[slowpogo]

That's exactly it tomb, where did you get those? From the source given above (superbrightleds) or somewhere else?

I once bought a "cyan" LED for my Pimeta, but it ended up looking plain old green. So I'm confused over that spectrum.

 

[tomb]

Quote:

Originally Posted by slowpogo /img/forum/go_quote.gif That's exactly it tomb, where did you get those? From the source given above (superbrightleds) or somewhere else? I once bought a "cyan" LED for my Pimeta, but it ended up looking plain old green. So I'm confused over that spectrum.

Sadly, LSDiodes. I'd tell you what wavelength they were, but that was on the LSDiodes site, too.

 

[cetoole]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif Sadly, LSDiodes. I'd tell you what wavelength they were, but that was on the LSDiodes site, too.

Using the Wayback Machine, from archive.org, it appears that the Sea Green 5mm LED from LSDiodes had a peak emission wavelength of 495nm.
http://web.archive.org/web/200610220...products_id=11

Tom said something about me experimenting with a speaker option for the Max a few pages ago. So far, this "experimenting" has just been me having some old (~10 years) Sony 3 way bookshelf speakers I had sitting around as part of a mini system, and powering them instead using my Max. I havnt really done anything different with this, though a note to any trying it is that you cant have any additional output resistance for it to sound like anything. I prefer the sound though to what I get from the Sony amp. I bet the Sony can go louder, as it is rated for 100WPC (at 10% THD

), but this sounds better to me, at the levels I prefer in my bedroom.

 

[tomb]

That Wayback Machine is pretty cool!

I was able to look up the wavelength the LSDiodes still in my parts box. The tricky thing has always been to match up a low-power panel LED with the high power ones under the tubes. It's been suggested before to use a much higher value resistor on the panel LED, but this is not an ideal solution. The panel LED should be diffuse. Also, the panel LED should be a 5mm (IMHO), whereas the 3mm's are under the tubes. All that conspires to mean that the panel LED is different.

Anyway, here are the wavelengths of the other 3mm LSDiodes for those that are interested:

Blue ...... 468 nm
Green .... 515 nm
Amber ... 586 nm
Red ....... 625 nm

I recently used the Green on a new MAX and that wavelength is a little difficult to find, too, unfortunately.

 

[slowpogo]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif The tricky thing has always been to match up a low-power panel LED with the high power ones under the tubes...The panel LED should be diffuse.

My solution to this was to use a white LED for the panel. But, I've found that it's hard to find a low power white LED for some reason (most are at least 1000mcd), and even harder to find one that has a diffuse or "milky" lens. I'm still looking...

 

[amb]

I have "converted" clear-lens LEDs to milky-diffused by sprayting a few coats of matte-clear finish over the lens. Krylon makes something like that (usually available at hardware or automotive supply stores), and there are also others that could be found at hobby stores. Allow each coat to dry thoroughly before the next coat until the desired finish is reached.

 

[slowpogo]

Thanks amb, I will probably try that.

So I'm waiting on parts for the can't miss build #1. I plan on following the suggestion of a PIO cap in CA8 and nothing in CA9. But, is there any advantage at all to using boutique caps in any of the other Wima positions? (CA3, CA6)

I ask because I have some Auricaps from another project that I never used, and I thought I might as well put them in the Max.

 

[tomb]

Quote:

Originally Posted by slowpogo /img/forum/go_quote.gif <snip>So I'm waiting on parts for the can't miss build #1. I plan on following the suggestion of a PIO cap in CA8 and nothing in CA9. But, is there any advantage at all to using boutique caps in any of the other Wima positions? (CA3, CA6)</snip>

No.

 

[pinkfloyd4ever]

hey I finally got all my parts to start my amp (thanks a TON to 04blumach) and I'm almost done soldering all the resistors and the small diodes, but I'm wondering, is it necessary to clean the flux, and if so, will alcohol hurt any of the other components? (if so I'll do it now, otherwise I think I'll wait till I'm done soldering on the board). I like to think I've been doing a pretty good job soldering, as nice as most that I've seen here, before cleaning flux anyway. Plus soldering on this board is SO MUCH easier than the ratshack protoboard most of us build cmoys on.

 

[xmokshax]

just thought i'd let everyone know that, after a misdiagnosed non-problem, my MAX is indeed alive and sounding excellent!

everything's up and running, DBs biased to 100mV... just needs to be cased up. i do have a couple of questions, though - perhaps someone can answer them for me.

first: i'm hearing a good bit of scratchiness from my volume pot (standard RK27). this is especially noticeable when i change the volume with no music playing - it sounds like the wiper is grinding along the contacts. i don't have a lot of experience with the RK27 yet, but is this normal? i'm not using unusually sensitive headphones, it happens with both Senn HD535 and AKG K240.

second: it takes a little while for the tube bias voltages to settle down to the ~13.5V set point, perhaps on the order of 3 to 5 minutes to get all the way down. i assume this is normal for tubes as they warm up, but i just want to make sure. there isn't any danger in listening to the amp when the tube biases are up in the higher teens rather than at 13.5V, is there?

