phono/preamp analog front end

What are you trying to achieve with changing your preamp?

Actually problem w phono section and getting it repaired. Just weighing options

Here's something to keep in mind.


Loading of low output moving coil cartridges is not for the cartridge- its for the preamp, but only if the preamp has problems with RFI. Cartridges generate RFI because they have inductance, which is in parallel with the capacitance of the tone arm cable. The resulting peak can be 30dB.


If the phono section has poor overload margins, this can also result in ticks and pops generated by the phono section rather than the LP surface!


If the designer has sorted this out then you will get less ticks and pops and it will sound right without the need for loading. Loading causes the cartridge to do more work, and so stiffens the cantilever, making it less able to trace higher frequencies, or affecting its mechanical resonance in the tonearm. This can result in the cartridge mistracking.

So its worthwhile inquiring about these issues; if you are told that the preamp has a loading switch, its a pretty good bet the designer hasn't thought this stuff through!

@atmasphere  Just so I understand, you're saying that all phono preamps that have a loading switch inherently haven't effectively dealt with RFI issues in their design?  

Just so I understand, you're saying that all phono preamps that have a loading switch inherently haven't effectively dealt with RFI issues in their design?  

Generally, yes, more to the point they've not sorted out how that peak affects the phono section. The loading resistor detunes that peak and so gets rid of the RFI and so the phono section sounds better (usually less bright). But the tradeoff is now the cartridge cantilever is stiffer so not performing as designed.


The thing is, if you talk to digital guys, they complain about ticks and pops. It turns out that many ticks and pops are generated by the phono section if it has poor RFI immunity and poor overload margins. This BTW is an epidemic in phono preamp design; I would think that anyone interested in LP playback would perk up their ears on this one!

sorry, fellas, but this is not my problem or concern

@atmasphere , with your statement above, I feel much better about my Allnic H1500se phono stage which I always felt was the best phono stage I have ever had in my system and it has no provisions for adjusting the load, I always wondered why. I quess my question to you is, should I feel good about that fact for the reason you stated? Thank you for your time and enjoy the music

I quess my question to you is, should I feel good about that fact for the reason you stated?

If its designed competently for LOMC cartridges, then there is no need for 'cartridge loading', so yes.

sorry, fellas, but this is not my problem or concern

If you found that you don't need to worry about cartridge loading in your system (doesn't sound bright with stock loading, and reducing the loading value does not help), then yes- I agree. Nor does the Classe DR6 have any such provision. But if you are looking at newer preamps the comments I made bear directly on this.

The Herron VTPH2A is in your price range. It sounds great, and I always hoped it was competently designed but never knew for sure until now- no loading switches! 

Whest makes a great SS phono amp. Check out their website for available models & professional / user reviews. 

@atmasphere 
Can you explain how the resistor loading makes the cartridge cantilever stiffer?  This absolutely does not make sense to me.

ARC Ref 2SE Phono gets my vote.  You'll have to pay a little more, but worth it.  There's one for $5500 at USAM - you could try and bring the price down a little.  It has a gain of 74 dB and balanced output. 

The Herron VTPH2A is in your price range. It sounds great, and I always hoped it was competently designed but never knew for sure until now- no loading switches!

The Herron uses external loading plugs, although the designer feels it sounds best unloaded. 

@sandthemall: I agree with you! I can't think of a way that resistive/capacitive loading can effect the stiffness (Young's Modulus) of a cantilever! 

Hi,
i can understand that energy has to go somewhere but still.

He doesn’t refer to the actual stiffness of the cantilever, but to the electromagnetic damping effect the loading applies, which affects the compliance of the moving system, I think...

@testpilot 

The Herron uses external loading plugs, although the designer feels it sounds best unloaded.

