Flat phono amp

[cubdukat]

Along the same lines of the question that originally started this thread, I have been running the output of my turntable (a Music Hall MMF-2.2) either straight into my computer with no preamp, or through an M-Audio Fast Track Pro interface to boost the levels. After the capture, I do the normal work on removing clicks, then I gain normalize to -3dB. But I have three questions:

1. Would this be considered a flat transfer;
2. Which should come first, the VPA or normalizing, and;
3. What exactly would be the correct workflow?

I'm currently transferring a lot of Deutsche Grammophon and CBS Masterworks digital recordings, and I want to bypass my preamp entirely because I've never really liked it.

[Craig Maier]

I am surprised that you can run a phono cartridge directly into a sound card and have enough gain to do the job, unless the phono cartridge is of the ceramic (piezoelectric) type. Nonetheless, going directly into a soundcard from a magnetic cartridge would yield a flat transfer, but I think that the overall gain would be low and the signal perhaps would be a little noisy. Here is how I do it:

1. Transfer to soundcard via a flat preamplifier from a magnetic phono cartridge at 96 kHz 16 bits (some folks like to use 24 bits)
2. Apply the proper curve using the VPA (Virtual Phono Preamp)
3. De-click the recording using the EZ Impulse Filte
4. De-hiss the recording using the CNF.
5. File convert the result down to 44.1 kHz so that I can make a CD and for my archive.

Craig

[cubdukat]

The Fast Track Pro has mic inputs, and I run the RCA cable into a female/female adapter which connects to an RCA to 1/4" phone stereo pair. I just have to crank the level up high enough to overcome any noise. After I capture it, then I de-click, then normalize. I do the declicking first so that the clicks don't fool the filter into thinking that they're the loudest part of the signal. I don't apply the VPA until the end, although from what I've read here, I should probably be doing that first since the declick filters respond to an EQ'd signal.

I haven't gotten the hang of the CNF filter, so I don't use it. It sounds fine on my system, but then when I put it on my phone and listen with headphones, I hear the birdies at the end of songs, and they cut off early. But I'm still getting the hang of the program and starting to get serious with it.

[Craig Maier]

The key to reducing the "birdies" (digital artifacts) is to use relatively long attack and release time settings and not trying to obtain a no-noise result. When using the normal CNF mode, I rarely use an attenuation value greater than 10. Values greater than that produce artifacts as a general rule. Using artifact suppression mode, I find that I can use higher values of attenuation without much artifacting - - - up to around 35. But, my taste is not to completely eliminate all background noise; it is a tradeoff that I make. I just try to reduce the background noise, but not eliminate it.

[Craig Maier]

As an aside, how do you provide the proper phono cartridge loading terminating resistance? Typically, most moving magnet (the common type of phono cartridge) wants to see 47,000 Ohms (47 kOhms). Does the Fast Track Pro mic input have 47 kOhm input terminations?

[cubdukat]

It doesn't have anything to do that. It was meant more as an audio interface for MIDI and DAW recording. I'm going to be replacing it soon. Avid no longer supports it, and the current drivers lock it down to 24/44.1 in Windows 10. I'm using it right now because the internal sound on my motherboard is crappy, even though it can go up to 24/96, not to mention there's some kind of 60Hz hum I can't track down with it.

I'm going to do some more experimentation later on. I have a bunch of DG recordings to re-do tonight.

BTW, is there any way to compensate for the lack of 47K Ohm termination within DC?

[Craig Maier]

I have no suggestion as to a way to compensate for the lack of a 47 kOhm Termination on a phono cartridge. I guess, in theory, it would depend on what the actual termination resistance was during the transfer. If it was very high (say 1 Meg Ohm), then you would have to reduce the treble. If it was too low, (say 10 kOhm), then the treble would need to be increased. The problem is "by how much"? That I can not say without knowing the specifics. Then, it becomes a network analysis problem to figure out.

[dbanani]

Would it not be possible to compensate using Diamond Cut DC8.5 by making a recording on a second system which has 47 kOhm input and a second recording of the same record using the sound card without the 47 kOhm input? Then, using the spectrum analyzer, develop a compensation curve preset in the paragraphic EQ which matches the spectrum analyzer curve of the sound card system to that of the system with 47 kOhm.
If you have a test record such as Hi Fi News Test Record, the process would probably be even more accurate using the pink noise track for the recording.
I haven't tried this with different input resistances but it seems similar to making compensation curve presets for different carts which I have had some success with using the same methodology.
D

[Craig Maier]

I suppose it could be done that way, but the trick is to be able to decipher between the normal RIAA top pole (its smallest time constant) and the pole formed by the L/R time constant of the cartridge (inductance and terminating resistance). Put another way, they are probably close in frequency to one another and may interact with one another in a less than obvious way. The best way to do it, imho is to just load the phono cartridge properly per its manufacturer's specification. So, if I had an unknown preamplifier, I would open it up, find the input termination resistor and change it to the value recommended by the cartridge manufacturer. The location of that resistor will be quite obvious via visual inspection. (I guess you can see that I am an old hardware guy).

Craig

[dbanani]

Yes Craig, I agree, that is definitely the best solution, but probably not feasible for a lot of users. Using DC8.5 to get a result which is close enough might be a satisfactory option.
I've managed to get paragraphic EQ presets for different Carts, which have varying curves, to sound exactly the same to my old ears using that method.
D

[Craig Maier]

Hi,

Problem is that with older ears like ours, the effect will be ultrasonic for us. Those two poles are both going to be at the top end of our hearing range, so hard to determine aurally. I probably could have done it that way when I was a kid, however.

Craig

[cubdukat]

I have no suggestion as to a way to compensate for the lack of a 47 kOhm Termination on a phono cartridge. I guess, in theory, it would depend on what the actual termination resistance was during the transfer. If it was very high (say 1 Meg Ohm), then you would have to reduce the treble. If it was too low, (say 10 kOhm), then the treble would need to be increased. The problem is "by how much"? That I can not say without knowing the specifics. Then, it becomes a network analysis problem to figure out.

I think I found a solution, and ironically, it's made by an Apple-centric vendor. ChannelD sells a cable that takes care of that. Not sure if it handles capacitance, but it handles the resistance issue. It was made for people who are doing the exact thing I'm doing.

I'm probably going to try to get one after the new year.

I'm also hedging my bets and replacing my current preamp with a Schiit Mani. I figure it's about time, since I've had the previous one for 10 years, and I've never really liked it all that much.

[Craig Maier]

How can a cable take care of that problem? The cable would need to know:

The required termination resistance for the cartridge (often 47 KOhms, but not always)

The input resistance (and/or impedance) of the preamplifier

The proper loading capacitance for the cartridge.

In short, I am suspicious about such a cable.

Craig

[Craig Maier]

Consider using the Diamond Cut Productions DCP-47K-F flat phono preamp. It meets all the requirement for proper flat transfers and works nicely with the Diamond Cut Virtual Phono Preamplifier. You can find that on our website at www.diamondcut.com