Preamp Headroom Question


Just bought a "lowish" output MC cartridge -- Lyra Kleos.

Background info: The Kleos' rated output is .5 mV. My phono pre is an ARC PH-8 which has rated gain of 58 db. The PH-8 is tied into an ARC Ref 5 SE which has rated gain of 12 db.

In most cases when playing vinyl the rig produces plenty of gain when the Ref 5 cranked up to 65 to 75 clicks out of 104 maximum clicks. But in a few cases, usually when playing some classical LPs, I have to turn the Ref 5 up to 85+ clicks to achieve acceptable gain levels.

The question: If the Ref 5 is cranked up to 85+ clicks, will I lose headroom in cases when the music hits dynamic passages? Also, I think playing the Ref 5 at such high levels increases the noise floor. That is I hear a lot of record hiss. Does all of this make sense?

I suppose the only solution is to insert a SUT, but it will come with its own cost. Probably need only another 5 to 10 db.

Any thoughts or suggestions.

Thanks.

BIF
bifwynne
Hi Bruce,

You won't run out of headroom as long as you don't find yourself wanting to turn the volume control up past its 104 maximum.

The main question is when you set the volume control to the highest position that you would ever want to set it at for serious listening, are the hiss levels then objectionably high when a record is NOT being played?

If so, there's a problem. If not, once you've optimized loading you should be good to go. (It looks like 100, 200, and 500 ohms are the choices provided by your phono stage which fall within the range that is recommended in the specifications of the Kleos, although there would be no harm in trying the 1K or 47K settings).

If you do have objectionable hiss under this condition, the one possible way of trying to reduce it that occurs to me, short of adding a SUT or headamp or changing phono stages, would be tube rolling the phono stage. However I have some doubt that this would help, because I see that the PH-8 uses a solid state (JFET) front end. When there are multiple gain stages in series the one that is furthest upstream generally tends to be the one that is most critical with respect to overall noise performance, since a given amount of noise that is generated at that point will be greater in relation to signal level than the same amount of noise would be if generated at points further downstream.

Re your question about record hiss, having to operate at a higher volume control setting will not change the amount of record-generated hiss (as opposed to phono stage-generated hiss) that you hear, compared to listening at the same SPL via a higher output cartridge, at a lower setting of the volume control. Although the design of the cartridge, as opposed to the volume control setting that its output level necessitates, can of course make a difference in how much record-generated hiss or surface noise is heard. But, that difference aside, the signal-to-noise ratio of the record itself is what it is.

Best regards,
-- Al
Thanks Al. Easy enough to check. Next time I turn my rig on, I'll turn the linestage gain up to 80-85 clicks on phono setting, with the TT running -- but leaving the tone arm elevated off the record. That should be a good test to see how much noise is coming through the system.

On a different note, some months ago, I posted a thread about dedicated power lines for my rig. Haven't executed yet. But ... last night, I disconnected my amp's power cord from a lightening arrester extension cord and plugged the amp's power cord directly into the wall socket. The lightening arrester extension cord feeds the rest of my gear. Major difference! It's kinda' like the amp was gasping for breath before. Across the board improvement, especially improved lower end and better kick with dynamic transient responses. This morning, I did the same with my linestage. It will be interested to see if there will be similar improvements.

Thanks as usual.

BIF
The rule of thumb with any phono stage is not how much noise there is when you lift the tone arm off the LP, but how much noise there is when the needle is in a good silent groove.

In the latter case the noise should be less than that of the groove. If not you have a problem and you can disregard what is happening when the needle is lifted off the LP (although it is nice if its quiet there, but with LOMC that is always a bit of a trick). An SUT could help, but you may well pay a price of reduced detail and impact (loading on LOMC cartridges is not critical but it is really critical on SUTs- you want to get it right).
Ralph, sorry to sound dumb, but not sure what you mean when you say "how much noise there is when the needle is in a good silent groove." Does that imply when the record is spinning??

I ask because I checked the phono noise level with the linestage set to 80 clicks (out of 104) with the TT motor running, but with the tone arm lifted OFF the record. Is there noise?? Yes. I can hear hissing about 2 foot away from the speakers. The noise level is about the same out of both channels. Much beyond 2 feet, it's pretty quiet, or quiet enough.

My linestage is pretty quiet, about -109 db; the phono pre is fair, about -74 db, but not outrageous for a tube phono pre.

I'm not sure how to assess noise if the stylus is in a "quiet groove" while the record is spinning. If you are referring to a quiet passage, like a single instrument playing (e.g., a flute or violin), I don't think it's too bad. If anything, on some records, I'm probably hearing the stylus tracing the groove. On other records, very little groove noise.

Having grown up in the 70s, vinyl was notoriously "hissy." OTOH, I just bought a brand new 200 gram Mahler LP re-issue from Acoustic Sounds. It's very quiet.

Not sure all of this is responsive to the comments and suggestions offerred by you and Al. But that's all there is to report.

My main Q was about dynamic headroom if I crank the linestage up. Per Al, shouldn't be a problem. If it is, it's likely happening on classical records which generally present large dynamic swings in volume. Less so on compressed rock.

Thanks

BIF

Ralph, I'm not sure I understand your comment either, especially the part about "in the latter case the noise should be less than that of the groove." Can you clarify? Did you mean "in the former case"?

Also, why would playing an essentially silent groove say anything more about the noise performance of the phono stage than an assessment that is made with the stylus lifted off of the record?

Best regards,
-- Al
My main Q was about dynamic headroom if I crank the linestage up. Per Al, shouldn't be a problem. If it is, it's likely happening on classical records which generally present large dynamic swings in volume. Less so on compressed rock

How you word your question suggests that you are thinking in terms of how an amplifier is set up. Specifically amps are almost always set up to achieve full output before you run out of volume control, anything farther causes overload/distortion. Preamps on the other hand are typically set so that as long as you do not overload the input you will not reach full output (before overload/distortion) even with the volume control all the way up.

IOW, in properly set up preamp/amp set up you never drive the preamp into overload and distortion no matter how much you open up the volume control. The overload is in the amp.

This is why the other posts are discussing noise levels/issues as that is the major concern when having to turn the volume control up all or nearly all of the way.

HTH
Ralph, I'm not sure I understand your comment either, especially the part about "in the latter case the noise should be less than that of the groove." Can you clarify? Did you mean "in the former case"?

Also, why would playing an essentially silent groove say anything more about the noise performance of the phono stage than an assessment that is made with the stylus lifted off of the record?

In most cases the noise floor of the LP is going to be higher than that of the phono stage. Since the noise of the phono section will be masked by the LP surface, it is only important for the phono section to be quieter than the LP. That is why lifting the needle off the spinning LP surface really isn't telling you much.

Now if the phono section proves to be the noise you hear when you set the needle down in the spinning groove, that is when you know you have a problem.

Silent grooves can be found at the beginning of LPs, and also between cuts.
Thanks Ralph. Yes, that makes sense.

Best regards,
-- Al