[tomb]

denden88,

Please refer to this pic from the MAX website to see if you've oriented your output transistors properly:

 

[denden88]

pictures:
http://farm4.static.flickr.com/3220/...76c60809_o.jpg
http://farm4.static.flickr.com/3269/...9438032c_o.jpg

ack didnt take any of the output transistors, ill check them real quick

 

[tomb]

I'm concerned that the way you've mounted those output transistors is causing problems. With those standoffs sticking out like that, it's probably very easy to short them out with a probe or something. In any event, you'll never be able to bias them properly without better mounting to the sinks.

Please verify that the MJE253's are on the middle heat sinks and that the MJE243's are on the outside sinks. Those are the only things I can see from here - except as you say, RB2R is smoked.

Did you turn the DB trimmers all the way clockwise (about 20-25 turns) before you turned it on? It's possible that they developed enough heat to burn that resistor out, if not. I really think it's a short somewhere, though.

 

[fran]

If you're using MJE253/243 you have them mounted in the wrong positions. And definitely something is wrong with the way the 2 are mounted in the centre of the board.

Have a look again at Tomb's earlier post above.


Fran

 

[slowpogo]

Quote:

Originally Posted by BoilermakerFan /img/forum/go_quote.gif Is it just polished metal like aluminum? If it's polished and not painted you can torch it to relax the memory, then flatten it under very heavy weight, books won't be enough. The other option is to use JB Weld to bond it to the case top, but it might bow again before the JB cures, so I'd try to flatten it first.

I think it's painted; it's not shiny metal colored, more a flat gray finish. I will try putting it between some books with about 75 pound of barbells on top for a few days. Hopefully it should be close enough to flat that the JB Weld will work. I'd forgotten about the "cold weld" stuff, thanks!

 

[slowpogo]

I read a ways back that it's possible to use the Max as a preamp..IIRC you can just run some RCA jacks to the extra output pads.

My question is, what DIY power amp project out there would go well with the Max as preamp? I'm thinking of something basic, two-channel and modest power, but with good enough sound to take advantage of the Max (and hopefully, a similarly great price/performance ratio). Any suggestions? Thanks!

 

[BoilermakerFan]

Quote:

Originally Posted by slowpogo /img/forum/go_quote.gif I read a ways back that it's possible to use the Max as a preamp..IIRC you can just run some RCA jacks to the extra output pads. My question is, what DIY power amp project out there would go well with the Max as preamp? I'm thinking of something basic, two-channel and modest power, but with good enough sound to take advantage of the Max (and hopefully, a similarly great price/performance ratio). Any suggestions? Thanks!

Yep. Colin's MAX board is pretty amazing and has a lot features built in that most peeps don't even use! My priority is headphone SQ, so that's why I'm using the MAX as a preamp for 3 out of 4 of my MAX builds.

My personal choice for my main MAX console build is a hybrid, tube-buffered inverted gainclone amp that uses a single 6992 tube for a stereo pair of LM3875 chips. It can also be built with the higher power LM3886 chip, but you lose a little of the SQ of the LM3875 chip. There are other chip amp kits or designs out there, but I like the simplicity of the tube buffer inverted gainclone. Output is 35W/ch or 50W/ch. SKA Audio also has a nice discrete stereo amp kit for 150W/ch that I'll be using in another build with his 300W/ch mono amp for a 2.1 system. The third build will be another 2.1 system with the LM3875 hybrid tube gainclones feeding a full range pair of speakers and the SKA 150W mono feeding a sub to cover the very low end bass, but with SQ being the priority. The LM3875 and LM3886 definitely top most peeps lists for best sounding chip amps though, so I wouldn't stray far from those for now if you are interested in the gainclone amps.

Twisted Pear audio also makes really nice amp kits that get rave reviews, so if your looking for kits, I'd start with SKA or TP. If you want a more challenging, but IMHO, better amp design, they go for the tube buffered inverted chip amp. FWIW, I'm going to be using Twisted Pear's Darwin Selector as my input switches for my console builds instead of higher end rotary switches.

Tomb has been helping me with this very long process of deciding what to do with these consoles for some time now and he's been a great help. I just wish I was further along in the process, but I still need to order my parts for the other two builds from Beezer, DK, Mouser, and Handmade Electronics among others.

