Taperssection.com
Gear / Technical Help => Battery Boxes, Preamps, Mixers, ADCs, and Processors => Topic started by: grayp on October 12, 2007, 11:31:14 AM
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i just got off the phone with a buddy that came into possession of a m118. he just got doug to give it a clean bill of health and fresh batteries.
obviously the phantom is different on the 2 boxes, he said doug mentioned that the transformers in the 118 are better quality than the ones in the 148.
anybody ever tested them side by side? i'd love to hear a comp.
gray
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wasn't there another thread recently, I believe a yard sale post of a recent sale of a 148, in which someone spoke with Doug and he says he uses better parts today? I wonder...............................sometimes........................................
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I'm willing to bet that the transistors available today have much lower self noise. Since we don't know what model transformers are in the pres it's kind of hard to say what is better, the 148 does have a nice warm sound though...
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wasn't there another thread recently, I believe a yard sale post of a recent sale of a 148, in which someone spoke with Doug and he says he uses better parts today? I wonder...............................sometimes........................................
yeah i remember that. i'm kinda confused. i have no issues with the way mine sounds. maybe i'll have to see if we can get the 2 of them together to run a comp. guess it would have to be with the schoeps as my 480s wont run on 18v
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Transistors available today are quieter and the transformer designs have surely improved. I'd love to see a schematic but I really doubt that's going to happen...
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I think that I could build something VERY similar to a 148 for $600 and a large number of hours...there's really only a few things going on:
DC power powering the circuits
Phantom power to the inputs
+20dB gain stage via op amps
Transformer based output stage
Sounds like a fun learning experience if you ask me.
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I think that I could build something VERY similar to a 148 for $600 and a large number of hours...there's really only a few things going on:
DC power powering the circuits
Phantom power to the inputs
+20dB gain stage via op amps
Transformer based output stage
Sounds like a fun learning experience if you ask me.
...except perhaps that Mr. Oade has posted several times on the old board that the circuit is discrete transistors. There are certainly lots of cool op amps out there though. It would make a cool project, if someone worked out the design, to do a community/group order and build.
Celac
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Op amps are just simpler, but with some brain busting i think even a discrete design is within reason. It's just a project I want to take on for myself in my quest for knowledge, a good book was recommend as a starting point for learning to do this sort of stuff. FWIW the guys who actually build and design extremely high quality preamps are for the most part self taught mad scientist types who don't have engineering degrees, it's just math and trial and error.
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Op amps are just simpler, but with some brain busting i think even a discrete design is within reason. It's just a project I want to take on for myself in my quest for knowledge, a good book was recommend as a starting point for learning to do this sort of stuff. FWIW the guys who actually build and design extremely high quality preamps are for the most part self taught mad scientist types who don't have engineering degrees, it's just math and trial and error.
Hey,
That sound good to me. I was not arguing for the superiority of one over the other. There are lots of great sounding preamps based around op-amps. If you have a book recomendation I would be interested. You might check out http://www.prodigy-pro.com/forum/index.php ...lots of very focused DIY going on there. It is focused on studio stuff, not taping but I'm sure the priciples apply regardless.
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Yeah I owned an m148 and also an Nbox+ (DIY opamp based pre). They both sounded really good, rivaling any high-end pres sound. I think the discrete transformer based unit is a more fun build for a beginner because it involves more old school type design. I'm gonna start this in a month or so once I get some cash in my hands again. I know enough people to figure this out on my own.
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After bustin' the brain a little bit the design on a preamp similar to the M148 is lookin like a fun project. There's basically 1 circuit to build and then picking out transformers and all that's left is assembly. If the case is a little bit larger the wiring can be made a lot cleaner and the transformers can be isolated from the circuitry some more. I'm going to balance the outputs and possibly add a heavy tented multi position gain knob if I feel up to it. Knowledge is power!
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But why are there only 2 transformers in the 148 instead of 4 like other discrete units I've looked at? One input and one output per channel = 4. So I guess the channels are both using the same transformer or there's only an input or ouput transformer going on. Strange it is...
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Evil Taper, have you gotten so far as to think about battery power? like will you stick with the lead like the 148 or go NiMh??
sounds like a neat project, best of luck
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I think the lead batteries simplify the design significantly since they're already supplying a solid 48-50VDC. It's my understanding that this negates the need for a "phantom power" circuit since that circuit basically consists of a 48VDC voltage regulator. I guess the same type of battery based 48V could be achieved with other types of batteries (like 4 12V) but the lead batteries hold their voltage really well.
What would make things a little more complicated would be a 48V on/off switch because then I'd need a non phantom based power option, probably not that complicated really but it's still more circuitry to deal with. There's this dilemma of simplicity vs functionality and really the M148 is designed specifically for concert recording. So it's only designed to power condenser mics and then interface very nicely with a recorders unbalanced inputs. Great for tapers, not great for studios. One of the coolest things about mic pres are the balanced outputs, kinda a big deal.
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cool project, good luck!