Interesting.....although I did believe that they WOULD make an improvement, it's good to know that is the case indeed. I am curious, though---what EXACTLY sounds better? Lower noise, better response..........????? Still think you should make power supply improvements, though, to get the most out of those excellent ICs.
NICE WORK so far, though!!!
MX-50N Capstan Motor Woes
Now fixed, but apparently MX-50, MX-55 and MX-5050BIII share the same capstan motor and servo electronics design.
A common complaint seems to be that the highest speed (usually 15ips) on these decks malfunctions - the motor runs backwards at high speed.
I replaced 3 electrolytics I missed, at least one of which was in a place where its failure resulted in a large increase in noise on the supply rail.
I also found a cold solder joint on the switch transistor that selects the pot that sets the servo gain at 15ips.
I checked all of the logic - all OK.
Replaced the caps, and resoldered the transistor.
Fired it up and everything worked as expected.
Performed the adjustment procedure outlined in the service manual, touched up the 15ips servo gain and the master clock, none of the multitude of other adjustments needed to be touched. The scope shot is the 15ips servo adjustment result which is ~50% duty cycle at 4800Hz.
Interestingly the motor now runs much more quietly, it was particularly noisy (buzzing) at 7.5ips. I have observed this in several other MX-50 including the N II and thought it was very strange. I now know it is not normal. I am sure replacing those caps is what fixed that issue. (It may also have fixed the speed issue as well.)
Now fixed, but apparently MX-50, MX-55 and MX-5050BIII share the same capstan motor and servo electronics design.
A common complaint seems to be that the highest speed (usually 15ips) on these decks malfunctions - the motor runs backwards at high speed.
I replaced 3 electrolytics I missed, at least one of which was in a place where its failure resulted in a large increase in noise on the supply rail.
I also found a cold solder joint on the switch transistor that selects the pot that sets the servo gain at 15ips.
I checked all of the logic - all OK.
Replaced the caps, and resoldered the transistor.
Fired it up and everything worked as expected.
Performed the adjustment procedure outlined in the service manual, touched up the 15ips servo gain and the master clock, none of the multitude of other adjustments needed to be touched. The scope shot is the 15ips servo adjustment result which is ~50% duty cycle at 4800Hz.
Interestingly the motor now runs much more quietly, it was particularly noisy (buzzing) at 7.5ips. I have observed this in several other MX-50 including the N II and thought it was very strange. I now know it is not normal. I am sure replacing those caps is what fixed that issue. (It may also have fixed the speed issue as well.)
Attachments
This one breaks on a fairly regular basis and came to me with a lot of other problems - so I fix them one at a time or as they occur. Once this one is fully sorted out I'll enjoy it, and start working on the last one which is in better mechanical condition.
It's sort of fun for me, particularly once I have overcome a particular challenge.
This one probably needs most of the remaining bearings replaced. I need to identify the right ones, the last ones I replaced have not been entirely satisfactory even though they are good bearings.
It's sort of fun for me, particularly once I have overcome a particular challenge.
This one probably needs most of the remaining bearings replaced. I need to identify the right ones, the last ones I replaced have not been entirely satisfactory even though they are good bearings.
The originals were SKF but were knackered due to storage conditions. The rollers from the other deck work fine on this one, but belong to the other deck.. LOL
The bearings I used were new production Japanese made NTN 607Z (7mm x 19mm x 6mm) and are very good quality bearings, but perhaps not suited to this use. Therefore I do not recommend them.
I am going to clean them out again and try a different lubricant.
I should not have replaced these bearings apparently, the problems I have with the new ones are appreciably worse than with the originals despite their worn and neglected condition.
I don't know what bearings to use, but I would recommend going to these guys: Bearings & Lubrication or Athan rather than wasting money on unsatisfactory replacement bearings.
A big part of the problem seems to be bearing frictional losses and lubrication viscosity.
The bearings I used were new production Japanese made NTN 607Z (7mm x 19mm x 6mm) and are very good quality bearings, but perhaps not suited to this use. Therefore I do not recommend them.
I am going to clean them out again and try a different lubricant.
I should not have replaced these bearings apparently, the problems I have with the new ones are appreciably worse than with the originals despite their worn and neglected condition.
I don't know what bearings to use, but I would recommend going to these guys: Bearings & Lubrication or Athan rather than wasting money on unsatisfactory replacement bearings.
A big part of the problem seems to be bearing frictional losses and lubrication viscosity.
Just curious---how did you deal with the OPA1642s max supply voltage of +/- 18 volts? (I thought you had 20 volt supplies?)
Pretty recently I considered purchasing Otari. I do not remember if it was mkII or mkIII. But then on second thoughts I decided to check first availability of heads, bearings, motors and their prices as being studio decks these did not sit there idle. Having done all that checking I gave up that idea of buying Otari. Electronics can be not only fixed but substantially upgraded but if there are no replacement heads and mechanical parts then it can be a dead end path.