I'll put together the links to all the relevant threads and web sites and I'll send them to you in a PM tomorrow... I've been down and out for the last three days with a nasty virus, so I'm behind on my paperwork and many other things like my electronics orders.

 

[Beefy]

Jeff hasn't got back to me yet with details of my kit, so I thought I'd have a bit of a play around on Mouser to see what I could do with my own BOM.

I'm finding that the cost of the Vishay Dale resistors has decreased by up to a half compared to both the offical and Jeff's BOM...... or have I just gone mad?

 

[Beefy]

Oh, and I saw it asked many pages back, but didn't see an answer. Now that LEDs - LSDiodes Optoelectronics is no more, are there any drop-in replacements for the MHM from the usual suppliers? Mouser would be preferred.......

 

[tomb]

Quote:

Originally Posted by Beefy /img/forum/go_quote.gif Jeff hasn't got back to me yet with details of my kit, so I thought I'd have a bit of a play around on Mouser to see what I could do with my own BOM. I'm finding that the cost of the Vishay Dale resistors has decreased by up to a half compared to both the offical and Jeff's BOM...... or have I just gone mad?

No, that's right, by gosh -8 cents for a RN55D1001FB14 (1K RN55 V-D resistor). It's nice to see prices going down for once. I doubt that we're going to see too much of that in the coming months.

Quote:

Originally Posted by Beefy /img/forum/go_quote.gif Oh, and I saw it asked many pages back, but didn't see an answer. Now that LEDs - LSDiodes Optoelectronics is no more, are there any drop-in replacements for the MHM from the usual suppliers? Mouser would be preferred.......

I just thought LSDiodes was a cool vendor and listed them on purpose. However, 3mm LED's are pretty much a commodity - anything with an mcd >1000 will probably work. It's been my experience, though, that "super-bright" LED's are more easily found elsewhere (and at a lower price) than Mouser or DigiKey. Here's one that many people have used instead of LSDiodes:
SUPER BRIGHT LEDS home

Note that I use 5mm, low power diffused LED's for the panel LED. These from Mouser have given me great results:
78-TLHB5400 Blue
78-TLHG5400 Green
78-TLHR5400 Red
78-TLHY5400 Yellow

 

[tomb]

Quote:

Originally Posted by fran /img/forum/go_quote.gif If you're using MJE253/243 you have them mounted in the wrong positions. And definitely something is wrong with the way the 2 are mounted in the centre of the board. Have a look again at Tomb's earlier post above. Fran

I think denden88 has them correct. It's just that we can't tell 253 from 243 from here, which is why I asked him to check which transistors were which. His photo is upside down relative to the image legend posted from the MAX website, so it looks wrong - but the MJE's are on the volume pot side of the heat sinks.

 

[Beefy]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif It's been my experience, though, that "super-bright" LED's are more easily found elsewhere (and at a lower price) than Mouser or DigiKey.

I suspected that, but I'd still be trying to keep things from one supplier.

Quote:

Note that I use 5mm, low power diffused LED's for the panel LED. These from Mouser have given me great results:

Don't recommend the one in the BOM anymore?

I used a really expensive Lumex one in my M^3, but it is pretty.

Oh, related question...... any problems with changing RA5C independent of RA5L/R?

 

[tomb]

Quote:

Originally Posted by Beefy /img/forum/go_quote.gif I suspected that, but I'd still be trying to keep things from one supplier. Don't recommend the one in the BOM anymore?

Hmm ... actually, no. That one is "clear." I guess I need to change that.

Quote:

I used a really expensive Lumex one in my M^3, but it is pretty. Oh, related question...... any problems with changing RA5C independent of RA5L/R?

No, each LED is independently sourced - but the ones I just posted do fine with the same 2K resistor.

 

[Kenneth S]

I am mulling over popping in a stepped attenuator in its place. You reckon that will improve things?

Gonna start on the second build am going for a full sized wooden chassis. With blackgates and MOSFETs, how you reckon it will sound? And yeah maybe a stepped attentuator.

 

[fault151]

Quote:

Originally Posted by Kenneth S /img/forum/go_quote.gif I am mulling over popping in a stepped attenuator in its place. You reckon that will improve things? Gonna start on the second build am going for a full sized wooden chassis. With blackgates and MOSFETs, how you reckon it will sound? And yeah maybe a stepped attentuator.

What does a stepped attenuator actually do to the sound? How is it better than say a decent alps pot?