third (related to the above): how important is it to have the tube biases precisely at 13.5V (i know that the tubes CAN run without damage at much higher voltages, but does this affect the amp's sound?)? also, must the two tubes be biased very closely to one another in order for the two channels to sound the same? my tubes seem to be taking quite a while to settle down and stop drifting.

fourth: how has everyone constructed the center support for the PCB? i read through the casework section of the MAX construction page, but i was still a bit uncertain what parts people use to make a nice, stable support and i couldn't quite glean this information from the pics on the site. is it just a screw with a nylon cap and a few washers stacked in between? what size screw fits best in the hole in the PCB?

 

[slowpogo]

Quote:

Originally Posted by xmokshax /img/forum/go_quote.gif fourth: how has everyone constructed the center support for the PCB? i read through the casework section of the MAX construction page, but i was still a bit uncertain what parts people use to make a nice, stable support and i couldn't quite glean this information from the pics on the site. is it just a screw with a nylon cap and a few washers stacked in between? what size screw fits best in the hole in the PCB?

I can tell you what I've constructed..my pcb is in the first slot of the Hammond case. I got it all from Mouser:

Nylon 4-40 thumb screw (1/2 inch, cut to size): 561-T0440050
Standard nylon washer: 561-D432

The screw and washer go through the top of the board, then on the bottom:

Lock washer (against pcb): 534-4693
Thick nylon washer: 561-D462
Nylon hex nut: 561-G440

If you're using a higher slot, you'd have to add some washers or a spacer under the board of course..maybe get a longer screw just in case. The thumb screw is nice because it gives you a little handle to slide the board out with.

 

[tomb]

Quote:

Originally Posted by xmokshax /img/forum/go_quote.gif just thought i'd let everyone know that, after a misdiagnosed non-problem, my MAX is indeed alive and sounding excellent! everything's up and running, DBs biased to 100mV... just needs to be cased up. i do have a couple of questions, though - perhaps someone can answer them for me. first: i'm hearing a good bit of scratchiness from my volume pot (standard RK27). this is especially noticeable when i change the volume with no music playing - it sounds like the wiper is grinding along the contacts. i don't have a lot of experience with the RK27 yet, but is this normal? i'm not using unusually sensitive headphones, it happens with both Senn HD535 and AKG K240.

It definitely sounds like you have a problem pot. I believe if you remove the screws from the back, the front plate can be removed and you can spray in some contact cleaner. Sometimes if you aren't careful with the flux or with rinsing the board, you can get some flux into the pot. That can cause the scratching. Similar questions have been asked on the general DIY forum - you might do a search if that's working.

If none of that works, it may be a bad pot.

Quote:

second: it takes a little while for the tube bias voltages to settle down to the ~13.5V set point, perhaps on the order of 3 to 5 minutes to get all the way down. i assume this is normal for tubes as they warm up, but i just want to make sure. there isn't any danger in listening to the amp when the tube biases are up in the higher teens rather than at 13.5V, is there?

You're lucky - it sounds like your tubes are broken in.

I suspect, though, that if you were to check it some 3-4 hours later you may find that they're running at 12.5V instead of 13.5. Regardless, it's perfectly normal. In some cases with new tubes, it may take a week of running before they calm down - taking an hour or two to settle into a semi-constant bias.

Quote:

third (related to the above): how important is it to have the tube biases precisely at 13.5V (i know that the tubes CAN run without damage at much higher voltages, but does this affect the amp's sound?)? also, must the two tubes be biased very closely to one another in order for the two channels to sound the same? my tubes seem to be taking quite a while to settle down and stop drifting.

Technically speaking, the bias provides the center point for the swing of the audio wave. We set our Millett and MAX tubes at 1/2 of the supply voltage. That gives a maximum voltage swing in both directions for the music signal sine wave.

However, if the bias is too high, then the music may clip - Supply voltage minus bias voltage is your signal swing capability in the positive direction. Conversely, if the bias is too low, then the music may clip in the other direction.

Is this precise? Heck no. Your bias can vary 2, 3 volts or more without you ever noticing it. Now, the reason I say always check bias if you change tubes is because going from a 12AE6 to a 12FK6 can sometimes result in a bias change of 8 or 9V. I think that's more than enough to make a difference.

My tubes probably vary between 13 and 14 all the time. I tend to set them a little high - maybe 13.6 to 13.7, knowing that they typically drop a bit over a period of hours - but none of this is hard and fast - or precise when it comes to tubes.

Quote:

fourth: how has everyone constructed the center support for the PCB? i read through the casework section of the MAX construction page, but i was still a bit uncertain what parts people use to make a nice, stable support and i couldn't quite glean this information from the pics on the site. is it just a screw with a nylon cap and a few washers stacked in between? what size screw fits best in the hole in the PCB?

