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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 15th Mar 2017, 8:25 pm   #21
Michael Maurice
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Default Re: Akai 4000DB / 4000DS

I bought a 4000DS back in 1973 and was somewhat dismayed when the price fell when we moved to VAT from purchase tax.

But the Akai failed within 3 weeks, the bolt on which the pinch roller arm swivels worked loose meaning that the pinch roller was not square to the capstan.

I took it back to Rank who cured that and mucked around with the levels, they were now incorrect.

There were various other failings including the now infamous LD3141 IC's,

The capstan sleeves were also a problem and I went through several.

I got fed up with the unreliability of the machine and bought an A77 with Dolby which I still have.
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Old 16th Mar 2017, 3:41 pm   #22
Ted Kendall
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Default Re: Akai 4000DB / 4000DS

In fairness, neither my 4000DS nor the one my Dad bought shortly afterwards gave any real trouble - to that extent I was lucky - and neither did the Sony.

The A77 was, of course, something different in kind rather than degree, especially the Dolby version, which had a couple of sillinesses in the original electronics ironed out. At twice the price of the Sony, never mind the Akai, it should have been.
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Old 16th Mar 2017, 11:21 pm   #23
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Default Re: Akai 4000DB / 4000DS

Quote:
Originally Posted by monaro0162 View Post
As the capstan and pinch wheel are bigger relative to the ones fitted on the Sony, shouldn't they provide more tape 'grip' and suffer from less w&f, if the pinch wheel rubber gets damaged?
Yes the larger contact area should help although it also means less force per unit area.

As I recall the Sony 366 has a standard permalloy head while the 377 has a ferrite head. I wasnt aware there was any change to the circuitry though. I think Ferrite heads were especially good for replay (so long as the hard, brittle gap edges were not damaged!).

Yes as to running out to 30khz, that was always possible with tape running at a fast enough speed. Even at 7.5ips it's possible to record frequencies well above human audibility. I read recently that even in 1949 Ampex were able to record and play back tapes virtually flat up to 15kHz at 15ips. So up to at least 30kHz was possible at 30ips in 1949.
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Old 17th Mar 2017, 6:43 pm   #24
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Default Re: Akai 4000DB / 4000DS

error with pics, edit below!
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Last edited by monaro0162; 17th Mar 2017 at 6:53 pm. Reason: upload error
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Old 17th Mar 2017, 6:50 pm   #25
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Default Re: Akai 4000DB / 4000DS

TIMTAPE thanks I read somewhere that the heterodyne effect adds to machines with higher HF response, above that of a typical human hearing range, sounding 'better', despite humans not being able to hear at these extended frequencies.

Attached are some close up photos of the suspect head set from the project DB. It may be that the heads were just too worn out and past it, rather than the problem being specific to the R4-150 record head, although it does seem to have a strange wear pattern.

Also attached is the audacity analysis on the noise issues that the DS had when I bought it. All of these issues have been fixed when I did a full transistor ic and cap replacement, the noise floor is lower too. Need to put the DS through a full test again and update the doc
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File Type: docx 2 sources of noise.docx (394.9 KB, 70 views)

Last edited by monaro0162; 17th Mar 2017 at 7:01 pm. Reason: typo
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Old 17th Mar 2017, 9:49 pm   #26
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Default Re: Akai 4000DB / 4000DS

Quote:
Originally Posted by monaro0162 View Post
TIMTAPE thanks I read somewhere that the heterodyne effect adds to machines with higher HF response, above that of a typical human hearing range, sounding 'better', despite humans not being able to hear at these extended frequencies.
I think the old rule of thumb in designing high fidelity tape machines was to set the bias frequency 4 to 5 times higher than the highest frequency you wanted the machine to capture, to prevent beat frequencies intruding. So, far from sounding "better", the heterodynes were seen as distortions to be avoided. That's my understanding at least.
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Old 18th Mar 2017, 10:09 am   #27
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Default Re: Akai 4000DB / 4000DS

Maybe it wasn't heterodyne, but some other effect that, on machines that can record way above audible frequencies, this somehow improves the sound in the audible frequency range during playback.

I also heard that a humans perception of sound is (obviously) dependent on how good your ears are, but is also dependent (to some extent) on subsonic frequencies picked up by the body. A Hi-Fi enthusiast I used to work with told me this many years ago, so possibly it could all be baloney!
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Old 18th Mar 2017, 3:27 pm   #28
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Default Re: Akai 4000DB / 4000DS

I'd guess that all the senses are involved to a greater or lesser degree. We've had many threads illustrating that listening is only one of the factors in music appreciation for many.
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Old 18th Mar 2017, 11:49 pm   #29
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Default Re: Akai 4000DB / 4000DS

If I remember right, the capstan on my 4000DS had a small conical section turned into the bottom of the section which ran against the tape/pinch wheel, just as its diameter stepped out larger for the bearing.

The capstan sleeve had a small chamfer leading into its bore on both sides which mated with the conical fillet on the capstan and made it self-centering. The lower end face of the sleeve didn't mate against the end face of he change in capstan diameter. The sleeve chamfers meant you could fit it either way round.

The retaining nut had a plain flat face which pressed against the plain flat part of the sleeve face.

So the bore in the sleeve had clearance over the diameter of the capstan, but the sleeve was centred and held there without slop. It looked a neat solution and wasn't obvious unless you went looking for it. I had no issues with flutter, only with wear on the spool hub bearings, but I could buy spares from J Arthur's merry men.

David

In a precursor to the Akai capstan sleeve, I found the rubber tubing (minus braid cover) of a standard bike pump was a good fit over the capstan of my old TD2 and roughly doubled the speed. Having developed my technique at home it was time to have a bit of fun with the TD2-based language lab at school......
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Old 19th Mar 2017, 12:19 am   #30
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Default Re: Akai 4000DB / 4000DS

It's funny when sometimes you can't understand the criticism over a particular design, suddenly the penny drops and you understand. When I took a closer look at the capstan and drive shaft and securing nut, on all the machines I have, and swapped them around a bit between machines, I found that with some combinations the adaptor didn't seem to screw on tight to the shaft allowing the adaptor to rotate. Which would cause tape drive slip. Measured all the adaptors at 8.00mm length on a vernier so I'm not sure what's going on there!

Just need a head cover and VU meter for the project DB and it will be finished. Then I shall probably sell it, keeping the original DS and the 'reference' DB that I have.

The recorder is part of the system that I am recreating, the system that my Dad bought, that I used alot in the '70's, that I have fond memories of. The system included a Goldring G101 turntable, a Rotel RA-310 amp with RT-320 tuner, and the AKAI 4000DS, the exact system my Dad had. I'm very pleased that both my Dad and Mum and I kept all our vinyl LP's and didn't chuck them out, despite switching almost exclusively to CD in the mid '80's. Lots of listening to catch up on.

All the parts of the system were from e-bay, and all requiring quite a bit of work to get them up to scratch
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Last edited by monaro0162; 19th Mar 2017 at 12:24 am.
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