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  #26  
Old 01-27-2008, 06:12 PM
Fred Bissnette Fred Bissnette is offline
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cool man ty very much !!!
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  #27  
Old 01-27-2008, 11:52 PM
Fred Bissnette Fred Bissnette is offline
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cutting or bending that pin on the track will work to disable the central bypass circuit but the quartz lock feedback is still on even when the bypass circuit is disabled thats why the 1200 is the king of decks because its the only deck locked from 8 to 8

peas
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  #28  
Old 01-28-2008, 06:32 AM
vinyl_junkie vinyl_junkie is offline
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Quote:
Originally Posted by Fred Bissnette
cutting or bending that pin on the track will work to disable the central bypass circuit but the quartz lock feedback is still on even when the bypass circuit is disabled thats why the 1200 is the king of decks because its the only deck locked from 8 to 8

peas

Yep and I do have to love it for that, I love mixing on them
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  #29  
Old 01-28-2008, 01:20 PM
Fred Bissnette Fred Bissnette is offline
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and you would be suprised at the number of ppl and djs i talk to that dont know that the 1200 is quartz speed motor controlled no matter where you put the pitch from 8 to 8 thats the only reason the 1200 is the most widely used deck well that and its build quality but even if it was made out of plastic and had a crappy arm if it still had the quartz motor control it would still out sell al other decks as it still does
the 1200 is the only deck that has this other decks have central bypass circuits and some have a zero lock quartz buttons that stay at 33.3 but no other deck has the feedback circuit with quartz contol

peas
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  #30  
Old 01-28-2008, 01:24 PM
Mistick Krewe Mistick Krewe is offline
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so, when someone cuts that resistor on an MKII and later technics, what controls the rotational speed then?

I know the original 1200 was servo-drive....

Is there a difference between a hacked MKII and an original 1200s 'feel'?
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  #31  
Old 01-28-2008, 01:28 PM
Fred Bissnette Fred Bissnette is offline
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well electricity like probablya voltage conrol of some kind like the size of the motor vs how much dc power it needs to spin at a low speed all other decks have low speed dc motoer like gemini and citronic etc vestax has a feedback conrol but its some other kind of control
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  #32  
Old 01-28-2008, 01:30 PM
Fred Bissnette Fred Bissnette is offline
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so no no difference in feel once hacked

peas
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  #33  
Old 01-28-2008, 02:27 PM
jnkarrik jnkarrik is offline
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There used to be a really good website that went into some of the details of the control circuit. It pointed out some things I had never really noticed. Like if you drag the platter a little bit then let go, it snaps back to not only the correct speed, but it actually speeds up a bit to catch back up to the position it should be in (i.e. the dots go back to where they would have been had you not touched the platter).

This made me wonder where the velocity and postion feedback come from? There is no encoder (that I can see), so is there a hall effect sensor under the platter? I originally thought that maybe the strobe was some kind of sensor, but putting your hand between it and the platter does nothing to the control circuit.
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  #34  
Old 01-28-2008, 04:06 PM
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mynameismatt mynameismatt is offline
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This one?

http://web.archive.org/web/200105220...s/mod1200.html
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  #35  
Old 01-28-2008, 04:15 PM
Mistick Krewe Mistick Krewe is offline
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Quote:
Originally Posted by mynameismatt


the "way back machine's" hit text for future reference...

Quote:
"Removing The Quartz" from the Technics SL-1200MKII
It should first be stated that although people often refer to this modification as "removing the quartz," that is not what is actually being done.

What is "Quartz" or "Quartz Lock?"
The Quartz Lock system is a very accurate method of controlling the rotational speed of the turntable's platter. It works by generating a reference frequency via the oscillation of a quartz crystal. As the platter rotates, it creates a frequency of its own via a frequency generation coil. The turntable's control system compares the reference frequency to the generated frequency and adjusts the speed of the platter to keep them matched. If you were to remove this system, the turntable would have no method of monitoring the platter's speed and would therefore rotate erratically, if at all.

