First Metro Build - 12-Series

[somethin'else]

Hi All,

Just edited this post to trim the fat somewhat...

First I want to say MetroAmp has been my greatest source of casual and not so casual (ie critical) reading for the last two years since I picked up my Metro 50 watter, that the time has finally come to build one "from scratch"... so Many Thanks to All for helping me gather a lot along the way, and for making this great site!

My Metro 100w Plexi Superlead kit arrives tomorrow, and I'm really looking forward to the build. After sorting everything, the first thing I want to do is punch out for an IEC power jack and the ground lug points to do the Larry Grounding.

So, right away, I have a couple of questions regarding Larry Grounding.

I'm getting one of Brian's fine boards and am stoked to loom it up! Which brings me to the board buss wiring. More often than not, I see really clean boards with just caps and resistors on top. Is this mostly an aesthetic preference? My 50 watter had the buss wires on top, which I kind of liked for some reason... maybe I'm nervous of having a bum connection underneath that might be hard to troubleshoot later on, though I plan to take it REAL slow and triple check things. What are your thoughts on this? My feeling is it might be cleaner with underneath buss, but those double tier turrets on Brian's boards are just calling out for clean, multi layer wiring! So maybe it wouldn't be so bad to have them up top?

And onto the Larry Grounding... Here's my diagram, with the exception of the long red center tap running to the front of the chassis to ground lug #1 (thanks Roe).



Thanks in advance, and Thanks to everyone who's already posted their Larry Grounding, so's I could cull them together for the Superlead.
I'll post pics as I go because I want the best eyes on it! ...as long as I can break away from the build long enough to do so!!
I loved the 1987 Metro Lead, and I can't WAIT to hear this thing.

[somethin'else]

Wow, what a messy intro/start.

Massive Thanks to George! for producing this fantastic monster of a kit!

The only downside is my engineer bud couldn't convince me to use silver solder to keep the werewolves away! I got the nice Kester 63/27 as mentioned here and between that and the kit components, I'm having a blast. Someone here also nailed it by saying that building is like meditation.

Got the Larry Grounding points in, Thanks to Kevin and Roe and arledgsc for setting me straight, even after all the threads I've read it still wasn't sinking in. With that I'm off and running...

Time to post some pics. Let me know if anything looks fishy! More later...

[Roe]

looks good to me. be careful with the violet nfb wire. putting it on top of primaries or secondaries may not be good idea. also, it is preferable that the secondaries cross the primaries at a 90 degree angel, or something close

[somethin'else]

Thanks Roe for pointing that out. And for the second time reminding me how important Lead Dress is. For the most part, 90 degrees is the way to go. But in the instructions, the OT Primaries and 2ndaries sort of 'meander' their way at 45 degrees, only to straighten out the last couple of inches to the back of the chassis. And I've seen different views on twisting or not to twist the 2ndaries. So I twisted them.

ACTUALLY, I had the 2ndaries perfect, and then forgot to scrape the enamel off of the leads! So, I went to re-do them, and didn't see anything to scrape off... Drats! The end result was that they came up even shorter the 2nd time around, but o.k.

How does this pic look for getting the primaries and 2ndaries crossing? I sort of nudged things around to get some separation.



Also, should I run the NFB purple along the chassis back with the heaters, then turn in between V3 & V4 for it's entry point to the board?

Another lead dress question. Along with the Mains Fuse, the Common (for the Neutral lug on IEC), and HT Fuse line, I have the PI cap ground (black) running to the front to make it's way to Larry Grounding lug #3. Sound o.k.? Or should I re-route around the outside and along the chassis front as well?



If you recommend best routing for the OT primaries/2ndaries, then I have no problem extending the leads with heatshrink, unless that would create a compromise to their function. I was just following a lot of pics I've seen, so there we are. I just want to prevent as many demon sounds (the bad ones of course) from entering the amp, and try to get it right the first time.

Thanks again, and here's Step 10 in a little detail... That is a full session + I tell ya!

Oh, last thing for now (I have more questions later), do you think my green heater wires should tighten up around V7? I think I might go back and do that... geez. Fun, anyway.

[Roe]

primaries and secondaries look good! you may need to experiment a little with the violet nfb wire (using a chopstick). it can be quite sensitive.

[somethin'else]

Thanks Roe! I had a couple days while Brian's board was on the way, so I got crazy with the zip ties. And THEN, the board came. Nice, and which I proceeded to scratch doing the buss wires. Man...

Got everything run up to the top o' the board, and the inputs and controls side done last night.

I'm cruising down the backstretch now and am having to put the last session or two at bay til next week, argh! We have guests this weekend, and no getting away to zone out on this... ahhh... I am just amazed at how awesome this "kit" is. It will be the nicest amp I've ever owned.

[somethin'else]

I think I'm done! The board is loaded and I formed the caps last night via Larry's prescription, and the voltage went down to 1.22 vdc! It took about four hours on the F&Ts. As Larry says, the amp is now "Valorized"! It was 3:30 am when I checked the final measure, so I haven't tubed and biased yet. Tonight for readings and biasing and... rocking the F out if all goes well. Final pics to follow.

[somethin'else]

Alright, here are the last shots of the board and the filter cap area after I ziptied and cleaned up the wiring. On first fire up, what can I say? It just sounds incredible! Incredible!

