Taperssection.com
Gear / Technical Help => Battery Boxes, Preamps, Mixers, ADCs, and Processors => Topic started by: thegreatgumbino on October 24, 2005, 07:37:06 PM
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I know the majority of this info is available through the search function or on the old Oade board, but I figured it would be benefitial to have it all in one place. Feel free to comment/correct/add information as needed. I'm not claiming any of this info as my own, but I was too lazy to quote the different sources.
The M148 is a purist design pre amp built by Doug Oade with the best quality components made. Originally built by Doug for Doug back in the 80's, he started building & selling to the public because so many other folks liked it. A limited number were produced, and they are no longer built (with the few exceptions every now and again). The design has been refined, due to parts improvements, but is basically the same today. High quality Jensen transformers and discrete transistors are hand matched to better than one percent tolerances. All point to point wiring is used to avoid the problems associated with PCB traces and to ensure the most transparent sound available. It features a max input of -10dB, a fixed 20 db gain stage, and all discrete transistor design. While it is solid state, it was built to sound "tubeish". It is colored by design with a warm, fat, grainless, punchy low end while still being transparent and detailed with no background noise. It was designed to help digital sound analog. It has one switch; on and off.
The M148 has XLR connectors, but has an unbalanced output. XLR's were used for their long life and solid connection. Since the cable length from the M148 to the recorder is short, no electronics were added to the signal path to balance the output.
It is constructed in an 8” x 2 ½” x 5” aluminum chassis with gold plated contacts for inputs and outputs and weighs about XX pounds. A handy battery meter lets you know the amount of charge in the batteries at the push of a button. This unit is now available in a 48 volt version, the M148. Like the M118, the M148 comes with a Five year parts and labor warranty, excepting the battery pack, which is warranted for 90 days.
The rechargeable battery pack will save the end user a surprising amount of money over the units lifetime (still unknown, we have 12 year old units still in the field today!). With over 12 hours of record time available (estimated 14 on full charge), it is unsurpassed as a reliable work-horse. The M148 uses 8 each, 6 volt gel cell (SLA) Powersonic PS-605 batteries in series to provide pure DC with no DC > DC converter. This is partly responsible for it being such a clean pre. The charger should output about 54 volts DC. After a full charge a real healthy voltage is 54-56V. If your battery is a little older it should be closer to 53V. Going below 48 is where you start having problems. If you are below 48 you might not want to start another set. The batteries have a 300 cycle lifetime, but should be replaced every 3 years max. The M148 should not be operated while plugged into the charger.
Lead acid batteries hate being left discharged, so remember to store it fully charged and with the power switch in the off position ( to the left). Recharge about 2 hours for every 1 hour used. The charger is not a "smart" chargers and will overcharge the batteries if left connected for too long, so overnight charge = GOOD, multiday charge = bad. The amber light on the front shows a full charge when the button above it is lit. The red one goes out when the unit is too low on juice to work. The amber light on the rear shows you’re getting power for a charge. The bottom right input is the right channel while the right output is directly above it.
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The M148 has XLR connectors, but has an unbalanced output. XLR's were used for their long life and solid connection. Since the cable length from the M148 to the recorder is short, no electronics were added to the signal path to balance the output.
Is this correct? I used standard cheapo xlr's from Guitar Center and didn't have a problem. I thought to go from unbalanced to balanced you'd have to pull some special magic? Perhaps Doug has changed this in the later models?
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has anyone ever tried to make one on their own?
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Someone who I went to electronics school w/ made a mono preamp w/ 60db of gain, sounded similar to an m148 the few test runs we did in class, but I quit going to school and havent talked to him in years, hes one of the best point>point solderers ive ever laid eyes on as well ;D
maybe its time to find him ;D
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i would like to see a m148 built on lundahl LL7903 and LL1674 transformers.
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i would like to see a m148 built on lundahl LL7903 and LL1674 transformers.
Muj,
Why ???
-Charlies
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i would like to see a m148 built on lundahl LL7903 and LL1674 transformers.
Muj,
Why ???
-Charlies
hey ;D
just to see if the coloration or lack of ??? is more desirable for some tapers.
peace
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here's photo of my m148
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I would give it a shot (building one)...if I had dumb'd up schematics...or even estimates.
I've wanted to build a preamp for a dogs age. all of the little 6v's is so purist cool (but heavy).
