Is a phono preamp necessary and noise troubleshooting

[NeoHippy]

well the thing with amping in a DAW is the noise.

If you have a preamp you bring the signal up to a level BEFORE some other noise from mixer or interface adds to it.

If you just record the low-level signal, youll pump up all the noise after the turntable!

CHEERS

[Lotus 7]

Originally Posted by Sforzando

Hi all,

I recently bought my first turntable, an AR EB101 with dynavector 10x MC cartridge (yea, hardly a beginners setup but it was at a bargain price), with the intention of digitizing some old vinyl to use in my productions. Unfortunately everything I record includes an insufferable amount of noise (mainly an overbearing 60hz hum) when it passes through through my TC 760LC preamp. Attaching the turntable ground to the preamp terminal only makes the noise louder

I have read quite a few times that the purpose of a phono preamp is to 1) apply the RIAA EQ curve to the signal and to 2) bring it up to line level. So after a few failed attempts at resolving the noise issue I decided to instead run the RCA outputs straight into my audio interface and apply the EQ curve and boost the gain in my DAW. Can anyone explain in straightforward terms what is wrong with this approach? Apparently it boosts low-level noise but how exactly? Personally I think the audio quality sounds great, but I'm paranoid about how it might be perceived by others. I'd also appreciate suggestions about how I might be able to eliminate the noise using the preamp.

Thanks.

You have a good turntable and an excellent cartridge. However the Dynavector is a very low output MC cartridge and requires either a high-gain, low noise "MC" preamplifier or more typically, a set of low-Z to high-Z step up transformers to properly load the cartridge (output load should be a very low 10 ohms or so) and to match the [47k ohm] input impedance of a moving-magnet phono preamplifier. With proper cables and proper grounding of the turntable you should have essentially no 60 Hz hum with the right preamplifier. I have no idea of the quality of your preamplifier, but doubt that it is designed for use with a MC cartridge.

The output from a MC cartridge is very low (10's to 100's of microvolts), so it needs plenty of local amplification and proper grounding of the turntable chassis and the tonearm is critical. A correct MC preamp will have a grounding connection near its input jacks. Connecting the turntable and tone arm grounds farther up the signal chain will almost always lead to hum/noise issues.

A proper MC preamplifier is expensive as are correct MC to MM step up transformers. If you're planning on transferring a limited number of records, a simpler solution may be to just replace your cartridge with a good moving magnet cartridge like a V-15 or a M-97 which will have 20 to 30 dB more output and will be much less prone to hum using your existing phono preamplifier.

Using a mic input and applying the 40 dB of equalization needed to match the RIAA playback curve is an option if you have two very low noise mic pres and are able to properly terminate the [low-Z] MC cartridge. That approach requires the most gain at low frequencies, and decreasing gain as the frequency increases as the RIAA curve dictates. Hum and LF noise will be amplified the most. Ideally, for the Dynavector, you will need approximately 75 to 80 dB of clean gain and a set of well-shielded phono, leads. That kind of gain is not often seen in mic pres except those designed for ribbon mics like the AEA TRP or the True P-Solo. And, of course, you would need a pair of them. Also, the mic pre input is balanced, and again is the wrong impedance for proper operation with a MC cartridge. It might work if you use special cables: 4-wire "star-quad" twisted-pair mic cables brought all the way to the output leads from the tonearm and then connected as single-ended there, but may again be prone to induced hum pick up.

Using post-pre EQ gain (boosting the low end by the 20 dB required by the LF part of the RIAA curve) will, of course, also boost the hum and noise. It's essential to be rid of that before applying the two RIAA EQ curve components.

If your current mic pres sound acceptable using a post-pre EQ, then that's fine. Using a "user-applied" EQ curve does have the advantage of being "tunable" to the program content, and even the track location on the record since the amount of LF roll-off does vary with radius on some records (sometimes more LF boost is needed for the inner tracks).

[Sforzando]

Thanks for the responses guys.

Originally Posted by Lotus 7

You have a good turntable and an excellent cartridge. However the Dynavector is a very low output MC cartridge and requires either a high-gain, low noise "MC" preamplifier or more typically, a set of low-Z to high-Z step up transformers to properly load the cartridge (output load should be a very low 10 ohms or so) and to match the [47k ohm] input impedance of a moving-magnet phono preamplifier.

Hmm. A few websites describe the dynavector 10x series as high output cartridges and the 10x5 has an output voltage of 2.5mV. I have seen posts on forums saying it's fine to use an MM phono preamp, and even that the dynavector 10x series is designed to work with them.

Originally Posted by Lotus 7

With proper cables and proper grounding of the turntable you should have essentially no 60 Hz hum with the right preamplifier. I have no idea of the quality of your preamplifier, but doubt that it is designed for use with a MC cartridge.

Well, it is supposed to work with both MM and MC cartridges and has a switch to select between the two. Obviously it's on the budget end of the spectrum but I decided to buy it after reading several positives reviews claiming it offered the same quality as some far more expensive alternatives. Link to the specs: Phonopreamps.com TCC TC-760LC Details and Hookup

Originally Posted by Lotus 7

The output from a MC cartridge is very low (10's to 100's of microvolts), so it needs plenty of local amplification and proper grounding of the turntable chassis and the tonearm is critical. A correct MC preamp will have a grounding connection near its input jacks. Connecting the turntable and tone arm grounds farther up the signal chain will almost always lead to hum/noise issues.