I loaded it with JJs to test up, 'cause I'm saving some old preamp glass - a Sylvania, couple GEs, an old Mullard CV4204 which is my killer V3 tube. Wellll, tonight I loaded these and almost immediately got the ZZzztt!! on top of my low E and B notes. I rolled through them, and ended up with the JJs back in, as the noise was most minimal with them. I chopsticked through the entire amp, everything, and couldn't aggravate anything enough to find a sign.

Anyone know where it could be coming from? I noticed it was way more prominent when either the treble or presence was turned up. The purple wires are routed cleanly. Everything crosses 90 degrees as best as I know. Could it be a carbon comp or a cap gone south this early? It didn't do it on first fire up, hmm.

Bias is between 33-35mA with B+ at 488 vdc, all pin readings are amazingly close to the instructions' chart. I do have 3.5vac instead of 3.15vac on pins 2&7 of V4-7, and pins 4,5&9 of V1-3. Eh... not sure why that is...

Other than that, I'm knocked out by everything in this amp. It pretty much blows away everything I've ever played before! Thanks for looking.

[vanhalen5150]

That looks good dude. Any noise?

[somethin'else]

Thanks! Yeah, I have the "ZzZzrRrT" when I lay into low notes like the low E chord, or the low B, or any 5th interval, it seems. It's been called Bad Distortion. Happens seconds after the chord is hit. I know I've seen vhjunkie change a bad cap on V1 in a search. I'm also just starting to read this thread to suss it out.

The amp sounds phenomenal stock. Sweet as hell, and totally pissed too.

If anything I might take a few of the carbon comps out. I have to find this "ZzZzrRrT".

Also, as I mentioned in last post, I have 3.5 vac instead of 3.15 on pins 2 & 7 (v4-7) and 4,5 & 9 (v1-3). I don't know how bad this could be. I need to re-check w/my meter.

I know I don't have any fat strays at the tube sockets that could create arching.

I also have to admit, there IS the slight transformer hum with just the Mains on (in Standby position). Same as you are having? I put a screwdriver up to the PT and OT, and put my ear to the other end like a stethoscope... the OT seems louder than the PT. It kind of bugs me, but not as much as the bad distort thing. I hear the transormer hum is fairly common, and authentic to the original design . It's definitely mild, and would be most noticeable in a recording situation. Oh, the hum is only in the chassis, not through the speakers. I guess this is different from your issue? As you say you have the hum coming through the speakers?

I'm gonna re-check all my grounds and solder joins. I might re-do the PT CT ground run to lug #1 (over by the input jacks). I ended up making two joins to extend it, and think that might be suspect.

Ahh, trouble shooting noise.

Nice build yourself vanhalen5150! Congratulations! I've been watching yours, too, as I'm working on mine. Have you sorted the hum?

[vanhalen5150]

Not yet, Im working on that this weekend. Lots of stuff to look at. High and low power setting sound pretty quiet for a 12000. Its the stamdby that has me puzzled. I had 3.1 across the board. As long as you have everything the same, I dont think 3.5 is really a big deal. Play a bit and keep checking the bias. I noticed mine started to go up, and just reduced it a bit. Seems like it has started to settle down. I still get a bit of "scratchy" with the presence knob. Great clean plexi sound with no tweaking yet.

[somethin'else]

Holy Cremoli Batman! The flying resistor on pin 2 of V3 totally knocked out the "ZZrrRRttTT!" on the low notes. Killer! Thanks Mark Rockstah and rgalpin for digging into this issue!

I put the 220k in and fired 'er back up, checked bias, and heard the sound for the first 20 seconds or so, and then it sort of smoothed itself out to a clean sound. The sound is pure and clean now, and without the low notes caving in, it also smoothed the "high cymbal crash" too. It seems EXTRA clean now, as I only get full burn when dimed. I usually run around 7-8 on V1. I like it.

I think the cymbal crash effect added to a perceived distortion/breakup sound, but now in comparison, it wasn't the best kind of sound. I might try a 100k or even a 47k there, just to see if some of that high cymbal might creep back in, 'cause it is kind of nice to have on tap

Now I can hear those carbon comps sizzling in there way nicer.

[vanhalen5150]

The "flying resistor" ?

[somethin'else]

uuhhhh... that's what I'm calling it. Check that thread link out in my last post (sorry, highlighted in blue). It's an awesome thread with other killer stuff in it too.

It's basically a 220k resistor attached directly to pin 2 of V3, then the green wire attaches to the other end of the resistor. It totally cleaned up my sound and distortion. I just tried swapping the 220k with a 100k, and some of the high end presence came back, giving up more "cymbalic" top end distortion. But I switched back to the 220k. It's tight, and I can really lay into low chords without the notes crapping out and going "ZZzzrrTT".

Flying Lead's what I call it, but I gives names to stuff that I don't quite understand, 'cause I like to pretend I'm making up a whole new language. Dangerous round here, I know, I should watch that! Correct me if I'm wrong?

[Roe]

Ok, its possible that you are experiencing blocking distortion in the pi (or even oscillation).

try reducing the .022 connected to the treble pot to .01-.001uf. this will have no or minimal effect on bass but will make the pi less prone to blocking distortion.

try reducing the 220k grid resistor to 47k - this way you wont kill so much highend