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Adding a volume pot to a PS-LX49 turntable

jrubins_03

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I just got my first older record player, and I'm looking to modify it. I'd like to add a volume knob.

To be clear, this is not a question about preamps, only about what type of potentiometer I need to get (I know the volume knob will not make the phono output louder). I have worked with electronics pretty extensively, but I'm no expert, and the math is mostly new to me. I can solder and drill and all that.

I'm not sure where to find what resistance range of potentiometer I need. I have heard that logarithmic scale is better for audio, and since this is a stereo system, I need a 2 gang potentiometer.

I'm attaching the user manual for this model, in case that is at all helpful.

In case anyone is wondering why I would need to do such a thing: I want to save a few bucks, and I live in an apartment where space is hard to come by. I have found small phono preamps online, but many lack a volume knob, and as I plan to listen mostly with headphones, this will probably get old pretty quickly.

This is my first post on the forum, so go easy on me. Any help is appreciated, and I'm willing to accept this isn't the best way to do what I want to do. I am mostly looking for a fun DIY project, and maybe some education on potentiometers.
 

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antcollinet

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Hi

Where are you hoping to put the volume knob? You can't put it directly on the output of the deck since that is a very low level signal that needs pre-amplification. (You need a phono preamp, or an integrated amplifier with a phono input)

You could put a volume control on the output of the preamp if you want to. However it might just be easier to buy one ready made such as the Behringer monitor 1

However, you can't drive the headphones directly from line level so will also need a headphone amp, or a speaker amp with headphone output - which will have it's own volume control.
 

BDWoody

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I have found small phono preamps online, but many lack a volume knob, and as I plan to listen mostly with headphones, this will probably get old pretty quickly.

A phono preamp does a couple of important things. In addition to boosting the very small cartridge voltage, it equalizes the recorded signal based on the RIAA equalization curve.


You may want to look at a basic phono preamp, then a separate headphone amplifier with volume control.

Cheaper yet might be an older A/V receiver with phono inputs and a headphone out jack while you sort out exactly what you might want to spend on.
 
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jrubins_03

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Hello!

I was thinking of getting this preamp, and possibly fitting it into the body of the turntable (without the outer case). Is it possible to get a pot sensitive enough to go straight on the phono lines? Otherwise, I could get a pot on the output of the preamp, if I'm able to integrate it into the turntable.

An old A/V receiver is not an option, as I have very little space in my small apartment.
 

antcollinet

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BDWoody

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Hello!

I was thinking of getting this preamp, and possibly fitting it into the body of the turntable (without the outer case). Is it possible to get a pot sensitive enough to go straight on the phono lines? Otherwise, I could get a pot on the output of the preamp, if I'm able to integrate it into the turntable.

An old A/V receiver is not an option, as I have very little space in my small apartment.

This one includes a headphone amp.

https://www.amazon.com/dp/B07JHBFGYS/ref=cm_sw_r_apan_glt_i_3VAB9WFTCPTRZX97JA10?psc=1
 

antcollinet

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Hello!

I was thinking of getting this preamp, and possibly fitting it into the body of the turntable (without the outer case). Is it possible to get a pot sensitive enough to go straight on the phono lines? Otherwise, I could get a pot on the output of the preamp, if I'm able to integrate it into the turntable.

An old A/V receiver is not an option, as I have very little space in my small apartment.
No you cannot put a pot on the phono lines from the deck. As I stated above, there is no point putting it on on the line level, since you cannot drive your headphones directly from line level. You need further amplification to drive the headphones.
 
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jrubins_03

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No you cannot put a pot on the phono lines from the deck. As I stated above, there is no point putting it on on the line level, since you cannot drive your headphones directly from line level. You need further amplification to drive the headphones.
Will the amplified signal not be decreased proportional to input signal?

Also, for context, I'm planning on mostly listening with 80 ohm BeyerDynamic DT990s.
 
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jrubins_03

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This is my (testing, clearly) setup, which gives me decent volume, but obviously awful audio quality, even for digital audio. I'm essentially thinking of adding some sort of control in the red and white wires, and replacing the computer with a preamp.
PXL_20220317_230416640.MP.jpg
PXL_20220317_230257191.MP.jpg
PXL_20220317_230307021.MP.jpg
PXL_20220317_230319150.MP.jpg
PXL_20220317_230349115.MP.jpg
 

antcollinet

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Will the amplified signal not be decreased proportional to input signal?

