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  #71  
Old 21st February 2014, 10:58 PM
Richard Richard is offline
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Default Re: Phono 3 with 5751 valves

Hi, I used a 0.1uF Soniqs there (standard value on the Phono 2 and 3) but you can't get them in smaller values. Give it a go perhaps unless you have problems with low frequency warp or cart/arm matching. The cathode bypass caps on the first stage are also well worth trying
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  #72  
Old 22nd February 2014, 12:49 PM
bevensee bevensee is offline
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Default Re: Phono 3 with 5751 valves

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Originally Posted by Richard View Post
Hi, I used a 0.1uF Soniqs there (standard value on the Phono 2 and 3) but you can't get them in smaller values. Give it a go perhaps unless you have problems with low frequency warp or cart/arm matching. The cathode bypass caps on the first stage are also well worth trying
Hi Richard, and thanks again for the advise. I have already added the first stage bypass caps, and I built it with GE 5157 from the beginning. The bypass caps are marvelous once settled!

I have no problems with conflap. I run an Ortofon Rondo Bronze on an Audiomods (what a thing of beauty!) on an Orbe. Iy sounds very good indeed. Even though I have no problems with coneflap, I do occatioannly get low freq. rumble from old records bourght second hand. Therefore, I would like to cut the subfrequencies. Also, there is no music on the record that low anyway...

I think to begin with; I will just go with the 0.022 uF and bypass the switch. I never really liked the switch since you have to be careful not flicking it with the volume cranked up.
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  #73  
Old 22nd February 2014, 01:17 PM
Richard Richard is offline
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Default Re: Phono 3 with 5751 valves

Hi, yes that sounds a good plan and you'll find a single cap can use 2 of the pcb holes to link across where the 3 caps used to go thereby taking out the switch.

You will notice if you put 0.022 and 1M into the filter calc it gives a corner f of 7.2Hz. In fact none of the cap values or combination appear to tie in with what we'd expect for a simple coupling. Yet the original design article for Phono 2 said they did, suggesting 0.015uF for 10Hz, 0.0082uF for 20Hz and 0.0039uF 40Hz could be used. If you'd like the original article send me a PM with your email address and I'll email a pdf.

When the kit came out though that had been changed to 0.1uF. The filters through an amp are cumulative so possibly it was found to need adjustment on test. (I checked mine, shown in the first post with bypass caps and 5751, using a reverse RIAA filter gen and scope and it is fine following the Hagerman curve down to LF.)
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  #74  
Old 22nd February 2014, 05:36 PM
bevensee bevensee is offline
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Default Re: Phono 3 with 5751 valves

Hi Richard, I will send you a PM with my e-mail. Thanks!

I thought the load was supposed to be calculated as the coupling parallel to the rest of the amp and not just the 1M?
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  #75  
Old 23rd February 2014, 12:44 AM
Richard Richard is offline
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Default Re: Phono 3 with 5751 valves

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I thought the load was supposed to be calculated as the coupling parallel to the rest of the amp and not just the 1M?
Yes, how did you get to 0.022uF for 20Hz?
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  #76  
Old 23rd February 2014, 10:04 AM
bevensee bevensee is offline
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Default Re: Phono 3 with 5751 valves

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Yes, how did you get to 0.022uF for 20Hz?
Well, I didn't exactly make any calculation because I was a bit unsure of how to calculate the load. I therefore looked at the original diagram, and 0.022 is what you get in the middle position where 0.01 and 0.012 are added. Since the middle position works for me in the sense that it seems to reduce the rumble of these problematic records without really reducing useful bass range. Besides, this would be a easy and reversible way for me to go as the caps I would need are already there. Doing this will allow me to simply take the switch out, i.e. only change one thing at a time. Later on, I can try with other caps to see if it will make a difference to me.

So I suppose the mthodeology is something like "a pragmatic apporach to what's on the shelf..."
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  #77  
Old 23rd February 2014, 11:04 AM
Richard Richard is offline
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Default Re: Phono 3 with 5751 valves

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Originally Posted by bevensee View Post
Well, I didn't exactly make any calculation because I was a bit unsure of how to calculate the load. I therefore looked at the original diagram, and 0.022 is what you get in the middle position where 0.01 and 0.012 are added. Since the middle position works for me in the sense that it seems to reduce the rumble of these problematic records without really reducing useful bass range. Besides, this would be a easy and reversible way for me to go as the caps I would need are already there. Doing this will allow me to simply take the switch out, i.e. only change one thing at a time. Later on, I can try with other caps to see if it will make a difference to me.

So I suppose the mthodeology is something like "a pragmatic apporach to what's on the shelf..."


Well, as you say, there's a parallel load of 316K +39K +reactance of 8.2nF (970K at 20Hz). For 20Hz that brings the 1M down to 570K. The coupling cap which gives -3dB 20Hz with 570K load is 0.014uF so we'd use preferred value 0.015uF. That may be the wrong way to look at it which is why I wondered if you had a method

In the original notes 0.015uF was used but it said that was for 10Hz.

In the Phono3S 0.015uF is used as the lowest cap value to which the others are added so must be the 40Hz setting.

Hence my wondering if the later values were chosen on test.

Anyway, I built Phono3S and only ever used it on the lowest switched frequency (whatever that was!) as the other 2 seemed obviously light compared with CD. When a friend wanted Phono3S, and I was not using the MC input, I sold it to him and built another for MM using the 3S pcb in a regular unswitched case which is the circuit at the start of this thread.

Your pragmatic approach seems the best if you've already found a setting you like but it's interesting to try and understand these things isn't it! It was getting late last night but I'll dig out that article and email it in a minute, cheers, Rich
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  #78  
Old 24th February 2014, 09:43 AM
bevensee bevensee is offline
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Default Re: Phono 3 with 5751 valves

Richard,

Yes it is interesting to get a better understanding of these things. I actually started reading the Morgan Jones book this weekend for the same reason :-). Thanks for the articles; they are nice.

Last edited by bevensee; 24th February 2014 at 09:43 AM. Reason: typo
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