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Post by zonkola on Nov 25, 2020 23:59:07 GMT -6
Took advantage of some holiday time off to build these:  I have a second CA-0252 to put together this weekend. The VP312s are the no iron kits, and I'm waiting on a couple of Cinemag RE-0887 and CM-3301 transformers to complete the builds. The plan is to get into the Heider/DeMedio ballpark by eliminating a few capacitors as well as the zobel network on the input transformer secondary... |
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Post by matt@IAA on Nov 26, 2020 9:02:04 GMT -6
I think the Heiders had a different load resistor after the input transformer as well.
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Post by zonkola on Nov 26, 2020 11:52:27 GMT -6
I think the Heiders had a different load resistor after the input transformer as well. Yes, that's my understanding as well. Cinemag's standard recommendation for the RE-0887 is 100K, but I believe that DeMedio used an even lower value resistor. A post by Mitsos on Group DIY suggests starting with 15K, so if I can't find a definitive answer I'll experiment in the 15K-100K range. |
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Post by Guitar on Nov 28, 2020 10:57:46 GMT -6
Cool! I was dreaming of doing some DIY'eiders too a while back, it's cool to see someone going for it.
I think you will love those CA-0252 op amps also if you haven't heard them yet.
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Post by zonkola on Nov 28, 2020 12:13:34 GMT -6
Cool! I was dreaming of doing some DIY'eiders too a while back, it's cool to see someone going for it. I think you will love those CA-0252 op amps also if you haven't heard them yet. I compared the CA-0252 to a GAR2520 in identical CAPI VP26 Litz preamps a few days ago. On voice and guitar my impression was that the CA-0252 sounded almost identical to the GAR2520 in that preamp, with the CA-0252 sounding just a teensy bit more "lush" and the GAR2520 having a very slight edge in clarity. YMMV, but to me the difference was so slight that there's no way I'd notice it in a mix. I enjoyed building the CA-0252 more, though—it's a tidier layout in my opinion. |
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Post by Guitar on Nov 28, 2020 12:16:15 GMT -6
Yeah the GAR2520 has been my sort of number one go-to for a long time. I guess I should shoot it out directly with the CA-0252 because I have no idea how they would compare but that sounds like a great listening test.
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Post by dreamsambas on Nov 28, 2020 13:10:01 GMT -6
Nice work! How much did that RE-0887 from Cinemag run you? I've got some VP28's I'm thinking about modding with different transformers, opamps.
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Post by zonkola on Nov 28, 2020 13:29:08 GMT -6
Nice work! How much did that RE-0887 from Cinemag run you? I've got some VP28's I'm thinking about modding with different transformers, opamps. In small DIY quantities the RE-0887PC input transformer is currently $54.84, and the CM-3301 output transformer is $30.31. |
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Post by dreamsambas on Nov 28, 2020 17:47:38 GMT -6
Good to know. Debating between putting a RE-0887PC or a Quad-Eight style QEE 3440A in mine.
Or maybe get some Beyer peanuts (lol) for a Melcor sound.
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Post by Bender on Nov 28, 2020 22:33:19 GMT -6
Cool! I was dreaming of doing some DIY'eiders too a while back, it's cool to see someone going for it. I think you will love those CA-0252 op amps also if you haven't heard them yet. I compared the CA-0252 to a GAR2520 in identical CAPI VP26 Litz preamps a few days ago. On voice and guitar my impression was that the CA-0252 sounded almost identical to the GAR2520 in that preamp, with the CA-0252 sounding just a teensy bit more "lush" and the GAR2520 having a very slight edge in clarity. YMMV, but to me the difference was so slight that there's no way I'd notice it in a mix. I enjoyed building the CA-0252 more, though—it's a tidier layout in my opinion. The layout thing is HUGE. Not to mention 10 packs come pre-sorted so its QUITE the time saver. They sound amazing and it's all I'll build now besides the occasional 1731. |
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Post by Bender on Nov 29, 2020 18:41:08 GMT -6
It would be pretty neat to incorporate a switch/mod to change input impedance too. That might be a fun project
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Post by matt@IAA on Nov 29, 2020 20:51:07 GMT -6
Maybe wire in a 100k pot.
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Post by zonkola on Dec 6, 2020 12:24:34 GMT -6
Maybe wire in a 100k pot. This is what I did to test load resistor values—I wired in a 250K pot I had lying around, marked off the 15K-100K range, then brought in a few mics to listen to as I adjusted the pot. This was on a workbench rather than the studio, so it wasn't an ideal test, but it did give me a rough idea of how the load resistor impacts gain and tone in this circuit. 100K had the most gain, and seemed to have the most extended frequency range after compensating for the differences in gain. 15K was WAY down in gain, and sounded anemic to me with not much low end. 35K sounded the most balanced to me in this (imperfect) test, so that's what I soldered in. Overall, the jury is still out on this experiment. I need to spend more time with the preamps in the studio to see if they beat the stock VP26 sound (which I'm a fan of) on any sources. Attachment Deleted |
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Post by Guitar on Dec 6, 2020 12:28:07 GMT -6
It just occurred to me the title of this thread is relevant to my taste, VP312 is my favorite CAPI mic preamp, and CA-0252 is my current favorite 2520 op amp.
I might recommend drilling a little hole. Put 100K on one side of a toggle switch, and the "lo Z" value (35K) on the other side of the switch. There's enough room on the CAPI panel for these switches, I did a DI on mine.
