Your choice for budget analog to digital converter

I took a look at the description and specs of the Linestreamer, and there are a couple of concerns.

One is that it is specified as having an input impedance of only 5,000 ohms. I couldn't find specs or measurements on the output impedance of the Grado phono stage, and without confirmation from Grado I would not assume that its output impedance is low enough at all frequencies to drive 5K with good results.

A second issue is the one Dtc mentioned, that the Linestreamer apparently has no input level control. And of course neither phono stages nor preamp tape outputs generally provide level controlled outputs. That creates two risks:

(a)Overdriving the ADC, such that volume peaks exceed its "full scale" range, which would cause clipping. The specified full scale input of the Linestreamer is 2.25 volts. With most recordings I would not expect that level to ever be exceeded when driving it from the output of your phono stage, but I wouldn't rule out the possibility that it could be a problem with some recordings.

(b)More significantly, on many recordings levels may be low enough at the output of your phono stage to leave a significant fraction of the 2.25 volt input range of the ADC unutilized, which would result in at least a slight degradation of signal-to-noise ratio and sonics. Or perhaps a more than slight degradation in some cases.

A possible way of avoiding both issues would be to drive the Linestreamer from the output of the headphone amp, using a suitable connector adapter or adapter cable. If you want to consider that possibility, let us know what model headphone amp it is.

Regarding the question about preamp tape outputs, while there are exceptions I believe it is most common for there to be no gain between the preamp's inputs and tape outputs, and for a resistor of some value to be placed between the main internal signal path and the tape outputs. Some preamps, though, provide separate buffer stages for their tape outputs. Putting aside the level-related issues, whether it would be preferable to drive an ADC from a phono stage output or from a preamp's tape output will be dependent on the respective output impedances and on the input impedance of the ADC.

Regards,
-- Al

Dtc, thanks. Yes, all or nearly all headphone amps will have output impedances that are easily low enough to be able to drive 5K with good results. And that is confirmed in the case of the SLP-05 by the indication in its manual that it is suitable for use with headphones having impedances of 30 to 300 ohms. (The reason headphones with higher impedances may not be suitable is undoubtedly due to limitations on output voltage, not output impedance).

The line-level main output of the SLP-05, btw, would not be suitable, as its impedance is too high to drive 5K with good results, perJohn Atkinson's measurements.

The other thing to consider is if the headphone output can provide enough voltage to the Linestreamer. I see in its manual a statement that it can provide 0.5 watts per channel. Making the worst case assumption that that is based on a 30 ohm load, that corresponds to about 3.9 volts, which would be fine (when reduced by the preamp's volume control).

A point to be aware of, that is mentioned in the manual, is that apparently the preamp's main outputs remain active when its headphone amp is switched on, so the power amp would have to be turned off if you don't want sound from the speakers while you are using the ADC.

Just pick up an adapter like this, and I'm pretty certain you'll have no problems interfacing to the Linestreamer.

Regards,
-- Al

You're welcome, Dtc. I might have spoken a little too soon, though. I see that the headphone output on the SLP-05 is transformer coupled. It would probably be a good idea to ask Cary if running that output into 5K would result in any sonic issues, due to the very light loading of the transformer, and if it would raise any issues with respect to long-term reliability.

As you are most likely aware, tube power amplifiers having output transformers should not be operated without a speaker or equivalent load being connected, at least when a signal is being processed by the amp, due to the possibility of damage or degraded long term reliability from "inductive kickback." I don't feel totally certain that that consideration is inapplicable to this situation, with 5K representing close to no load for the transformer coupled headphone output.

I suspect the answer will be "no problem," but I'd suggest checking with them to be sure.

Regards,
-- Al

KN, yes it is analogous to optimizing the match between signal levels and the dynamic range of recording tape. The main difference, of course, being that a modest amount of analog tape oversaturation may still provide reasonable results, while any overload of digital recording equipment will produce very hard clipping.

There doesn't seem to be much meaningful technical information on the Grado headphone amplifiers. But assuming you are using the non-high gain version, that is intended for use with Grado headphones, unfortunately I suspect that its gain and output voltage capability are such that it would not provide enough voltage to fully utilize the dynamic range of the Linestreamer, when driven by a signal level corresponding to the output of a phono stage.

It appears that the high gain version was introduced for the purpose of driving non-Grado phones having impedances of 100 ohms or more, which require higher voltages than the 32 ohm Grado phones require, for a given amount of input power. And I did find some review comments indicating that the non-high gain version can't drive certain Sennheiser and other models to high volume levels. Finally, the fact that a similar model exists which runs on battery power, and is described as being able to run for 40 to 50 hours on two 9 volt batteries, would seem to indicate that the design is not particularly high powered.

All of that is speculative to some degree, of course, but the lack of technical specs on the amplifier precludes anything more definitive.

Regards,
-- Al

Dtc, I suspect KN is using the high output version of the Platinum cartridge, which is spec'd at 5 mv under the standard test conditions. He would most likely be using, and have to use, the low gain setting of the phono stage with that cartridge, which apparently provides a gain of 40 db. That is a voltage gain of 100 times. So under the standard test conditions the phono stage will be putting out 0.5 volts.

Particularly high volume peaks on some recordings would no doubt put that into the 1 to 2 volt range, but many other recordings will be at levels that are considerably less than 0.5 volts most or all of the time.

The key questions to ask Grado, as I see it, would be what the gain of the headphone amplifier is, at the maximum setting of its volume control, and what its maximum output voltage is.

Best regards,
-- Al