It does not mean that I'm all logic. I like r2r decks, have four and recently bought akai gx-636. That was not very rational but I explained my folly to myself that akai gx-635 to gx-747 decks were built on the sound principle: direct drive, induction motors and hard heads. And the gx-635 and 636 were most solidly built of that series. The rest is luck. I'll see how much of that I have when it arrives and is fully tested.
Good luck with Otari. I vaguely remember seeing new heads for Otari made somewhere. There are also some used on Australian EBay and from Lithuania for Technics rs-1500. Apparently these are exchangeable.
cheers,
It does not mean that I'm all logic. I like r2r decks, have four and recently bought akai gx-636. That was not very rational but I explained my folly to myself that akai gx-635 to gx-747 decks were built on the sound principle: direct drive, induction motors and hard heads. And the gx-635 and 636 were most solidly built of that series. The rest is luck. I'll see how much of that I have when it arrives and is fully tested.
Good luck with Otari. I vaguely remember seeing new heads for Otari made somewhere. There are also some used on Australian EBay and from Lithuania for Technics rs-1500. Apparently these are exchangeable.
cheers,
Don't forget that Akai has ferrite heads. Pretty much garbage and most manufacturers returned to mu-metal heads. A Sendust head would have been really interesting!
I'd say that the Studer / Revox, Otari and Tascam machines were the best of the ones I have come across. Teac machines were good for consumer - as was Revox. Technics was too complicated with that loop tape path. Fostex machines are a disaster. Then you get to Sony and Akai consumer machines. Too many idlers and clutches on these, like scaled up cassette machines. The older machines like Roberts were minimalist type designs. They would go, but not well. The Revox G-36 is a nightmare (the transport switches are a weak point). Tandberg were also pretty simple machines. Not a fan. Now there are a lot of those iffy machines coming out of the woodwork again. They all need work.
-Chris
I'd say that the Studer / Revox, Otari and Tascam machines were the best of the ones I have come across. Teac machines were good for consumer - as was Revox. Technics was too complicated with that loop tape path. Fostex machines are a disaster. Then you get to Sony and Akai consumer machines. Too many idlers and clutches on these, like scaled up cassette machines. The older machines like Roberts were minimalist type designs. They would go, but not well. The Revox G-36 is a nightmare (the transport switches are a weak point). Tandberg were also pretty simple machines. Not a fan. Now there are a lot of those iffy machines coming out of the woodwork again. They all need work.
-Chris
Now don't forget the KING----AMPEX!! Actually, the last and best of their machines---the ATR-100---used ferrite heads, although they too had some issues. But an ATR-100, when was introduced in 1976, was ~$7500 for a two-track. About half my annual salary for working on them in the factory!
Hi dotneck335,
I didn't see any Ampex machines to work on, which is why I didn't list them. I even saw Scully machines, but they were so old that you couldn't really use them in production. They would be something to restore and collect. Mostly people using them at home I would think.
-Chris
I didn't see any Ampex machines to work on, which is why I didn't list them. I even saw Scully machines, but they were so old that you couldn't really use them in production. They would be something to restore and collect. Mostly people using them at home I would think.
-Chris
I was told that the ATR series Ampex were actually made by Teac but were designed by Ampex. (Dot can you confirm?) They're excellent machines, one of my friends owns a 100 series machine.
Two of the 4 Otari machines I own are unlikely to ever need spare parts, the other two have required a lot of intervention, due mostly to neglect and abuse - neither had significant mechanical issues due to wear. Parts for the MX-5050BII/BIII and MKIII are extremely plentiful and at reasonable prices on eBay and a number of online sellers.
New heads for most Otari decks are still available if expensive, relapping is a good option in a lot of cases.
The Panasonic heads used on RS series decks and a few others are identical to the Panasonic heads on Otari decks according to someone who should know.
The MX-50 is a viable alternative to some much more expensive machines, and sounds great, the brakes though leave a lot to be desired particularly on RWD onto the take up reel.
Two of the 4 Otari machines I own are unlikely to ever need spare parts, the other two have required a lot of intervention, due mostly to neglect and abuse - neither had significant mechanical issues due to wear. Parts for the MX-5050BII/BIII and MKIII are extremely plentiful and at reasonable prices on eBay and a number of online sellers.
New heads for most Otari decks are still available if expensive, relapping is a good option in a lot of cases.
The Panasonic heads used on RS series decks and a few others are identical to the Panasonic heads on Otari decks according to someone who should know.
The MX-50 is a viable alternative to some much more expensive machines, and sounds great, the brakes though leave a lot to be desired particularly on RWD onto the take up reel.