What's to gain by modifying?
Put your unmodified turntable's pitch control in the center and start it rotating. Look at the big row of strobe dots in front of the red light emitted below the power switch and notice how they are standing still. Now touch your finger to the platter very gently to shift the position of the dots by no more than one dot's width. Remove your finger and notice how the dot slid back to its original position. If you are doing very accurate beat mixing, and touch your finger to the platter to slow down a record who's beat is slightly ahead of the other, you will correct it as long as your finger is on the platter, but as soon as you remove your finger, the song's beat will be ahead again when the turntable slides the dots ahead. The same thing applies inversely to pushing the record ahead. This is what many good DJs refer to as "The Quartz Fighting the Mix." Making the modification disables the turntable's abiltity to fight the mix.

Why does it "Fight The Mix?"
The turntable has a three-phase motor, similar in concept to the stepper motors used in intelligent lighting fixtures. The full 360 degree rotation is broken up into fractional degree increments refered to as steps. Let's say that the turntable's motor had 360 steps in one rotation, therefore it would have one degree per step. Actually, it seems that two of the large dots are about one step. As it spins, the motor is staying in the middle of a step. If you slow the platter down and fight its position within the width of half of one step, it will recenter in the step once you remove your finger. If you fight its position beyond one-half of a step, the motor will jump into the next step. This is a result of the turntable's phase detection system, which can be disabled.

WARNING!!
I am not condoning or recommending modifying your tables in any way! If you continue with this, it's solely at your own discretion. I am not to be held in any way responsible for any damage you may cause to your turntables in this process. If you don't feel completely competent to do this, take it to someone who is, or send it to me and I'll do it for a nominal fee. You WILL void your warranty by making these modifications. So it's said.

Remove Resistor Number R209

Remove the resistor R209 shown above or lift one leg by desoldering and pulling through the top of the board. This will prevent the phase detection circuit from feeding back into the speed control circuit. This is the extent of the modifications I've seen done on some turntables. There is more that needs to be done, as this will solve the fighting problem but will cause the turntable to rotate a bit too slow.

Add 1.6 MOhm Resistor

You will need to add 1.6 MOhm across pins 6 ang 19 of IC101 which is the AN6675. There is no 1.6 MOhm resistor made that I know of, so I use a 1.5MOhm in series with a 100KOhm. Solder them nicely on the bottom side of the board as shown. You can also use a 250KOhm pot in place of the 100KOhm resistor to make a fine trim adjustment, just use a bit of wire and glue the pot beside the board. However, you will need a frequency counter to make its adjustment. If you don't have one, just use the two fixed resistors and put your turntable back together, you're good to go.

Fine Adjustment with a Trim Pot
Connect a frequency counter to the points shown below by sticking two pieces of wire into the turntable through the hole in the plate next to where the AC cord comes in.

Connect the ground of the frequency counter to the test
point shown here with the G next to it on the board.


Connect the positive side of the frequency counter
to the left side of R205 as shown above.

Making the Adjustment
With the turntable spinning, set it to zero pitch, 33 RPM, and adjust for 50.55 Hz on the counter. You may want to let it spin a few minutes before making this adjustment. If your counter has a slow or averaging mode, use it.

I have other mods for the turntable including removing the pitch control center click and replacing it with seperate return to zero switch, a backwards rotation switch, chrome dipping the upper part of the table, and pitch bend buttons. These are too complicated to describe here. If you want them done, email me and I'll let you know how much and particulars involved.

Happy spinning!!!, Dave Rosenbloom
"Before you can stand up and walk, first you have to learn to mix."

(the pics referenced in the article were not in the wayback machine as far as i could tell)
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  #36  
Old 01-28-2008, 04:15 PM
jnkarrik jnkarrik is offline
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Yep, that s the one!

I was looking for that page because I remember that guy saying you needed to add another resistor but I couldn't remember where or why. After rereading it though, it doesn't sound that important because it just fine tunes the platter speed a bit.

<edit> And there's the answer to my question too - a frequency generation coil (whatever that is).

