Lovely Akai 4000DS.

[monaro0162]

Hi all, first post here.

Back in 1974 my Dad bought his first decent hifi system which consisted of a Rotel RA310 amp with the RT320 Tuner, a Garrard G101 turntable, an Akai GXC-46D Cassette player and ... an Akai 4000DS reel to reel. I loved the system and used to use it more than he did when I was a teenager. I used record the BBC Radio1 top 40 shows. At the time Radio 1 was only on medium wave but on Sundays it was broadcast on the Radio 2 frequency in FM stereo. I used to record all of the show on reel to reel then dub to cassette.

Eventually my dad sold the system and it was replaced with a Trio system as far as I remember, but I always remembered that lovely 4000DS.

I've had a hankering for one for years and after finding a couple of my original reels at my dad's house, I decided I just had to have one again.

Picked up this lovely 4000DS for £67 including the cover, owner and service manuals, in cosmetically very good condition with nothing missing. It also came with 30 reels and a book meticulously listing all the artists and songs on the reels - mostly LP recordings from the 1970's.

After a minor clean up of the heads and wheels, and look inside, I've had it running for the last month and it sounds lovely. No problems with it at all, even the cams look fine. Whoever owned it looked after it because inside the service manual I found pencil notes in the servicing section where the owner has serviced it sometime in the past.

Very pleased with my purchase. Abba have never sounded so good in glorious analogue stereo!

Going to try some frequency response tests on it soon and do an alignment on the amps. As it's mark 1 it has the infamous LD 3141's in it, but they sound fine here

[julie_m]

The 3141s are no longer so much of a problem, since they have been successfully reverse-engineered. It's possible to build a "plug-'n'-play" replacement on copper strip breadboard, with a few discrete components and a steady hand. Search online for the details.

I have the Mark II version of this deck, in a very well-cared-for example. These machines, together with contemporary offerings from Sony, represent the evolutionary peak of single-motor reel-to-reel tape decks. There are certainly higher-fi machines out there, but these punched above their weight.

Keep the heads clean and de-magnetised, and the mechanism lubricated to reduce stress on the cams, and you should enjoy your Akai for years to come. You really only need the high speed 19 cm/s for sound-on-sound recordings; the standard speed 9.5 cm/s is fine for taping CDs and LPs. And the pressure-pad-free tape path is very useful for making accurate splicing marks -- but doesn't suit all tape grades. Still, you can presume the reels of tape that came with it will all work with it.

I think you got yourself a nice deal there!

[Radio Wrangler]

Takes me back to when I bought a new one as a student in '73 or '74. It worked very well, but I did wear out a pair of the bearings for the spool shafts. It sounded fine, but I stuck to 7.5 ips and TDK SA tape.

David

[monaro0162]

Hi, thanks for the replies

It so happens that I have acquired a Sony TC366 from the same era to compare with the akai.. I got the Sony from a friend who's ex-father-in-law gave it to him. It seems to have various problems though, it had very crackly switches, but the main problems are difficulty holding it in the play position (it uses a single lever compared to the two on the akai) and noticeable wow and flutter sometimes. It looks brand new on the outside though.

Back to the akai - at the moment I'm running it a 7.5ips, on fairly good used Maxell and TDK tapes. I want to use it primarily to record selected tracks from some of my vinyl LP's from the 1970's and '80's, and re-live them in genuine analogue I've done a few test recordings and they sound good, but some of my LP's appear to be a bit worn out as on some there are plenty of pops and crackles! I'm not going to bother to record any of my CDs as they are in the digital arena, it will be kind of missing the point with the analogue akai.

But I'm using the BBC 6Music 'HD' stream on the internet (@320kb HLS AAC) as a source, combined with an upgraded HD audio card for my PC, and to be honest I'm very pleased with the akai, I can hardly tell the difference between the source and the akai.

A new 1800' RMGI LPR tape has just arrived from tapecity, I'll be using this to set up the machine

[monaro0162]

Hi folks,

The restoration on my Akai is progressing well.

To start I did a noise analysis on all the signal paths and (aside from some general 50hz mains hum on both channels) I found 2 issues:

The first being a 'waterfall' sound on the left channel coming from the mic preamp as the mic level was turned up. This was caused by a noisy 2SC458LG transistor TR1 which was replaced with a BC549C which cured the problem.

On the right channel there was a low frequency 50/150hz random rumble and hiss noise coming from the tape head playback circuit. This was caused by TR4 again replaced with a BC549C which cured the problem. For good measure I then replaced all of the transistors with BC549's although I haven't replaced TR2 yet.

Next, to tackle the background hum, I did a replacement of all the electrolytic capacitors, checking the noise both before which definitely reduced the hum.

I recorded all the noise issues and the results after using using the line out of the akai into a HD PC audio card running 192khz/24bit, and then into Audacity for analysis. I also used an old analogue scope brought from e-bay for £30 to have a look around the signal paths. Turns out only 1 channel works on the scope but that was enough to see what was going on within the circuit!

So the machine is now sounding even better, and the next stage will be to do the amp channel alignment and then check and set the mechanical systems.

For wow and flutter I used an (admittedly crude) method to measure it by sending 1,3 and 5khz tones from the PC into the machine, and then measuring the output and then playback with a frequency counter and looking at the variation to determine w&f. I can definitely hear a wobble in the tones when played back and by my calculations I'm seeing about 0.6% w&f above the 0.3% that Akai quote. Hopefully a new belt and pinch wheel will improve this, although I can't really detect any w&f when playing music.

