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Noise

levimax

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Thanks - am I right in thinking that all it needs is a 15V power supply and a suitable case and you’re good to go? Guess it could even be mounted inside my turntable plinth if there was space. Would this take care of the capacitance needs of MM carts?

Sorry to bombard with questions, but just one more thing - I understand phono cartridges are inherently balanced, so could this be wired with balanced ins from the cart to balanced outs as well?

The reason I use the balanced buffer is that my ADC has 10K ohm input impedance on the balanced inputs and you need 47K for a MM cart to work correctly. As explained above by @sergeauckland carts are "kind of balanced / depends on cart and TT wiring/ etc" but if you use a buffer you can keep the leads from the cart to the buffer short, get the loading correct (less capacitance is usually better so short leads/ built into TT is great), and then after the buffer you have a true balanced connection to the ADC which is great for keeping noise down. In my case my ADC has plenty of gain on the balanced input (any balanced microphone input should have plenty of gain) so I don't need any extra gain from the buffer or a phono stage. I did ask Tom from Neurchrome about possibly adding gain to the buffer and he said with a couple of resistors changes 20 db is "easy" and with a little more work you could get more.
 

sergeauckland

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The reason I use the balanced buffer is that my ADC has 10K ohm input impedance on the balanced inputs and you need 47K for a MM cart to work correctly. As explained above by @sergeauckland carts are "kind of balanced / depends on cart and TT wiring/ etc" but if you use a buffer you can keep the leads from the cart to the buffer short, get the loading correct (less capacitance is usually better so short leads/ built into TT is great), and then after the buffer you have a true balanced connection to the ADC which is great for keeping noise down. In my case my ADC has plenty of gain on the balanced input (any balanced microphone input should have plenty of gain) so I don't need any extra gain from the buffer or a phono stage. I did ask Tom from Neurchrome about possibly adding gain to the buffer and he said with a couple of resistors changes 20 db is "easy" and with a little more work you could get more.
One issue, which may or may not matter is that the buffer will have its own noise, that the ADC will see as signal. As the buffer is unity gain, or even with 20dB (10x) gain, the output of the buffer will be at the mV level, whilst the excellent S/N ratio of the buffer is based on it being used at line level, so some 40dB or more higher level. This will degrade the S/N ratio of the system by the 40dB or so, then further by the noise level of the mic preamp of the ADC. If you could get 40dB or so gain out of the buffer, then this problem would go away, and you'd have a system with low noise and good overload margin.

S.
 

levimax

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One issue, which may or may not matter is that the buffer will have its own noise, that the ADC will see as signal. As the buffer is unity gain, or even with 20dB (10x) gain, the output of the buffer will be at the mV level, whilst the excellent S/N ratio of the buffer is based on it being used at line level, so some 40dB or more higher level. This will degrade the S/N ratio of the system by the 40dB or so, then further by the noise level of the mic preamp of the ADC. If you could get 40dB or so gain out of the buffer, then this problem would go away, and you'd have a system with low noise and good overload margin.

S.

Interesting points about the gain ..... from a practical level in my system the unity buffer to ADC has less noise than the phono pre-amp I previously used and in either case the noise floor is much lower than that of any record I have. The one thing I don't know is that since my ADC automatically engages the gain structure for microphones (up to 60 db) when ever a balanced input is connected I am not sure how much I would gain by adding gain at the buffer stage. As far as I can tell the only way to get the ADC to use the "line level" gain structure is to use an unbalanced connection which defeats the main reason I did this project which was to use balanced connections to reduce noise (which was successful).
 

sergeauckland

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Interesting points about the gain ..... from a practical level in my system the unity buffer to ADC has less noise than the phono pre-amp I previously used and in either case the noise floor is much lower than that of any record I have. The one thing I don't know is that since my ADC automatically engages the gain structure for microphones (up to 60 db) when ever a balanced input is connected I am not sure how much I would gain by adding gain at the buffer stage. As far as I can tell the only way to get the ADC to use the "line level" gain structure is to use an unbalanced connection which defeats the main reason I did this project which was to use balanced connections to reduce noise (which was successful).
What you would do is to reduce noise that the buffer stage is generating. Depending on the circuit details of the buffer, putting gain in the buffer will increase the noise generated by the buffer's input stage(s) but as the output stage noise is constant, that should improve the overall S/N ratio. Also, by having gain in the buffer, that means that the mic amp gain can be less, and it depends which is noisier, the buffer or the mic input.

