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Problems adding 3.5mm jack to record turntable

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Turntable Dan

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Greetings!

My friend and I decided to add a 3.5mm headphone jack to his Crosley CR49 turntable. We went to Fry's and picked up the headphone jack, (3.5mm Phone Jack (No. 502J) by Philmore) and went to work cutting and soldering.

Our work resulted in a pretty clean project. The sound continued through the in-case speakers just fine.

The problem came when after inserting a 3.5mm cable into the newly-mounted jack, the sound coming out of the jack sounded bad. Instead of the clean sound coming from the onboard speakers, we heard very muted and distored vocals along with loud and precise keyboard sounds.

After reading another post on this site regarding turntable modification, I wonder if it is possible that there is too much power going through the headphone jack. If that is the case, is there something I could insert between the input and the jack to tone it down? Or, in your experience, is there another problem that I do not know how to address? Pictures are attached. Also, let me know if you need any further specs on the turntable or its speakers.

Thank you for your time!

Turntable Dan
 

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Let's see...enough power to run a pair of speakers and you want it in your headphones. Yes, that could be a "too much power" problem. Can you turn it down with the volume control? Did you wire it so the volume control works? The basic answer to "too much power" is to add resistance, which is what a volume control does.

Another answer could be that the headphones are very different from a speaker in the way they are built. This is where I get off the bus. I am not up to speed on modern earbuds, headphones, and such as that.
 
It's best to use a dedicated Headphone amplifier, but ersatz adding headphone jacks just added a resistor. Try between 100 and 470 ohms. The signal/noise will be lower.
 
a shielded cable won't hurt either!

Boncuk
 
At that point, it's relatively high level. The resistor will add audiable hiss because of the current noise which is exaborated by the resistor.
 
Sorry, Nigel it's not nonsese.

If you do I-V sweeps of a resistor with different sense resistors and voltage noise in the sweeping supply, noise appears on the resistor. The sense resistor has to be less than or equal to the DUT resistor for good s/n performace, With a damping factor of 100 the Z of the amplifier is really small, like 8/100 ohms or .08. 470/0.08 is in the wrong direction for good current noise performance. The sweep measurements were performed with a 12 bit sample/hold succive approximation A/D converter.

If you physically take a high quality audio amp (70 W/ch), Something that has < 5.0 mV offset and a DC to 0.8 Megahertz frequency response intentionally rolled off to 0.5 Hz to 40 Khz and add a headphone jack using the resistor approach hiss appears at the headphones.

The amp has power gain which is a combination of voltage and current, If both are not amplified accordingly, the current noise will be imposed on the resistor resulting in hiss.

I've been there. Done that.

I will also tell you that paper conducts electricity due to primarily because of water absorbtion. It will be in the pA range at 100 V, but it's still measureable. Washing a piece of glass with Acetone leaves a film that's measureable.

It got really annoying when a photolithography process used to create a 100 um gap in molyibdinum was conductive at the pA level at 100 V and was messing up ourmeasurements. Only Touluene would remove the contaminatiion. A triple rinse in, Acetone, trichlorofloroethane, and liquid Freon TF with a blow dry would remove the contamination.

I doubt you have seen a 1 Gig ohm, 10 G ohm or 100 G Ohm 1% resistor, have you,
Try a 1 MEG ohm 300 WATT wire wound resistor?

I have real life experiences to back this up.

Do you?
 
After examining it further, it seems to be a channel issue more than a power problem. It is as if only certain tracks (specific instruments or vocals) are playing while others are not. But it works fine when playing through the speakers that are built in to the unit. It is only when the headphones or external speakers are connected that certain channels are eliminated. Any ideas?
 
Sorry, Nigel it's not nonsese.

If you do I-V sweeps of a resistor with different sense resistors and voltage noise in the sweeping supply, noise appears on the resistor. The sense resistor has to be less than or equal to the DUT resistor for good s/n performace, With a damping factor of 100 the Z of the amplifier is really small, like 8/100 ohms or .08. 470/0.08 is in the wrong direction for good current noise performance. The sweep measurements were performed with a 12 bit sample/hold succive approximation A/D converter.

If you physically take a high quality audio amp (70 W/ch), Something that has < 5.0 mV offset and a DC to 0.8 Megahertz frequency response intentionally rolled off to 0.5 Hz to 40 Khz and add a headphone jack using the resistor approach hiss appears at the headphones.

The amp has power gain which is a combination of voltage and current, If both are not amplified accordingly, the current noise will be imposed on the resistor resulting in hiss.

Sorry, you're still talking nonsense - almost all high quality power amplifiers do exactly that for headphone outputs - and they don't hiss.

