The Sony WM-D6C and Dolby NR

[Furunzl]

Hi everyone!

I am lucky to own two WM-D6C machines, and I recently got both working fine again by cleaning, replacing the belts, etc. By the way, strange fact: both are Revision 2, judging by the head type (35711) and orange pcb without the smt components. However, one of them has serial number 652***! How is that possible? I thought, Rev 2 ends at s/n 260000??

Anyway, now that both machines are working, I wanted to compare record quality between the two, play around a little etc. And here is my problem: If I record on machine A using Dolby C NR, it plays back fine on the same machine, but as soon as I try to play it in machine B, the sound is very muffled and distorted, completely off. The levels are also different.

Vice versa, when I attempt to record on machine B and play it on machine A, I have exactly the same problem! This only occurs when using Dolby NR. With Dolby B, it is noticeable, but with dolby C, catastrophic. Does anyone have an idea, why this could be the case?

I also attached some spectrum analyzer screen shots without NR and then with Dolby C NR for both machines. I think, the spectra are very similar, can't explain, why they cannot play each other's tapes porperly.

I am a first-time poster and certainly not the most tape-litterate person in the world, but I would still very much appreciate some thoughts. Maybe the solution is obvious for a pro, if so, that would be great Thanks!

[TIMTAPE]

Dolby B and even more so C magnify misalignments between your two machines. It's referred to as Dolby mistracking. Without Dolby you may not notice the misalignments but they are there. In short, reliable fidelity on cassettes using Dolby was problematic. For Dolby to work well, pretty much everything had to be working
and aligned perfectly.

[TIMTAPE]

I should have added that Dolby also exaggerates record vs playback misalignments within the one machine.

[Mooly]

The only answer to this one is to align one machine 'correctly' and then set the second one up using the first machine as a reference.

Ideally you need proper reference tapes but without these this is what I would do... it will get both machines very close to one another.

1/ With Dolby B turned on play back a selection of pre recorded tapes and find one that that sounds 'good'. You must be prepared to to tweak the head azimuth to get the best possible HF response.

Listen with good headphones and alter the internal playback levels so that the audio sounds correct with no obvious mis tracking of the Dolby process. Be sure to get L/R balance correct i.e vocals centred correctly.

Re-test using different tapes and tweaking azimuth.

2/ Turn off Dolby and record and playback a 400Hz tone. Alter the preset record levels to get similar output levels on replay as compared to monitoring during record. You need a scope for this.

3/ Do a check of the bias adjustment comparing 400Hz and 10kHz levels on record and playback. Adjust as required and repeat step #2

4/ Now test with recording music. Results should be very close between play and record.

5/ Test again using Dolby C

Now set up your second machine in the same way.

6/ Having done that use the 10kHz recording from machine #1 to set the azimuth on machine #2

7/ Play back the Dolby C recording done on machine #1 and if necessary tweak the internal playback levels of machine #2 such that the results sound correct i.e. no obvious Dolby mis-tracking.

[TIMTAPE]

Mooly mentioned prerecorded tapes as a reference instead of a proper calibration tape. Many later such tapes from the big record labels carry at the start of side 1 and end of side 2 a complete set of alignment tones across the spectrum. They happen very quickly and need to be time stretched digitally to make sense of them but can be used to check playback frequency response. Once playback level and frequency response are known to be within tolerance, that can be used to adjust record parameters such as bias and level. But a Service manual gives more complete information. Of course it depends on how deeply you are wanting to go with it.

[Mooly]

Thanks TIM. It is many many years since I had any tape machines in use although I was a big fan of the format. Didn't have any pre recorded tapes though, certainly not later ones.

I do have though a pristine WM6DC that was a rebuilt write off. It was almost new when its owner connected it to a car lighter socket with reverse polarity. DC-DC convertor needed fixing, a bit of OC print and the reverse polarity protection diode as I recall. Other than that... perfick.

Edit... no, I remember, the servo chip for the motor was goosed as well.