Alternatively, run the buffer on the lowest voltage that will still meet its spec, as that's likely to reduce the noise voltage too, making sure that the buffer still has enough volts to provide the necessary overload margin, which shouldn't be hard if the buffer has unity gain.

Overall, gain ranging, i.e. where do you put the gain, and how that relates to overload margins, isn't always obvious.

S.
 

TimW

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I have been experimenting with a phono setup that includes an ADC. At first I was using a Pro-Ject Optical Box E Phono connected to an AudioEngine D2 wireless DAC. The Pro-Ject gave me an optical SPDIF output that the AudioEngine could accept and transmit wirelessly to my digital preamp. This allowed me to have the Turntable right next to my listening position without cables running to the rest of my equipment.

Then Amir reviewed the Pro-Ject which showed less than stellar performance. I didn't expect high performance from the thing and honestly it doesn't look that bad to me, but I decided to swap it out with some other equipment I had laying around. Now I've got a Hafler PH50B performing RIAA equalization and gain duties and a Behringer SRC2496 carrying out the ADC function. This setup has an audibly lower noise floor than the Pro-Ject but it also sounds better to me, probably due to a frequency response but maybe also due to overload margin? Or it could just be in my head.

I also have a miniDSP OpenDRC-DA8 (8 analog outputs) that's not being used right now and I was thinking of transforming it into an OpenDRC-DI (Digital I/O). The parts for this only cost $50 from miniDSP. The idea of performing RIAA correction using a custom biquad in the miniDSP intrigues me. I could also add a steep subsonic filter and perform EQ to correct for the response of my phono cartridge. Maybe based on measurements from a test record? I could have 4 presets for different RIAA and EQ settings to choose from on the fly.

The thing is I would then need some sort of flat phono preamp to provide proper cartridge loading and signal boosting for my ADC. That is what led me to this thread. I had been eyeing the Neurochrome Universal Buffer for a while but I'm not sure 20dB of gain is enough for my setup. I also don't know what the input capacitance of it is but I'm sure @tomchr could answer that. I found a purpose built flat phono preamp circuit designed for studio use from KA Electronics that has the features I want. It has adjustable input impedance, capacitance and gain of up to 46 dB using the balanced outputs. I can't find any real specs on it though unfortunately. I also found these interesting phantom powered adapters designed to connect phono cart outputs to microphone preamp inputs with proper cartridge loading. All of these options are somewhat expensive for a setup I'm just experimenting with though. Does anyone know of any other options out there for simply adding gain to a MM cart's output?
 

levimax

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I have been experimenting with a phono setup that includes an ADC. At first I was using a Pro-Ject Optical Box E Phono connected to an AudioEngine D2 wireless DAC. The Pro-Ject gave me an optical SPDIF output that the AudioEngine could accept and transmit wirelessly to my digital preamp. This allowed me to have the Turntable right next to my listening position without cables running to the rest of my equipment.

Then Amir reviewed the Pro-Ject which showed less than stellar performance. I didn't expect high performance from the thing and honestly it doesn't look that bad to me, but I decided to swap it out with some other equipment I had laying around. Now I've got a Hafler PH50B performing RIAA equalization and gain duties and a Behringer SRC2496 carrying out the ADC function. This setup has an audibly lower noise floor than the Pro-Ject but it also sounds better to me, probably due to a frequency response but maybe also due to overload margin? Or it could just be in my head.

