D3a Phonostage reloaded Assistance required

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Cressy Snr
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#91 Re: D3a Phonostage reloaded Assistance required

Post by Cressy Snr »

Look forward to hearing it Thomas.
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thomas
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#92 Re: D3a Phonostage reloaded Assistance required

Post by thomas »

Oh Fanks!

Likewise watching your latest behmoth with interest….
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IslandPink
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#93 Re: D3a Phonostage reloaded Assistance required

Post by IslandPink »

It's about time we had another open-plan phono breadboard to inspect :D
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jack
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#94 Re: D3a Phonostage reloaded Assistance required

Post by jack »

Very interested!

..but not a little scared :)
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thomas
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#95 Re: D3a Phonostage reloaded Assistance required

Post by thomas »

IslandPink wrote:It's about time we had another open-plan phono breadboard to inspect :D

Actually I feel its rather disappointingly orderly and tidy (for me). Fortunately my accompanying px25 amp is more umm discordianistic….
Amazing place this forum for learning new ideas. Is that a real word I wonder….
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#96 Re: D3a Phonostage reloaded Assistance required

Post by Andrew »

Cressy Snr wrote:Look forward to hearing it Thomas.
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thomas
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#97 Re: D3a Phonostage reloaded Assistance required

Post by thomas »

OK so here is the schematic of the phonostage I brought to Owston again.
It's nothing new. The network impedance was designed to be around 15K. This was problematic as at these levels valve sample variation was all over the place. I used an online network calculator as the starting point, here; http://www.mh-audio.nl/calculateRIAA.asp and paralleled up bunches of resistors, eg 27k, 47k and 75k to get the 13k85, etc.
Warning!! I wouldn't try building it unless you are prepared to match valves for u and ra, and spend hours tweaking the network whilst measuring it through an inverse riaa. This project persuaded me I had to have the Dekker valve tester! Those D3a's want about 20 mins warm up before they settle, too.
The reason I used e180f's for V2 was because I had a reasonably matched pair. You could also use 6J52p for V1 or V2 but I found the ra of these were a bit higher and I'd have to re tweak the network.
Really it has a high input capacitance ( about 190uf) but the output impedance isn't bad (about 1k6?) - I toyed with another e180f on the end as a cathode follower with a ccs under it but it didn't seem to need it.
If anyone wanted to build something like this I'd advise settling for a 25k+ network version....
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pre65
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#98 Re: D3a Phonostage reloaded Assistance required

Post by pre65 »

thomas wrote: Thu Jun 15, 2017 3:16 pm
Warning!! I wouldn't try building it unless you are prepared to match valves for u and ra, and spend hours tweaking the network whilst measuring it through an inverse riaa.
Are u and ra, when matched, likely to remain in sync for the life of the valve ?
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izzy wizzy
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#99 Re: D3a Phonostage reloaded Assistance required

Post by izzy wizzy »

thomas wrote: Thu Jun 15, 2017 3:16 pm If anyone wanted to build something like this I'd advise settling for a 25k+ network version....
In mine I had the anode load as 4k7 and used a network with about 21k series R. Dunno what the bias is with an LED as I used n AAA alkaline on the grid.

And then I used the D3a as a pentode which IMHO was a better bet.

I should add, I don't measure things so have no idea how accurate it was as I simm'd it, didn't calculate anything as I find that almost impossible with all the variables - there are way more than you would imagine which no calculator I've seen can take into account esp at the low end.

cheers,

Stephen
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#100 Re: D3a Phonostage reloaded Assistance required

Post by Mike H »

izzy wizzy wrote: Thu Jun 15, 2017 7:02 pm And then I used the D3a as a pentode which IMHO was a better bet.
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thomas
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#101 Re: D3a Phonostage reloaded Assistance required

Post by thomas »

izzy wizzy wrote: Thu Jun 15, 2017 7:02 pm
thomas wrote: Thu Jun 15, 2017 3:16 pm If anyone wanted to build something like this I'd advise settling for a 25k+ network version....

And then I used the D3a as a pentode which IMHO was a better bet.


cheers,

Stephen

Yes I made a leisurely start modifying one of my earlier efforts to do this, err a few months back....
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izzy wizzy
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#102 Re: D3a Phonostage reloaded Assistance required

Post by izzy wizzy »

thomas wrote: Fri Jun 16, 2017 8:46 pm Yes I made a leisurely start modifying one of my earlier efforts to do this, err a few months back....
:) - nice 'n slow. Don't want to upset anything in there.

Just sim it. Solves all the issues I think. Not sure if you're a sim'er?

Do one channel. Compare it to the other one by monoing the input signal. Pentode has a little more gain tho.

cheers,

Stephen
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IslandPink
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#103 Re: D3a Phonostage reloaded Assistance required

Post by IslandPink »

Stephen, do you feel the pentode is more tolerant of the reactive load of the RIAA ?
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izzy wizzy
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#104 Re: D3a Phonostage reloaded Assistance required

Post by izzy wizzy »

IslandPink wrote: Fri Jun 16, 2017 10:05 pm Stephen, do you feel the pentode is more tolerant of the reactive load of the RIAA ?
I don't really know. Just not knowledgeable enough to say. I guess it must tho being high Z out. As you probably know, the pentode drives the EQ in a different way. I hear it as easier with less fuss and better high end detail. The triode sounds a bit more closed in and darker (still nice) but ...

I could imagine if it was voiced bright for the triode, the pentode could be a bit much. Having the cutter lather time constant could make the pentode unbearable (I did and now don't - can make the triode sound "better") The lathe time constant is another that can't be calc'd properly either IMHO.

I don't voice my circuits or tailor them to my taste with cap types, resistor types, valve rolling and so on. Oh oh, there goes any credibility I might have had :) I've learned I dislike metalised caps, bypass caps and regulators which some folk like for the "detail" and "punch" if that means anything so maybe that's why I like the pentode? I don't think so but it's possible.

To make things worse, I only sim, don't measure the circuit or the parts. I only use low to very low tolerance parts and cross fingers it goes and sounds nice/right to my ears.

cheers,

Stephen
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IslandPink
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#105 Re: D3a Phonostage reloaded Assistance required

Post by IslandPink »

Yes I didn't spend any time measuring my phono, just measured parts and as you say, things like D3a's are tight tolerance. When I looked at values for pentode-driven first stage I remember that 3k or 4k anode load looked very feasible - so the output impedance wouldn't be that high . I think the D3a triode at 13ma as I have now, is over 2k Zout. Pentode did look good . Will be using something like that with the new LCR phono ( currently a top-plate and a big of bits ) although now the Gm amp idea from JC has come along and this opens up the possibility of a SUT-less MC input at the front end.
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