in most of the systems: restricted dynamic range; lack of (true/controlled) lows or steely highs.  The exception was the Orca room where the magnificence of the ?Commonwealth Christmas Overture? astounded all listeners and provoked applause at the end ? each time ? I was held captive there for a while.  As I mentioned to Paul, one can think of this selection, played through the right equipment, as (IMnotsoHO) the absolute, BEST ?tool? to demonstrate the weaknesses (dare I say strengths) of a system.  Every dealer and manufacturer espousing to be truly high end should consider this Absolute Sound.

Finally ? didn?t run into any Projectapesters at the allotted Saturday 2PM time (gotta get screaming yellow t-shirts) but did meet a few during the course of the show ? great conversations ensued.  THANKS as always

Charles   

32
General Discussion / SO - who'se going to Rocky Mountain?
« on: September 07, 2009, 12:17:50 PM »
See you there - somewhere TBD?

Charles

33
Tape Tech / Technics 1500 - How does one replace the VU meter bulbs?
« on: July 09, 2009, 05:28:12 AM »
I see that this question was asked once before but not answered. AND - is there a "current" replacement bulb?

THANKS (in advance)

Charles

34
Reel to Reel Tape Machines / Technics 1500 motor control "analysis"
« on: July 07, 2009, 05:50:54 AM »
I've heard/seen that certain members have been having speed/torque problems with their decks.  I looked in the manual(s) I have and it appears that all that's there are schematics; with no mention of how things work or any troubleshooting tips.  So I spent some time "doping out" the circuitry and the resulting "analysis" appears below.  Unfortunately, any intense troubleshooting will require certain test equipment, most notably a DVM and oscilloscope and the ability to use and interpret the measurement results.  A modicum of circuit analysis ability also helps.

Looking at the schematics reveal that there are similarities between the operation of both the capstan and reel motors.  For both sections there is a (separate) 50kHz oscillator (TR931 and 932 for the capstan) and TR791 and 792 for the reel) that generate a 50Khz squarewave? into the ?position detector coil primary? of the motor windings.  This waveshape is sensed in a three-phase manner by the ?position detector coils secondary? and fed to a series of transistors which then generate three phase control signals to the motor armature coils.  One thought to troubleshoot these sections is to put a scope on the output of the 50Khz oscillators (collector of TR792 for the reel motors ? collector of TR 931 for the capstan motor) and see if they are working.  You could also look at the output signals produced by the three sets of armature coil driver transistors (A1, A2 and A3) to see if the waveshapes ?look? similar - if say one is "missing, then one or more of its transistors is probably bad.  Unfortunately, because the circuitry appears to be working in a three-phase manner, to see if the ?correct? phase relationships are being maintained, you?d have to use a multi-channel scope to be able to view all three phases simultaneously.  Actually, it makes sense that if the motors turn at all, this portion of the circuitry should be OK and a speed control problem is undoubtedly somewhere else.

The control signals for what I?ll call the motor ?drive circuits? appear to come into TR947 for the capstan motor; TR747 for the supply reel motor and TR748 for the takeup reel motor and may be ?viewed? on test points TP911 and 912 ? capstan motor; Is ? supply motor and It- takeup motor.  You should see what I?d call ?similar type? of signal here (don?t know the actual waveshape), but a LACK of a signal signifies something wrong ?upstream? allowing the motor to run in an "uncontrolled" manner.

For the reel motors; when playing/recording a tape, the control signals come from the circuitry on the right hand side of the schematic which is labeled ?torque control?.  As both the supply and take up motor control circuitry seems to be identical, I?ll describe the supply portion.  A signal from Phase 2-2 of the position detection coil is detected and amplified by transistors TR701 and 702 and sent to TR801 which is called the ?Waveform Shaping? transistor.  This signal is somehow compared with a current corresponding to the selected speed (through switch S3) and a resulting what I?ll call ?torque control signal? coming from TR817 is fed to the ?drive circuits? mentioned above.  To troubleshoot a potential problem in this circuitry, I?d compare signals between the upper supply motor section and the lower take up motor section ? they should ?look? the same.  If you lose a signal somewhere, proceed "upstream" till you find it and see what component blocks it's passage.  In thinking about this, it makes sense that if either the supply or take up motor control circuit has a problem, then the tape reeling would get all screwed up, with the "bad" motor running (or attempting to run) at a totally different speed than the other. 