I also have a miniDSP OpenDRC-DA8 (8 analog outputs) that's not being used right now and I was thinking of transforming it into an OpenDRC-DI (Digital I/O). The parts for this only cost $50 from miniDSP. The idea of performing RIAA correction using a custom biquad in the miniDSP intrigues me. I could also add a steep subsonic filter and perform EQ to correct for the response of my phono cartridge. Maybe based on measurements from a test record? I could have 4 presets for different RIAA and EQ settings to choose from on the fly.

The thing is I would then need some sort of flat phono preamp to provide proper cartridge loading and signal boosting for my ADC. That is what led me to this thread. I had been eyeing the Neurochrome Universal Buffer for a while but I'm not sure 20dB of gain is enough for my setup. I also don't know what the input capacitance of it is but I'm sure @tomchr could answer that. I found a purpose built flat phono preamp circuit designed for studio use from KA Electronics that has the features I want. It has adjustable input impedance, capacitance and gain of up to 46 dB using the balanced outputs. I can't find any real specs on it though unfortunately. I also found these interesting phantom powered adapters designed to connect phono cart outputs to microphone preamp inputs with proper cartridge loading. All of these options are somewhat expensive for a setup I'm just experimenting with though. Does anyone know of any other options out there for simply adding gain to a MM cart's output?
Maybe my experience will help. I built this cheap and easy but good performing "Balanced Transmitter" and substituted 47K ohm resistors on the input to match a MM cart. https://sound-au.com/project87.htm I then connected it directly to the balanced inputs of a Steinberg UR22 MK2 ADC. When connecting "balanced" it uses hi-gain (like for a microphone) and there is plenty of gain for a MM cart. The ADC connects to a PC via USB. I then used Rephase to create a RIAA convolution curve (super easy to also add rumble filter or other EQ) and I use the "Recorder" and "Convolver" plug ins for Foobar2000 and it works quite well. It is also easy to use Audacity to make "needle drops". Hope this helps.
 

TimW

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Maybe my experience will help. I built this cheap and easy but good performing "Balanced Transmitter" and substituted 47K ohm resistors on the input to match a MM cart. https://sound-au.com/project87.htm I then connected it directly to the balanced inputs of a Steinberg UR22 MK2 ADC. When connecting "balanced" it uses hi-gain (like for a microphone) and there is plenty of gain for a MM cart. The ADC connects to a PC via USB. I then used Rephase to create a RIAA convolution curve (super easy to also add rumble filter or other EQ) and I use the "Recorder" and "Convolver" plug ins for Foobar2000 and it works quite well. It is also easy to use Audacity to make "needle drops". Hope this helps.
So this "Balanced Transmitter" simply converts a single ended signal to a balanced signal right? You have changed the input resistors for proper impedance matching with the cartridge also. But it does not add gain? Is there any performance specifications or measurements available?

I would either need to replace my ADC with an audio interface or add a microphone preamp to the signal chain to use this circuit. I was hoping there was a ready made circuit that could add the needed gain while matching the impedances with excellent noise and distortion specifications.
 

levimax

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So this "Balanced Transmitter" simply converts a single ended signal to a balanced signal right? You have changed the input resistors for proper impedance matching with the cartridge also. But it does not add gain? Is there any performance specifications or measurements available?

I would either need to replace my ADC with an audio interface or add a microphone preamp to the signal chain to use this circuit. I was hoping there was a ready made circuit that could add the needed gain while matching the impedances with excellent noise and distortion specifications.