If you claim to have measured (or ever heard) hiss, then you're doing something wrong.
 
You know why? The freq response of the headphones are rolled off. The noise is slight, but it's there.

So you can't hear it? - no one except yourself has even suggested such a thing even exists.

I fail to see the supposed mechanism that 'causes' this claimed effect - you have a resistor connected to the output of the amplifier, it has an offset voltage in the low millivolts. The other end of the resistor will connect to the headphones, usually with a resistor in parallel (making a potential divider). Where does the noise come from?.
 
Sorry, Nigel it's not nonsese.

If you do I-V sweeps of a resistor with different sense resistors and voltage noise in the sweeping supply, noise appears on the resistor. The sense resistor has to be less than or equal to the DUT resistor for good s/n performace, With a damping factor of 100 the Z of the amplifier is really small, like 8/100 ohms or .08. 470/0.08 is in the wrong direction for good current noise performance. The sweep measurements were performed with a 12 bit sample/hold succive approximation A/D converter.

If you physically take a high quality audio amp (70 W/ch), Something that has < 5.0 mV offset and a DC to 0.8 Megahertz frequency response intentionally rolled off to 0.5 Hz to 40 Khz and add a headphone jack using the resistor approach hiss appears at the headphones.

The amp has power gain which is a combination of voltage and current, If both are not amplified accordingly, the current noise will be imposed on the resistor resulting in hiss.

I've been there. Done that.

I will also tell you that paper conducts electricity due to primarily because of water absorbtion. It will be in the pA range at 100 V, but it's still measureable. Washing a piece of glass with Acetone leaves a film that's measureable.

It got really annoying when a photolithography process used to create a 100 um gap in molyibdinum was conductive at the pA level at 100 V and was messing up ourmeasurements. Only Touluene would remove the contaminatiion. A triple rinse in, Acetone, trichlorofloroethane, and liquid Freon TF with a blow dry would remove the contamination.

I doubt you have seen a 1 Gig ohm, 10 G ohm or 100 G Ohm 1% resistor, have you,
Try a 1 MEG ohm 300 WATT wire wound resistor?

I have real life experiences to back this up.

Do you?
Sorry but how does any of that pertain to hooking headphones up to a low power, low audio quality turntable. Andy
 
I would suggest that pointing out that something is utterly incorrect is seriously useful!.

May be that's enough for you.

A suggestion for a better approach how to solve the problem would be utmost useful.

I just guess that we're here to help each other. Is that wrong?

Boncuk
 
I would still like to address this issue, but noise theory is not oneof my strengths. I do think that what I observed is related to noise analysis of OP Amps. See https://www.electro-tech-online.com/custompdfs/2010/12/sboa066a.pdf

The amp I built was essentially a big OP amp. It is a varient of this https://www.electro-tech-online.com/custompdfs/2010/12/ckt.pdf designbuiltin the early 80's. One of the noise notes that I came across says to reduce the overall noise of an OP amp, you need to reduce the feedback resistor. Reducing the voltage gain would have a profound effect when operating at low signal levels. As a tweak, this would be one improvement that I would add. The larger the resistor, the larger the contribution of current noise. I do belive, but cannot prove, that the AMP when operating into an 8 ohm load the voltage noiseis the dominant term. When the large resistor is added to the output, the current noise becomes the dominant term.

I did do some laboratory tests that measured currents using the voltage drop across various resistors using a sample/hold kind of A/D converter and saw the noise. I wish I had the plots. I-V converters do a much better job in reducing the noise. I designed a 4-terminal version of one of these.

Tp some what back up my experience. Back in the 70's my parents bought me an all in one kind of stereo system. It came with speakers, headphonesand a ceramic cartridge.

I won speakers and put them on the system which souded OK on the speakers it came with and the hiss drove me nuts. I built a small AMP with a switching power supply that ran off of 12 Volts and the sound was much better. I then abondoned the stereo all together and found a broken AMP at a white elefant table, so I used the pre-amp section of that. I bought a turntable and had to use an external pre-amp all because I had very little money.

The headphones were the same way. Higher quality headphones yielded hiss and actually made the sound worse and it used the series resistor thing for the headphones. The same thing happend in my car. The factory speakers sounded good, but I upgraded them to plate speakers, the hiss from the tuner was horrible.

The noise is real when you use a series resistor in a high quality amp with a freq respose of 0.5 Hz to 40 Khz. If you can hear it depends onthe quality of the output device(headphones).