The speed of the capstan motor looks to be ?locked? to a crystal-controlled oscillator called IC903.  Apparently a sawtooth-shaped waveform is available "downstream" at TP907 that should have a period of 256hz if S3 is switched to 15ips (128hz for 7.5 ips).  S2 (before TP907) selects the output from either the crystal oscillator or a variable-frequency oscillator controlled by the (front panel) pitch control, so you should see a similar-shaped signal regardless of S2's position if both oscillators are working properly.  The ?actual? speed of the capstan motor appears to be sensed by an internal coil labeled FG which is then amplified, shaped and divided by the circuitry on the upper left-hand and center portion of the schematic.  If this circuitry is working correctly, a ?higher? frequency squarewave? should be available at TP903 (frequencies aren?t listed) and a ?lower? frequency which should be ? of the ?higher? frequency should be available at TR902 (misprint) ? schematic says 64 hz, whatever that means.  The ?actual? and ?desired? frequency signals appear to be compared in a differential amp circuit at the bottom right of the schematic and a control signal fed to the motor control transistors via TR947 and available for viewing at TP912 as mentioned above. Again, for troubleshooting I?d look for an absence of a ?meaningful? signal at the various testpoints and if you spot something untoward look ?upstream" from there.

Of course you should also first check that the various circuits are getting the correct power supply voltages.  All the circuits use 5, 15 and 21 volts from the main power supply; with the 21 volts used in the motor drive circuits, the 15 volts used in what I?ll call the analog control circuits and the 5 volts used in what I?ll call the digital control circuits.  Makes sense that a failure of the 21 volts should not allow a motor to operate at all.  A failure of either the 5 or 15 volts could allow a motor to operate but certainly in an uncontrolled manner.
 
Hope this helps.

Anyone with more info, corrections to the above or troubleshooting tips PLEASE contribute.

Charles

35
Reel to Reel Tape Machines / Squealing Technics 1500
« on: June 03, 2009, 05:29:48 AM »
My 1500 squeals in rewind/FF once it gets up beyond a certain speed - sounds like it's coming from the rewind motor.  Any thoughts - Lube the shaft; brake problem??

Thanks

Charles

36
Reel to Reel Tape Machines / Technics 1500 side panel info
« on: May 26, 2009, 06:20:04 AM »
I picked up a 1500 without side panels.
1. Anyone have two decent panels they are willing to part with?
2. If no to above; anyone have dimensional drawings (w/mounting screw info) for the panel?
3. If no to above; anyone willing to let me borrow a panel so my carpenter can copy it?
Email me @ [email protected]

THANKS
 Charles

37
OK I found the information on the preamp on this website.

Now I've hooked up a Stellavox with a Pro Nortronics 2 track head wired out to it.  HF response is down 2 dB @ 10Khz and 5 dB @ 20Khz on both channels and this happens with the switch in either the NAB or IEC position (using the correct EQ test tape).  Took off the top and can't find any internal adjustments.  Would you please tell me what component(s) to "tweak" so I can dial in the HF properly.

Thank You

Charles   

38
General Discussion / Bottlehead Tube Repro Specs / Manual?
« on: April 15, 2009, 02:06:39 PM »
Doc,

I just got in one of your units for "comparison" against some other preamps and after searching your Bottlehead website, can't find any info or specs on it (when you click on tape machines/products it sends you to this forum).  Can you provide some info?

Thanks

Charles

39
General Discussion / Group Buy of Multi-format Alignment Tape?
« on: April 15, 2009, 09:58:52 AM »
I've had this discussion with a few of you enough times to warrant posting the idea here.

Project subsctibers apparently receive a 15ips alignment tape with IEC equalization.  For NAB EQ you are out of luck.  When you go to MRL you find that their "normal" tapes are one speed / one EQ only, and getting multiple tapes runs up a big bill real quick.

