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Post by krcwell on Mar 26, 2016 12:50:05 GMT -6
Finished up the schematic. I'm going to go back through it later and double check for errors, but I need to step away from it for a bit. The mess in the upper left is the CAPI relays. I've come to realize that I don't make pretty schematics, but as long as they work, should be good to go. Transformers are shown as connectors as I'm not that good with kicad, so I just try to figure out something that will work. Attachments:
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Post by rocinante on Mar 26, 2016 21:42:24 GMT -6
It looks pretty right but by no means do I have the eye for circuit design. Ill download it and compare it to my other documents to see if I see anything. Really Ian is the one who knows this shit in and out and he probably would have some good suggestions as well.
I'm switching the doa's in my helios eq tonight to see what it's like with all melcors.
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Post by krcwell on Mar 28, 2016 20:32:33 GMT -6
I've been looking more into line in transformers, and, if I understand correctly, a 10k:10k line in transformer can replace the whole THAT input stage, with just a 10k shunt to ground between the transformer and eq? I'm referencing this Jensen transformer, as they have good documentation: Jensen JT-11P1hpc
The use of R(L) in the above link seems to mimic the 10k (R101) right before the low band 2-deck switch in the schematic I posted earlier that I, well, copied. This would present the eq with it's desired 10k in both the transformer in and THAT in shown in the schem I posted? Does the eq even want 10k? Am I anywhere close to correct on this? Just trying to "think/learn out loud". Thanks, Keith |
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Post by rocinante on Mar 29, 2016 7:54:10 GMT -6
Sorry I couldn't respond quicker. For a mic input stage you actually want more than like a 1:10 xfmr (Jensen jt-115k, cinemag cmmi-10c). For just eq; yes 10k:10k would work great.
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Post by krcwell on Mar 31, 2016 20:24:37 GMT -6
Sorry I couldn't respond quicker. For a mic input stage you actually want more than like a 1:10 xfmr (Jensen jt-115k, cinemag cmmi-10c). For just eq; yes 10k:10k would work great. From the cinemag line, would I be looking at something like the CMLI-15/15? CMLI-15/15PCA |
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Post by rocinante on Mar 31, 2016 23:10:23 GMT -6
For the helios eq that cinemag should work very well.
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Post by rocinante on Apr 1, 2016 1:48:57 GMT -6
Hey Krc,
Aren't you using the front end as a mic pre though? Thats a line transformer so wouldn't be the best application for it if you are using it as a mic pre.
If just as an eq than you are fine.
I understand your logic and as far as I know the eq wants to see 10k. Soooo... well maybe a 150:10k? Or something similar to the vtb 9045?
You want a helios 2128 amp card? I believe I have one left over that im not using.
Looking back in the thread;
As far as what Igor had done with the original transformer in his helios, its good to remember the dude was kind of a genius. And he also liked rare and often difficult circuits. The 7101 is a very specific transformer and needs a specific op amp follower for it to work.
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Post by krcwell on Apr 1, 2016 6:29:07 GMT -6
Hey Roc, just doing the eq in 500 series.
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Post by rocinante on Apr 1, 2016 14:29:16 GMT -6
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Post by krcwell on Apr 1, 2016 18:24:37 GMT -6
Beatiful, Roc.
I've got those PMTGMU boards I bought off you a while back sitting around collecting dust... I was trying to figure out how to properly use the 6cg7 setup, but think I'm just going to reconfigure for the 6922 as it seems more understandable (and better documented, since I have no idea what I'm doing with tubes).
What edcor are you using for the line in? I just ordered a bunch of edcor's the other day for a few different projects, also a pair of wsm10k:10k and 2k4:600 to use on either a stereo pultec or stereo helios with Ian's boards. Probably will go with the pultec, figure I need a pair of those.
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Post by rocinante on Apr 1, 2016 23:02:39 GMT -6
The edcor 10k:10k are the inputs and the output transformer carnhills are 2k4:600. Imo the output xfmr seems more noticeable (which is strange since original helios ran unbalanced with no output xfmr).
*i have to make a correction; I used 6cg7 tubes in the helios eq. I had debated u sing 6922 but decided as gainst it and had been looking at old notes when i posted. My bad.
Tubes are great man. I love what they do to audio. Another great feature (other than sound) about tubes in diy builds is they actually let you know you are on the right path by glowing. Too bright and too much voltage is being applied. Too low and they Might just need more voltage.
I built a two channel one of a kind tube preamp designed by Ian. Its actually "the classic" but a two channel pcb.
The 'classic' mic pre, a couple of CAPI's, and some ez1290s have been giving me results that is nothing less than amazing. I smile when i turn them on.
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Post by rocinante on Apr 2, 2016 9:47:11 GMT -6
And now for the solid state Helios 69 EQ using Pier's in/out boards. So many different options. You can go IC or DOA. Or IC and DOA. I've been experimenting. I gotta make up a few more of Gar 2520s and order some APP992 from Pier to try out. I am really happy with this though. It can be clean and transparent or driven. Right now I have OPA604 to 1731 but I have tried many configurations. I used the exact same sized par metal case as I did for the Tube Gain Make Up since they both needed to be long. The front Panel is the exact same layout as well. Got Helios?   |
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