Reducing phono gain?

Suppose I wanted to reduce the gain my amplifier sees from the phono stage. What would be the best way to do this with the absolute minimum degradation of sound quality. It would not need to be adjustable. Is a high quality potentiometer the way to go, or should I look into a simple voltage divider (is that the right thing). A pair of step up transformers in reverse? Am I making any sense at all?

Judd

 

how about a phono stage with adjustable gain? many such exist.

 

RCA attenuators

"Harrison Labs 12 dB RCA Line Level Audio Attenuator Pair" from www.parts-express.com!

 

You do NOT want to put an RCA attenuator in circuit with phono level input. It will have a major impact on the sound; consider that even adding 5 feet of rca cable and 100pf of capacitance can cause 5dB of response difference in the high frequencies.

On the output of the Rega Fono preamp you list in your profile, such additions are fine, and you could indeed mod inside the preamp box with a simple voltage divider dumping half the voltage to ground with a minimum 10k resistor network.

A clever person might even be able to mod the preamp, identifying the resistor(s) that set the op-amp gain and connecting a dual-pole pot in series or parallel to change the value.

 

5 dB? Do you have a source for that?

 

Yes, in this case the attenuation would be between the phono section and the integrated amp. I'll be using the Ifi Phono 2 (coming this week) into the back of a tube amp. The cartridge looks to be a medium output MC (0.9 mV). The Ifi is adjustable gain (I can do 48 or 60db in this case). They are recommending 60db for a cart that is 0.3 to 1.2 mV. And 48 for 1.3 to 4.9. I am concerned that the 60 will be too much for my line stage - it seems it is very sensitive to being overloaded). And 48 will be too little. Hence, plans for a simple attenuator that would knock off 5db, for instance.

Judd

 

Just use the 48 db setting. That's too much for any MM cart but would work well with the the odd medium output cartridge that you are getting. It makes life a lot easier and allows many more options to keep things to the simple standards such as 36db for typical MM and 60db for typical LOMC. The 48db will come in handy for the oddball cartridge but will not work as well with most others.
-Bill

 

iPhono2 has four gain settings from two switches, but you have to find a hi-res screenshot of the unit to suss them out; the manual doesn't depict them:
http://ifi-audio.jp/_src/sc2848/iphono2-05.png

MM <-> MC switch: 36db <-> 60dB
+12dB switch: adds 12dB to this

MM input has a selectable capacitance; MC input instead a selectable impedance, but it seems the gain setting is common to both.

I also agree that one of the settings will work; LPs also vary by 12dB, so you can't expect to match other components. 12dB = 3x the apparent volume. The receiver's line in will have a much lower self-noise than the noise made by the phono preamp, so you aren't losing anything by setting the preamp well below the max line input level.

Here's two of the PC boards inside the iPhono2's box, showing the the front and back (doesn't look like a $500 bill-of-materials for something made in China, btw), one might even be able to trace the +12dB switch and change the component values that the switch puts into effect, to take the 48dB setting to 54dB, for example:

 

Just a quick google image search of this forum gives:




When your DAC or amp is -0.05dB 20Hz-20kHz, these variances from phono loading are pretty wild.

 

How about this?
Schiit Audio, Headphone amps and DACs made in USA.

 

Wait, you'll be using the Ifi into a tube amp? What's the input sensitivity of the tube amp? The tube amp is the integrated? What tube device are you talking about? In your profile I seem the Naim Nait XS-2 listed as your integrated -- what additional tube amp are you planning to stick between the phono pre and the intergrated and why, or are you/have you replaced the Naim? You say your line stage is easy to overload, do you mean the Nait XS-2? The input sensitivity spec on that suggests it is pretty sensitive at 130 mV. Maybe, if you're overloading that with any kind of regularity with multiple sources you should be looking into a less sensitive integrated; or if you're sticking an extra tube line stage ahead of the integrated, just pull that out. Who is the "they" recommending 60 dB of gain for a 0.9 mV output cart. Around 50 dB of gain would probably be more like it. You might be a little low with 48 dB of gain, maybe you won't have optimal SNR or the most possible punch and low frequency slam, but especially with the phono pre feeding a sensitive line stage with gain of it's own, 48 seems a perfectly reasonable choice and you know better 2 or 3 dB less gain than 8 or 10 dB too much gain. If you want "minimum degradation of sound quality" then don't stick extra attenuators in line, just use the 48 dB gain setting.