A few years back, I needed an alignment tape for my Sound Technologies 1500A and contacted MRL about making me up one "all purpose" tape with different speeds and EQ's.  They did and a 3 speed, 2 EQ tape cost me less than two single tapes.

Here's what I propose.  If there is sufficient interest, I'll contact MRL and see what they will charge for the following tape:  15ips - 30 seconds reference tone (250mw?), 60 seconds 10khz (or whatever HF tone) for azimuth adjustment; then say 15 seconds (each) of a series of 5? or 6? tones with IEC EQ, followed by the same number/frequency of tones at NAB equalization.  THEN, the same thing with NAB EQ ONLY for 7 1/2 ips.  Now you should have everything you need on one tape for most all playback needs - UNLESS you also want 3 3/4 ips NAB playback EQ.

I'm guessing that we could get a pretty decent price if we could guarantee MRL a quantity of say 6 tapes.

Waddyathink????

Charles


40
General Discussion / Happy Holidays to all
« on: December 19, 2008, 06:43:25 AM »
This is going to be a rambling missive with (I guess) two purposes; one to inform folks what I?ve been doing since the beginning of the summer, the other to reinforce my opinion about what I refer to as the ?ultimate? audio accessory-  an equalizer.

Let?s start with the recent past:  I had a GREAT time at VSAC 2008 - was also disappointed by the low attendance and the lack of what I will call a ?DIY turnout?. It seemed like everyone was there to sell something. I?d opine that the DIY wave may have crested with VSAC 2003.  Enjoyed seeing the Bottlehead and Tape Project entourage along with a few of you Project participants.

In the tape deck world - Had an opportunity to finish up my ASC 6002 deck (at the moment I can?t find or don?t have a picture of it all back together again):



The 6000 is a direct descendant of the Braun TG1000 (a VERY NICE sounding machine) and was one of a few neat HiFi products produced by a group of personnel who left to form Audio System Componeten in the late ?70?s when Braun decided to discontinue that consumer product line.  Whereas the 1000 could only go to 7 1/2ips and hold a max 8 ?? reel (some kind of European standard), the 6000 could play 15 ips and hold a 10 ?? reel.  It has very nice tape handling; what I?ll call ?quasi ? constant tension? via the use of a mechanical/electronic feedback mechanism ? if you look closely, you can see that the outer tape idlers are mounted on swing arms which are coupled to a photo-optical assembly.  This then produces a variable DC component which when when added to the AC feed to the Papst reel motors varies their speed proportional to tension (pressure on the rollers).  The heavy, machined capstan assembly is belt driven from a DC motor with speed feedback via an integral tachometer.  The 6000, while "common" in Europe was never imported into the US and this must be one of a very few here ? a friend actually carried it over from Germany on a trip.  It did require a little work (shorted electrolytics) and tweaking of the playback EQ but was worth it as its audio quality is exceptional ? due in large part to the Bogen heads.  Next related project is to modify my Tandberg infrared remote control to operate it.

Current tape machine fav is the Lyrec Frieda  (never heard of it ? too bad - neither did I till a few years back ? veerrry rare) which blows away most other decks I?ve heard and nudges the Stella.

Over the summer a friend stumbled across the remaining inventory of Cello Inc. in a Bridgeport, CT warehouse.  I?m not going to bore you with a long story of that (currently) defunct brand, beyond saying that they produced some of the world?s most highly respected audio components.  Chief among them was the Audio Palette, a six-band equalizer and sibling, the Palette Preamplifier. 

Among the discovered parts were a set of populated printed circuit boards for the Preamplifier along with enough documentation to allow me to get it going.  There was no cabinetry, so I proceeded to have the sheet metal and front panels fabricated to my own specifications.  The front panel engravings are identical to the original with the exception that no mention of ?Cello? appears, to keep away from any potential copyright problems (and Front Panel Express wouldn?t reproduce it anyway without written permission from the trademark owner).

What I did differently from the original product was to separate the equalizer portion of the Palette from the preamplifier section and fabricated a 10 meter umbilical cable to connect both units.  This allows the equalizer to be placed right at my listening position to make adjustments in ?real time? without moving from my seat. The controls on the equalizer are identical in function to the original and it is mounted on an original accessory Lucite stand with 4 casters (wheels) on the bottom so it can be easily moved.



