DIY EAR 834p phono stage - a short evaluation/ test with those chinese PCBs

[Chris65]

John, not that easy to implement switches for the heater wiring with the PCB. Point to point wiring no problem but here, you have cut traces/lift tube socket legs & have a mess of wiring going to each switch.
Just not worth it in IMHO, use adapters if you can.

The original thread starter modified his PCB for the 6N2p, you see what he did in the photos. Then you can really only use that tube, as opposed to the many 12AX7 options.

[Jessica_K]

I think pin 9 should go to the centre of the bottom part of the switch with the bottom 6.3 rail to the right and gnd to the left. This would still provide 6.3V correctly to pin 9 for the 12AX7 and ground pin 9 for the 6N2P.

Using a DPDT switch would do the job with no "off" position.
Care would need to be taken to ensure all three switches are in the correct position before powering otherwise 36V would go across the heater of a 12AX7 if pin 9 is in the grounded position

Robert

[spaceistheplace]

Before implementing Roberts wiring diagram fully:



After:



Same conditions. I have way more gain than I'd ever need... so I just raised the volume to what would be ear splitting so I could get a "baseline" of noise for improvements.

The changes in tube rush is just because the graph refreshes quickly.

It's obviously not very scientific, however it illustrates that most of the lower frequency (read: not tubes) hum and noise has dropped by 10db+.

So, when I get a moment I'll type it up more clearly, make a better diagram and put it on the build guide.

[spaceistheplace]

John, not that easy to implement switches for the heater wiring with the PCB. Point to point wiring no problem but here, you have cut traces/lift tube socket legs & have a mess of wiring going to each switch.
Just not worth it in IMHO, use adapters if you can.

The original thread starter modified his PCB for the 6N2p, you see what he did in the photos. Then you can really only use that tube, as opposed to the many 12AX7 options.

At $2 or so ea. for mil spec tubes that are more or less 12ax7 with different pinout..... would you really want to use anything else?!

I have a stock of 12ax7 and variants already so I'm not really in a position to benefit, but the more I think about it and the more I learn I think the OP had the right idea.

[behind the rock]

Andy- I asked Robert to sim with the 6N2P seems everything checks out and will just be 1db lower gain. However, it will require a modification to V2 grid resistor for most accurate bass performance under 100hz. Currently it's 2M (as it comes) however we've inserted 680k to provide better 12ax7 response with the modified riaa values.

You should leave the 2M or use a 3.3m grid resistor. I might try this their quality looks very promising and they are dirt cheap. The difference in cost between an NOS 12ax7 of high quality is so great that it almost begs comparison.

Will you use an adapter or a switch? I'm thinking of implementing a switch to go between the two types as I'm not sure the chassis will accommodate the height of the adapter plus the tube.

If using a switch what type did you select? Have you done it or still in planning stages?

Here is a layout of the pin out changes to switch between the two tube types.

John, I have not yet decided on valves, but those who already use them have their pet reasons for choices made. You have lots of a particular type to hand, so it makes financial sense to at least start with them. I could go with any number of options that have been put forth here, simply because I need a starting point myself. Just today I was being swayed by a suggestion that ECC82 is a better sounding valve than the 83. At the end of the day achieving a working, low noise, low tube and signal ground hum free set-up is paramount. After that, play around a bit if you feel in the mood. I have a feeling that if I achieve a nice sounding set up straight off my curiosity will dampen considerably for changes.  It would need something off-putting to make a change.  Plus, how would I know if it is the valves sound characteristic at fault? 

Andy

[behind the rock]

BTW, I have trolled through this thread again(!) from start to finish almost and have written down a bullet point list. Now it will be subjective as to content as I skipped round some comments about peripheral ideas. I'm up to page 59 with the list.  When its complete would it be helpful to post it in some suitable format or send to an administrator so updating to it can be done once it is active on LH by others. I have ignored passing comments, including my own that may be praise for this or that build for instance unless it also contains pertinent information regarding the build in some respect. I thought of roughly grouping it into various themes such as "valve choice", RIAA values" and suchlike.  Would that be a help?  I could also include the super duper 834 thread replies.    I have found that I see something then flick past it, then next day I wonder where exactly it was.  maybe I should use the search facility better. 

Andy

[Chris65]

John's already done it Andy http://www.lencoheaven.net/forum/index.php?topic=26658.0

[Chris65]

At $2 or so ea. for mil spec tubes that are more or less 12ax7 with different pinout..... would you really want to use anything else?!

I have a stock of 12ax7 and variants already so I'm not really in a position to benefit, but the more I think about it and the more I learn I think the OP had the right idea.

No denying they are cheap John! Would you want to use anything else - well, yes. Depends what you might have, your desire/need to save a few dollars, etc. In my limited experience of using them, they are not obviously better or worse than 12AX7/ECC83 (in my gear, in my system, in my room.....)
Anyway, worth trying if you want.

Here's a wiring scheme for the heater switching, in line with what Robert mentioned:

           

[behind the rock]

Yeah, I know that but I've looked at all the thread responses.  John's list is the back bone of the build in most respects. But to take a few random examples that I have noted for a list with points of interest:-

P8 #108 :- Adding resistors to heater lines  keeping hum potential lower.
P10 #146 :- Valuation of various tubes tried.
p42 #618 :- Tweaked  RIAA values R & C.

Andy 

[Chris65]

Maybe mention those to John in the 'TRLH' thread & he can add/update his first posts regarding the build. Probably better to try & keep the info in one area (as tricky as that might be...!? )

[behind the rock]

Ordered some tubes, never thought I would be saying that a few years ago!  Bought Genalex Gold Lion ECC83's and 82.  That will get me started. 

Andy

[spaceistheplace]

Yes if you feel something is missing in my thread (it's still a bit incomplete, though) please post it there not here so I can keep track.

But I will try and steer away from providing too many options, or alterations which haven't been simulated or verified with measurements because it's too easy to be led astray by perceived differences in ones particular system.

Also, things which provide substantial cost savings will be noted as I don't want the build cost to get out of hand. That's part of the 6N2P appeal even though it doesn't do much for me personally at this stage.

Re: gems buried deep in the thread and listing listing page and #:

You can use the "quote" feature to reprint it. page numbers are different via mobile and desktop site or whatever forum application you might have.

Chris, I will likely stick with 12ax7s for now as my board can't take much more brutality without giving up the ghost entirely.

By the same token 3x 6N2P at $15 vs 3x selected Genalex Gold Lions at $120ish US may make this build more "doable" for some.

[spaceistheplace]

Regarding tube selection, V2 I think is the real kicker with the grid resistor that forms the other RIAA point. This effects only sub 100hz and depending on tube choice (within 12ax7 family) that could vary between 680-3.3M ish.

I'm not sure what tube characteristic causes this but again it's something that can vary by manufacturer within the 12ax7 family.... not 12au7, that's v3.

I believe Roberts 680k value was with a Sylvania 12ax7 in V2

Perhaps Robert can comment on this and we can chart it for some common options.

[spaceistheplace]

Ok here we go the revised grounding scheme diagram. This is the config I used that resulted in the substantially lower noise floor.

Fairly certain this is a reproduction of robert's more or less. Hope this helps. Took a lot of head scratching.

Once I sort out confusion of how to address switching with the RCA shields exactly I'll add to the build guide.

It's a lot of text so it will look small here to not break forum image rules. Follow this link to see full size.

[spaceistheplace]

Maybe mention those to John in the 'TRLH' thread & he can add/update his first posts regarding the build. Probably better to try & keep the info in one area (as tricky as that might be...!? )

Chris have you built one of these yourself yet? Nudge nudge, wink wink.