Valve phonostage build

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Bigman80
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Valve phonostage build

Post by Bigman80 » Fri Nov 17, 2017 10:34 am

Hi all,
This is my first build other than a little DC blocker. I have been trying to improve my knowledge and ability so felt I should probably do something I can enjoy. Maybe.

I decided to go for this Valve wizard designed PCB http://www.valvewizard.co.uk/phonopcb.html
Merlin (apt name) was a lovely guy to deal with and offered me a PSU PCB too. In total i spent £9 for two boards. Cheap enough to not mater too much if I make a mess of it!

I also got a very useful flow chart of components and “build options” and here is my first sticking point. What’s the “best” choice in terms of Capacitance, Output impedance and gain. I am set on a split equalisation configuration, so I’d love your input!! What valves types would you use???

Flow chart here: http://www.valvewizard.co.uk/Phono_PCB_BOM.pdf

PS any recommendations on components would be welcome too. I’d like to go for high quality parts.

Cheers

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IslandPink
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Re: Valve phonostage build

Post by IslandPink » Fri Nov 17, 2017 12:01 pm

Not a bad circuit. I would prefer the coupling cap from stage 1 to stage 2 to be AFTER the RIAA section, that way the RIAA caps are biased up to around 100 to 120V which makes them sound nicer. However this will not be easy to modify on the PCB.

I'm not sure on the all-in-one vs. split option. I have only built all-in-one, which can be very good as long as the impedance of the RIAA is at least 8x the output impedance of the driving valve.
For that reason I'd suggest ECC88 or 6N1P as V1, then you can go for gain in V2 ( as it is backed up by the V3 C.F. ) so depending on your gain requirement, probably ECC83 as V2, then ECC88 as V3. I would recommend good NOS ECC88's , they sound a lot better than cheap modern ones.

If you used split RIAA it might compromise your option to use ECC83 for gain in V2, since it would also be loaded by a filter.

Are the RIAA resistors & caps fixed and already specified ?
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Firebottle
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Re: Valve phonostage build

Post by Firebottle » Fri Nov 17, 2017 9:22 pm

I also prefer the coupling cap after the RIAA network but I think it sounds better because the signal is going through the cap into a fixed impedance, rather than the pre EQ signal going through into a very varied impedance over the audio band.

The drawback of course is that the EQ caps have to be rated at the full supply voltage, however I have used a cheat by fitting a zener to limit the voltage, which becomes non-conducting once the anode voltage drops to operating level.

:)
Don't you just love valve phono stages 8)

Bigman80
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Re: Valve phonostage build

Post by Bigman80 » Sat Nov 18, 2017 11:15 am

IslandPink wrote:
Fri Nov 17, 2017 12:01 pm
Not a bad circuit. I would prefer the coupling cap from stage 1 to stage 2 to be AFTER the RIAA section, that way the RIAA caps are biased up to around 100 to 120V which makes them sound nicer. However this will not be easy to modify on the PCB.

I'm not sure on the all-in-one vs. split option. I have only built all-in-one, which can be very good as long as the impedance of the RIAA is at least 8x the output impedance of the driving valve.
For that reason I'd suggest ECC88 or 6N1P as V1, then you can go for gain in V2 ( as it is backed up by the V3 C.F. ) so depending on your gain requirement, probably ECC83 as V2, then ECC88 as V3. I would recommend good NOS ECC88's , they sound a lot better than cheap modern ones.

If you used split RIAA it might compromise your option to use ECC83 for gain in V2, since it would also be loaded by a filter.

Are the RIAA resistors & caps fixed and already specified ?

It's a bare PCB nothing on it at all.

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IslandPink
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Re: Valve phonostage build

Post by IslandPink » Sat Nov 18, 2017 4:50 pm

Ok, useful . I see he refers to his book on that, but do you get the RIAA info with the purchase ?
If not, I have the constants for the parts in the all-in-one RIAA from years back off DIY Audio ( think it's from Lipshitz originally ) . Once you set one value eg. the first resistor, or the first cap to ground, you can calc all the other values from there.
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Bigman80
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Re: Valve phonostage build

Post by Bigman80 » Sat Nov 18, 2017 6:32 pm

The flow chart provides all the values for the RIAA depending on what valve is used in that stage as far as I can see? Like I said, I'm very green in this area so I may have that wrong.