The (separate) preamplifier has 5 inputs with the other level and balance controls identical to the original Preamplifier, with one exception.  In the original Audio Palette, the ?Equalizer In-Out? switch offered the ability to reverse the absolute phase of the outputs (180 degrees) whether the equalizer is in or out of the circuit.  This feature was eliminated on the Palette Preamplifier but I added back to this version. The preamplifier is also self-powered (the original Preamplifier required a separate power supply) and supplies power to the equalizer over the umbilical cable.
 


Now in previous posts I?ve extolled the virtues of having some kind of frequency contouring ability in your HiFi system.  With a tape deck, high frequency adjustment can be easily? accomplished by making the ?R? in the high-frequency equalization network variable (and accessible).  An equalizer adds even more capability to all sources BUT I?d opine that the problem with most all equalizers (and the reason that they have been categorically trashed) is that they introduce a sound of their own.  The Palette seems to be about as neutral as it gets ? aided by the fact that the equalizer section can be bypassed via a front panel switch on the preamp. I've used it mostly in a "subtractive" mode to help take the edge from female vocalists on a few CD - actually allows me to listen through the program rather than having to eject after 2 songs.  Next plan to go back through my tape collection and probably use it in an "additive" mode - mid bass and the like.   

Finally, a few words about my current system ? speakers are Quad 63?s driven by a tweaked Lazarus Class A hybrid 50 watt amplifier.  Homebrew, center channel, Quad woofer with self contained combiner / amplifier / 4th order low pass filter from 100 hz down.  System goes down into the 20?s.  CD is a Norh CD-1 and Tape includes the Stellavox; (borrowed) Lyrec; ASC and a MCI JH110 deck with modified electronics.  FM is a SUMO Charlie (of course) with a tubed output. FM in Oneonta NY sucks ? that?s why I added an SONY XM radio tuner (not half bad). 



The device on the rug in front of the center speaker is the best antidote to bad sound that I've found.

Nuff for now - Keep your heads clean and your tails out!

MERRY CHRISTMAS

Charles

O yeah, THANKS Steve for the info on how to use Imageshack to upload and attach photos.
    



41
Tape Tech / What speed is your deck ACTUALLY running at???
« on: May 12, 2008, 06:18:40 PM »
Thought you?d thunk enough today? Well think again! Here?s a think piece for you.

How do you know if your recorder is running at the correct speed?  And who cares? Let?s leave the ?who cares? part for later.  OK, I cared - this afternoon when I was trying to finish up tweaking my ?new? ASC 6002 recorder.  Finished setting the tape tensions, then the instructions mentioned how to adjust the tape speed.  Simple I thought, just record a high frequency tone and measure its frequency coming off the tape.  But; wait a minute dummy ? the tone gets converted to a wavelength on the tape and as long as the tape is playing at the same velocity when I ?listen? to it, it will have to be the same frequency ? which is certainly the case if I listen off the third (playback) head.  Even if I had a two head machine, as long as its capstan motor keeps turning at a constant speed, when playing back I?ll still measure whatever frequency I record.

OK, how to get the recorded wavelength "right"?  Let?s see, I guess you need to get a tape with some "standard? frequency recorded on a deck that?s running EXACTLY at whatever speed you want to check your deck at, with low enough wow and flutter to be able to measure the frequency ?precisely?.  Running to my trusty MRL Calibration Tape catalog, I find that these tapes certainly exist and are part of their 3150hz flutter and speed test tapes, which of course I don?t have as this test is not part of my ?standard? tapes (with level, azimuth and frequency sweeps only).  The MRL flutter and speed tapes have specs better than +/- 0.1% which equates to +/- 3.15hz from a speed perspective.  Oh great - another $100+ tape.