 

No. I am no longer using the Nait XS2 (I need to update my profile). My current integrated is the Leben CS300XS, and I have found it's easy to over-drive - and its get aggressive when overdriven even at low volumes - the high end becomes uncouth. In this case, I have the Ortofon 2M black (5mv) into a Rega MM Fono (which I believe is 42 db of gain). That's too much into the Leben. Into the Naim, no issues at all.

The Schiit Mani has a 30 db gain setting, and this is perfect into the Leben when driven by the 2M. But as a device, the Schiit Mani is noisy and I'm not happy with it. And it does not sound as good as the Rega unit (when driving an amp that can manage it, such as into the Naim, for instance).

So I upgraded to the Ifi phono 2, which has a 36 db setting. I've only got about 2 hours on it. I'll have more to say on this in another thread. But I would say as a preliminary matter, 36 db is too much gain when drive by 5mv into the Leben as well. I only have access to the about 10:30 on the volume control.

I should add that I have not purchased the medium OP MC I anticipated (0.9mv). It's up in the air.

Judd

 

I have this already.

Judd

 

That shouldn't be. The Leben ought to be able to handle a much higher input signal level before clipping than the Naim based on the input sensitivity specs for the amps. Are you sure the distortion is not output stage distortion? That's a pretty low power integrated. The spec says 15W, but also say the thing is pushing clipping at 10W (.7% THD at 10W), and that's probably with a fixed 8 ohm load. If you're trying to drive speakers that drop below 8 ohms and/or have acute phase angles, and/or are not very efficient, you may be reaching clipping pretty quickly with that integrated, but not by overdriving the input stage, by asking too much of the output stage. If you're really overdriving the input stage on that with the output from a phono pre, there's something wrong. Maybe try fresh, known good tubes. But are you sure your problem with distortion is at the input, not the output stage? What speakers are you using? What's the lowest impedance that the speakers reach and at what frequencies and with what phase angles? Does that integrated have a pre-out and the NAIM a power-in? Might be instructive to see if it's the input or output stage where you're having the problem.

 

Check out the used gear section of this forum...lots of phono preamps that would fit your needs. I have a medium output cartridge and 52-54 db is about perfect.

This one would be a much better choice (IMO)

http://forums.stevehoffman.tv/threa...tage-with-hc-1-dual-mono-power-supply.660719/

Sorry wrote this up before I read you already made a purchase...but others may find this info valuable.

If you can score Acoustech Sutherland PH1-P used, it is my phono preamp and it is very good for the used price point

http://forums.stevehoffman.tv/threads/acoustech-sutherland-ph1-p-phono-pre-mm-mc.650903/

 

The Leben is 15 watts per channel. I drive a pair of Rega Rx-5,'s which are 89 db/w/m and a fairly constant 6 ohm load. Driven by a cheap blue tooth adaptor (interfacing wirelessly with my phone) or an apple airport expressed, for instance, it sounds GREAT with useable volume from about 9 o'clock to 1 o'clock on the volume control. Beyond 1 o'clock, it too loud to tolerate and it begins to clip anyway.

My 2M black into a phono stage with 30db of gain is also perfect, with good range of use of the volume control. No clipping till way too loud. On the other hand, the 2M black into the Rega phono (at 42 db) is too much gain for the Leben. It is uncomfortably loud at 9:30 on the dial, clipping at 10 o'clock. And just ragged all around.

I feel this is just that combination of a 5mv cartridge into a stage with 42 db of gain is too much for the input stage, and overloads it. It works fine on the Naim because nothing is going to upset a Naim.

The Leben sounds great - no issues with almost every combo. I just don't think you can drive it with such a high OP cart into a fairly high gain stage.

 

I should add - I don't know if it's the input stage or the output stage that is being overdriven. All I know is that when the signal is too hot at the input, I run into problems. 5mv output on a cart is quite high. Combined with 42db of gain, it's too much. The Leben doesn't like it.

 

Well, yeah 42 dB of gain is a lot more than you'd need for a 5 mV cart. 35 dB would be more like it. And I suspect that 48 dB would be OK with a 0.9 mV cart. The Leben line stage must have a lot more gain than the Naim line stage.

I wonder if the Leben would work with 5751s in place of the 12ax7s in the line stage, that could reduce the line stage gain considerably, but that's not a sub that works perfectly in all cases.

 

Just get a Phonomena baby!

 

I use these and have been very impressed:

Attenuators



Rothwell attenuators [English]