Maximising phono gain without clipping inputs?

[rDin]

Any methods for objectively setting maximum phono gain without clipping inputs on the pre-amp/receiver?

I have a PC oscilloscope and can put signals through the hifi to it, so I can see, for instance, a 1khz sine wave from one of my test records - but it's recorded low so I cannot cause it to clip, even at max gain, whereas music clearly does clip as I can hear distortion. So, I was thinking there must be test records or other methods out there for pushing gain on the phono output to maximise the signal being passed but without clipping the inputs on the pre-amp/receiver when music is present? I have quite a few test records with all sorts of tracks, recorded at various levels, but no idea as to what levels are within spec from vinyl recordings and so which tracks I might use to push up gain, eg what is the maximum level of audio we should expect on vinyl?

Anybody have an objective method for doing this?

 

[mtemur]

I highly doubt that you can clip a high-end preamp’s input with vinyl playback equipment. Most phono preamps don’t even reach cd player standard 2V level. Could it be the phono preamp’s input you’re clipping?

 

[rDin]

I was listening to the Kevin Gray Kirsten Edkins earlier. On the PH-1000 with output gain +4, all is good. At +6 or higher, there is distortion in her sax. Drop back to +4 and it's clean again. This is what set me off thinking about optimising gain...

 

[mtemur]

I was listening to the Kevin Gray Kirsten Edkins earlier. On the PH-1000 with output gain +4, all is good. At +6 or higher, there is distortion in her sax. Drop back to +4 and it's clean again. This is what set me off thinking about optimising gain...

There could be a couple of reasons for that. IMHO the least possible one is clipping preamp’s input.

One of the possible reasons can be exceeding phono preamp’s maximum output voltage with +6dB setting.

For a reference gain adjustment you can use AP test record. Side 1 Track 1

 

[rDin]

I have that record, so will take a look.

 

[mulveling]

Agree with @mtemur, the preamp input would be my last suspect for clipping. Most high quality preamps put their attenuator BEFORE all circuitry, so that the volume control effectively protects it from clipping. You won't be in danger of the preamp circuitry clipping until long after the actual SPL from the speakers runs you out of the room. Sometimes they will specify this like "Max Input: INFINITE".

There are exceptions, but they should be rare. I can't fathom why anyone would design a preamp with any active stage before the attenuator, but apparently some do. I've heard reports (on audiogon forums) that the Cary SLP-05 might do this, but I can't confirm.

Anyways, the usual danger with selecting too-high a gain in a phono stage (for a given cartridge output level) is that you're cutting into the overload margins for the phono stage's own circuitry. This can make the sound quality harsh and grainy well before you hit overt clipping. It can also exacerbate the effect of pops and ticks from the record surface. On the flip side, I've had cases where the phono stage gain was too low (for a given cartridge) where the resulting sound was dull and dynamically flat. You really need to work to get in that "sweet spot" gain zone for a given cartridge. It's worth it!

 

[rDin]

You are both right. Just hooked up the output of the PH-1000 to the scope.

At +4dB gain, which I had been using - I'm getting average max 1.7v and no clipping warnings (over 2V) from fluctuations
At +5dB gain, avg max 1.8v, and no clipping warnings
At +6dB gain, avg 1.97v and continual peak over readings (over 2V)

Which matches my hearing distortion at +6dB due to the overs.

+5dB looks ok, but as you say less overhead.
+4dB is what I was using anyway and is safe and sounds good so far, with one question - the test signal is at 0VU - can music go higher than that? If so, by how much? I find the VU/dBu terminology confusing! If music can go higher than 0VU then I need to drop the gain further.

 

[mtemur]

You are both right. Just hooked up the output of the PH-1000 to the scope.

At +4dB gain, which I had been using - I'm getting average max 1.7v and no clipping warnings (over 2V) from fluctuations
At +5dB gain, avg max 1.8v, and no clipping warnings
At +6dB gain, avg 1.97v and continual peak over readings (over 2V)

Which matches my hearing distortion at +6dB due to the overs.

+5dB looks ok, but as you say less overhead.
+4dB is what I was using anyway and is safe and sounds good so far, with one question - the test signal is at 0VU - can music go higher than that? If so, by how much? I find the VU/dBu terminology confusing! If music can go higher than 0VU then I need to drop the gain further.

In analog medium signal can go over 0 dB. In digital 0 dB is the limit.

 

[rDin]

In analog medium signal can go over 0 dB. In digital 0 dB is the limit.

