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Satyrnine

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Posts posted by Satyrnine

  1. and now for something completely different part 3

    in Do It Yourself

    Posted

    Fired up first two cfa2's last night. A couple issues:

    Board 1) Without servo, I'm seeing around 400mv (!) offset on output with input shorted. If I plug in the opamp, it slowly comes down to 1-2mv over 30sec or so. 

    I started with bias pot all the way counter clockwise. Not seeing anything across the 1R resistors after a good 8 turns clockwise, do I just need to keep going, or should I be seeing some idle current by that point?

    Board 2) LED's not lighting. It was late, and I gave up before investigating further.

  2. and now for something completely different part 3

    in Do It Yourself

    Posted

    14 hours ago, audiostar said:

    I would stick to 10k

    10 minutes ago, Pars said:

    I haven't had any issues with the 25K, but I'm using JFET input on the DynaFET (only option). If you use the THAT BJT quads on an SS input stage, that would probably be a problem as those require low input impedance. CFA3 with JFETs is probably not a problem, though Kevin could clarify.

    Thanks for the input guys. As a testament to their great customer service, Goldpoint is letting me exchange my (unused) 25k quad for a 10k quad, for cost of shipping only. Their shipping is prompt too. I haven't used one of their pots yet, but so far so great. My config will be just 4x cfa2 at first, and then the tube ubaltobal input once I get boards/bom/iron ordered up and together. Since it's a free exchange for the 10k, might as well take advantage I figure.

    As mentioned earlier my legit dealer sourced 15031's range from 70 to 120hfe, approx evenly distributed. If it even matters, what would be the best way to distribute this range across my 4x cfa2 boards? If I recall correctly, one of the 7 sinked devices on each board doesn't get as hot as the main 3/3 set, should I put outliers in that position, or...???

  3. and now for something completely different part 3

    in Do It Yourself

    Posted · Edited by Satyrnine

    On 11/24/2017 at 6:37 PM, Pars said:

    What would the sonic effect be of running a 25K pot with this? It is what I have (TKD) in my DynaHi/DynaFET and I was planning on running these boards in that. I know you usually spec a 10K.

    Thanks!

    On 11/25/2017 at 5:47 AM, kevin gilmore said:

    Slight DC offset unless you match input parts. So a whoosh as you turn the knob

     

    Just rereading some of this thread. So uh... lets say someone ordered a Goldpoint in 25k. How much of a problem is that. Asking for a friend. 😑

  4. and now for something completely different part 3

    in Do It Yourself

    Posted

    18 hours ago, JoaMat said:

    Inspired by Satyrnine's project and an attempt to recover from my Tube input CFA3smd failure some time ago I’ve been busy with this today.

    Screenshot_8.jpgScreenshot_7.jpg

    I call it Cascode Tube Input Something - intended for my CFA3smd something. +220/+15/-15V and filament needed. Based on ubaltoblatubeschem2, thank you Kevin.

    So is this still the balanced/current mirror design of kevins but cascoded 6922's? I love it. Cascoded 6SN7's is one of my fav recipes. I have a SE pre setup that way, and it sounds great. I'm shooting for balanced all the way through for this build though. 6SN7's ideally should get more B+ vs 6922 obv, not sure how far down a that rabbit hole I want to go. Tempting as heck.

  6. and now for something completely different part 3

    in Do It Yourself

    Posted

    1 hour ago, audiostar said:

    Think about keeping it modular and separate the tube pre from the power amp. Same as you separated the PSU already and not stuff everything into a single like 6U 800mm deep chassis :)

    So you you suggest three different enclosures? Even with the tube pre in the power amp chassis, it would be only DC coming into the power amp chassis. Would put the tube pre powersupply in the PSU chassis. Are you concerned more about the 6v and 100v or some sort of other interference/issue I'm overlooking? So far, everything should fit in two 2U chassis, (one a pessante, one a dissipante) with plenty of room. Thank you!

  7. and now for something completely different part 3

    in Do It Yourself

    Posted · Edited by Satyrnine

    1 hour ago, kevin gilmore said:

    there are a few units with the tube front end that have been built. less than 5 i think.

    boosting the front end high voltage will increase the power in the current mirror that follows the tube. so you might have to change some of those parts.

