D3a Phonostage reloaded Assistance required

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Andrew
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#76 Re: D3a Phonostage reloaded Assistance required

Post by Andrew »

Hi Thomas, great stuff, looking at those plots I bet that amp sounds much better now.

Talking of microphonics, it amazing what damage vibration can do to something sensitive like a phono.

Some of the sensitive instruments at work with free running oscillators inside them have modules suspended on rubber mounts.

I keep meaning to work a decent way to replicate this on our designs.

cheers,

Andrew
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thomas
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#77 Re: D3a Phonostage reloaded Assistance required

Post by thomas »

Andrew wrote:Hi Thomas, great stuff, looking at those plots I bet that amp sounds much better now.

Talking of microphonics, it amazing what damage vibration can do to something sensitive like a phono.

Some of the sensitive instruments at work with free running oscillators inside them have modules suspended on rubber mounts.

I keep meaning to work a decent way to replicate this on our designs.

cheers,

Andrew
Ah my other millett mentor!

Yes all sorts of ideas about suspended boards, rubber mounts, chassis dampening pads and knicker elastic :shock: etc are running through my mind…. :D

I'm having second thoughts about this phonostage with my particular mm cart…..
I've now switched to an mc-and-sut set up and the sound seems more 'balanced', and more like the sound I am used to (only better…). It now seems just as 'musical' but has less 'sheen' / 'forward' / 'brightness' than with my mm (an AT150). Actually it now sounds very good if I say so myself.
My back-of-envelope calculations suggest the input capacitance of my old Thorsten stage was around 88pf (ecc83 with 100k load, 10m gridleak) ,whereas the D3a is a hefty 190pf , and I haven't added any cable to these figures yet. I reckon this may have made my mm a tad too bright for me, perhaps. The AT150 mm specifies 100-200 pf loading. Is this feasible?!
I have a hi out mc DL110 to try, but I'm now thinking D3a as pentode for my mm, as my next project….(thanks Stephen!)

All good fun :)
Last edited by thomas on Sun Jan 31, 2016 11:06 am, edited 1 time in total.
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#78 Re: D3a Phonostage reloaded Assistance required

Post by thomas »

IslandPink wrote:I'm sure the 20uF RIAA helps - I found more transparency, tone and dynamics in going from 105k to 20k .
Bear in mind the output caps may not need to be as big as 2.2uF . If you aren't driving anything worse then say 100k into the next amp you can run under 1uF , for instance 0.68 or 0.82uF , in which case you can use film/foils like the Mundorf ZN ( oh, did I ever mention I'm fond of MUndorf ZN's ? :D ) instead of metallised film.
Yes you may have mentioned them on occasion!

And yes the 2.2uf are somewhat 'hefty', and what I had to hand tbh. I'm eyeing up the Mundorf ZN 1uf s on hifi collective now though…. :)
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#79 Re: D3a Phonostage reloaded Assistance required

Post by simon »

This thread has really whetted my apetite to play with phonos again, good stuff Thomas.

Mechanical vibrations is an interesting topic. I think MJ used knicker elastic for his phono, or was that Philip@Bluebell? You can buy shock absorber mounts from Farnell etc. but I wonder if they're soft enough for a sensitive phono circuit.

I was looking on ebay yesterday for some sheet rubber to damp two small transformers in my DAC that buzz. After my initial surprise I searched for sheet rubber rather than just rubber... But what to choose? Butile, nitrile, neoprene, silicon, sponge, black solid hard. One or two gave the shore hardness but it was the equivalent of car tyres and I wonder if this is too hard? I thought I'd start with a bike inner tube but that might be just a little too soft.

Interesting topic, not sure we've experimented much with it???
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#80 Re: D3a Phonostage reloaded Assistance required

Post by IslandPink »

thomas wrote:It now seems just as 'musical' but has less 'sheen' / 'forward' / 'brightness' than with my mm (an AT150). Actually it now sounds very good if I say so myself.
My back-of-envelope calculations suggest the input capacitance of my old Thorsten stage was around 88pf (ecc83 with 100k load, 10m gridleak) ,whereas the D3a is a hefty 190pf , and I haven't added any cable to these figures yet. I reckon this may have made my mm a tad too bright for me, perhaps. The AT150 mm specifies 100-200 pf loading. Is this feasible?
Extra input capacitance is more likely to make the cart sound dull, than bright , Thomas.

Other notes :
Should edit my post about "20uF RIAA" - that doesn't make much sense !