I still have one query on the PSU: The Akai 4000DS MK1 service manual circuit diagram quotes the amp supply rail at 25.1v, but I'm only seeing 24.1 here with about 2mv ripple. All caps have been replaced in the PSU. The AC output from the transformer secondary is at 27vac as quoted on the diagram.

Should I be concerned that the supply rail appears to be 1v down?

[RojDW48]

I have had mine from new (around 1972) still going strong. I had access to a good engineering workshop at the time and I turned up sleeve for running at 15 ips - mechanically it worked fine but I wasn't clever enough to make the appropriate equalization circuitry - so it remained a bit of a party trick!

[SteveCG]

RojDW48,

Were you aware that the NAB tape replay standard use exactly the same equalisation for 15 ips as 7.5 ips. So it is highly likely you can replay 15 ips tapes correctly using your sleeve. However the record equalisation will not be same...

[RojDW48]

I guess that was the problem, Steve - I didn't have any 15 ips tapes, so I was only playing what I recorded - hey ho!

[monaro0162]

Originally Posted by RojDW48

I had access to a good engineering workshop at the time and I turned up sleeve for running at 15 ips - mechanically it worked fine but I wasn't clever enough to make the appropriate equalization circuitry - so it remained a bit of a party trick!

That's a good idea, should be very easy to make.

I'm still working on the DS and have more or less finished the electronic restoration.
I made up some hybrid pre-amps to replace the LD3141's using a circuit that I found online which seem to work great reducing the noise floor. I also experimented rewiring some of the earths to a star config to reduce mains hum. Also fitted a new belt and pinch roller to reduce the w&f.

One thing I've noticed is that while playing back a 5khz test tone I notice a little instability in the amplitude on the left channel. if I apply a little pressure on the feed reel whilst the Akai is playing the instability reduces. So clutch torque adjustments are next on the list.

Balancing up the channels seems a bit of a hit and miss affair due to the way the rec and pb potentiometers work within the circuit. whats the best way to measure the actual signal laid to tape? If I balance up the signal modulation shown on a scope at TR2 when I play back the channels are off balance. Worn head?

Looking forward to doing my first proper recording using a brand new tape on my recalibrated machine

[Michael Maurice]

Be careful making those clutch torque adjustments as it also affects the brakes, you may find that tape spills out when going from FF or Rew to stop.

[Ted Kendall]

I think the output variation and level difference may indicate worn heads. Look (or feel) for a step at the edge of the tape path.

[monaro0162]

I think that the heads are ok, I can see (and feel with a finger) a slight indentation across the head where the tape runs, but it seems even on both sides (channels) and the surface of the head itself is absolutely smooth. When I first took a look inside my unit I noticed that the rec/pb pots weren't central/equal to each other so may be the slight VU offset that I see was there in the first place - a difference in the gain on each amp? I haven't tried de-magetising yet as I don't have a demagnetiser (I looked all through my dads loft but I couldn't find it)

All the cams have been greased and I'm going to get some sets of hybrid LD3141 pre-amps made up on a proper PCB and have them potted next. I'll do another alignment once they are in and the job will be finished

[monaro0162]

My restoration project is complete. The 4000 DS is now part of my HiFi.
Here's what I did:

• Brand new Pinch Roller and drive belts fitted
• Motor and Flywheel bearings lubricated
• Supply and Take Up Reel clutch torque checked in all operating modes
• All idlers cleaned and lubricated
• Heads cleaned, de-magnetised, azimuth checked
• All cams and levers checked and greased where necessary
• All switches and potentiometers cleaned with switch cleaner
• All transistors in the Record and Playback amplifiers replaced with new modern equivalents
• Obsolete LD3141 IC’s replaced with transistor based circuits (as on the DS MK2) built on small vero-board PCBs and then potted using epoxy resin
• All electrolytic capacitors in the Record and Playback amplifiers and the power supply replaced with new higher rated 105c items
• Channel signal earthing noise performance improved by addition of a common star earth point
• Record and Playback amplifiers measured for noise and gain, with the Left and Right channels adjusted and balanced to each other
• Tape tension micro-switch re-purposed to only turn off the motor rather than power down the complete unit. The front panel on/off switch can still be used as normal. This enables running of the amplifiers and listening to the source input, without the mechanical noise of the motor running being heard in the background. The motor isn’t noisy, but it just seems a waste to leave it running all of the time.
• Case cleaned and polished, the facia and all the control knobs and levers cleaned

[Radio Wrangler]

Nice!

Sounds like a comprehensive refurb. I enjoyed my 4000DS a lot.

David

[dave walsh]

The micro switch re-purpose is a mod that I haven't heard of before. I suppose the original idea [ie to switch off automatically at the end of the reel] made sense in a general domestic market but now, when the deck is more likely to be in the hands of a dedicated enthusiast, that's a new useage

Dave W

[Grubhead]

My friend Philip had one of these machines, but I don't know what he did to it, but he was always bringing it back to me and every time it needed a new head. It just caused a little bit of distortion. Tiny amount really. But he went through four heads!

I put it down to the fact he liked heavy metal!

[Radio Wrangler]

Mine saw very heavy use, it was my primary source of music for several years. The bushes for the spool shafts needed replacement, but the heads stayed fine. What on earth was he using for tape?

David