Last edited by jnkarrik : 01-28-2008 at 04:18 PM.
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  #37  
Old 01-28-2008, 04:56 PM
vinyl_junkie vinyl_junkie is offline
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Or you could just adapt on how to mix on a 1210, if you spend enough time with it there are certain techniques with touching the platter to get round this "torque fight" trust me I have spend nights on end trying to learn how to mix on these babys lol
Saying that I would have it a guess even armed with that technique mixing oldies (disco and such like) would still be better with the mod.
Thing is in a club the deck would be standard unless you like to take your wire cutters and soldering iron with you lol
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  #38  
Old 01-28-2008, 10:39 PM
Digitalis Digitalis is offline
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The "frequency generation coil" is an hall effect incremental encoder of sorts. The black inner ring on the platter is the encoder wheel. The small tape head looking things inside the motor assembly are the sensors. See attached images from webland:





Since the direct drive motor is in essence a "brushless motor" the sensors should also provide timing for the individual motor windings. Speed control is one aspect of motor timing but direction, and smooth movement are others. I am fairly certain the turntable will be inoperable or permanently damaged if you try to turn it on without the encoder working properly.

Depending on how the motor control is implemented, advancing the platter one or more full encoder pulse positions should be required to prevent it from returning it's original place. With a little more speculation 8 encoder positions x 3 sensor positions = 24 pulses per rotation.. or you need to push the record 1/24th of a rotation for it to stick.... This correlates with the 12 motor coils but the 1/24 number is a bit more speculation than I care for. It could be 1/12, 1/8, 1/4, or 1/3 for example. I will play with it when I get home.
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Last edited by Digitalis : 01-28-2008 at 10:59 PM.
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  #39  
Old 01-29-2008, 04:07 AM
Digitalis Digitalis is offline
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OK... so I played with my decks a bit. It is a little hard to tell but they do seem to respond in 1/24 rotation increments. Watching the "dots," with the zero pitch lock on, if you push the platter you can see it "cogging" and snapping into place every 4 dots or so (give or take a couple dots, measurement by eye, caveat emptor and all that....). That is, if you push or drag the platter less than 2 dots or so, it will return to the original location when you release the record. If you push or drag the platter more than 2 dots or so, it will snap ahead to the next position.

I like taking things apart too much... at least I could get this back together.
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  #40  
Old 02-02-2008, 11:00 PM
Fred Bissnette Fred Bissnette is offline
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my apologies in that deep attitude article it is the same resistor (tp17 is r209)lol i need to pay closer attention

the mod i have done to my deck involved snipping the resistor and desoldering the yellow and orange wires on the pitch board and removing the ball in the pitch slider. so now my deck has no zero point(well its super close at the middle point) i calibrated the pitch pot to 2.7kohm exactly as per factory recommendations and then adjusted the pitch pot on the motor board so when the fader knob is where zero is the dots don't move

the result is very smooth grooveriding due to no click and no dead zone and the platter is more responsive but still maintains good control it still holds the platter in tight rotational control even tho the quartz is no feeding back. when i pull on the platter it does not over compensate but it still snaps back to its place so its still very good for mixing and really i cant notice any difference in the abillity to hold pitch when mixing house records and it does seem to be able to play live drummer tracks a bit better when thummbing the deck platter

peas

ps this was a mod done to an sl 1200 mk2
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  #41  
Old 02-04-2008, 11:45 AM
garydeepblue garydeepblue is offline
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sorry guys but the description of what happens to the dots whenyou look at the strobe and put your finger on the platter to slow it down....that doesnt make sense to me.
when your at pitch zero, the dots LOOK stationary, you put your finger on to slow it down your changing the frequencies the dots go past the strobe so yeah they seem to move. you take your finger off and of course they are going to look like they are "snapping back"...but only due to the dots and the strobe sincronising again....what this sounds like is if i slow down a record and then take my finger off the deck will then play 'catch up' to where it was....this isnt the case...
the quartz is only functioning when being allowed to spin under the motors power....
im not trying to be predantic here im just trying to see the reasoning in this modification....i dorp disco sets myself and i can be a bastard to gete the changes right...gary
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  #42  
Old 02-04-2008, 01:15 PM
Fred Bissnette Fred Bissnette is offline
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yeah i understand what your saying with the motor only being under control when its on its own and not interrupted by cuing or fingers from pitch corrections but what im saying is with this resistor cut the normal over compensation the motor was doing is now 90% less so now when you let go it just goes back to where it was and not past it either way thats all