There is a MAJOR difference between Koss Porta Pros and a Bose Quiet Comfort II. There's a big difference betwen the II's and the QC III's. The Koss Porta Pros sound the best. Probably the best headphones I had the opportunity to listen too was a set of Electrostatic headphones by Stax such as these: https://www.electro-tech-online.com/custompdfs/2010/12/4070-bro.pdf They will set you back about $3,000 USD.

My friend and I did a side by side comparison of my amp and a McIntosh Tube amp diving Klipsh horns and we both agreed that mine had much better bass than the tube amp. The tube amp was louder driving the horns. The quality of the sound was about the same. We also discovered that I like folk music and it sounds better with a dome tweeter whereas, my friend likes classical music. My friend built a few tube amps.

My preamp has a -3db point at 100 kHz. M y eqipment is not typical audio. It's high end. The preamp actually has 3 voltage gain stages and each stage gets a volume control. That's not typical either.
 
Last edited:
I would still like to address this issue, but noise theory is not oneof my strengths. I do think that what I observed is related to noise analysis of OP Amps. See https://www.electro-tech-online.com/custompdfs/2010/12/sboa066a-1.pdf

The amp I built was essentially a big OP amp. It is a varient of this **broken link removed** designbuiltin the early 80's. One of the noise notes that I came across says to reduce the overall noise of an OP amp, you need to reduce the feedback resistor. Reducing the voltage gain would have a profound effect when operating at low signal levels. As a tweak, this would be one improvement that I would add. The larger the resistor, the larger the contribution of current noise. I do belive, but cannot prove, that the AMP when operating into an 8 ohm load the voltage noiseis the dominant term. When the large resistor is added to the output, the current noise becomes the dominant term.

I did do some laboratory tests that measured currents using the voltage drop across various resistors using a sample/hold kind of A/D converter and saw the noise. I wish I had the plots. I-V converters do a much better job in reducing the noise. I designed a 4-terminal version of one of these.

Tp some what back up my experience. Back in the 70's my parents bought me an all in one kind of stereo system. It came with speakers, headphonesand a ceramic cartridge.

I won speakers and put them on the system which souded OK on the speakers it came with and the hiss drove me nuts. I built a small AMP with a switching power supply that ran off of 12 Volts and the sound was much better. I then abondoned the stereo all together and found a broken AMP at a white elefant table, so I used the pre-amp section of that. I bought a turntable and had to use an external pre-amp all because I had very little money.

The headphones were the same way. Higher quality headphones yielded hiss and actually made the sound worse and it used the series resistor thing for the headphones. The same thing happend in my car. The factory speakers sounded good, but I upgraded them to plate speakers, the hiss from the tuner was horrible.

The noise is real when you use a series resistor in a high quality amp with a freq respose of 0.5 Hz to 40 Khz. If you can hear it depends onthe quality of the output device(headphones).

There is a MAJOR difference between Koss Porta Pros and a Bose Quiet Comfort II. There's a big difference betwen the II's and the QC III's. The Koss Porta Pros sound the best. Probably the best headphones I had the opportunity to listen too was a set of Electrostatic headphones by Stax such as these: **broken link removed** They will set you back about $3,000 USD.

My friend and I did a side by side comparison of my amp and a McIntosh Tube amp diving Klipsh horns and we both agreed that mine had much better bass than the tube amp. The tube amp was louder driving the horns. The quality of the sound was about the same. We also discovered that I like folk music and it sounds better with a dome tweeter whereas, my friend likes classical music. My friend built a few tube amps.

My preamp has a -3db point at 100 kHz. M y eqipment is not typical audio. It's high end. The preamp actually has 3 voltage gain stages and each stage gets a volume control. That's not typical either.

Sorry but who the f*%$ cares, Will any of that help the OP? Andy
 
KeepItSimpleStupid:

Sorry, still nonsense - resistors DO cause noise, that's a well known effect (which is why you use metal film ones), BUT it's at highly sensitive parts of the circuit, not when you're feeding it from 30 or 40V RMS attenuating down to headphones.

Your problems with your homemade designs are probably due to design or construction errors.

OP:

You need to show us the circuit, and how you've connected it - a picture of a few wires soldered to the bottom of a board is no use at all. But essentially you just need a resistor from the speaker output to the socket, and one from socket to chassis, making an attenuator. The chassis side of the socket obviously needs connecting as well, and you add the resistors for both sides. Add a separate double pole switch to turn the speakers OFF -it's difficult to find a jack socket with the correct switching.
 
Every single resistor in my amp except for the fusibles and the metal oxide
on the nobel network are all 1% metal films. The amp is built with a 100%
ground plane on the circuit side. The ground is a single point where all
the grounds and signal returns terminate.

The bias adjust is 10 turn.

Yep, that's why you use metal film ones and I did, nearly throughout.

Try again.
 
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