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Post by unit7 on Jan 29, 2014 9:21:14 GMT -6
Have been thinking about building an LA2 for a few years now, but never felt comfortable dealing with high voltage. Now after like fifteen 500-format module kits - though still not super confident about the risks - I've finally decided to give it a shot. I'm going to let this take some time to be really sure I get everything right. And if there's any interest I could do some simple documentation here among good friends.
When looking at the LA2 documentation I felt that this design isn't that crowded, and after a lot of discussion and mailing with GS member Bowie I decided to skip the PCB route and go for point to point. Bold decision already there!
Deciding and sourcing parts, and studying the design and documentation has been really slow. I believe I've invested like 6-7 full working days. I use Cayocosta's (Rec pro forum) drawing as starting point and then Bowie has showed some serious patience with endless emails discussing the options. He is also going to provide hand picked tubes and some other bits and pieces that I'll need.
I've got AndroidTube's (GDIY) wonderful chassi here, VU meter (Sifam) ordered from Canford, yesterday I placed an order at Mouser and today I got confirmation from Sowter that they are sending a 6kg(!) package with the audio transformers. Then hopefully the stuff from Bowie will complete the parts list. Obviously passed the point of no return!
Again, if there's any interest I'll be back later with some pics and documentation while building. But be prepared, I don't think I'll have this ready until sometime April/May.
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Post by horvitz on Jan 29, 2014 10:43:45 GMT -6
Awesome! Looking forward to seeing the progress. I've thought about doing one of these off and on for a long time and somehow I just don't get motivated. Too many other projects.
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Post by cenafria on Jan 30, 2014 3:35:27 GMT -6
I'm interested in seeing how this turns out. Keep us posted!
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Post by tonycamphd on Jan 30, 2014 14:09:49 GMT -6
Paul...dude....this would be AWESOME!!!!! I'm probably going to build one soon also, I was thinking drip, but I think it would be MUCH cooler to follow ur lead mang
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Post by fishnmusician on Jan 30, 2014 23:29:35 GMT -6
I built a few 500 series and have been wanting to branch out to a tube build also. Really looking forward to following this.
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Post by sparqee on Feb 6, 2014 15:15:44 GMT -6
Tell us more! P2P sounds liberating!
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Post by unit7 on Feb 6, 2014 16:06:03 GMT -6
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Post by jfoc on Feb 28, 2014 14:51:31 GMT -6
Excited to check this out. Thx for the link!
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Post by unit7 on Mar 6, 2014 15:38:04 GMT -6
So all parts except the Sifam meter (AL39WF) has arrived! AndroidTube's wonderful chassi (source: GDIY White market) Hammond 369JX Power transformer (Mouser) Sowter Audio transformers - 1009 (input) with threaded grommet mounting & 1290 (output). I was looking at getting vintage UTC transformers, but after getting info that buying these could be a bit risky and that the Sowters do the job great I decided to settle for the latter. Kenetek T4B Some say this sounds a bit more grabby and modern than the Drip T4Bs, and despite this being an old design, that's what I prefer…at least in theory. I've never worked with a real LA2 but I really love the action of my ADL1500s (using ADL's own T4B) and they are quite grabby, so that's why I went for the Kenetek. Tubes from 'Bowie' - One GE 12BH7A, two alternate 12AX7 for output - Mullard and Telefunken. The latter are told to affect the sound the most so I treated myself with the possibility to experiment a little here. Btw, I already have a NOS GE 6AQ5, and despite perhaps some bad karma I'm going to settle for a Sovtek 12AX7 for the sidechain as that tube has the least effect on the sound. PEC potsCarling switches for on/off and Limit/compress (Mouser# 691-110-73) Davies knobs (Mouser #5164-1919AE) Carbon resistors (Mouser) Capacitors more or less as Cayocosta's build including orange drops etc (Mouser) Chose to save some money on the three way switch for the meter ($72 at Studio Electronics), so Bowie sold me a much cheaper four way switch. So it will go one notch past the markings on the chassi. Substitute for the obsolete NE2 neon lamp (not for illumination but affecting vu meter action old school style) Zener diode 62V 1.3W which does a better job for the meter action than that lamp. Not too many corners cut except for the choice of Sowters instead of vintage, and also the 4 way switch, so I believe budget is around $1100-1200. On the other hand I went for a superb looking and a bit pricey chassi and specially selected and sought