Search found 1018 matches

by Thermionic Idler
Mon Feb 20, 2023 5:56 pm
Forum: Everyones Projects
Topic: It's time I built a D3a -> 5687 phonostage
Replies: 78
Views: 52011

Re: It's time I built a D3a -> 5687 phonostage

So post-RIAA I go a bit off-piste: https://user.fm/files/v2-9fe738e8842bcf5d04640679e3bb6961/Screenshot%202023-02-20%20at%2017.48.33.png I was looking at the output stage of Stephen's (izzy-wizzy) circuit and couldn't help noticing a similarity to Lynn Olson's Raven . This is a version of that, with...
by Thermionic Idler
Mon Feb 20, 2023 2:48 pm
Forum: Everyones Projects
Topic: It's time I built a D3a -> 5687 phonostage
Replies: 78
Views: 52011

Re: It's time I built a D3a -> 5687 phonostage

Fixed it! Found a model on https://www.diyaudio.com/community/threads/xys-ixtp08n50d2-and-ixtp08n100d2-ltspice-model.307318/ which makes use of the VDMOS model, pasted it into standard.mos and I was able to pick it as a transistor. Sim seems to work now, I get about 44dB gain before it hits the RIAA...
by Thermionic Idler
Mon Feb 20, 2023 2:20 pm
Forum: Everyones Projects
Topic: It's time I built a D3a -> 5687 phonostage
Replies: 78
Views: 52011

Re: It's time I built a D3a -> 5687 phonostage

What you have missed is the line that says that the depletion mosfets are IXTP08N100's I just used the 740 models as they have the same pinout. The mosfet that's driving the d3a g2 is a STU3N45K3, but most high voltage N chan will be fine there I just wanted one with a low Cgs Ahhhhh... like footpr...
by Thermionic Idler
Mon Feb 20, 2023 1:18 pm
Forum: Everyones Projects
Topic: It's time I built a D3a -> 5687 phonostage
Replies: 78
Views: 52011

Re: It's time I built a D3a -> 5687 phonostage

Thanks Nick. Well, this is frustrating. I've laid out the first stage in Spice so that I can study the circuit and work out what's going on. Unfortunately, I'm getting next to no gain (in fact it's a loss), there's almost nothing on the 5687 cathode. The current going through the first two MOSFETS i...
by Thermionic Idler
Sun Feb 19, 2023 7:45 pm
Forum: Everyones Projects
Topic: It's time I built a D3a -> 5687 phonostage
Replies: 78
Views: 52011

Re: It's time I built a D3a -> 5687 phonostage

My search foo is good today! Though I see some battles with Spice on the horizon... Thanks Mark - that image is a bit clearer. The only thing I still cannot make out is the value of the two caps in parallel going to the three pin connector from the 5687 cathode (which I presume is the interface to t...
by Thermionic Idler
Sun Feb 19, 2023 2:55 pm
Forum: Everyones Projects
Topic: It's time I built a D3a -> 5687 phonostage
Replies: 78
Views: 52011

Re: It's time I built a D3a -> 5687 phonostage

Found it: Link

Wow... that's interesting...

Yeah, that looks DIY-feasible. How hard can it be?

Time to knock up a Spice sim...
by Thermionic Idler
Sat Feb 18, 2023 6:17 pm
Forum: Everyones Projects
Topic: It's time I built a D3a -> 5687 phonostage
Replies: 78
Views: 52011

Re: It's time I built a D3a -> 5687 phonostage

This was what I had in mind for stage 1:

Image

To the right of the RIAA, probably an interstage?

Will hunt around for Nick’s arrangement too.
by Thermionic Idler
Sat Feb 18, 2023 3:10 pm
Forum: Everyones Projects
Topic: It's time I built a D3a -> 5687 phonostage
Replies: 78
Views: 52011

Re: It's time I built a D3a -> 5687 phonostage

Seems to me that one obvious way to get around the low impedance input to the RIAA is to use a step-down interstage in front of it. Though if I were to go for a hybrid solution, an op-amp may be much cheaper. Have you considered Nick's method and rejected it ? I'm just a bit concerned about transpa...
by Thermionic Idler
Sat Feb 18, 2023 12:02 pm
Forum: Everyones Projects
Topic: It's time I built a D3a -> 5687 phonostage
Replies: 78
Views: 52011

Re: It's time I built a D3a -> 5687 phonostage

I thought you had cinemag lcr units in the one you built, could you not take those out instead of shelling out for the sowters? The s&b ones in my cole are 600r ones iirc, are there different impedance ones available? I always wondered why 600r which seems a little bit of a strange value, but i...
by Thermionic Idler
Fri Feb 17, 2023 10:09 pm
Forum: Everyones Projects
Topic: It's time I built a D3a -> 5687 phonostage
Replies: 78
Views: 52011

Re: It's time I built a D3a -> 5687 phonostage

Right then. I've decided to be ambitious. So Sowter make the 1280 RIAA 600 Ohm EQ Unit - an off-the-shelf RIAA EQ similar to the classic Tango units. I'm keen to design a circuit around that. Ha! as if I know anything about phono stage design. But I really like what the Pete Millett LR does, so I wa...
by Thermionic Idler
Wed Feb 15, 2023 4:12 pm
Forum: Everyones Projects
Topic: It's time I built a D3a -> 5687 phonostage
Replies: 78
Views: 52011

Re: It's time I built a D3a -> 5687 phonostage

I've had to go back to the Whest stage for the moment whilst I try and get the LR stage fixed. Whilst I can hear its full bandwidth, I immediately missed what the LR stage was doing in the midrange (as heard at Owston) despite its response anomalies. The Whest just isn't as good. I don't know how mu...
by Thermionic Idler
Wed Feb 15, 2023 12:15 am
Forum: Everyones Projects
Topic: AMB linestage rebuild
Replies: 68
Views: 36887

Re: AMB linestage rebuild

Well Dave, obviously, as you are aware, it takes a great deal of blood, sweat and tears to produce work of such incredible shoddiness. :D I wouldn’t know where to start with that stuff. Thanks Steve - over a year's worth of blood, sweat and tears in fact, looks like I started this thread last Janua...
by Thermionic Idler
Tue Feb 14, 2023 4:27 pm
Forum: Everyones Projects
Topic: AMB linestage rebuild
Replies: 68
Views: 36887

Re: AMB linestage rebuild

OK, it's done. That was quite possibly the hardest thing I've ever designed. Interior picture before the lid went on: https://user.fm/files/v2-b5cc1e6d69b2421c5d52cb89db835b93/completed_interior.jpg Front panel (getting the blackout film stuck on behind the perspex was a lark): https://user.fm/files...
by Thermionic Idler
Thu Feb 09, 2023 7:21 pm
Forum: Everyones Projects
Topic: It's time I built a D3a -> 5687 phonostage
Replies: 78
Views: 52011

It's time I built a D3a -> 5687 phonostage

I have a hankering to try a good valve phonostage again, and having read through several threads here, and on Hi-Fi Haven, we seem to quite regularly come back to the D3a for stage 1, and more often than not a 5687 for the second stage, to get really good results. Yesterday I impulse bought a couple...
by Thermionic Idler
Mon Feb 06, 2023 8:04 pm
Forum: Valves
Topic: What are the oldest affordable valves you can still buy?
Replies: 13
Views: 8433

Re: What are the oldest affordable valves you can still buy?

IslandPink wrote: Mon Feb 06, 2023 5:56 pm Do you need to look into different equalisation curves ?
Yes, that’s part of it.