    Sounds like something I don't want to mess with. :) Thanks Kevin.

    1 hour ago, Pars said:

    If it were me, I'd source 2 quads of Toshiba 2SK170/2SJ74 from punkydawgs on ebay, and just do the SS bal/ubal board with JFET input. But that's me. It seems like someone on HF has a tube input CFA3, but I didn't see any pics or direct posts by the person who supposedly has it. I know dukei has been talking about it. Kevin would probably know. A lot of the HF crowd seems to run a tube preamp into the CFA3 and use that to get their "tube" sound. I guess you could do that if you wanted.

    I used to have a tube pre, a Counterpoint SA5.1, which used 6922s and sounded good. It had a slight hum to it which took me about 6-7 years to find (PSU board layout error), and I sold it right after that and never listened to it after I fixed it, other than to verify it was now dead quiet.

    I feel like I need a shower now after being on HF for a few minutes :rofl:

    Just chatted with Miroslav/Dukei, and he had great things to say about the sound/performance of the tube bal/ubal input. I think I'm going to go for it. This will likely be my endgame amp, so why not go all the way. :)

  8. and now for something completely different part 3

    in Do It Yourself

    Posted

    14 hours ago, Pars said:

    I don't know about going that high. Assuming this is a full wave bridge, you would have around 161 Vdc on the first filter caps. That is quite a bit of voltage to burn off. You could actually drop down to 80Vac and still get about 113Vdc, which would be plenty.

    I wonder how easy it would be to adjust the reg output above 100v on the grhv100. I definitely don't understand all of what's going on there with the hv regulation. I was playing with the idea of using 6sn7's vs 6922's, which can handle quite a bit more voltage, and imo, sound a bit better. I don't want to make too much extra work for myself though. 

  9. and now for something completely different part 3

    in Do It Yourself

    Posted · Edited by Satyrnine

    10 hours ago, Helium said:

    Any specific reason why you would put tube unbal-bal converter in front of CFA? Just to make it as complicated as possible? There will be ~100 more parts in signal path, hardly they will make amplifier sound better.

    To make a CFA3. bal/unbal + CFA2 = CFA3 right? ignoring that I'm going w the tube version, Not much more components in path than a base CFA3 I figure? It seems people really enjoy the added ss/zf (zf only in the tube version of course) part of the CFA3, and if I'm going through all this trouble I figure why not go the full distance. Plus, having a little tube flavor on the input is always appreciated, since I typically prefer tube amps/designs. A balanced tube pre isn't common, so when I saw a tube bal/unbal, that seemed like a perfect match vs a standalone tube pre. Last, seems like not many people have built the tube bal/unbal, so figure I can be of some use by guinea pigging it. I figure this is the best of both worlds. Am I off? If yall think there's nothing to be gained, I'll consider skipping it. Thanks!

  11. and now for something completely different part 3

    in Do It Yourself

    Posted

    6 minutes ago, Pars said:

    Not sure if the Hammond has enough current capacity. Hammond 229B88. It's only 88V, 130mA.

    The only issue with using 100V or so is a bit more heat on the pass device(s).

    I was planning on sinking directly to the 10mm 2U front plate (along with 2x 30v grlvs) with good thermal compound. Think that'd cut it? Obviously "try it and find out" is the best answer. :)

  12. and now for something completely different part 3

    in Do It Yourself

    Posted · Edited by Satyrnine

    1 hour ago, Pars said:

    Also, I might have a couple of GRHV 100 PCBs here, though they aren't mine. I would have to ask the owner if he wanted to sell one of them.

     

    That looks like the one! I would definitely be interested in buying one. I'm in Madison, WI USA. Thanks for suggestions on connectors. 

    1 hour ago, luvdunhill said:

    I also have run those voltages through Switchcraft EN3 series which I like a lot.

    Excellent! I like switchcraft. I'll check all the options out. Many thanks! Since you ran those voltage, you don't happen to have a recommendation for a 90vac trafo around .5A or so? Seems to be a uncommon range. That is, unless I can use higher voltage ac than 90vac, 100-115 or so would be easy to source. Edit: nvmd on trafo rec. found some good options.