after vintage tubes. Still around a third of what the UA reissue costs. Re the build to come, I still don't have a real plan on which order to do all things. My instincts tell me to prepare all the hardware stuff first - drill holes and expand existing holes to fit transformers etc, to avoid metal work later with all components in. I also believe removing the lovely painted faceplate and rack ears would be a good idea to save me from scratching those, and also make the work easier while installing everything that goes to the back plate. Then I believe I'll copy the Hairball 1176 build progression by starting with the PSU and make sure it delivers the right voltages before proceeding. Only drawback would be having that heavy block of metal attached to the body while proceeding with the entire build. Could be a bit inconvenient. Decisions decisions!…  Without a Hairball- or Horvitz build manual this requires some planning! And of course any educated input would be appreciated. Attachments:
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Post by tonycamphd on Mar 6, 2014 21:37:56 GMT -6
So all parts except the Sifam meter (AL39WF) has arrived! AndroidTube's wonderful chassi (source: GDIY White market) Hammond 369JX Power transformer (Mouser) Sowter Audio transformers - 1009 (input) with threaded grommet mounting & 1290 (output). I was looking at getting vintage UTC transformers, but after getting info that buying these could be a bit risky and that the Sowters do the job great I decided to settle for the latter. Kenetek T4B Some say this sounds a bit more grabby and modern than the Drip T4Bs, and despite this being an old design, that's what I prefer…at least in theory. I've never worked with a real LA2 but I really love the action of my ADL1500s (using ADL's own T4B) and they are quite grabby, so that's why I went for the Kenetek. Tubes from 'Bowie' - One GE 12BH7A, two alternate 12AX7 for output - Mullard and Telefunken. The latter are told to affect the sound the most so I treated myself with the possibility to experiment a little here. PEC potsCarling switches for on/off and Limit/compress (Mouser# 691-110-73) Davies knobs (Mouser #5164-1919AE) Carbon resistors (Mouser) Capacitors more or less as Cayocosta's build including orange drops etc (Mouser) Chose to save some money on the three way switch for the meter ($72 at Studio Electronics), so Bowie sold me a much cheaper four way switch. So it will go one notch past the markings on the chassi. Substitute for the obsolete NE2 neon lamp (not for illumination but affecting vu meter action old school style) Zener diode 62V 1.3W which does a better job for the meter action than that lamp. Not too many corners cut except for the choice of Sowters instead of vintage, and also the 4 way switch, so I believe budget is around $1100-1200. On the other hand I went for a superb looking and a bit pricey chassi and specially selected and sought after vintage tubes. Still around a third of what the UA reissue costs. Re the build to come, I still don't have a real plan on which order to do all things. My instincts tell me to prepare all the hardware stuff first - drill holes and expand existing holes to fit transformers etc, to avoid metal work later with all components in. I also believe removing the lovely painted faceplate and rack ears would be a good idea to save me from scratching those, and also make the work easier while installing everything that goes to the back plate. Then I believe I'll copy the Hairball 1176 build progression by starting with the PSU and make sure it delivers the right voltages before proceeding. Only drawback would be having that heavy block of metal attached to the body while proceeding with the entire build. Could be a bit inconvenient. Decisions decisions!… Without a Hairball- or Horvitz build manual this requires some planning! And of course any educated input would be appreciated. Awesome Paul! You are truly the "machine", u are up to this challenge, uve been training for this ur entire life, now go out ther and get em fella!!!!( crowd goes crazy!!!) but be careful, hi dc tube currents!!!  |
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Post by unit7 on Mar 8, 2014 16:09:26 GMT -6
Slow started today with some really tedious and a bit nerve wrecking work: Drilling holes for most screws for tube sockets, transformers etc, also for the main turret board on the bottom plate. Waiting with holes for ground terminals as I'm not 100% sure how many I'll need and placement. Guess I'll figure that out when things come together. Probably won't use the two small turret boards for in/out as the Sowters only have 600Ω in/out. They come with wires instead of pins so I figure I could wire directly to the XLRs instead of going via those original style turret boards. Re the progression of the build, after some tips from Whitmore I've decided to do the main turret board next and solder other small stuff that can be done outside the chassi, both for convenience and to avoid as much flux splatter as possible. Haven't noticed before but AndroidTube obviously failed on the word 'Output' and the lower/left tube should be 12AX7 on the back panel  Attachments:
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Post by unit7 on Mar 14, 2014 17:11:32 GMT -6
Baby steps... Quite content that I found black screws for the IEC inlet, and also the rubber bushings to protect the hi voltage cables from the power transformer. I'd also like to announce the first soldering joint. Not my proudest moment, showing my 'life long training' for this epic project  but I'll keep working that turret board and see if I'll improve at least half way in. Attachments:
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Post by unit7 on Mar 15, 2014 18:16:16 GMT -6
Ready with main turret board for now. I think it looks ok for a first time turret board, but not more than ok I'm afraid. It took way longer than I thought. A little tricky and I actually never really felt 'ok, I've got it'. It took a while to heat those pins enough for the solder to float out so I hope I haven't smoked anything. Also, I was surprised to find metal film resistors as I thought I had only bought those for meter and power stuff. Had a short chrisis about that but decided to ignore it Don't know when I'll have time to continue. Hopefully before next weekend. A lot left to do! Attachments:
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Post by tonycamphd on Mar 15, 2014 20:16:29 GMT -6
Ready with main turret board for now. I think it looks ok for a first time turret board, but not more than ok I'm afraid. It took way longer than I thought. A little tricky and I actually never really felt 'ok, I've got it'. It took a while to heat those pins enough for the solder to float out so I hope I haven't smoked anything. Also, I was surprised to find metal film resistors as I thought I had only bought those for meter and power stuff. Had a short chrisis about that but decided to ignore it Don't know when I'll have time to continue. Hopefully before next weekend. A lot left to do! Looks good Paul, what kind of iron u using? Use a bigger flat tip, higher heat, and a heat dissipating alligator clip on component legs, higher heat gets the area to be soldered hotter, quicker. polystyrene caps are usually the ones to worry bout over heating, U'll be fine with what's there I think |
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Post by unit7 on Mar 18, 2014 10:36:23 GMT -6
Shouldn't be doing DIY right now because I'm buried in work, but couldn't resist mounting the sockets...and then the big caps... Attachments:
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Post by unit7 on Mar 23, 2014 17:34:44 GMT -6
A few more steps: - Turret board mounted - Cables from turret board cut to proper lengths (I hope!) - Sowters mounted - Drilled the first hole for grounding (close to input XLR) Things are going very slow because all along I'm looking at pics of a few other builds and referencing the original schematic and Cayocosta's drawing just to be sure I don't miss anything and also to find any smart/special solution. For instance grounding can be solved in a few different ways. Whitmore told me that he managed to get his build super quiet and free from hum, which is not always the case with LA2 builds, so I'm trying to copy as much as possible from him. But my Sowters has cables instead of pins as the original UTCs so eventually I'll have to find my own solutions on a couple of things. Also it's very hard to try to anticipate cable lengths and cable management for a descent look in the end. Hard to see on the pic but for flexibility very few of the cable ends are actually soldered in. Edit: BTW, I appreciate the 'likes' from you guys, and that you only comment if there's something you really need to say, to give a tip or to warn me. That way, if this build ends up successfully the diary will be kept compressed, pun intended Attachments:
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Post by svart on Mar 23, 2014 20:57:05 GMT -6
I gotta say that I really respect that you are doing this the way you are. Over the years of my own DIY, I became really tired and jaded with the DIY community and the constant influx of kit kiddies who don't care about learning or doing anything with pride. They are only interested in buying a kit and getting something for nothing out of it.
But.. you refresh my belief in DIY with the obvious care you are taking to build your LA2A!
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Post by jeromemason on Mar 24, 2014 18:42:47 GMT -6
Grounding schemes are where it's at man, finding the right way can make all the difference in the world. When I built my Tweed Deluxe I had to come up with a grounding scheme and I'm proud to say my vintage spec TD doesn't have any hum whatsoever. Working in an area that produces over 400 volts is a little scary at first, but once you understand how it can and can't kill you it becomes a little easier.
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Post by mulmany on Apr 16, 2014 7:22:57 GMT -6
unit7, How is the build going?
