Question About Flat Capture Workflow

[Craig Maier]

The DCP-47K-F has a gain factor of 29 dB (which accidently also turns out to be a Vgain = x29). We have sold a ton of these with zero complaints or issues. It just works.

Craig

[Craig Maier]

To Cudukat - Basic circuit analysis of the phono cable adapter (shown in your post above):

Looking at that circuit diagram of the phono cable adapter, the phono load resistance can NEVER be correct. The effective cartridge load resistance will always be less than what is called "Rload" on the circuit. So, if Rload is 47 KOhms, the actual cartridge load is always going to be less than that value when connected to a sound card A/D load. Here is an example. Assume that the A/D converter input resistance is 50 KOhms (which is not an atypical value). The effective load resistance on the magnetic phono cartridge will be 47 kOhms // 50 KOhms which = 24.23 KOhms. That is a far cry from what is prescribed for most all phono cartridges and will have a dulling effect on the top - end of the audio spectrum.

Another common line level input resistance for sound cards is 10 KOhms. In that case, the effective cartridge load resistance shall be 47 KOhms // 10 kOhms = 8.25 KOhms.

So, you can see that there is a fundamental issue with that approach. A flat phono preamp not only provides the proper gain, but isolates (buffers) the 47 KOhms loading resistance from the A/D input resistance, removing the A/D input resistance from the cartridge loading equation.

I hope that helps.

Craig

[Craig Maier]

To Cudukat - Another design flaw with that adapter cable

Turntables are provided with a ground strap wire. It is not connected to the internal grounding of the phono cartridge signal wiring for a very good reason. Turntables produce a small amount of current (ac leakage current) into the chassis of the turntable. The grounding strap is intended to take that leakage current away from the signal wiring and directly into the pre-amplifier via it's own pathway so as to avoid ground loop noise injection into the signal cable shields. That cable violates that principle, since it returns the leakage current into the bottom most (as seen on the diagram) signal shield. Ground current should always be connected independently to the preamp chassis and/or the computer chassis if the lowest level of line frequency related noise is to be expected from your transfer system.

Feel free to post my comments regarding that cable design on other sites for peer review.

Craig

[DougE]

Hello I'm resurrecting this thread to ask a question about flat recording. I record onto a TASCAM DR05X digital recorder using the mic input. I have to attenuate the signal from my pre-amp due to the TASCAM not being a line level device. I have plugged the TT directly into the recorder, recording to disk and then transferring the file to my workstation to eq in DCart10. I have plenty of gain with the TASCAM so S/N is not an issue. The cartridge is a Denon DL110. I've done a couple of records this way and do not discern any dulling of the signal, but that might be my hearing. I can post a snip of what I have recorded.

The question is the REK O KUT sold here is a line level out device and I will need to attenuate to input into the TASCAM, even in flat mode, correct? REK O CUT also sells a switch box that will connect a TT to a phono input. Am I to assume the cartridge will still not see the proper loading if I put this in line with TASCAM? It works with either phono or standard line in.

I *could* find a internal sound card to use, but I invested in this recorder when my old soundcard died. The attenuators are the bullet type, a -12 and -6 ganged.

Thanks for your attention and any advice.

[Craig Maier]

The issue with going directly into the Tascam mic level input is the termination resistance of the Tascam. Usually, mic level inputs have around 10 kOhms terminations, but your phono cartridge likely is designed to operate with a 47,kOhm termination. If the cartridge is not properly terminated, the frequency response will not be what the company who made it says that it should be. If the loading is too low in resistance, the top end will be dull. The Rek O Cut preamp is a line level device. It will need an attenuator if you are to connect it directly to a mic level input. btw - I have a HD recorder here that I use, but it has a mic or line level input that can be selected. Are you sure your Tascam does not have that feature? You should only put an attenuator between a line output and a line input; never put it between the phono cartridge and any input on a soundcard.

[DougE]

Craig:

Yes, I am sure that it is only a mic input. There is no 20dB switch to attenuate the input. This is a 2 in/2 out handheld digital recorder 24/96 max resolution. I had the TASCAM plugged into the tape out of my pre-amp with the aforementioned attenuators.

Per the tech manual

If an external audio device with a fixed output line level is connected, it might not be possible to control the gain level of excessively loud input signals. In such cases, use the headphone jack or other level-controllable output for connection to the unit.

From other boards, I found out you can purchase an inline variable attenuator, volume control if you will, but I had already purchased the in-line attenuators. The headphone or variable out of the preamp would be fine, but I'll futz with the tone controls and I'd hate to forget to bypass.

I'm leaning towards the REK-O-KUT and use the flat out for recording. Plus side, I can attach my semi-auto turntable I use for casual listening and have both TT plugged into the pre-amp. I would reconnect the recorder to the tape out for my needle drops.

Thanks.