Quick google search throws up:

0 VU is equal to 1.228 volts RMS

So, perhaps this is the answer for quantitative setup - adjust the gain so the 'scope is showing 1.228vRMS with a 0VU test record. This then leaves the correct amount of headroom for the full analogue range?

edit: My peak of 1.7v at +4 gain above converts to 1.2021v RMS... perfect!

 

[MaxwellsEq]

Do you know what the input headroom is for the phono amplifier? It might be that "hot" cuts are making the phono stage itself run out of headroom.

 

[Alrainbow]

Some thoughts on clipping and pre inputs all pre inputs can clip this we know
Now what the maker says is not always accurate or too has more then just voltage to make things not sound well.
lower or higher gain needs to heard to
Make the preamp in it’s sweet spot on typical playback volumes
Too low lousy dynamics
Too high it’s not just possible clipping it’s bad sound
Hardness or other things
Analog needs to be at its best to be analog too low or too loud is bad analog

if the preamp has settings to change gain as well as phono pre it becomes a game we need to listen
And take notes same songs then we can move forward
vinyl has many loudnes pressings this too is an example of needing possible changes or a happy
Medium

 

[rDin]

Would be handy to have a list of some HOT albums which could be used to check and adjust gain, if necessary.

 

[rDin]

Do you know what the input headroom is for the phono amplifier? It might be that "hot" cuts are making the phono stage itself run out of headroom.

I don't.

 

[MaxwellsEq]

Would be handy to have a list of some HOT albums which could be used to check and adjust gain, if necessary.

I don't have a list, but this article is an interesting read. It also includes a picture of the "legendary" Shure analysis about real world maximum velocities:

Stereo Lab - Maximum recorded velocities on gramophone records

Stereo Lab Maximum recorded velocities on gramophone records

www.pspatialaudio.com

 

[Neil.Antin]

Stereophile measured the Gold Note PH-1000 Gold Note PH-1000 phono preamplifier Measurements | Stereophile.com. headroom varies with gain and frequency. Hugh Finnimore, Disc cutting in theory, Studio Sound and Broadcast Engineering, July 1975, page 68 shows 33 rpm/45 rpm velocity curves Studio-Sound-1975-07.pdf (worldradiohistory.com). The book PACVR Figure 45 – Record Groove Velocity, shows this a bit clearer.

 

[rDin]

Further to this - I put one input to the oscilloscope onto the phono stage, and one output on a line out from the amplifier. Then I fed a HOT record (Iron Maiden) through the system and watched both channels on the 'scope. I was able to see that when the phono stage output more the 4V, the signal through the amp got clipped (by the input of the amp). Adjusting my gain output on the phono stage I was able to set it just under 4V to maximise the signal received by the amp without clipping. Testing a bunch of other records, none then went over 4V output. Job done.

 

[mulveling]

Ah, ok. Looking at your sig, you list the "Bel Canto Black Ex" and Amp & Preamp. I assume that means you have the Integrated? It specs a maximum input of 2.2V RMS RCA. Which is 3.1V peak. So if you don't see input stage clipping until 4V, that's actually beating spec.

This is not typical configuration - most preamps & integrateds protect their input circuitry from overload conditions with an analog volume control up front. Then they can spec "infinite" max input level. In these cases the SPL from your speakers will most likely run you out of the room before you'd hit any observable clipping.

Most of us with analog volume controls don't have to worry about the OTHER side of the phono stage. But I'm glad you got it sorted

 

[Alrainbow]

Add to listening and compare to scope as well.
what good is it if it’s not clipping ona scope but is still not sounding well.

 

[rDin]

Add to listening and compare to scope as well.
what good is it if it’s not clipping ona scope but is still not sounding well.

All good so far.

 

[rDin]

Ah, ok. Looking at your sig, you list the "Bel Canto Black Ex" and Amp & Preamp. I assume that means you have the Integrated? It specs a maximum input of 2.2V RMS RCA. Which is 3.1V peak. So if you don't see input stage clipping until 4V, that's actually beating spec.

This is not typical configuration - most preamps & integrateds protect their input circuitry from overload conditions with an analog volume control up front. Then they can spec "infinite" max input level. In these cases the SPL from your speakers will most likely run you out of the room before you'd hit any observable clipping.

Most of us with analog volume controls don't have to worry about the OTHER side of the phono stage. But I'm glad you got it sorted

Yes, it's the integrated. I swapped my Mark Levinson 33H for the Bel Canto a few years back. Seems, in doing so, I created this problem for myself... but solved now so, onwards!

I can see the peak of a 1khz sine wave squaring off when I go over 4V on the input, so I know it's good up to that level.