Interestingly I have always found my Herron to sound better with loading - and in fact at a loading usually very close to cartridge manufacturer recommendations.  I know some stages like Sutherland's Little LOCO uses transimpedance amplification so you never dial in the loading using a switch but there is still loading.  And then you have some Boulder stages that have fixed loading but with no switches.  It seems that @atmasphere is saying that only phono stages they don't present any cartridge load are properly designed...I'm still not totally understanding this, especially since the cart manufactures recommend a load.

I like the Tavish design preamps....I paired the classic with jensen transformer and running a hana el. The adagio comes fully equipped with the Jensen’s for more money....I think its Herb’s reference phono preamp....they are tube preamps made in NY USA....

Can you explain how the resistor loading makes the cartridge cantilever stiffer? This absolutely does not make sense to me.

Sure! All inductive electro-mechanical devices (like loudspeakers for example) have a magnet and a coil that interacts with that magnet. Now there’s a rule in electricity called Kirchoff’s Law which basically says that whatever energy you put into a system will be dissipated by that system. Its like Ohm’s Law in that it can’t be broken (unlike a speed limit); literally if you were able to get around it you would be creating Free Energy and with it a new branch of physics :) Seriously though, that’s the truth.


So in the case of a phono cartridge, normally it is driving a 47,000 ohm load which is the industry standard for the input impedance of a phono stage. Now let’s do a little math- if we put 5 millivolts into that 47000 ohm load, the resulting current is 0.00000011 amps. If we then change the load its driving to 100 ohms, then the current goes up if the voltage stays the same- it becomes 0.00005 amps; increased by a couple of orders of magnitude (since the resistance is reduced by a couple of orders of magnitude).


I used the 5mV number as an example. Obviously LOMC cartridges put out less voltage but are governed by the same rules.


If you multiply the volts times the amps you get watts. That’s the energy that the cartridge puts out. That comes from the cantilever, which is driven by the groove information interacting with that magnet. So now you’re asking it to put out a bit more energy and that energy has a price- whatever is causing it is going to be harder to move. In this case, the cantilever.


You can simulate this easily with any woofer. Without anything connected to it, its easy to move with your hand. But if you short out its terminals, it gets quite stiff! Try it sometime- this happens for the exact same reason.


Now I’ve known about the effects of loading, the RFI issue and the ticks and pops issue with phono sections for about 30-35 years. But I’d not really thought about the effects on the cantilever until Jonathon Carr (of Lyra fame) pointed it out to me in a conversation about loading we had at the Munich show in Germany a few years ago. Of course what we are talking about are very small forces, but the groove itself and some very audible changes that you can do by adjusting the cartridge are all microscopic. So this should come as no surprise.

It seems that atmasphere is saying that only phono stages they don’t present any cartridge load are properly designed...I’m still not totally understanding this, especially since the cart manufactures recommend a load.

They do- and its hard to say how many cartridge manufacturers actually understand what’s happening here. But some do (Lyra for sure), even so they won’t have any idea what phono stage the customer is going to use (nor for that matter the tone arm cable, whose capacitance is a variable in all of this) so they usually specify a ’load’ resistance regardless. But it should be understood that the actual correct value will vary from system to system as the tonearm cable capacitance and the input capacitance of the phono preamp are variables.


Here’s a link that gives a bit of info on how the resonant peak sets up:

http://www.hagtech.com/loading.html

@atmasphere  Thanks for taking the time to share your thoughts and provide the link.

Nice explanation by Ralph on this widely misunderstood phenomenon. One minor quibble:

atmasphere

Its like Ohm’s Law in that it can’t be broken (unlike a speed limit); literally if you were able to get around it you would be creating Free Energy and with it a new branch of physics :) Seriously though, that’s the truth.

While Ohm’s law remains valid for what most of us are likely to do, there are exceptions in what’s known as "non-Ohmic circuits." Examples of these include the common incandescent lightbulb and vacuum tubes. It’s all part of what makes electronics so tricky.

Some details about the principle are here, but none of it invalidates Ralph’s explanation about phono cartridge loading.