Valve Itch phono

Valves SHARED between both channels

Hi Gatisozo. :cool:


You may or may not have realised this already.

It has caught out a few people in the past I believe. :(


But looking at the photo of your provisional 'layout' in the tin box ...

... you have got all the parts placed in a nice symmetrical Left/Right looking way.


BUT ... All of the valves for 'The Itch' are SHARED between BOTH Left AND Right channels ! :eek:


As far as planning for as little 'spaghetti-wiring' as possible, this is important to consider.


Placing all the components in what seems like a sensible Left/Right way ...

... will result in a HUGE MASS of wiring, all crossing over each other in the middle. :(


Just thought I'd point that out, as it isn't always obvious.


Thinking about the parts layout in a 'circular' or 'spiral' way is probably a good thing. :eek:


If you use an earthing buss-bar, it too could be placed in a 'circular' or 'spiral' way.

For best performance it needs to follow a sensible path & be easy to connect to.


:)


Si.

.
 
All that scratchin' is makin' me ITCH !

:D


I thought I'd have a go at a fast & dirty 'Valve Itch' layout. :cool:

This is a 'first draft' obviously.

But it is going very much in the right direction after the first bash at it.



Clearly it's not to scale yet, but I don't see that many problems in fitting 'real world' sized parts in.

4" between all the 4 valves I figure would do for most things.



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I decided to put RCA socket stuff left to right, as viewed from the top, valve side of the chassis.

Valve bases V3 & V4 on the 1st draft, need rotating about 180-degrees for optimum signal path.

Triode No.1 in each envelope is always the LEFT channel, and Triode No.2 in each envelope is always the RIGHT channel.

The heater wiring isn't shown yet & can generally pass around the very outside of the main action.



The passives were simply divided up into 'sensible' groups for each of the 4 small group panels.

I would use PTFE or SRBP sheet for these, with holes drilled for the component leads.



I have most of the parts for this, so may well measure them & have another bash at drawing MKII.

V1s cathode IR LED and V2s cathode resistor are not shown & probably would be soldered directly to their valve bases.



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Spinning the schematic around 90-degrees anti-clockwise & it appears as the chassis from the underneath front would do.

The parts groupings correspond more or less to the 4 main groupings found looking at the schematic.

Moving in an anti-clockwise direction around the schematic & chassis ...

V1 & V3 component group.

RIAA EQ component group.

V2 & V4 component group.

PSU parts & output caps are group 4.


:)


Si.

.
 

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Last edited:
diyAudio Chief Moderator
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They can be used for ver1.2 because there is far less grid current chance due to the infrared voltage bias Led. But there will be no compatibility in the base wiring to readily swap back from 12AX7 and listen with 6n2p-ev. See also a detailed differences thread between types: 6n2p-ev-vs-12ax7.html

There is BOM to download in post #410 for version 1.1 and you can easily work out the differences in parts values or anything extra between 1.1 & 1.2 by comparing the published schematics.
 
diyAudio Chief Moderator
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You need one 300V clean and stable B+ rail and two about 6.3V heater rails, preferably in low noise DC, the one for V3 V4 heaters should be 100V elevated. Those requirements don't change for any version. You may follow one of the PSU examples given here or devise your own configuration that suits for stocked parts you may have, or make other rectification and regulation type choices. PSU quality has its impact on final audio performance of course. Especially for low input signal high gain circuits like phonos which are sensitive to noises.
 
My contact in The Kremlin swapped K72s for thermal underwear ...

.

" Just now picking components "



Hi Gatisozo :cool:



That's good news ! :)

Just don't take as long doing it as I have. :eek: ;)



I was just released from The Insane Asylum last week ...

... so I thought I'd get straight back on The Valve Itch right away. ;)

:lifesavr:

I have had some problems locating some parts not listed on the BOM.

In particular Round Tuits ...

... & Unobtanium. :confused:

:rolleyes:

But I think I struck lucky with some non-stick NOS Ruskie capacitors ...

... My contact in The Kremlin only wanted 1 case of Johnnie Walker & some thermal underwear !

A lot cheaper than the $250 Op-Amp which I noticed in the Digikey catalogue the other day !!! :eek:


:bigeyes:


Hi Salas :D

Still slingin' the solder I see. :p



I might actually have enough time & parts to make an Itch now. :eek:

I thought I could keep off the Valves & just feed my addiction some SS sand technology now & again ...

... But it obviously hasn't worked ! ;)



Boris traded me all his K72s, but I could be up $4!7 creek on the values ! ? :lifesavr: :(

I've messed about with some of the FORBIDDEN online RIAA calcs. :fight:

But I know the SIM you have on your vintage 6SN7 'puter is better, but thirsty on Amps to run !! ;)



Can I do anything with these ? :confused:

They don't quite fit ... Mmm ... But I'd like to somehow use them & could adjust the resistor values if needed.

Can you tell me what you think ? :eek:



K72s - 15.47 - 15.50 - 15.51 - 15.59 - 15.66 - 15.72

K72s - 47.1 - 47.9 - 48.0 - 48.2 - 48.2 - 48.3 - 48.3 - 48.6



I have loads of small Cs I can choose from to add to ^^ these ...

... & of course loads of resistors to make up oDd values with. :rolleyes:


:)


Si.

.
 
diyAudio Chief Moderator
Joined 2002
Paid Member
That's an interstage transformer to employ as plate load and output AC coupling for tubes of (optimally) 3kΩ rp. It would take some substantial redesign to usefully employ it in this circuit. Must replace the second stage mu follower with just common cathode of similar gain when loaded with that transformer. In other words save it for somewhere already designed for interstage and build the standard Valve Itch schematic.
 
diyAudio Chief Moderator
Joined 2002
Paid Member
I tried the LED as the bias on a 6922 instead of a resistor and bypass cap, oddly the waveform on the scope was terrible but the sound was ok. The led is a current variable resistor.

In a mu follower there is constant current bias coming from the bootstrapped top so the cathode LED shows steadier resistance especially around small signal swing. The less mA bias though, the more resistance in all types of diodes.