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IslandPink
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Re: Valve phonostage build

Post by IslandPink » Sat Nov 18, 2017 7:05 pm

Oh, yes, I see now.
Odd that the RIAA impedance doesn't go down ( from 180k ish ) with the higher-current, lower Zout V1 valves like the 6N1P or ECC88. That's an opportunity missed. I would definitely recommend something lower in the 20k to 40k region ( for R5/6) , depending on how much current you can use in the first valve.
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Bigman80
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Re: Valve phonostage build

Post by Bigman80 » Sun Nov 19, 2017 12:11 am

I'm not entirely sure what that means in its entirety but luckily, Alan is giving me a hand so I shall confirm with him.

There is already a bit of an anomaly as to the valves. There's going to be two PCC88 (Tesla NOS) and one ECC83 Telefunken going in so it's already not sticking to plan.

Firebottle
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Re: Valve phonostage build

Post by Firebottle » Sun Nov 19, 2017 9:51 am

Yes squeeze it till the pips hurt :shock:

That is a very good suggestion, let's see what current the '88 can stand and take it from there.
I'm a fan of larger current flow, as is Mark :mrgreen:
Don't you just love valve phono stages 8)

Bigman80
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Re: Valve phonostage build

Post by Bigman80 » Sun Nov 19, 2017 11:55 am

I'm going to start buying components on DEC 1. looking forward to this!

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IslandPink
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Re: Valve phonostage build

Post by IslandPink » Sun Nov 19, 2017 12:39 pm

Looks like a great project. You should get a fine result with Alan helping out. I like the valve choices - is someone sitting on a stash of Telefunken ECC83's ? :!:
88's could run 10ma at 120V comfortably ( 2/3rds max dissipation ) which gives some scope to get a lowish-impedance RIAA. I run D3a's ( triode ) at 13mA into a 20k network, where the cap in the 500.5Hz leg comes out at a round 0.1uF.
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Bigman80
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Re: Valve phonostage build

Post by Bigman80 » Sun Nov 19, 2017 7:22 pm

IslandPink wrote:
Sun Nov 19, 2017 12:39 pm
Looks like a great project. You should get a fine result with Alan helping out. I like the valve choices - is someone sitting on a stash of Telefunken ECC83's ? :!:
88's could run 10ma at 120V comfortably ( 2/3rds max dissipation ) which gives some scope to get a lowish-impedance RIAA. I run D3a's ( triode ) at 13mA into a 20k network, where the cap in the 500.5Hz leg comes out at a round 0.1uF.
Not quite sitting on some, rather discovering them in Alan's storage!! The Tesla's were bought in error for something else so may as well go in this. I'm heavily reliant on Alan's help but can't learn everything all at once ay!

I hope it turns out well, it'd be nice!

Bigman80
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Re: Valve phonostage build

Post by Bigman80 » Sat Jan 13, 2018 3:31 pm

Hi all,

The project is finished and cased up (too big of a case) and being listened to daily. I tried to upload a few pics but they are too big. Instead, here is the link to the AOS thread if any of you are interested in having a look.

http://theartofsound.net/forum/showthre ... -PCB-build

I have learned a lot from this but also gained a lot of respect for those who make them for a living!!

Next step.........not sure yet but i have a few ideas ;D

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Dave the bass
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Re: Valve phonostage build

Post by Dave the bass » Sat Jan 13, 2018 4:04 pm

Coolio! I followed your build on that link after reading about that phono stage in Merlin Blencowe's book which featured that cct.

Nice work fella, well done.
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Bigman80
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Re: Valve phonostage build

Post by Bigman80 » Sat Jan 13, 2018 4:11 pm

Dave the bass wrote:
Sat Jan 13, 2018 4:04 pm
Coolio! I followed your build on that link after reading about that phono stage in Merlin Blencowe's book which featured that cct.

Nice work fella, well done.
Thanks Dave! I am very happy with the end result. I'll probably transfer it to a smaller case and add a power button but other than that i cant see (or hear) any need to tinker with it!!

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