audio-talk

At one time Russian capacitors were highly thought of.

I have a pair of 4uf 630V PIO (although in this case the P in PIO is not paper).

They are almost identical to the Ebay listing below but mine are +/- 5%

If suitable for your needs I would donate them to your project. :)

https://www.ebay ...

So I think the valve choice is finalised then.

The thing that's bugging me the most now is what to use for the parafeed cap.


Best sounding cap you can use and it's all good.


Right then. So if I model a 1uF cap in that position, I get a clear 10Hz resonance point, but it does not cause the ...

What does the phase look like?


Good question, I am curious to know what the phase looks like too. I haven't worked out how to do that in Microcap yet.


According to Kevin, the 1635 is an old design and bettered by later designs. There's a thread someplace if you want to dig on AA.

I used the ...

One possibility would be monolith magnetics, either IT-02, ITA-02 or ITX-02
Tell them you are going parafeed so you will need access to four terminals on the primary. Also four terminals on the secondary if you want to bias the output tubes separately?
Also discuss if you want a gap - probably gap ...

Wait a minute...

Nick wrote: Sun Nov 24, 2024 3:33 pm The interstage sees no DC so can be high impedance so the cap doesn't have to be huge. Similar to the Raven output stage.

So why the hell am I still speccing the LL1692A? Duh!

Back to the drawing board...

Well, initial test suggest a 3.3uF value for the parafeed cap, about the same as specced for the early Raven pre, so at least I know I'm in the right ball park. Much lower than that and you start getting a bass resonance.

The model indicated another resonance peak at about 50kHz which was tamed ...

Well, the layout is done, this is an initial 'dynamic dc' analysis showing voltages and current flow, all the operating points look good.

Now to do some frequency sweeps to iterate to the ideal parafeed cap value cos I've no idea what that should be...

https://user.fm/files/v2 ...

Thanks Nick.

So I remembered you could run two CCS's in parallel to get more current. Looking at the circuit, I then pondered if this would work (input stage, single CCS split into two and moved each side of the choke, centre tap still referenced to the voltage regulators.

EDIT - picture deleted - no, I'm an ...

Well, here is what I have so far. Next thing is to figure out how to model the interstage as Microcap doesn't have an existing transformer model that has enough separate windings.

Pondering how best to protect the 0C3's from 70mA of current if the 5687 heater fails - simplest solution I can think ...

Paul Barker wrote: Sun Dec 01, 2024 3:15 pm Too much to hope for EL38

Sadly that one does appear to be missing, yes.

So one huge advantage I just discovered, probably more applicable to those new to simulation as most of you will probably already have these set up - the installed version has 457 vacuum tube models already defined - they've got the Ayumi models in there as well as Koren. No need to faff about ...

Thought you good people might appreciate a heads-up on Micro-Cap... which you could also call YASS (Yet Another Spice Simulator).

I have no idea at this point if it is any good in reality, but it used to cost $4700 and now costs $0. For your $0 you get the software and manuals but no updates or ...

I'm considering the 5687 for a future phono stage build, so I'm now also thinking about using it choke-loaded for the input valve along with EL84 drivers again - we all love the EL84 and I'm really curious about what it could bring to the party. Likely in Nick's suggested parafeed arrangement with ...

TBH, no idea whats going on there with the "cascode".

Not sure I've got much of a clue myself, I need to draw it out properly in QSpice and test it.

All I can say, is that for the parafeed output, the CCS's connect to the anode of the valves, the other side of each primary windings.

Huh ...