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Millett "Starving Student" hybrid amp
Sep 9, 2009 at 12:43 AM Post #3,826 of 7,277
Quote:

Originally Posted by PJPro /img/forum/go_quote.gif
Actually, I may have just identified a problem with my amp.
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If I turn the sound right down and slowly turn it up, the sound comes out of one headphone while the other is silent. As I turn it up, the other channel gradually gets louder (but always quieter than the other) until it gets to normal listening volume (not that loud) where it appears to have "caught up". I some ways it's like a balance knob being turned from the left to the middle but getting louder at the same time. If I turn it right, right up the sound stays fixed in the middle, rather than continuing on past the middle.

I haven't noticed this until now because I don't really fiddle with the volume once it's set. The amp had warmed up and had a couple of hours under it's belt that day (50 hrs total) when I discovered the issue.

Any ideas or is this normal for valves?


It's the tracking error in the Alpha pot. The Alpha pot is not built for very low-level precision volume adjustment. One of the reasons for using the input resistors is to "level" this trait out, as in the "low volume" progressively extends over a greater range of volume travel. So, you might try higher-value input resistors if this continues to bother you.
 
Sep 9, 2009 at 6:31 PM Post #3,830 of 7,277
OK Guys. Thanks.

I'm using the 100K resistors supplied in the kit. I did try the 50K resistors first but had almost no movement of the pot before it became unbearably loud. So, what to you think might be an appropriate value to try?
 
Sep 9, 2009 at 7:20 PM Post #3,831 of 7,277
Quote:

Originally Posted by PJPro /img/forum/go_quote.gif
OK Guys. Thanks.

I'm using the 100K resistors supplied in the kit. I did try the 50K resistors first but had almost no movement of the pot before it became unbearably loud. So, what to you think might be an appropriate value to try?


It sounds like you may have a particularly strong source and/or sensitive headphones. I built one SSMH that had 48K resistors with a 10K pot, so that was almost a 5-to-1 ratio. It was fine with efficient phones, but wouldn't drive Sennheisers very well.

You want as little as you need, so I'd try 150K or 200K ohm resistors (don't worry about being exact - just use a prevalent size that's close). One option might be to take your 50K resistors and 100K resistors and solder them together. It takes a bit of acrobatics, but if you can imagine an "A" frame formed by the two resistors - with their leads soldered together at their tips forming the top, and the bottom of each placed into the pads on the board - /\ .
 
Sep 9, 2009 at 7:44 PM Post #3,832 of 7,277
After I get my wire in, pick up a Dremel for case work and finish my first CMOY I intend to give this a shot. What's the worst that could happen?


Any fancy hints that are hidden amongst the 256 pages I should know about? :p
 
Sep 9, 2009 at 7:46 PM Post #3,833 of 7,277
Quote:

Originally Posted by tomb /img/forum/go_quote.gif
You want as little as you need, so I'd try 150 or 200 ohm resistors (don't worry about being exact - just use a prevalent size that's close).


That's 150k or 200k (I'm sure everyone got that, but just wanted to make sure there were no accidental blind Mouser orders of 200 ohms resistors
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)
 
Sep 10, 2009 at 12:32 AM Post #3,834 of 7,277
Quote:

Originally Posted by Juaquin /img/forum/go_quote.gif
That's 150k or 200k (I'm sure everyone got that, but just wanted to make sure there were no accidental blind Mouser orders of 200 ohms resistors
wink_face.gif
)


Actually, it's been my experience that if you order 220 ohm resistors from Mouser, you get 220K ohm resistors, instead ... but yeah, all the world was lost in that post for the lack of two K's.
 
Sep 12, 2009 at 4:23 PM Post #3,836 of 7,277
What heatsink and mounting combo is the cheapest? Both the ones beezar and the original recommend runs ~$10. And any cheap power supply?

The input resisters lead into the L/R ins of the pot right? I'm building the beezar version without a PCB.

What would be the best way of wiring ground? I'm using a metal case.

Thanks
smily_headphones1.gif
This is only my second DIY project after the CMOY.
 
Sep 12, 2009 at 5:54 PM Post #3,838 of 7,277
Quote:

Originally Posted by Nonchalance /img/forum/go_quote.gif
What heatsink and mounting combo is the cheapest? Both the ones beezar and the original recommend runs ~$10.


It's true that Mouser and DigiKey have doubled their price on the heat sinks, but doubling $1 and some change still doesn't equal ~$10 (even X2). I'm not sure how you get that.
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Quote:

And any cheap power supply?


Power supplies are all over the place, including ebay. Google "Cisco PSA18U".
Quote:

The input resisters lead into the L/R ins of the pot right?


Yes, but you're going to have enough problems air-wiring a pot without getting resistors stuck in the muck. Personally, I'd stick the input resistors on the ends of the RCA jacks - much simpler. Quote:

I'm building the beezar version without a PCB.

What would be the best way of wiring ground? I'm using a metal case.


Run every negative connection to the case. Quote:


Thanks
smily_headphones1.gif
This is only my second DIY project after the CMOY.


Good luck.
smily_headphones1.gif
 
Sep 12, 2009 at 6:36 PM Post #3,839 of 7,277
Quote:

Originally Posted by tomb /img/forum/go_quote.gif
It sounds like you may have a particularly strong source and/or sensitive headphones. I built one SSMH that had 48K resistors with a 10K pot, so that was almost a 5-to-1 ratio. It was fine with efficient phones, but wouldn't drive Sennheisers very well.


Source - Modded Beresford TC-7510; Headphones - Grado SR80.
 
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