1200 Without Quartz Lock Engaged

[WOStantonCS100]

Whilst recapping my 1500MK2, I've now put a 1200M3D in it's place. I re-calibrated the pitch slider so the middle position "quartz-out" speed matched the "quartz-lock" speed. At least, I couldn't really detect a difference on the strobe when eyeballing it with a guide. Then, I listened. Curious, why I've never thought to do this test before.

I re-checked the strobe 4 to 5 times during one side of Ahmad Jamal Happy Moods, each time for about 15 to 20 seconds. No difference, really. Is it just my imagination or is the non quartz locked performance of the 1200 just that good?

If the "harshness" of the 1200 is a byproduct of it's quartz lock, would that then go away without the quartz lock engaged. I can't answer that, personally, without a lot more critical listening. As of right now, all I can say is that a 1200, at least this one, in good nick, even without quartz lock, doesn't seem to have appreciable (annoying and/or noticeable) speed drift.

Anyway, just my thoughts and observations on this Saturday afternoon...

[thinker10]

You know that a lot of dj disconnect the quartz lock

They (dj) disconnect the quartz because it create two zero on the pitch fader

It is then just servo lock like older models (MK1)

Something for everyone to try ...

Remember that quartz only work at zero pitch

You might like the sound better

Thanks

[Marco]

Hi "thinker10",

Welcome to AoS. Interesting idea, and it deserves to be explored further :)

However, on your next visit, before you post any further on the main areas of the forum, please pop into the Welcome area and tell people your real first name and basic geographical location (the details of which should be added to your profile), what system you use and what music you like, as this procedure is now required of all members.

Cheers! :cool:

Marco.

[MartinT]

The pitch adjustment only changes the waveform frequency to the motor and the zero-set pot is to ensure that when the slider clicks into the centre detent, the variable waveform matches the 'lock' waveform. I can't see what advantage there would be from not using the lock position.

[Mike_New]

Actually if you look at the block diagram, there are two methods for disabling the pitch control. One seems to be valid for the MK5 & MK6
Which have a separate “reset’ switch
Whilst the earlier MK2 3 & 4, use a switch on the slider.

The “reset” switch actually blocks the input to a two-input quad NAND gate and gates just a divided down master clock frequency back to the Speed/Phase control chip. In the ‘off’ position the NAND gate input is high
(5V) and the combined output from the Pitch Control is fed to the control chip.

In the case of the slider switch, this switch appears to control the input of the master clock to the NAND gate.
The actual Pitch control chip does not seem to have any external input from the control logic other that the master clock divided by sixteen.

I believe that the logic diagram in it’s detail, is incorrect in this area as the defined “ON” position blocks any variable Pitch signal going to the Speed/Phase control. I think that perhaps it should be the other way around.
As the green LED is ‘ON” when the input NAND gate low (LED is at 0V) and the variable pitch control signal is blocked.

In other words, when the green led is “ON” this indicates that the variable pitch is disabled. Actually the manual confirms this.

However it does appear that with the reset button on the MK5 and MK6 the “ON” option causes the speed to be controlled by the crystal generated clock frequency.
On the MK2-MK4 the slider switch would appear to allow the fixed pitch to be adjusted by the pitch-control-pot VR301. independent of the crystal frequency, thus allowing a choice of fixed pitch.

[WOStantonCS100]

Hey Martin,

Bear with me, as I try to comprehend... :o

If the variable waveform isn't being compared to the "lock" waveform", wouldn't that mean that it is also not making "all those little speed corrections" that some complain makes the Techy sound harsh. Or, does it always, somehow, mathematically, compare the two? Am I just daft? Wouldn't a heavier platter (fly wheel effect) also contribute to lessening the number of corrections in "lock" mode?

I should drink more; less chance of me thinking about such things.

Mike,

I would comment; but, I haven't at all looked at the logic diagrams for the 1200. I'm going to have to re-read your post a time or two and then look at the diagrams. Right now, all I've got is, "...blink, blink... ...blink, blink...". :lol: Give me time. I'll catch up.

[MartinT]

If the variable waveform isn't being compared to the "lock" waveform", wouldn't that mean that it is also not making "all those little speed corrections" that some complain makes the Techy sound harsh.

No, looking at the diagram, as far as I can see a waveform is generated (whether the fixed 'locked' frequency or a variable waveform depending on the pitch slider position) and then used as a reference by the motor drive circuit to generate the drive phase waveforms. There is never any hunting as in previous generations of direct drive decks.

All this is pretty immaterial, though. Unless you're a DJ, why on earth would you worry about variable pitch?

[WOStantonCS100]

No, looking at the diagram, as far as I can see a waveform is generated (whether the fixed 'locked' frequency or a variable waveform depending on the pitch slider position) and then used as a reference by the motor drive circuit to generate the drive phase waveforms.

Okay, I think I'm catching on.


All this is pretty immaterial, though. Unless you're a DJ, why on earth would you worry about variable pitch?

The variable pitch is actually extremely useful if one intends to get a 78 rpm mod done (as there weren't any real speed "standards" agreed upon among record companies of the time). I do plan on having a 78 rpm mod done to at least one of my 1200's as I have inherited a few hundred of the old platters.

Come to think of it, I heard that James Brown's old record company (King?) used to routinely speed up or slow down his records (for whatever reason, I don't know, perhaps to fit a prescribed time limit?). That would certainly explain why his range seems all over the place on that early material. Likewise, now that I think of it, I wonder if I could actually play my original pressing of Miles Davis - Kind of Blue at the correct speed, instead of playing the reissue.

In everyday use, I never use the variable pitch. But, it would be fun for little projects like the aforementioned. That's really not why I was asking; just curious about the way things work.

[MartinT]

Ah, understood Biff.