Also, for context, I'm planning on mostly listening with 80 ohm BeyerDynamic DT990s.
The signal on the phono line is so weak that any pot you connect to it will destroy the signal. It is directly from the cartridge and the signal is generated only by the stylus cantilever waving a tiny magnet a tiny distance next to some tiny coils. Forget trying to connect anything to it except a properly designed preamp.
 
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jrubins_03

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The signal on the phono line is so weak that any pot you connect to it will destroy the signal. It is directly from the cartridge and the signal is generated only by the stylus cantilever waving a tiny magnet a tiny distance next to some tiny coils. Forget trying to connect anything to it except a properly designed preamp.
Alright then, what about a pot for the preamp output?
 

restorer-john

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What you are doing isn't totally wrong. You can use the microphone input of the sound card for a MM cartridge and pull the levels down with the level sliders to prevent overloads. Also, turn off an auto level (mic) setttings. The main issue of course is you need to apply an RIAA EQ curve or the resulting sound will be absolutely rotten.

The sensible way is a cheap outboard RIAA phono stage with line level outputs and maybe a headphone stage.
 

DVDdoug

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You can use this at the preamp output (in-between the preamp & power amp or between the preamp & headphone amp).
 

antcollinet

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What you are doing isn't totally wrong. You can use the microphone input of the sound card for a MM cartridge and pull the levels down with the level sliders to prevent overloads. Also, turn off an auto level (mic) setttings. The main issue of course is you need to apply an RIAA EQ curve or the resulting sound will be absolutely rotten.

The sensible way is a cheap outboard RIAA phono stage with line level outputs and maybe a headphone stage.
AIUI the OP is not intending to use the PC in the finished setup. So needs alternative amplification for the headphones. A couple of examples of combined RIAA phono stage with HPA have been linked above.
 
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jrubins_03

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What you are doing isn't totally wrong. You can use the microphone input of the sound card for a MM cartridge and pull the levels down with the level sliders to prevent overloads. Also, turn off an auto level (mic) setttings. The main issue of course is you need to apply an RIAA EQ curve or the resulting sound will be absolutely rotten.

The sensible way is a cheap outboard RIAA phono stage with line level outputs and maybe a headphone stage.
I was able to fiddle with the mic settings a bit and got it working a bit better (recording attached). Would this work on something like a raspberry pi? Or is a dedicated sound card necessary?
 

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antcollinet

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headphones? Would I require a headphone amp for 80 ohm headphones?
Well, probably. Because your line output from the preamp will have an impedance possibly up to a few hundred ohms. So if your pot will need to have a high resistance so as not to reduce the voltage. But then it will have a much higher resitance then than the impedance of the headphone. So for example if you have a 10K pot, the line voltage will be reduced by aprox 80/10,000 - so from about 1V to <1mV - not enough to drive your headphones. So reduce the pot say to 1K. Now if the preamp output is 200ohm, you'll get about .8V drop between the ouput impedance and pot, and then another 80/1000 due to the headphone loading. So now only around 0.06V (it's actually more complex becaue it depends on the pot setting, and also the headphone frequncy/impdedance curve - but the result is a non linear behaviour due to the interactions of the ouput impedance, pot and headphone impedance.)

Basically most line levels are not powerful enough (too high output impedance) to drive headphones - and this is made worse by adding a pot.
 
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jrubins_03

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Well, probably. Because your line output from the preamp will have an impedance possibly up to a few hundred ohms. So if your pot will need to have a high resistance so as not to reduce the voltage. But then it will have a much higher resitance then than the impedance of the headphone. So for example if you have a 10K pot, the line voltage will be reduced by aprox 80/10,000 - so from about 1V to <1mV - not enough to drive your headphones. So reduce the pot say to 1K. Now if the preamp output is 200ohm, you'll get about .8V drop between the ouput impedance and pot, and then another 80/1000 due to the headphone loading. So now only around 0.06V (it's actually more complex becaue it depends on the pot setting, and also the headphone frequncy/impdedance curve - but the result is a non linear behaviour due to the interactions of the ouput impedance, pot and headphone impedance.)

Basically most line levels are not powerful enough (too high output impedance) to drive headphones - and this is made worse by adding a pot.
Would I not have this issue with this preamp?
 
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