the reasoning behind this is to make the changes sound smoother is all so you dont get as much of a wah wah effect when mixing live drummer tracks and yes it can be done on an un modded deck i know many that know exactly where to tap the record to get it back its just a matter of preference is all

peas
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  #43  
Old 02-05-2008, 08:11 AM
jnkarrik jnkarrik is offline
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Quote:
Originally Posted by garydeepblue
sorry guys but the description of ....what this sounds like is if i slow down a record and then take my finger off the deck will then play 'catch up' to where it was....this isnt the case...

Actually it is the case. You can both see it and hear it. But it only does it if you make small disturbances to the platter. Once you slow it beyond a certain point, it stays at the new position. (The speed of course goes back to normal).

All cutting the resistor does is change the response of the control loop. If you know anything about controls, you are basically changing it from a critically damped response to an underdamped response. I.E. it will still "fight" to maintain the correct speed/position, but not as hard. As a result you can get away with thumbing the platter much gentler which is not as audible.
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  #44  
Old 02-05-2008, 02:25 PM
Fred Bissnette Fred Bissnette is offline
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that is exactly what is happening and exactly what my turntable does now that i cut that resistor in all reality im willing to bet my dozen biscuits that the motor is still using quartz to control itself albeit like you said less control

this thread is verty interesting and i like that

peas

so what would happen if i cut the rest of the resistors in that loop?
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  #45  
Old 02-05-2008, 02:27 PM
Fred Bissnette Fred Bissnette is offline
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so really theres no way to disable the quartz just make it less responsive to manual change
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  #46  
Old 02-05-2008, 02:56 PM
Fred Bissnette Fred Bissnette is offline
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so i did a little experiment just now i popped open the platter cover and snipped r 210 and lo and behold the deck turns on but when i hit the start button the plater jerked forward about 1 cm and then stopped so that resistor controls the actual turning of the platter and snipping it makes the platter not spin at all, so i resoldered that resistor and then moved on to the r 208 resistor and when i snipped it the platter does turn but jerks foreward and backward while spinning foreward(the dots jerk back and forth causing total unstable speed) so i resoldered it and left r 209 snipped as before so i guess disabling the r 209 is as far as we all will get to the type of control an original 1200 had (pre mk2) or the thorens

peas and thanks for all the good info
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  #47  
Old 02-05-2008, 03:02 PM
Mistick Krewe Mistick Krewe is offline
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LoL


at least we're not afraid of hacking up electronics around here
in the name of science....


:lmao:
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  #48  
Old 02-05-2008, 03:10 PM
jnkarrik jnkarrik is offline
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This is TOTAL speculation here, but it could be that the three resistors effect the gains on the proportional, derivative and integral elements of a classic PID loop.

And if I had to further speculate, I would guess that 209 effects the integral part (which is what is usually responsible for overshoot in a PID system.)

Wikipedia has a decent write up on PID controls if anyone is interested.
http://en.wikipedia.org/wiki/PID_controller

To summarize, the proportional aspect increases output in proportion to the error. The integral portion sums the error over time and adds that to the output. The derivative action is proportional to the rate of change in the error.

God this brings back horrible memories of engineering classes.....
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  #49  
Old 02-05-2008, 03:11 PM
jnkarrik jnkarrik is offline
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Quote:
Originally Posted by Mistick Krewe
LoL


at least we're not afraid of hacking up electronics around here
in the name of science....


:lmao:

or washing them in the sink!
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  #50  
Old 02-05-2008, 03:54 PM
Fred Bissnette Fred Bissnette is offline
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yeah im def not affraid to noodle plus i keep a few motor boards in stock so if i mess up one i have one to replace it

peas
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