I have the ground connected to the ground terminal you can see in the pictures at the link above, and yet this significantly amplifies the noise? I never expected super hi fidelity from such a cheap preamp but I don't understand how I'm producing far better recordings without it. Is it probably just faulty then? I wouldn't mind buying a new one if I could be reasonably sure that the problem is with the amp itself and not how I'm using it.

Originally Posted by Lotus 7

Using post-pre EQ gain (boosting the low end by the 20 dB required by the LF part of the RIAA curve) will, of course, also boost the hum and noise. It's essential to be rid of that before applying the two RIAA EQ curve components.

If your current mic pres sound acceptable using a post-pre EQ, then that's fine. Using a "user-applied" EQ curve does have the advantage of being "tunable" to the program content, and even the track location on the record since the amount of LF roll-off does vary with radius on some records (sometimes more LF boost is needed for the inner tracks).

OK. So stupid question but just to verify: the noise that I can deal with is whatever persists as long as the turntable is hooked up (as opposed to noise that is generated only while a record is playing).

[Lotus 7]

You are absolutely correct, the Dynavector 10X3 and 10x5 are high output (2.5 mV) cartridges and should be fine with a conventional, moving magnet input phono pre they sound best with a 1k ohm to 4.7k ohm load, but should work fine with a 47 k input circuit.

My comments were for the low-Z Dynavector cartridges. The 10X series put out enough that they should actually interface quite well with a typical mic input. Even the impedance is a good match.

If you're getting more hum with your external phono pre than without, and are using a good ground lead between the turntable and the phono pre input, either inserting the phono pre in the signal path is creating a ground loop that's inducing some hum in the cartridge cables, OR you're getting some ground currents in the output cables feeding the input to your system.

The noise (input stage hiss and hum) when the turntable is hooked up completely and the needle is off the record should ideally be about 60 to 70 dB lower than the peak signal levels on a loud passage. The very best, "state of the art" cartridges and phono preamps might reach a 80 dB signal to noise ratio. Noise in a quiet lead-in groove or a connecting groove between tracks will be much louder and will depend on the quality of the vinyl and the amount of wear on the record and stylus. It's not unusual for the noise to go up by 15 or 20 dB when the stylus is lowered. Achieving a 55 dB signal to noise ratio is pretty good and 63 dB is excellent when the stylus is actually tracing a groove. With a properly working phono system, the stylus tracing noise ( record hiss) will be much louder than the noise when the stylus is raised.

[zephead64]

I recently purchased the same TC-760LC phono preamp for use with my new Denon MC cart and am getting the same hum issue. I had previously purchased a preamp made by the same company with no issues and when I connect the older non moving-coil preamp I don't have any hum. I suspect it might be a defect with this particular pre-amp.
-Joe

[Sforzando]

Thanks for all the help Lotus.

Originally Posted by zephead64

I recently purchased the same TC-760LC phono preamp for use with my new Denon MC cart and am getting the same hum issue. I had previously purchased a preamp made by the same company with no issues and when I connect the older non moving-coil preamp I don't have any hum. I suspect it might be a defect with this particular pre-amp.
-Joe

I've actually just figured out the cause of my problem.. the solution was embarrassingly simple and I think it might be the same in your case. My cartridge is a high output moving coil cartridge and is actually intended to work with an MM preamp. I switched to the MM mode on the 760 and ta-da, problem largely gone, although a quiet hum still persists. So if your cartridge has a high output try it on the MM setting.

[zephead64]

Originally Posted by Sforzando

Thanks for all the help Lotus.

I've actually just figured out the cause of my problem.. the solution was embarrassingly simple and I think it might be the same in your case. My cartridge is a high output moving coil cartridge and is actually intended to work with an MM preamp. I switched to the MM mode on the 760 and ta-da, problem largely gone, although a quiet hum still persists. So if your cartridge has a high output try it on the MM setting.

I agree that the Denon MC I have is designed to be able to be used with a regular MM pre-amp, but the documentation didn't specifically say to 'not' use a MC pre-amp. When I switched to the MM side I also still got some hum. When I switched to the previous MM only pre-amp (model TC-753LC) I have no hum at all. Strange. This is why I think that the 760 is defective in some way. Is there any potential sound quality difference by using a MM pre-amp with our high-output MC carts?

[Bill Way]

If you're still getting some hum, play with the ground connections to your preamp. You've got at least separate grounds from the arm and turntable, so try all possibilities. Also, some cartridges offer removable ground straps from the cartridge body itself.

WW

[Lotus 7]

Originally Posted by zephead64

I agree that the Denon MC I have is designed to be able to be used with a regular MM pre-amp, but the documentation didn't specifically say to 'not' use a MC pre-amp. When I switched to the MM side I also still got some hum. When I switched to the previous MM only pre-amp (model TC-753LC) I have no hum at all. Strange. This is why I think that the 760 is defective in some way. Is there any potential sound quality difference by using a MM pre-amp with our high-output MC carts?

No disadvantage, that's what the high-output cartridge is intended to be used with. The whole concept of using high output, high impedance MC cartridges was to be able to make them easier to use since all home audio preamps and receivers will have a MM input (usually with a 47 k ohm input-Z), but only the more esoteric, audiophile grade preamps would have a real MC (high-gain, low-Z) input thus making it more difficult, complicated and expensive to use a MC cartridge.

Using a preamp input designed for a MC cartridge with a MM cartridge is not a good idea because of a high probability of overdriving the input as well as poor frequency response because of the (usual) low input impedance.