[mitajohn]

In order to calibrate both machines for compatibility the recommended procedure by the SM in my opinion must be followed. Using prerecorded tapes will lead to misalignment. We all know the way prerecorded tapes are produced.

Sony test tapes or similar:
P-4-L300 Level tape 315 Hz. ( Dolby Level ),
WS-48B Flutter 3 kHZ. ( Speed Test ),
P-4-A100 Azimuth 10 KHZ. ( Head Alignment ) or
P-4-A063 Azimuth 6.3 KHZ. ( Head Alignment ).

[TIMTAPE]

Originally Posted by mitajohn

In order to calibrate both machines for compatibility the recommended procedure by the SM in my opinion must be followed. Using prerecorded tapes will lead to misalignment. We all know the way prerecorded tapes are produced.

Pre recorded tapes varied in quality from abysmal to excellent. The tape dubbing speed often had little to do with the final product quality.

Some of the best quality pre recorded dubs by the majors used digital masters and were duplicated at over 100 times normal cassette speed. I occasionally check good examples of these cassettes in a decent cassette player, properly aligned, such as a Tascam 122 MkIII. Azimuth is often very close to my calibration tapes, and even more impressive, Dolby B tracking can be pretty good. The recorded test tone set (from about 32 Hz to over 16 kHz, 1/3rd octave) allows even closer checking of the actual frequency response pre encoding. I wonder how many home users ever recorded a complete set of 1/3 octave lineup tones when making their own cassette recordings, and on all 4 tracks. These pre recordeds were often good Chrome formulation tape stock but EQed for Type I playback with Dolby B, meaning they were less liable to demagnetisation from playing in poorly maintained cassette decks). I maintained more modest pro duplicators for many years. Easy to beat budget commercial cassette releases but I could not match the majors, and they were dubbing at much faster tape speeds.

[murphyv310]

Hi.
Dont forget that alignment tapes are not supposed to be used over and over again. The procedure is also to replace the pinch roller check for capstan slack, clean the tape path and check torques firstly before head alignment.
Did many WM-D6 recorders in the 90s when I worked for Sony. Brilliant when right but awkward to work on.

[TIMTAPE]

Yes good alignment tapes are very precisely made and easy to damage. Not surprised you say the Sony was difficult to work on. Did it have user adjustable variable record biases for optimizing recordings on different tapes? Without it extremely difficult to make consistent fidelity recordings esp. using Dolby C. No surprise towards the end of cassette deck production
some manufacturers introduced auto calibration for the particular tape being recorded to.

[Furunzl]

Thanks for all your advice!

So I got myself an azimuth calibration tape from eBay (pretty expensive, supposedly manufactured using quality components and from a Sony master tape) and adjusted both machines to it at 10 KHz. I figured, even if it is not the quality, it claims, at least both machines will be calibrated to the same standard.

I did the best job, I could, to get both channels in phase (see attachments). Does this look acceptable??

This also coincided with the highest total output level from both channels combined, although the right channel is about 0.5-1 dB quieter for both machines (--> level issues with the recording? or could this be my machine bias? It's a pain to adjust these with the WM-D6C, since you need to solder some pads).

In general, one of the recorders was way off and the levels increased dramatically after azimuth adjustment. It also sounds a lot better now, so that is definitely a plus.

Unfortunately, the Dolby issues persist. Both Dolby B and C don't sound quite right when played on the respective other machine. However, I noticed that the playback is much more uniform now. Before, I had very muffled parts in quick succession with less muffled ones, now it is all still muffled, but all the way and less so... lol

Not the great success, I hoped for. I don't really know, how to improve it further. I am recording on Sony metal tape, so this should be perfect in theory... Anyway, if someone knows, how I can get a better result, that would be great.

[TIMTAPE]

I would try the easy (or easier) thing first:

Set up one machine to play back its own recordings with accuracy (fidelity).

1. easiest: no Dolby

2. harder: Dolby B

3. hardest Dolby C