[cricket]

Make that a league of four. I evidently finished my coaster 29 July, when I started the notes for this:

It took 1.5 hours to install surface mount components. Most of that time was determining a sequence so I wasn't blocking components that would be added later. A lot of SMD time was spent locating the correct component location on the board. I found out it's better to install U3 before C11, even though U3 is larger and taller than the cap. The tab of the regulator is difficult to solder with C11 in the way. Overall, Jason's design is nice and open compared to many boards I've designed and built. I'd call the coaster a good beginner's project.

Through-hole components took about 30 minutes.

I used machine pin sockets to make tube swaps easier than repetitive soldering and desoldering, but they're still a pain. If I were planning a lot of tube matching, I'd use terminal blocks like https://www.mouser.com/ProductDetail/Phoenix-Contact/1725685?qs=sGAEpiMZZMvPvGwLNS67143eXz6yLKIOODcchidcDdY%3d

Jason has mentioned that the tubes have microphonic characteristics. The first thing I noticed when listening was a constant oscillation around 4KHz. The oscillation can't be measured on my oscilloscope, although it fades to near inaudibility after about a minute. The least amount of movement brings it back, however.

Bass and midrange are quite good, while highs seem a little attenuated. This quality is what I imagine when someone describes an audio component as having a 'warm sound'. I have no other headphone amp, so can't make any comparisons.

I have an idea for mounting the amp and a unique concept for an alternate power switch. Given the way things are right now, it may be a month or so before that gets started.


Important edit: For anyone following this thread, don't order the terminal blocks I linked to above. The pins are square and oversize for the holes. There are similar designs that have smaller round pins, but I haven't looked for any yet. Knowing the hole diameter would help in the search.

 

[Paladin79]

And now we are four. Congrats cricket!

 

[CAPT Deadpool]

So I'm going to put this out to the group. I have a crackle that seems loud when the attenuator is a low volumes in the left channel. But the crackle is not really noticeable once you get up into the 85db-90db range. I'm guessing it is a problem with the left channel tube. I've only got the two tubes right now as I sent my other 10 tubes off for some help with matching.

Anyone have any thoughts on what else it could be or agree that it is likely the tubes?

 

[cricket]

So I'm going to put this out to the group. I have a crackle that seems loud when the attenuator is a low volumes in the left channel. But the crackle is not really noticeable once you get up into the 85db-90db range. I'm guessing it is a problem with the left channel tube. I've only got the two tubes right now as I sent my other 10 tubes off for some help with matching.

Anyone have any thoughts on what else it could be or agree that it is likely the tubes?

Swapping left and right tubes might be the easiest way to test.

 

[Paladin79]

Good answer. Hopefully you have solder wick or a solder extractor. It takes a while but it can be done.

 

[CAPT Deadpool]

Good answer. Hopefully you have solder wick or a solder extractor. It takes a while but it can be done.

Unfortunately or fortunately I do. I've almost used up the super wick roll I have.

 

[Ripper2860]

Posted in error

 

[Th3Drizzl3]

for the time being my coasters have been put on the waiting shelf. i have some alpine car amps i was given for free that im looking for parts for to repair. they are turning out to possibly be paperweights. these are the pdx line i was given 4 of the pdx 1.1000's all had a fet blow but these are controlled by the "ice" chips and im finding parts almost impossible to find. i was hoping to use them since i loved my pdx amps i had back when they came out. that and im building my mainline and a couple other tube amps. i did get most of the parts in this week though for the coasters. i ordered enough to build 4 to start with

 

[cricket]

CAPT Deadpool,

I'll make another suggestion about the crackling noise based on your pic on Schiit Happened. Try cleaning the flux from your board. We have to be obsessive about flux removal where I work or we don't get readings of ~48 gig ohms on leakage tests. I'm guessing you used the no-clean variety and alcohol should remove it. Gently scrub with denatured alcohol and a brush then flush again with alcohol. Avoid getting it in the jacks or the pot. Blow the board off with compressed air when you're done. All the usual precautions apply when working with flammable liquids.

 

[CAPT Deadpool]

Thanks much, I'll do that. My 33W at work suggested much the same yesterday. I was using 70% iso to clean with less than stellar results. Yeah there is even more flux on it now. I'll get that stuff soon and try it out. Learning a lot here. Thanks again for the tips.

 

[CAPT Deadpool]

CAPT Deadpool,

I'll make another suggestion about the crackling noise based on your pic on Schiit Happened. Try cleaning the flux from your board. We have to be obsessive about flux removal where I work or we don't get readings of ~48 gig ohms on leakage tests. I'm guessing you used the no-clean variety and alcohol should remove it. Gently scrub with denatured alcohol and a brush then flush again with alcohol. Avoid getting it in the jacks or the pot. Blow the board off with compressed air when you're done. All the usual precautions apply when working with flammable liquids.

Do you have a recommended brush type? My friend the 33W gave me a recommendation but I can't remember what he said.

 

[cricket]

Do you have a recommended brush type? My friend the 33W gave me a recommendation but I can't remember what he said.

An acid brush, the type with a tubular sheet metal handle, with bristles trimmed to about 1/4" works well. An old toothbrush with the handle bent slightly backwards works, too.

 

[CAPT Deadpool]

https://www.amazon.com/AES-Industri...=flux+brushes&refinements=p_89:AES+Industries

I found these on Amazon. Made in USA. I probably won't use a gross though.

 

[Paladin79]

Most any hardware store carries them, they are used a lot with paste flux for soldering copper pipe.

If any of you are getting a very noticeable audio pop when the music kicks in after 20 seconds or so, there are 10k bleeder resistors than can be lowered to around 3k , I believe they are R106 and R206 but I left my schematic at home and only have a Bom in front of me right now.

This weekend I hope to test some replacement transistors for the 2SA1312-BL, if all parts arrive by then I hope to be building a couple more coaster amps.

I got the transistors and the size looks pretty good, all other specs look identical from what I can tell.

 

[cricket]

Don't forget the BOM and schematic are available on Schiit's website.

I'm sure I've got some 3K3 resistors in 0603 size. Those should barely fit Jason's 0805 pads.