What kind of ADC do you have? How much gain do you need? Stock the buffer is "unity gain" i.e. no gain. You can get some gain out of this buffer by changing the feedback resistor on the op amps... not sure how much and what resistor value, you could ask Rod... he is good at answering e-mails. As far as specs go it will be similar to the published op amp specs. If you use good op amps and a decent PS you will have orders of magnitude better performance than your TT can deliver. I looked at the Neurochrome buffer (looks great) and that would probably work... I asked Tom about the gain and he said 20 dB of gain is easy... more with some resistor changes... changing SMD resistors is a lot harder than through hole though. Like you I looked around and there is not a lot... to get the 47K input you almost have to build it yourself although the Neurochrome is 47 K stock I believe. Good luck and let us know how it works. I would encourage you to keep after this project, mine worked out much easier and better than I thought it would.
 

levimax

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So this "Balanced Transmitter" simply converts a single ended signal to a balanced signal right? You have changed the input resistors for proper impedance matching with the cartridge also. But it does not add gain? Is there any performance specifications or measurements available?

I would either need to replace my ADC with an audio interface or add a microphone preamp to the signal chain to use this circuit. I was hoping there was a ready made circuit that could add the needed gain while matching the impedances with excellent noise and distortion specifications.
Or this would work as well http://parksaudiollc.com/
 

TimW

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What kind of ADC do you have? How much gain do you need? Stock the buffer is "unity gain" i.e. no gain. You can get some gain out of this buffer by changing the feedback resistor on the op amps... not sure how much and what resistor value, you could ask Rod... he is good at answering e-mails. As far as specs go it will be similar to the published op amp specs. If you use good op amps and a decent PS you will have orders of magnitude better performance than your TT can deliver. I looked at the Neurochrome buffer (looks great) and that would probably work... I asked Tom about the gain and he said 20 dB of gain is easy... more with some resistor changes... changing SMD resistors is a lot harder than through hole though. Like you I looked around and there is not a lot... to get the 47K input you almost have to build it yourself although the Neurochrome is 47 K stock I believe. Good luck and let us know how it works. I would encourage you to keep after this project, mine worked out much easier and better than I thought it would.

My ADC is the Behringer SRC2496.

Hmm I didn't know about the SMD resistor changes needed to get more than 20 dB of gain with the Neurochrome. Looking at his performance graphs it seems like overall gain is limited by the power supply limit of +/-17V. I don't think the opamps can handle more then that. However, I suppose if you're feeding the amp a very low input voltage like 5mv then you could crank up the gain without ever pushing the output to its limits.
1608610710385.png


Do you know which opamps would be the top performers compatible with the Balanced Transmitter? I don't know where to begin to look, so I should probably just email Rod.

Or this would work as well http://parksaudiollc.com/
I've been eyeing that ever since Amir reviewed it here. The features certainly look very cool, especially since they added the digital out option. $639 for the toslink output version is more then I want to spend though.
 

levimax

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My ADC is the Behringer SRC2496.

Hmm I didn't know about the SMD resistor changes needed to get more than 20 dB of gain with the Neurochrome. Looking at his performance graphs it seems like overall gain is limited by the power supply limit of +/-17V. I don't think the opamps can handle more then that. However, I suppose if you're feeding the amp a very low input voltage like 5mv then you could crank up the gain without ever pushing the output to its limits.
View attachment 100825

Do you know which opamps would be the top performers compatible with the Balanced Transmitter? I don't know where to begin to look, so I should probably just email Rod.


I've been eyeing that ever since Amir reviewed it here. The features certainly look very cool, especially since they added the digital out option. $639 for the toslink output version is more then I want to spend though.

I am not an engineer but don't confuse gain with rail voltage.... you don't need anywhere near +/- 17 volts... your ADC can be driven to full power with 0.5 volts and a MM cart outputs 0.005 volts so you will need 100X or 40 dB of gain. I would ask Tom about getting 40 dB of gain from his buffer, I am pretty sure you won't get that from one op amp stage (probably need 2) so the buffer probably won't work but you might check with Rod as well. I have built a bunch of ESP stuff and the recommended op amps are opa2134 https://www.ti.com/product/OPA2134 and NE5532 https://www.ti.com/lit/ds/symlink/ne5532a.pdf?ts=1608551219601 and I have had good luck with both.
 
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