Phono input capacitance

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Graeme
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#1 Phono input capacitance

Post by Graeme »

I don't really understand this, but it's becoming apparent that I could do with at least understanding it a little.

Since I've had this decca cart I've been trying to tame an element of its sound by adjusting loading, effective mass, set up etc but nothing was working.

It sort of sounded like it was maybe ringing in some way. Almost like what i imagine an overly loud or badly matched super tweeter would. Hard to put my finger on it as it wasn't something you could hear as such, just something that made listening tiresome.

I then read somewhere that some people add 200-500pf capacitance to tame it a little. The reviewer said this made no difference to his but adding 10,000pf did.

I had a route through my boxes and found some 3300pf polystyrene caps and just put them across the input of my Phono 3 clone.

Low and behold, it's sorted it right out.
Not only has the tiresome edge gone but it seems to sound more open and have more space around the sounds. It all sounds more natural too.

So considering folk seem to want to keep input capacitance to 200pf or so, and everyone seems to be concerned about low capacitance Phono leads etc, what's actually going on here?

It doesn't in any way seem to have been detrimental to the sound.

If it's going to stay having a big dollop of extra capacitance across the input, what kind of caps should I be using ideally?
Thanks.
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Toppsy
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#2 Re: Phono input capacitance

Post by Toppsy »

I don't really understand this, but it's becoming apparent that I could do with at least understanding it a little.
Does this link help any? http://www.hagtech.com/loading.html
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#3 Re: Phono input capacitance

Post by Graeme »

Toppsy wrote: Tue Mar 02, 2021 5:39 pm
I don't really understand this, but it's becoming apparent that I could do with at least understanding it a little.
Does this link help any? http://www.hagtech.com/loading.html
It will certainly help me understand what should be going on, thanks. I'll read it properly after dinner.

What I don't understand though is why my cart needed 10x the capacitance you would expect.
Maybe once I've fully understood what's in that link I'll have an idea about that too.

Thanks.
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#4 Re: Phono input capacitance

Post by Graeme »

The site won't allow me to copy the text, apparently showing his writing to other people is theft or something 🙄
Bit this is the article that made me try adding capacitance, he talks about it around 2/3rds of the way down the page.

http://www.adventuresinhifiaudio.com/23 ... cartridge/
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Toppsy
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#5 Re: Phono input capacitance

Post by Toppsy »

The site won't allow me to copy the text, apparently showing his writing to other people is theft or something 🙄
Graeme, I have just copied the whole text of that Hagerman Technology link using the Ctrl 'c' to highlight it all then posting it into a blank page of MS Word using Ctrl 'v'. It has fully copied over. I have saved it on my laptop but not sure how to attach a 'word' document onto the forum thread?
Graeme
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#6 Re: Phono input capacitance

Post by Graeme »

Toppsy wrote: Tue Mar 02, 2021 6:30 pm
The site won't allow me to copy the text, apparently showing his writing to other people is theft or something 🙄
Graeme, I have just copied the whole text of that Hagerman Technology link using the Ctrl 'c' to highlight it all then posting it into a blank page of MS Word using Ctrl 'v'. It has fully copied over. I have saved it on my laptop but not sure how to attach a 'word' document onto the forum thread?

Sorry, I wasn't very specific.
I was trying to copy the relevant part of the link I posted so you could see what the reviewer had to say about having to ad 10000pf capacitance, but he is very protective of his content.
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Mike H
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#7 Re: Phono input capacitance

Post by Mike H »

Nuts, every browser can Save Page As, or do what Toppsy did. Anyway he was saying he put 10nF on his Decca cartridge to curb the shrill treble artifacts, and thought it may be specific to that one example.
 
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Graeme
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#8 Re: Phono input capacitance

Post by Graeme »

Mike H wrote: Tue Mar 02, 2021 8:59 pm Nuts, every browser can Save Page As, or do what Toppsy did. Anyway he was saying he put 10nF on his Decca cartridge to curb the shrill treble artifacts, and thought it may be specific to that one example.
He also said the maths of adding that much capacitance makes no sense. Doesn't go into any more details than that though.
That sort of made me wonder what happens, sonically or electrically, when you add loads of extra capacitance, more than it should in theory need.
If it sounds better, did it just inexplicably need it, or is it covering something up, or is it a case of it just means you have enough capacitance now and the extra serves no purpose. Like pouring 10L of water into a 500ml glass, you still end up with 500ml of water, the rest was just wasted overkill.

I've not had chance to go through toppsys link yet, maybe once I've been through it I'll understand.
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rowuk
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#9 Re: Phono input capacitance

Post by rowuk »

Well, caps pass high frequencies. The bigger the cap the lower the frequency where it takes effect. Putting it across the + and - of a cartridge channel, just means that it is shorting high frequencies to ground with a phase shift. The output impedance for "most" DECCA cartridges is 4400 Ohms. 10,000pf across that is off the top of my head around 36kHz. If that improved something, It sounds like there was some serious HF getting in (radio station? smps?). In any case, there are certainly less intrusive ways to fix something like that.
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Graeme
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#10 Re: Phono input capacitance

Post by Graeme »

rowuk wrote: Wed Mar 03, 2021 8:03 pm Well, caps pass high frequencies. The bigger the cap the lower the frequency where it takes effect. Putting it across the + and - of a cartridge channel, just means that it is shorting high frequencies to ground with a phase shift. The output impedance for "most" DECCA cartridges is 4400 Ohms. 10,000pf across that is off the top of my head around 36kHz. If that improved something, It sounds like there was some serious HF getting in (radio station? smps?). In any case, there are certainly less intrusive ways to fix something like that.

This is very interesting! Thanks.
Fits in with what I was saying about it previously sounding like it had a badly matched supertweeter.
There just seemed to maybe be a load of high frequency information that you couldn't really hear, but made the sound overly alive and would stress my head after an hour or so.
Only this cart has done this.
There may well be an issue with the cart , it's going in for a clean, check and recalibration soon so that may show problems up.
In which case I may then be able to remove the caps.

Other than blocking high frequency, would it have any other bad effect? It certainly doesnt seem like it.

If the cart for whatever reason was chucking loads of random HF out, the huge metal dome tweeters in my tannoy would certainly let me know about it!
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Nick
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#11 Re: Phono input capacitance

Post by Nick »

That's ignoring the effect the cap may have on the generator. It may be the reducing load with frequency is damping the cart at those frequencies.
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#12 Re: Phono input capacitance

Post by Graeme »

Nick wrote: Wed Mar 03, 2021 8:33 pm That's ignoring the effect the cap may have on the generator. It may be the reducing load with frequency is damping the cart at those frequencies.
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It does feel (sound) like rather than just removing something, the cap is letting the cart behave better. The sound has improved, as well as now being almost free of the annoyance it had.
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rowuk
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#13 Re: Phono input capacitance

Post by rowuk »

Something else popped into mind: Which Decca ist it? The Decca London is a variable reluctance cartridge that is designed to work with a phono corrector that has a lot of headroom. It puts out 5mV (more than many MM cartridges). It is possible that it is overdriving your front end causing serious distortion. Just perhaps, the big cap is reducing the output level where the distortion is worst.
I looked the AR Phono3 up. The specs say that it is supposed to work with up to 240mV inputs. This would not support the overdriving theory.

A last thought, if the cartridge does not work well in your arm, there can be HF "hash" messing the sound up.

Here is a good place to figure out what should work:
https://www.vinylengine.com/cartridge_r ... luator.php
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