I've had an Akai 4000ds MkII for a couple months now and I absolutely adore it and have made some great recordings with it but lately the amount of hiss has been driving me crazy. Now I would expect a considerable amount of hiss from analog tape as it's an unavoidable consequence of the format but the real kicker here is that the hiss occurs when the tape isn't even playing, when there's no tape even loaded into the machine. As long as the machine is on and the monitor switch is set to tape I get this awful noise that sounds a bit like pouring rain. I'm pretty sure this hiss does't exist in the recordings I have made but it occurs in the playback section somewhere. The machine is in good mechanical order and has been lubricated and the heads have been cleaned with TEAC head cleaner since I got it but I have no idea what the machine would have been through before I got it in October 2013 although I suspect it was used in a home to make backups of LPs as It came with a bunch of homemade tapes of classic albums. Anyways does anyone know what might be causing such an evil sound in my machine?
It's a combination of resistive self noise in the playback head along with noise generated by the playback electronics. The gain in replay electronics is quite high, and depending on the topology of the replay electronics, active devices and resistors used, and noise contribution by the head, improvement may or may not be possible.
(Sorry for the wishy washy answer)
Note that if you can short the inputs to the replay electronics and the noise level decreases significantly the head is the culprit, if OTOH the change is not significant then the replay electronics might respond to some careful redesign.
Something else to bear in mind is if you are listening through headphones the nuisance is magnified as compared to speakers in the room, the same would be true if the speakers have a rising room response somewhere in the region beyond say 5kHz..
(Sorry for the wishy washy answer)
Note that if you can short the inputs to the replay electronics and the noise level decreases significantly the head is the culprit, if OTOH the change is not significant then the replay electronics might respond to some careful redesign.
Something else to bear in mind is if you are listening through headphones the nuisance is magnified as compared to speakers in the room, the same would be true if the speakers have a rising room response somewhere in the region beyond say 5kHz..
So I finally had a chance today to check this on my tape recorder and I found that when the two leads from one channel of the head are shorted together using a screwdriver that all noise disappears in that channel. That would point to at least in my mind ambient EMI as the source of the noise, does this mean that the head is the cause of the problem? Does it need replacement? Degaussing? or was there simply far less EMI in the 70s?
I'm gonna try re-calibrating the heads today to see if I can get more signal out of the heads so that the noise is less significant in comparison. Anyone else have suggestions?
Most likely it is Johnson noise developed by the dc resistance of the head windings. It is not impossible for it to be EMI, but if it disappears with the crude antenna of a screw driver that is very unlikely.
If one channel is noisier than the other that may be indication of additional electrical problems such as noisy transistors or bad electrolytic caps - if shorting the head makes it go away on that channel then it is a head issue or you are generating excess noise due to dc current flowing in the head - and this may gradually erase the HF content of your tapes. Have you recapped this unit? This could still be the problem on both channels.
Possibly replacement heads are available from JRF for this model, but you are not going to like the price.
I finally abandoned open reel tape (Otari MX-50-T, 1/2 track ReVox G36 MKIII) because of noise and distortion issues, that and the fact that an inexpensive prosumer sound card made needle drops (copies) that sounded considerably closer to the sound on the record than the tape recorders could.
Don't mess with the heads unless you have the proper alignment tapes!
If one channel is noisier than the other that may be indication of additional electrical problems such as noisy transistors or bad electrolytic caps - if shorting the head makes it go away on that channel then it is a head issue or you are generating excess noise due to dc current flowing in the head - and this may gradually erase the HF content of your tapes. Have you recapped this unit? This could still be the problem on both channels.
Possibly replacement heads are available from JRF for this model, but you are not going to like the price.
I finally abandoned open reel tape (Otari MX-50-T, 1/2 track ReVox G36 MKIII) because of noise and distortion issues, that and the fact that an inexpensive prosumer sound card made needle drops (copies) that sounded considerably closer to the sound on the record than the tape recorders could.
Don't mess with the heads unless you have the proper alignment tapes!
Hmm, actually that's quite possible. In the nearly 40 years of this machine's existence I'm sure it must have been calibrated at least a few times and I imagine someone could have screwed up somewhere along the line. Its probably best to get some calibration tapes and do it myself. Anyone know the best place to get these for a 1/4" 2 channel 4 track machine like this one?
Hey guys,
I´m digging out this old thread because I got the same issue with my Akai 4000Ds MkII.
Just revisited it after leaving it on the shelf for a few years lately and I get this irritating noise when the machine is set to tape monitor. On input monitoring there is absolutely no noise.
And as mentioned before, the noise is there while there is no tape playing back or no tape on the machine at all. The noise is only on the left channel, the right channel seems fine. Also the VU meter of the left channel responds to that noise.
Did anyone find a solution for this with this particular machine or another?
Here is what it sounds like: Akai 4000 DS MkII Noise.wav - Google Drive
I´m digging out this old thread because I got the same issue with my Akai 4000Ds MkII.
Just revisited it after leaving it on the shelf for a few years lately and I get this irritating noise when the machine is set to tape monitor. On input monitoring there is absolutely no noise.
And as mentioned before, the noise is there while there is no tape playing back or no tape on the machine at all. The noise is only on the left channel, the right channel seems fine. Also the VU meter of the left channel responds to that noise.
Did anyone find a solution for this with this particular machine or another?
Here is what it sounds like: Akai 4000 DS MkII Noise.wav - Google Drive
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That´s not a bad idea. These old Akai´s (and similar) have two main reasons for noise: Corroded rec/play switches and the widespread use of Hitachi´s 2SC458´s. These transistors have a tendency to corrode on the legs, and with time the corrosion creeps into the plastic house and gradually destroys the chip, and thereby causing all kinds of strange behaviour, mainly all kinds of noises.
Just remember, after replacing them with a suitable substitute, the unit needs to be recalibrated/readjusted to perform to spec´s
I know this post is a couple of years old but if anyone comes across it, a known fault with these Akai decks is the 2SC458 transistors used in both the replay and microphone amplifiers. They deteriorate because of corrosion on the pins and initially become very noisy leading to a complete failure to pass a signal. Confusingly the DC conditions test out fine. A good clue that they're failing is the legs have gone black. I have just refurbished two of these Akai decks and swapping the dud transistors for 2SC3200 and 2SC1845 brought them back to spec.
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Surely its random leakage that leads to cap noise?
But its quite possible almost any component in the signal path has degraded over time - the situation might be worse than when new (or then again it might be the same) - the spec's will indicate what the electronics noise floor is perhaps?
Clearly something has degraded over time then. The spectrum is that of flicker noise which is a strong indication of component imperfection. If you are lucky the relevant component will respond to being tapped so you may be able to track it down.
Yes, I think that would be a highly probable noise mechanism which I was not thinking about when I posted. IMO more likely than high ESR to be a cause.