Slowpogo already gave you a great answer. I've also posted an answer further back. I typically use a 4-40 x 1/2" long screw and some combination of washers and spacers so that a thick nylon nut is just scraping along the bottom of the case.

 

[xmokshax]

slowpogo: thanks. i think i have most or all of those parts lying around. i'll also have the pcb in the bottom slot (Jeff's kit with the big tall KZs and 1.5" sinks), so what you've described will work perfectly. much appreciated.

tom: thanks for the explanations. i haven't logged any serious listening hours on the amp yet, so it may well be that the tube biases will change a good bit after a few hours, as you say. i'm hoping i don't have to replace the pot, but we'll see.

 

[cetoole]

Quote:

Originally Posted by pinkfloyd4ever /img/forum/go_quote.gif hey I finally got all my parts to start my amp (thanks a TON to 04blumach) and I'm almost done soldering all the resistors and the small diodes, but I'm wondering, is it necessary to clean the flux, and if so, will alcohol hurt any of the other components? (if so I'll do it now, otherwise I think I'll wait till I'm done soldering on the board). I like to think I've been doing a pretty good job soldering, as nice as most that I've seen here, before cleaning flux anyway. Plus soldering on this board is SO MUCH easier than the ratshack protoboard most of us build cmoys on.

I like to clean as I go, since taller parts make it difficult to access the flux on the component side of the board. Wont hurt anything, though I like to be careful around the pot, since that is pretty much the only part that isnt hermetically sealed. If you use acetone like I sometimes do though, it will remove all of the ink from parts, especially capacitors.

As to the board being easier than ratshack protoboard, you will get no arguments from me on that number, but I like to use pad-per-hole protoboard for prototyping, with all connections made using component leads as traces, and this, at least for me, is also much easier than struggling with that ratshack ****.
Quote:

Originally Posted by xmokshax /img/forum/go_quote.gif just thought i'd let everyone know that, after a misdiagnosed non-problem, my MAX is indeed alive and sounding excellent! everything's up and running, DBs biased to 100mV... just needs to be cased up. i do have a couple of questions, though - perhaps someone can answer them for me. first: i'm hearing a good bit of scratchiness from my volume pot (standard RK27). this is especially noticeable when i change the volume with no music playing - it sounds like the wiper is grinding along the contacts. i don't have a lot of experience with the RK27 yet, but is this normal? i'm not using unusually sensitive headphones, it happens with both Senn HD535 and AKG K240. second: it takes a little while for the tube bias voltages to settle down to the ~13.5V set point, perhaps on the order of 3 to 5 minutes to get all the way down. i assume this is normal for tubes as they warm up, but i just want to make sure. there isn't any danger in listening to the amp when the tube biases are up in the higher teens rather than at 13.5V, is there? third (related to the above): how important is it to have the tube biases precisely at 13.5V (i know that the tubes CAN run without damage at much higher voltages, but does this affect the amp's sound?)? also, must the two tubes be biased very closely to one another in order for the two channels to sound the same? my tubes seem to be taking quite a while to settle down and stop drifting. fourth: how has everyone constructed the center support for the PCB? i read through the casework section of the MAX construction page, but i was still a bit uncertain what parts people use to make a nice, stable support and i couldn't quite glean this information from the pics on the site. is it just a screw with a nylon cap and a few washers stacked in between? what size screw fits best in the hole in the PCB?

Glad you got it working; it feels great for me to see these things come online.

The scratchiness could be a result of a bad or dirty pot, but it also could be a due to DC voltage on the input. I would measure this, and quickly, since it can do damage to the pot, and generally isnt good to have DC on the input of the amp. It may be that you are one of the cases where input capacitors are advisable. If this is the case, there isnt a board location for these caps, but you just replace the input wire from the RCA jacks. I recommend ~1.5uf or so, but this is pretty flexible.

As for the bias, the other guys covered this pretty well. I will say I am running Tung Sol 12FK6 right now, and each are holding constant at 13.5v on the plate after some hours of operation. I rolled these in about a week ago; they had been NOS prior to that.

I am a bit different when it comes to the center hole than some of the others here; I use an aluminum standoff, screwed tightly to both the board and case, and use this as my only ground connection to the case. RCA jacks are isolated, as is the output jack. Makes a good, solid connection, which is the main reason I use it, and I have no worries about board flex when inserting or removing tubes. Really though, any of the listed methods work.

 

[xmokshax]

colin: i hear scratchiness only when i turn the shaft of the pot. i wasn't terribly specific about this in my initial post. is this still a symptom that would be consistent with DC on the input? i've only used an iPod as the source thus far, and i've measured very little DC on its output in the past.

i'm thinking of ordering some 12FK6 tubes for the next MAX i build (this one is a gift, so now i have to take care of "number one"). where do you recommend buying them online? i'm sure this information can be found readily on the forums, and i'm doing a search as we speak, but i thought i might as well ask since your mention of your own 12FK6es reminded me.