Soft-mounting of valves : somewhere there was a thread about this, my bright idea was to use "3mm well nuts" to mount octal and loctal valve sockets into a chassis . I haven't put it into action yet on a phono, but the 4P1L driver valves on my 300B amp have this method.
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#81 Re: D3a Phonostage reloaded Assistance required

Post by IslandPink »

This was it, but I see my idea didn't get much 'traction' ( except for Thomas Mayer :wink: ) :
http://www.audio-talk.co.uk/phpBB3/view ... =compliant
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pre65
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#82 Re: D3a Phonostage reloaded Assistance required

Post by pre65 »

I remember that topic. :)

Is there a boing scale ? :lol:
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thomas
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#83 Re: D3a Phonostage reloaded Assistance required

Post by thomas »

IslandPink wrote: Extra input capacitance is more likely to make the cart sound dull, than bright , Thomas.
:oops: Well I imagined it would knock the top top end down but for some reason I thought it effectively 'lifted' the mids/ low highs….. :oops: I'd better do some further reading…...
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Nick
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#84 Re: D3a Phonostage reloaded Assistance required

Post by Nick »

I found a copy of IEC61938 here

https://law.resource.org/pub/in/bis/S04 ... 2.2005.pdf

For high output cartridges it states amplifier input should be 47k and 220pf (page 18), this talks about the issues:

http://audio-forum.gspaudio.co.uk/phono ... ic992.html
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#85 Re: D3a Phonostage reloaded Assistance required

Post by thomas »

Nick wrote:I found a copy of IEC61938 here

https://law.resource.org/pub/in/bis/S04 ... 2.2005.pdf

For high output cartridges it states amplifier input should be 47k and 220pf (page 18), this talks about the issues:

http://audio-forum.gspaudio.co.uk/phono ... ic992.html
Oh my, fascinating reading but in a way now I'm even more confused!

Obviously the sorts of things I've read in the past, a brief search brought up this straight away-
http://www.hagtech.com/loading.html
was enough to suggest to me that for your average mm 'lower capacitative loading was best' ….. now Graham Slee points out that cantilever resonance should cancel out the peakiness….

…I'd better put another record on!
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#86 Re: D3a Phonostage reloaded Assistance required

Post by Mike H »

pre65 wrote:I remember that topic. :)

Is there a boing scale ? :lol:
I did try Maplin rubber couplings as anti-microphonic mounts, trouble was once there's four of them to a board or panel (one at each corner) they're so solidly mounted might as well have used metal pillars. Best I've seen is small grommets very loosely supported on rods, or even flat strips.
 
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#87 Re: D3a Phonostage reloaded Assistance required

Post by cressy »

Andrew wrote:Hi Thomas, great stuff, looking at those plots I bet that amp sounds much better now.

Talking of microphonics, it amazing what damage vibration can do to something sensitive like a phono.

Some of the sensitive instruments at work with free running oscillators inside them have modules suspended on rubber mounts.

I keep meaning to work a decent way to replicate this on our designs.

cheers,

Andrew
On my nuvistor phono stage that you guys did the riaa correction for for me i built the circuit up in veroboard and hung it from 4 turrets like a td 150 or an lp12.
The top of that section of the case is perforated steel for ventilation with the turrets through it, the board then sits on little silicone blocks instead of the lp12 style springs.
Seems to work well.
I filled a steel tube with white bathroom silicone, let it cure for a couple of days so it all went solid, removed it and cut it into the blocks.
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#88 Re: D3a Phonostage reloaded Assistance required

Post by jack »

The silicone sealant method is a very good one - you can embed nuts (with temporary bolts in the to keep the threads clear) or bolts in the mould to allow them to cure in-place - I've found that a very thin smear with Vaseline on the mould helps...

Used this method a while back for another project (an amateur seismograph) as the cost of commercial small anti-vibration mounts is in the order of £1.50+ each in qty. ISTR that we used a Polymorph plastic (Rapid 87-0091) mould ...
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thomas
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#89 Re: D3a Phonostage reloaded Assistance required

Post by thomas »

Well I've had another crack at a D3a phonostage, this time reducing the impedance network to around 15K. Valve selection seemed quite important at this level, the slightly higher ra of the Russian 6j52p seems apparent (and sample variation all over the place….) so I ended up bunging in some e180f's for the second stage.
Rather than squeezed in a box I've left this rather umm open plan so I can play with capacitors etc. and the microphonics seem to be much reduced.
I'm rather pleased with this one...
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thomas
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#90 Re: D3a Phonostage reloaded Assistance required

Post by thomas »

….and it measures OK…
Think I'll bring this one to Owston….
Top graph shows 1kHz test at 1mv
Lower graph shows control millett loop (blue) and channel matching.
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Last edited by thomas on Sun May 29, 2016 7:20 am, edited 1 time in total.
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