[Craig Maier]

Ok - just be sure never to put an attenuator between a turntable cartridge output and a low-level phono preamp input. That will produce a miss - match in impedance between the cartridge and the preamp and it will also raise the noise level of the ultimate output signal from the phono preamplifier.

Craig

[Marc Hildebrant]

DougE

I'm sure that you want to use your TASCAM, but if you are going to spend your time transcribing records, I would use an internal sound card (with line in connections ) or an external USB converter. I show some setups in my Handbook (available on this site).

What you are trying to do is have the largest signal into your A to D converter to have the greatest Signal to Noise ratio. I have found that a volume control in the signal path is useful since the music sources vary so much and the external volume control makes adjusting the setting easy for each record.

Marc

[DougE]

Hola Marc

I am able to adjust the signal level in the recorder. I can, and have, used it for the A/D conversion like a USB soundcard, to record direct to HDD. I found that -18 dB will allow me to keep the signal -12dB below FS, or lower. I use the memory card to bypass the USB interface. I understand about really trying to boost a low level and probably will get the REK-O-CUT and attenuate.


Here are two transcriptions, one via the NAD 1700 pre-amp -> TASCAM and the other the TT is direct into the TASCAM -> DCArt10 VPP.
https://drive.google.com/file/d/13Bl...ew?usp=sharing
https://drive.google.com/file/d/1xzx...ew?usp=sharing
I can't really hear any difference, but maybe there's stuff that I can't hear. I'll look thru my collection and see what else I have I did direct into the recorder.

here's a link to some needledrop samples most were done using the tape out of the NAD using the A/D passthru mode.
https://drive.google.com/drive/folde...Pw?usp=sharing

I think they sound fine. If there's anomolies, please let me know.

AFA sound card, the TASCAM came about because my emu pci card bit the dust. It seemed the best A/D card was ASUS which has issues with support and expensive. Also at the time, there was issues with Win10 and USB A/D devices and this came recommended by some people at SteveHoffman.tv. The problem is it has no line-in feature. Truly a soundcard would be the ticket, but funds go elsewhere at the moment.

Thank you for your remarks. The book does peak my interest.

[Marc Hildebrant]

DougE,

The posts sound fine (eggs & Sausage is nice).

I would look into a Focusrite scarlet 2i2 gen3 as a nice device for a A to D and D to A. It has adjustable gain controls and would work well connected to a flat preamp.
You need to be careful when you use it with the DCart software to make sure that it's 96 kHz sample rate and that of the recording software are "in-sync" (examples in my Handbook).

By the way, I like to set the max on the level meters to -3 dB when recording to give a strong Signal to Noise ratio.

Marc

[DougE]

Thank you, Marc. Eggs and Sausage is from a 180 gm Rhino reissue of Nighthawks at the Diner....sealed. A used record store find.

I did look into that unit as a possible A/D, but I didn't like the un-ganged level controls. I paid something like $100 for the TASCAM, currently $119. I'll certainly entertain a higher grade A/D down the road, but for now, I'll get the REK-O-KUT preamp for the loading and flat passthru. The Re-EQ III by them looks like the feline's behind, but the price is more than I can pony up right now.

For the near term, the TASCAM will work out, as you heard. I'll use my in-line attenuators to allow for recording level adjustment. The phono pre will go into my NAD, then tape out to the TASCAM.

I had been running my peaks at -3 or a bit below, maaaybe a stray -2/-1dB, as long as the peak light stays off. I read how these cheaper A/Ds do better at a lower volume, so even with peaks closer to -6 I've had good results. I will peak normalize to -3 once I get the file in DCArt. I had a Art Tatum recording that had really load pops, that I allowed to clip. I used the peak normalizer to reduce to -3dB prior to declicking. Once it's cleaned up, I gain normalize again to -3dB.

Thank you for your response.

[Marc Hildebrant]

DougE

With regard to the Focusrite gain controls, I want individual channel gain controls since there are times when a slight gain change for say the right channel deliveries a BALANCED input for vertical or horizontal stylus motion.

Marc

[Craig Maier]

To a reasonable degree, those gain adjustments can be done using the software itself via the VPP (balance control) or the File Conversion Filter (Amplitude Sliders). These are done at 24 bit depths, so there is very little error added in that way (1 part in 5,242,288).

Craig

[DougE]

I ordered the REK-O-KUT flat preamp and Marc's book.

AFA balancing the input, I have always been loth to adjust L/R balance because I didn't want to change the intent of the recording engineer. I've never noticed a noticeable difference between the L level and R levels, maybe I should pay more attention. I've been transcribing LPs since the Reel to Reel/Cassette days. :^) Only difference between then and now is the use of digital conversion and the inability of going over 0dB.

[Craig Maier]

That's a good point assuming that your audio system is balanced to begin with. Most are. I have a test record (made by Hi Fi News) that I use to verify my system's intrinsic balance which I only do once ever few years. Not too much to go wrong there, so I do not do it too often since it does produce some wear on that expensive test record.