Then I remembered that the idlers on both sides of the Stellavox headblock have concentric marks which when viewed under a neon light (switching on and off at 60hz) create a stroboscopic effect that results in a non-rotating ?circle? when the tape speed is exactly ?on?.  The circle starts rotating slowly clockwise if the speed is too slow and counter-clockwise if too fast (I might have gotten that backwards).  Had an extra idler in my parts bin and was able to ?jury rig? a temporary mount on the deck; which enabled me to determine that the speed was a little slow.  In the process I found that the pinch roller pressure also seemed low and that the tape was slipping due to a hardened roller. Oh well; Terry Witt gets another pinch roller to rebuild, and I?m dead in the water till after VSAC2008.  More time to pack! 

This also reminded me that back in the 60?s??!! these stroboscopic, speed measuring, wheel thingies were advertised in Allied and Lafayette catalogs.

Does correct speed matter?  You tell me.  Enough thinking; now where?s that aspirin bottle ? better yet, a cockatail.  O yeah, PLEASE feel free to correct any missed-conceptions or outcomes mentioned above.

Charles

43
Tape Tech / Tape Preamp Variable EQ
« on: April 20, 2008, 07:13:00 AM »
Guys  (and Doc),

I continue to see posts regarding NAB / IEC equalization and using or "converting" other (non IEC) machines to that EQ.  Let me expand a bit.

May have mentioned this before but my own "playing" with the electronics of many machines AND listening to hundreds of pre-records has convinced me that having the ability to vary the high frequency response can be of great benefit - especially when listening to early 2 tracks when the standard playback curve didn't exist or wasn't adhered to.  In many cases, just making the resistor variable in the RC circuit that determines the HF EQ can allow for, say a boost or cut of 6dB at 10Khz.  This can make all the difference in the world when "taming" the bright high end on certain tapes OR boosting/compensating for too much treble rolloff in others.  The variable control need only have it's "center position" indicated - which "exactly" follows the NAB curve. Understand too that this is NOT a tone control  per se, in that it is part of the EQ circuit.

I have added this type of control to the front panel of Revox G36 and A77's and it's a fairly simple mod - hardest part is mounting it.  This control also allows "tweaking" of the HF response to match the IEC curve

Doc - I strongly suggest you consider adding something like this to your preamps - could be implemented with a screwdriver adjust pot. I would hope that folks who buy your equipment won't JUST listen to Tape Project tapes - or maybe not.

Charles

DDoc you might         


44
Tape Project Machines / Technics 1500 series IEC / NAB equalization musings
« on: February 16, 2008, 07:46:22 AM »
Back in time, I mused about the NAB / IEC playback equalization circuits in the 1500 series machines and opined that they all seemed identical based on the schematics available to me at the time.  Well I was half wrong.  I'm visiting the beautiful Newburyport home of a Walter Clay, fellow tape enthusiast and Tape Project member.  Walter happens to have both a 1500 (without switchable IEC/NAB) and a 1520 (with switchable IEC/NAB) along with the service manuals for both so I spent some time this beautiful New England winter morning comparing schematics and PC board layouts and here's what I came up with.

The Playback PC board, called the "Main Amp" circuit board" have identical layouts for both machines.  The 1520 differs in that there is some additional circuitry on its "Sub Amp" board which switches an IEC-related time constant at the output of the playback preamp. This "stuff" is difficult to follow as it is not completely shown on the schematics and can only be traced by comparing both them (pages 65 and 67), their parts layouts and the wiring diagram on page 71.  To try and simplify things, it appears that during IEC playback, an additional time constant consisting of a series-connected 5.6K ohm resistor and 22 nanofard capacitor is switched in between the "top" side of the (PC board-mounted) playback level controls on the Main Amp board (VR106/206) and ground. Thats it!.

If I've got this right and please understand that no testing has been done, it should be relatively easy to add a a DPST switch and the four IEC EQ components.  I removed the bottom panel of the 1500 and there is the bottom of the Main Amp board sitting there - with the connections to VR106/206 readily exposed.  Don't know where you'd put the EQ switch - that's your problem.  Have a ball!!!!


               

45
Tape Tech / Technics 1500 Schematic wanted
« on: January 05, 2008, 07:32:31 AM »
Could someone please post / refer me to / send a schematic of the playback amo section of the 1500? I want to clear up this NAB/IEC equalization question - at lease in my own mind!

Thanks

Charles

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