Search found 1018 matches

by Thermionic Idler
Sat Mar 04, 2023 4:04 pm
Forum: Assorted Stuff
Topic: Nothing In Particular
Replies: 16439
Views: 4666658

Re: Nothing In Particular

Downloaded and installed KiCad 7 to my desktop and getting it sorted out so that it's ready to go for the next project. I have to say, much as I love it, the library management protocol is terrible, especially if you are trying to configure it to be usable with a cloud drive across more than one dev...
by Thermionic Idler
Mon Feb 27, 2023 8:02 am
Forum: Everyones Projects
Topic: It's time I built a D3a -> 5687 phonostage
Replies: 78
Views: 52483

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

That's rather adventurous. The paradise was a bjt version of the same idea and certainly sounds good. I think PCB layout will be a big part of the work. I do note that the article suggests that the first stage can drive <600 but that's far from saying that it should. They then load it with a 20k ne...
by Thermionic Idler
Sun Feb 26, 2023 1:40 pm
Forum: Everyones Projects
Topic: Pete Millett LR phono preamp
Replies: 39
Views: 21682

Re: Pete Millett LR phono preamp

Well, I've managed to get the response a lot flatter than before. I got my Spice sim of the circuit up and started to experiment to see if dropping any of the resistor values would act to bring up the missing top end. Practically, this would mean I'd only need to solder an additional resistor in par...
by Thermionic Idler
Sun Feb 26, 2023 9:41 am
Forum: Everyones Projects
Topic: It's time I built a D3a -> 5687 phonostage
Replies: 78
Views: 52483

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

Okay, so after much pondering I've decided to take a chance and go down the current-input route with the Proteus circuit (Erno Borbely and Sigurd Ruschkowski, Linear Audio Vol 6, Sept 2013), but with LCR RIAA lovelyness in the middle. From the research I've done, it has a very good chance of working...
by Thermionic Idler
Sat Feb 25, 2023 8:22 am
Forum: Everyones Projects
Topic: It's time I built a D3a -> 5687 phonostage
Replies: 78
Views: 52483

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

Depends on the cartridge. It's not a totally universal solution and only for MCs. A bunch of commercial stages do this. I think my current cartridge is about 16 ohms coil impedance, but the one I'm buying this year has a coil impedance of about 3 ohms. Seems ideal to me. Naturally I'm doing lots of...
by Thermionic Idler
Fri Feb 24, 2023 11:47 pm
Forum: Everyones Projects
Topic: It's time I built a D3a -> 5687 phonostage
Replies: 78
Views: 52483

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

Not discounting any design options at this stage (cos I still effectively have a clean sheet) I'm currently studying a Linear Audio article I purchased a couple of years ago with a current input design for MC cartridges, where you get around the need for a step-up transformer by taking advantage of ...
by Thermionic Idler
Fri Feb 24, 2023 8:20 pm
Forum: Everyones Projects
Topic: It's time I built a D3a -> 5687 phonostage
Replies: 78
Views: 52483

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

I feel that as the availability of a lot of these things tends to zero many of the traditional choices and designs will become impractical. This is why I'm still periodically getting cold feet over this - I don't want to put a whole heap of effort and expense into something that I can't use after 5...
by Thermionic Idler
Fri Feb 24, 2023 3:19 pm
Forum: Everyones Projects
Topic: It's time I built a D3a -> 5687 phonostage
Replies: 78
Views: 52483

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

Forget the number but there is a Russian high GM pentode that works as well. But I remember measuring some and finding two sets of curves as if there were two construction types. Yeah, the 6J52P - I think I saw a post from Kevin of K&K Audio mentioning those, that he also found them all over th...
by Thermionic Idler
Thu Feb 23, 2023 10:21 pm
Forum: Everyones Projects
Topic: It's time I built a D3a -> 5687 phonostage
Replies: 78
Views: 52483

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

izzy wizzy wrote: Thu Feb 23, 2023 5:31 pm D3a last for ages. In the end they are vfm.
Rated to something like 10k hours IIRC?
by Thermionic Idler
Thu Feb 23, 2023 1:34 pm
Forum: Everyones Projects
Topic: It's time I built a D3a -> 5687 phonostage
Replies: 78
Views: 52483

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

Ha ! How about £25 each nowadays ? I should have bought more :roll: More than that, at least the two I've bought were. And this is a perennial worry because I didn't get in when they were cheap. I found some NOS Siemens for sale from a Netherlands supplier at a reasonable price that seemed perfect,...
by Thermionic Idler
Thu Feb 23, 2023 1:14 pm
Forum: Everyones Projects
Topic: It's time I built a D3a -> 5687 phonostage
Replies: 78
Views: 52483

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

Nick wrote: Thu Feb 23, 2023 8:40 am 5687 CF is about 100R output impedance, and it does have feedback wrapped around it. I would check if its a problem before you try and find a solution. But YMMV.
Ah yes, that's the feedback into g2 of the D3a isn't it, I should be able to work that one out.
by Thermionic Idler
Thu Feb 23, 2023 1:20 am
Forum: Everyones Projects
Topic: It's time I built a D3a -> 5687 phonostage
Replies: 78
Views: 52483

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

I don't think I'm going to lose too much sleep over the cap coupling - the Spice model is suggesting that whilst the LF rolloff will occur earlier, it's still tolerable. I still have 4 big 47uF Obbligato film caps kicking around from an abandoned project years ago, I might press those into service. ...
by Thermionic Idler
Wed Feb 22, 2023 10:14 pm
Forum: Everyones Projects
Topic: It's time I built a D3a -> 5687 phonostage
Replies: 78
Views: 52483

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

I guess you could use a interstage, but again I think you are assuming the problem exists that needs a solution. I guess you could use a small cap into a high impedance buffer such as a op amp with voltage protection clamps on its inputs. Now there's an idea, I think the OPA161x series that I used ...
by Thermionic Idler
Wed Feb 22, 2023 7:23 pm
Forum: Everyones Projects
Topic: It's time I built a D3a -> 5687 phonostage
Replies: 78
Views: 52483

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

I guess you could use a interstage, but again I think you are assuming the problem exists that needs a solution. I guess you could use a small cap into a high impedance buffer such as a op amp with voltage protection clamps on its inputs. Now there's an idea, I think the OPA161x series that I used ...
by Thermionic Idler
Wed Feb 22, 2023 5:32 pm
Forum: Everyones Projects
Topic: It's time I built a D3a -> 5687 phonostage
Replies: 78
Views: 52483

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

IslandPink wrote: Tue Feb 21, 2023 6:38 pm Yes, of course, i asked you similar questions when I first saw the circuit.
So that's the reason for the 2 x 33uF caps from the 5687 CF - to get a low time constant with the 1.5K termination.
So with a 600R termination it looks like those values need to go up a bit. :shock: