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Posted new design: "Jonokuchi" destop amp - Page 5

post #61 of 67

Update #2:

 

Hey Guys,

 

I have some good news! The amp is working 100% when I select the input to be the front 1/8" jack. However, when I select the rear inputs, I have the same problem as before, where the right channel is fine but the left channel you can barely hear. I had 2 327 ohm resistors lying around, and so I did the hum mod listed on Pete's website. That seems to have gotten rid of the noise/buzzing/hum. Also, shorting JP1 seems to have almost no effect for me, so I removed the jumper.

 

If anyone has any idea how to fix the left channel problem for the rca inputs, I am all ears (yes, pun intended)! You guys have been great so far, thanks for all the help!


Edited by guppysb - 2/22/15 at 2:17pm
post #62 of 67
Quote:
Originally Posted by guppysb View Post
 

Update #2:

 

Hey Guys,

 

I have some good news! The amp is working 100% when I select the input to be the front 1/8" jack. However, when I select the rear inputs, I have the same problem as before, where the right channel is fine but the left channel you can barely hear. I had 2 327 ohm resistors lying around, and so I did the hum mod listed on Pete's website. That seems to have gotten rid of the noise/buzzing/hum. Also, shorting JP1 seems to have almost no effect for me, so I removed the jumper.

 

If anyone has any idea how to fix the left channel problem for the rca inputs, I am all ears (yes, pun intended)! You guys have been great so far, thanks for all the help!

Well that is good news. At least now you know the amplifier itself is working correctly. If you had an oscilloscope you could signal trace that pesky left channel input and see just where the signal disappears. Somehow the signal is getting lost before it ever gets to the amplifier section. There can't be a whole lot to look at, but not having a schematic I really can't suggest what to look for. A cold soldered  connection. A wrong value resistor in the signal path. A reversed capacitor. Or something as simple as the shield of a cable shorting to the center conductor.

 

Good luck.

post #63 of 67

Update #3:

 

Hey Rick, as always thank you so much for the quick replies. Too bad you're in SoCal, I'd buy you a few drinks if you were in the Bay Area!

 

So I took everything apart and applied a bit more solder to shifty looking joints. Then I went through every single part to make sure it was working well. It turns out that R18 and R19 were burned out. They were supposed to be 1M ohm resistors but weren't given even 1/3 of that resistance. So I just happened to have some spare resistors and put them in. Turned on the amp and both the rca and 1/8" inputs are working well!!!!!

 

Once I get the chassis powder coated and stuff, I'll post some pictures. I am just happy that the amp is finally working well, that was like a good 14 hours of debugging lol. I don't really know if the speaker out section works yet since I have no passive speakers, but maybe in the future I'll give it a shot.

post #64 of 67
post #65 of 67
Quote:
Originally Posted by Mr Rick View Post
 

A little celebration music.

 

https://play.spotify.com/track/31JOjxeYaeORVmV41pqgAo

Very nice choice!

post #66 of 67

Glad to hear it worked out! I forgot to mention I had the pictures of my build on my user gallery. I was looking to see how I had it grounded. Moot point now I suppose. What speakers are you using?

post #67 of 67

I am currently using Beheringer Audio Truth 3030A, which are active near fields. I need to find some cheap passive bookshelf speakers to test the speaker outs on the amp.

What is seriously impressing me about the amp is like no harmonic distortion, what so ever. I have maxed the pot to max volume and no hissing, buzzing, humming, or anything. The sound seems good so far, although I am not that impressed by it. I guess a good amount of burn is going to be needed for the amp. I have Motorola 13EM7 tubes in there. Maybe sometime this week I'll order another pair and see how they fare.

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