AUDIOLOGIC AKA YORK boombox - Adjusting bottom deck speed problem

Cpl-Chronic

Cpl-Chronic

Member (SA)
I have the YORX AKA of the famous audiologic double cassette boombox as seen in this video:


The problem is after getting a 3000Hz tone test tape, the decks were running at about 3035-40Hz instead of reference 3000Hz. The top deck is now dialed in correctly & runs between 2997-3001Hz & sounds quite good but I cannot find any adjuster on the motor for the bottom deck. I was considering changing out the motor for a 12v that can be dialed in but the supply voltage to the motor reads 15v with a digital meter.

My questions are as follows:

1. Is there a separate adjuster somewhere on the main circuit board for the bottom deck?
or
2. Can I use a 12v motor on this circuit assuming of course the Vdroop under load would be close to the proper 12v DC?
or
3. Is there a way I can use a resistor in line with the motor to drop the voltage to 12v under a load so I can use another motor?

Any suggestions would be greatly appreciated.
 
Superduper

Superduper

Moderator
Staff member
I doubt that a service manual exists for that model, or for the aka. Accordingly, it’s gonna be hard for anyone to answer #1. I suspect that #2 may work, but the motor is likely to not last as long. A better solution is to add voltage regulation circuitry to that supply line to accommodate your new motor. This can be as simple as a few resistors, a zener diode and a power transistor, or an LM7812 IC with a few additional components. #3, resistors drop current, not voltage.
 
Cpl-Chronic

Cpl-Chronic

Member (SA)
Superduper said:
I doubt that a service manual exists for that model, or for the aka. Accordingly, it’s gonna be hard for anyone to answer #1. I suspect that #2 may work, but the motor is likely to not last as long. A better solution is to add voltage regulation circuitry to that supply line to accommodate your new motor. This can be as simple as a few resistors, a zener diode and a power transistor, or an LM7812 IC with a few additional components. #3, resistors drop current, not voltage.
Click to expand...
Uh, you're partly right about resistors. If you put a resistor in series with the load, you do get a voltage drop to the motor, as well as current. I'm surprised at your statement & maybe I don't fully understand the meaning of your answer. A reduction in current to the load is a reduction in voltage too. I remember Ohm's law & how voltage is a product of current times resistance/inductance. So, yes, reducing voltage to the motor by using a resistor in series would work, especially for a simple motor supply circuit. I'm just wondering how to calculate the right resistance & wattage to use for the resistor, if that's the route I have to take. Of, course it is dependant on the current draw of the motor itself, under load.
 
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Superduper

Superduper

Moderator
Staff member
A resistors primary function is to resist the flow of current, so it therefore is a current limiting device. Can it affect voltage? Yes, but indirectly since as you alluded, resistance is a factor in ohms law. However a motor doesn’t always consume the same current during use and its current consumption depends on its rpm and load. During spool up, it will consume more current and as rpm increases, current consumption will fall. You may notice that power at the tape changes depending on whether a tape is at the beginning or end of the tape spool, especially on very long tapes. Because a series resistor will create a voltage divider circuit with the load, therefore the varying current consumption by extension also means that the voltage will be fluctuating too. If it were so simple to just toss a resistor in series with everything to control voltage, there would never be a need for voltage regulation circuitry of which there will be many in a boombox. In fact, if you do the circuit up like you are proposing and measure both sides of the resistor with the motor not running, both sides of that resistor will measure 15V with motor off. Only when the motor begins to consume current will voltage drop at the junction between resistor and motor and it will vary with current consumption depending again on whether motor is spooling up or under load etc. You asked about reducing voltage from 15V to 12V. I’ve already given you examples on how to accomplish that. Both examples will provide a steady 12V to the motor if designed properly. So you can do with the advice what you will. If you want a stable 12v supply to the motor, employ a voltage regulator. If you just want to reduce chances of blowing the motor and don’t care if the voltage varies with load, you can experiment with your resistor choice.
 
caution

caution

Member (SA)
My vote is for a 7812. It does need a minimum input of 14.5V, which will be fine if ran on external power, but on batteries it might be borderline after they start to lose charge. All you need is a cap on the input and output pins (and a diode across them if you want to prevent reverse bias). A small heatsink might also be wise if it the tab feels hot to the touch during playback
 
Cpl-Chronic

Cpl-Chronic

Member (SA)
Ok. Now I understand better what you are saying Norm & thank you for your thoughtful explanation & the time you took to help me understand this more thoroughly. It's just so strange that the motor has no speed adjuster & the voltage supplied is 15v instead of the standard 12, 9 or 6v you see in other tape decks, whether portable or discreet home audio decks. I'm going to try to sort it out a bit further before I try to replace the motor since I can't find any adjustable replacements at 15v.

The YORX in question is absolutely pristine & it's a bit OCD to care about the bottom deck being spot on as far as speed. It still sounds great but just a hair faster when compared to the top deck. You can barely hear any difference in speed by ear, when comparing the 2 directly. I just would like to have it dead on if possible.
 
Cpl-Chronic

Cpl-Chronic

Member (SA)
Well, I decided to not mess with a good thing & let the 0.1% speed discrepancy go since it really doesn't affect my ability to enjoy the music. I know there are some 15v motors out there but rare so I'll just keep my eye out for one. If anyone has a spare 15v CCW capstan motor they would like to sell for a few bucks, DM me. I can pay with PayPal. Brand new scammer members don't bother. I won't deal with anyone who isn't an established member with a good reputation.
 
S

sp1068

New Member
Cpl-Chronic said:
Ok. Now I understand better what you are saying Norm & thank you for your thoughtful explanation & the time you took to help me understand this more thoroughly. It's just so strange that the motor has no speed adjuster & the voltage supplied is 15v instead of the standard 12, 9 or 6v you see in other tape decks, whether portable or discreet home audio decks. I'm going to try to sort it out a bit further before I try to replace the motor since I can't find any adjustable replacements at 15v.

The YORX in question is absolutely pristine & it's a bit OCD to care about the bottom deck being spot on as far as speed. It still sounds great but just a hair faster when compared to the top deck. You can barely hear any difference in speed by ear, when comparing the 2 directly. I just would like to have it dead on if possible.
Click to expand...
Another thing you could do is just install a series of diodes in line to the motor to drop the voltage. I'd just do 4. 1n5400 diodes are plenty strong. Could probably get away with regular old 1n4001 diodes. I'm not sure how much current cassette motors draw, but it seems like it would be less than one amp. The problem with the four wire dubbing motors is getting the rpms right, and making sure the A and B circuits are compatible.
 
S

sp1068

New Member
Cpl-Chronic said:
Well, I decided to not mess with a good thing & let the 0.1% speed discrepancy go since it really doesn't affect my ability to enjoy the music. I know there are some 15v motors out there but rare so I'll just keep my eye out for one. If anyone has a spare 15v CCW capstan motor they would like to sell for a few bucks, DM me. I can pay with PayPal. Brand new scammer members don't bother. I won't deal with anyone who isn't an established member with a good reputation.
Click to expand...
Could always take a folded piece of 220 grit sandpaper and take the OD of your motor pulley down a tiny bit, then recheck your speed.
 
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