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Post by svart on Apr 16, 2014 7:52:59 GMT -6
Grounding schemes are where it's at man, finding the right way can make all the difference in the world. When I built my Tweed Deluxe I had to come up with a grounding scheme and I'm proud to say my vintage spec TD doesn't have any hum whatsoever. Working in an area that produces over 400 volts is a little scary at first, but once you understand how it can and can't kill you it becomes a little easier. Grounding is interesting. I work in high speed design, and grounding is one thing we have to get right or nothing else will work. It's not like audio where you get to have a couple ground traces and everything is fine. Here, we have to have multiple full planes, the right amount of vias in the right places, staggering parts for optimal ground current flow, impedance matching, thinking in 3 dimensions for E-MAG fields, etc. And that's before we even start decoupling! In the audio world, much of the source of problem is ground currents, AKA, ground loops. People assume ground is always 0V, but people also don't think about things in terms of currents, where ground has many currents. Where do folks think the current goes when the device is done with it? Designers used to call "ground" the "return", but now it's common (pun intended) to simply call it ground, even though it has to return all of the current from all the devices. Ground loops happen when a device has a higher impedance ground than those it is attached to, thus the current attempts flowing to ground through another conductor that shouldn't have significant currents.. The best way to fix this is finding a way to lower the impedance to the line source, like using a much thicker gauge power cable with a much thicker ground. Another common myth is the "star" ground. It's not "the" cure for a bad design, it's simply an orderly way to organize ground currents so that the ground around sensitive devices is not bouncing. Taking a circuit with ground issues and simply lowering the impedance of the ground to a point where it is the lowest impedance power conductor of the system is the true way to fix such things. Increasing ground wire gauge, or running ground through heavy planes is the best way to fix these issues. |
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Post by unit7 on Apr 16, 2014 14:33:09 GMT -6
unit7, How is the build going? Thx for asking! Have had crazy busy weeks and absolutely zero time left for DIY. Perhaps this weekend. Oddly enough still no Sifam VU in sight... |
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Post by unit7 on Apr 20, 2014 14:53:01 GMT -6
Finally some action. Guess I'm about halfway thru now. Double checked my Sowter wiring today and according to the Sowter schematics I wired the i/p xformer the wrong way earlier. It does feel odd though that the blue wire should be connected to XLR hot and the red wire to cold... Will double check that detail with Sowter before first test ride. Notice how Christian Whitmore showed me how the two/three point terminal blocks can do double duty - as grounding point and insulated connection. This is not how things were done in the original LA2 but Christians idea to save some work and have less holes drilled in the chassi - pretty brilliant! |
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Post by unit7 on Apr 25, 2014 14:37:12 GMT -6
I figured it would be awkward to install the power transformer (Hammond 369JX) after the face plate is installed, so no more escape from PSU wiring and measuring of deadly voltages... Please note that this is wired for 240VHad to use four spacers on the transformer to not squeeze the rubber bushings too much.  I have the utmost respect for this part of the build. Hopefully not time to die yet and I don't want to start a fire, so all measures taken for safe installation. Heat shrink over all unused cable ends:  All unused cables bundled and another layer of heat shrink:  ...and tucked away before wiring for 240V (brown connected to black):  Brown + black cables heat shrinked and tucked away too:  ...and ready for measuring!.. 6.3V wires (for tube heating and VU illumination) measured 6.2V on my cheap DMM, so good enough. BTW I was pretty intimidated thinking about the voltage present in the two red cables to the left...  Ok, after unplugging, time to connect the red cables to my DMM and measure the high voltage...  Only 2-3% off, so success!! So heavy sigh and time to connect to the turret bords, solder/wire grounding cables and tidying up a bit:  |
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Post by unit7 on Apr 25, 2014 16:56:32 GMT -6
Dang!!... With the faceplate it's beginning to look a lot like an LA2! Attachments:
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Post by unit7 on Apr 27, 2014 12:19:10 GMT -6
Funny, I've been so into all the details that I didn't realise until today how little is left!.. Unfortunately the VU meter is going to take a while more, and today when I was soldering the last resistors to the small turret board by the VU meter when reaching for the final resistor R24/3.9K I found the first real error on my Mouser order - the resistor was 3.9Ω instead of 3.9K!...  Having some Mouser items pending I'll just add that resistor. For tidy cable management I've found this:  A silicone glue that sticks the cables to a surface, good for a couple of cables running along the edges/corners inside the chassi: Edit: Note that this glue is approved for electronics work, as it doesn't react chemically with cables, components etc. So final wiring of the stuff on the faceplate and some preliminary cable managament today:  Also attached the rack ears and the knobs!  Now...where is that VU?? I'll have to check if I could test voltages without the VU. In that case I'll be back soon with the results. Testing will be without tubes/T4B first, then with the tubes but without the T4B. Would be great to be able to do that while waiting for the VU... |
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Without a Hairball- or Horvitz build manual this requires some planning! And of course any educated input would be appreciated.
but I'll keep working that turret board and see if I'll improve at least half way in.
Having some Mouser items pending I'll just add that resistor.