  13. and now for something completely different part 3

    in Do It Yourself

    Posted

    On 5/14/2023 at 7:39 AM, kevin gilmore said:

    would need a higher voltage opamp. otherwise should work.

    Excellent! What about the 90vac, and 8vac are they flexible too? 100vac seems a bit more prevalent in a reasonable VA. Or a 1:1 115v trafo would be great too. Will it reg down to 100v ok still? Same with the 8vac heater supply, I find a lot of 9vac trafos in a good size. 

    Here's a very preliminary mockup of what I was thinking. To anyone: Will bundling all these DC rails (6vdc, +/-30dc, and 100dc) together in a single multi-conductor connection work? Best connector for that? A bit new to external power like this.

    image.thumb.png.b06cca35be8041a292d109501859c7b4.png

  15. and now for something completely different part 3

    in Do It Yourself

    Posted · Edited by Satyrnine

    1 hour ago, kevin gilmore said:

    grhv100 for the tube input stage.

    Kevin, is there any way the ubaltobaltubeschem2 can be made to take +/-30 vs the +/-15? Otherwise I'd need a third grlv I think. Would be running 4x cfa2 from 2x grlv30. That is, unless a separate supply is recommended for the ubaltobaltube +/-15v requirement regardless. Also, suggestion for VA on the 90vac and 8vac transformers? I'd like to have 1.2A min available for heaters and 40ma plate current available if possible, to try 2x 6sn7's. (pinout is dif, but compatible)

  18. and now for something completely different part 3

    in Do It Yourself

    Posted · Edited by Satyrnine

    Reading EL_Ken's post about grounding, (even though I know the incorrect grounding didn't cause a device failure in the end) I assume plastic shoulder washers are best to make sure boards don't ground to chassis through standoffs. Are brass or alum standoffs the best move, or would a nylon standoff/screw be a better option? I know it "depends" but does anyone have a suggestion for best size/height/etc for those?

  21. and now for something completely different part 3

    in Do It Yourself

    Posted

    7 minutes ago, jamesmking said:

    almost no authorized seller except farnell has MJF15030G in stock at the moment.

    Farnell has 347 https://uk.farnell.com/on-semiconductor/mjf15030g/transistor-npn-150v-8a-to220fp/dp/9556303

    meanwhile the nonauthorized sellers claim to have about 300000 in total between them - I call BS...

     

     

    Oh wow, that must have been recent stocking! I just ordered from Farnell/Newark. Thanks! Definitely not something to risk.

  22. and now for something completely different part 3

    in Do It Yourself

    Posted · Edited by Satyrnine

    I started populating my grlv's tonight. I tested my MJF15030 and 31's and they vary quite a bit. I recall it said that matching isn't too terribly important, but want to double check. I know I'll get scolded, but I DID source the 30's from a seemingly legit and well reviewed ebay seller, since they are out of stock everywhere. I'm wondering if I got a batch of rejects. Here's what I found:

    MJF15031 from mouser: All around 280hfe +/- 5.

    MJF15030 from THIS ebay seller: 80-150hfe. Oof.

    Visually they look identical, even with a loupe. I know that doesn't nec. mean much. Is this normal? If these are questionable, anyone have a source for 30's?

    Also, the larger tantalums are 36v, not sure if they see full 30v or not, that's a bit too close to 30v if so. I ordered from an existing bom, and didn't catch this.

    unnamed.thumb.jpg.745a104ba59c3161a8062407370ae46a.jpg

  24. and now for something completely different part 3

    in Do It Yourself

    Posted

    8 hours ago, johnwmclean said:

    FWIW with 2 X 100VA the GRLVs are not going to run hot, you can mount them to the base plate.

    1722213503_IMG_5859copy.thumb.jpg.e0463d73d4e4b31605d75fe55ea8a152.jpg.8b8c0db073cfa52b081d2774c03b8c1d.jpg 

    2 hours ago, audiostar said:

    Not really going to work as there are caps on the GRLV boards. Maybe, with a 5U case 😎

    The pass transistors you better mount directly to the bottom plate, like John has shown above. Oriented to center, straight below the Goldpoint stepper.

    Well hell, wish I would have come across that photo earlier, haha! That sounds like a great solution. I'll set it up just like that. Thanks Guys!

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