I took Carls apart once or twice...and got a good feel for the layout.
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I would give it a shot (building one)...if I had dumb'd up schematics...or even estimates.
I've wanted to build a preamp for a dogs age. all of the little 6v's is so purist cool (but heavy).
i wouldn't mind spending a winter tooling around on one either.
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wow, not much to these things. to a trained electronics tech i bet this would be cake. once I get mine I'm gonna have a tech take a look at it and see what he thinks...cuz there's like 40 parts total to this thing probably. wouldn't you be pissed if it really only costed like $200 to build on your own?
edit: k, there are some jensen transformers that are 200+ per piece. So that's at least $400 assuming those are what are actually in the brick. I'll have a better estimate in say 2 weeks after I get mine to study a bit.
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there should be schematics at the jensens xfmrs website
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anyone have the part number on the transformers?
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http://www.jensen-transformers.com/apps_sc.html
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edit: k, there are some jensen transformers that are 200+ per piece. So that's at least $400 assuming those are what are actually in the brick. I'll have a better estimate in say 2 weeks after I get mine to study a bit.
there is a lot of dough in parts in there...dispite the fact that they are few.
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Word, I don't imagine doug would charge astronomical overhead on anything, just curious what it would actually cost to DIY.
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i'm sure it would be less money than a new one.
:)
but still, its not a legendary preamp due to cheap parts, that much is for sure.
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It could probably be done, but it's Doug ear & talent that make this pre what it is.
How's the old saying go? You can duplicate, but never recreate...
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It could probably be done, but it's Doug ear & talent that make this pre what it is.
How's the old saying go? You can duplicate, but never recreate...
that is BS, IMO. anything that is made by somebody can be (1) remade and (2) made better.
that being said, i have loved the m148> modSBM-1 and m148> V3 recordings i have made.
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that is BS, IMO.
Pardon me. :P
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that is BS, IMO.
Pardon me. :P
this is my personal philosophy about products and engineering. once great builders of things will always be overshadowed by what lies ahead, though they might not be able to get there without the knowledge of brought by those that went before them. "Standing on the shoulders of giants," so to speak.
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i'm sure it would be less money than a new one.
:)
but still, its not a legendary preamp due to cheap parts, that much is for sure.
Sure it would be less money to DIY...it always is...but no, the parts aren't cheap. If you search around on the Oade forum you can find the part numbers for the transformers...I used to know what they were. There was also a thread somewhere in there where someone added up the cost of the components and it was a higher number than I expected. I've looked for that thread again at one point, and couldn't find it....hard to search that forum. At one point I did look up the transformers on Jensen's site and they are expensive ~$175-200 each. Doug also hand matches the rest of the components to get very tight tolerances. Granted, anyone w/ the proper experience could do the same, but it does require effort on the part of the builder and that is also part of what you are paying for.
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i'm sure it would be less money than a new one.
:)
but still, its not a legendary preamp due to cheap parts, that much is for sure.
Sure it would be less money to DIY...it always is...but no, the parts aren't cheap. If you search around on the Oade forum you can find the part numbers for the transformers...I used to know what they were. There was also a thread somewhere in there where someone added up the cost of the components and it was a higher number than I expected. I've looked for that thread again at one point, and couldn't find it....hard to search that forum. At one point I did look up the transformers on Jensen's site and they are expensive ~$175-200 each. Doug also hand matches the rest of the components to get very tight tolerances. Granted, anyone w/ the proper experience could do the same, but it does require effort on the part of the builder and that is also part of what you are paying for.
You can't throw this thing together in 20 minutes, that's for sure. Reguardless of how much the parts cost, I'd like to see how much a shop would charge for assembly, I'm guessing that for the $, the m148 was a bargain.
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You can't throw this thing together in 20 minutes, that's for sure. Reguardless of how much the parts cost, I'd like to see how much a shop would charge for assembly, I'm guessing that for the $, the m148 was a bargain.
That was exactly the conclusion that the person who added up the cost of the parts came to. Not to mention I've never really known Doug to be out to screw the taping community out of $$$$ either. Hell, he GAVE me the controller board he needed to fix my D8 b/c he said he had some used ones laying around and only charged me for the labor. Not that anyone here is saying it's over-priced, but still, thought it was worth saying.