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Post by zonkola on Dec 6, 2020 12:32:29 GMT -6
It just occurred to me the title of this thread is relevant to my taste, VP312 is my favorite CAPI mic preamp, and CA-0252 is my current favorite 2520 op amp. I might recommend drilling a little hole. Put 100K on one side of a toggle switch, and the "lo Z" value (35K) on the other side of the switch. There's enough room on the CAPI panel for these switches, I did a DI on mine. Yes. Another thought would be to use the existing mute switch (it has those handy terminals on top) after bypassing it on the PCB. |
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Post by Guitar on Dec 6, 2020 12:56:19 GMT -6
It just occurred to me the title of this thread is relevant to my taste, VP312 is my favorite CAPI mic preamp, and CA-0252 is my current favorite 2520 op amp. I might recommend drilling a little hole. Put 100K on one side of a toggle switch, and the "lo Z" value (35K) on the other side of the switch. There's enough room on the CAPI panel for these switches, I did a DI on mine. Yes. Another thought would be to use the existing mute switch (it has those handy terminals on top) after bypassing it on the PCB. Good point. I probably use the mute switch maybe 2 times in a year, so it would be a great candidate for repurposing. |
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Post by Bender on Dec 6, 2020 20:24:07 GMT -6
It just occurred to me the title of this thread is relevant to my taste, VP312 is my favorite CAPI mic preamp, and CA-0252 is my current favorite 2520 op amp. I might recommend drilling a little hole. Put 100K on one side of a toggle switch, and the "lo Z" value (35K) on the other side of the switch. There's enough room on the CAPI panel for these switches, I did a DI on mine. Sweet Idea!!! Any pics!!!?? |
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Post by Guitar on Dec 7, 2020 7:37:13 GMT -6
Here's a quick pic  |
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Post by zonkola on Dec 7, 2020 20:36:17 GMT -6
Guitar you've definitely got the mad scientist vibe happening in your rack
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Post by Guitar on Dec 8, 2020 6:24:30 GMT -6
Guitar you've definitely got the mad scientist vibe happening in your rack Yeah some people cringe at my hand labeling but I assure you all the electronics works is right and tidy, and everything sounds good. Also the closeup photo doesn't do any favors, haha. |
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Post by EmRR on Dec 8, 2020 14:32:08 GMT -6
Guitar you've definitely got the mad scientist vibe happening in your rack Yeah some people cringe at my hand labeling but I assure you all the electronics works is right and tidy, and everything sounds good. HELL YES to hand labeling. Don't let that Madison Ave. branded 'manufactured is better' mentality win. That was designed to make poor farm folk feel inferior, and inspire lust for goods from the city. |
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Post by Guitar on Dec 8, 2020 15:05:16 GMT -6
Yeah some people cringe at my hand labeling but I assure you all the electronics works is right and tidy, and everything sounds good. HELL YES to hand labeling. Don't let that Madison Ave. branded 'manufactured is better' mentality win. That was designed to make poor farm folk feel inferior, and inspire lust for goods from the city. Thank you for saying that. I just need to work on my calligraphy skills a little more I guess if I'm going to be a gear artist. The ones that get sold get slightly more attention to detail than some of the ones I keep. Not always but I've made some pretty sweet looking gear for other people. I'm trying to get more meticulous about the metalwork too, using templates and so forth. |
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Post by zonkola on Dec 9, 2020 1:38:55 GMT -6
Guitar you've definitely got the mad scientist vibe happening in your rack Yeah some people cringe at my hand labeling but I assure you all the electronics works is right and tidy, and everything sounds good. Also the closeup photo doesn't do any favors, haha. If it's got the sound keep it around |
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Post by Bender on Dec 9, 2020 12:56:24 GMT -6
Well I ordered some transformers from cinemag going to pop them in the 312’s and try em out.
They should touchdown in about 4-6 weeks lol
Very nice over the phone, and very helpful. Loved the old school direct ordering vibe. They sure don’t do it like this anymore!
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Post by zonkola on Jan 2, 2021 22:52:51 GMT -6
A followup: After testing the 35K load resistor in the studio I didn't love it, so I swapped it out for the 100K resistor recommended for the RE-0887 by Cinemag. I like it better, and it sounds especially good on acoustic guitar.
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Post by Bender on Feb 18, 2021 15:51:49 GMT -6
Finally got my cinemag iron that I ordered back in December- woot woot!!! Gonna pop em in and try em out with the 0252’s!! Cant wait to start grinding out tracks with these babies
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Post by zonkola on Jul 24, 2023 18:24:26 GMT -6
I occasionally get questions on this mod, so here are my notes.
Parts required:
• Special order RE-0887 input transformer from Cinemag
• Special order CM-3301 output transformer from Cinemag
• Additional 100k resistor
For the CAPI VP312, non-DI version, rev. B/C schematic:
1) Omit C5 & C6
2) Omit C1 & R2 (the zobel network)
3) Put the 100k resistor Cinemag recommends for the RE-0887 in R3
For the the CAPI VP312DI, DI version, rev. D schematic:
1) Omit C8 & C9
2) Omit C1 & R3 (the zobel network)
3) Put the 100k resistor Cinemag recommends for the RE-0887 in R2
Note that R2 and R3 for the 100K resistor are swapped on these two versions of the mod—mix them up and you'll effectively take the 100K resistor out of the circuit.
That's it. A pretty simple mod once you have the parts in stock. Even the wire color codes on the CM-3301 output transformer matched those of the stock CAPI VP312 output transformer on my build, but double-check the datasheet just in case.
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