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Longest Ever Amp Build ?

post #1 of 5
2/4/12 at 10:10am
Thread Starter 

Hi everyone,

 

First post, but I've been lurking here recently.

 

I'm pretty pleased as I've just finished building my first ever DIY project and I reckon it's probably the longest headphone amp build ever. I first built an SDS Labs amp back in 1999 to power a set of Grado SR 80's I'd just bought (and still have) but for a variety of reasons I could never get it to work properly and so I gave up and bought a Creek amp. It was badly distorted and seemed unstable.

 

The SDS amp sat in my garage ever since, until last week I figured I'd have another go at getting it to work. I looked it up again on the web and there was some comments about the problems I'd seen and one guy had made a few changes to the biasing network and had added some gate resistors.

 

Anyway, long story short, I've just spent my afternoon doing the ammendments suggested in the Project Addendum, and it works. Not only that, it sounds tremendous and currently has a yellow glow (the shop only had yellow 2v LED's), which looks a bit funky.

 

No photos yet as it's still in rough prototype mode and will need reboxing now that I know it works.

 

See the details here

 

http://gilmore2.chem.northwestern.edu/projects/showproj.php?file=stokes_prj.htm 

 

 

Rather confusingly, the circuit shows the updated version and not the earlier version that I (started) building but the PCB is the original version which used a zener for bias.The modifications are discussed in the Addendum.

 

I think I'm addicted again, I'm already looking to upgrade the SR80's to 225's or 325's.

 

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post #2 of 5
2/6/12 at 4:19pm

Hi DMC

 

I don't like to see a poster get ignored for too long.

 

It's nice to hear you found the problem with your amp after so long a time.

 

Many years ago I built a stereo amplifier based on one of the first chip amps, a Sinclair IC10, or IC12. Despite the fact that it had a problem it was used for years, being the only source of music we had, and money too tight to mention. It used to drop out and restart every few minutes or so when the demand of the bass got too much. It's amazing what you will listen to when there's nothing else.

 

I just couldn't find the fault.

 

Years later I came across the PCB which had eventually fallen into disuse. Looking at it, I immediately noticed that 2 caps were of the wrong value. How I missed that previously I just don't know, I must have inspected the damn thing dozens of times immediately after building it. Of course it worked fine when I replaced the caps.

 

I learned something from it, that you can look and look at a thing, particularly something you've built, and just not see what you've done wrong. Since I changed careers to do electronics it's been useful.

 

Just one of the things that keeps me DIYing electronics still, the satisfaction of debugging something.

 

w

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post #3 of 5
2/6/12 at 7:10pm



 

Quote:
Originally Posted by wakibaki View Post

Hi DMC

 

I don't like to see a poster get ignored for too long.

</snip>


There might've been a reason.

 

Sheldon Stokes' opamp-MOSFET-buffered amp was the basis of an improved design from Morsel and AMB (with help from Tangent and PPA): the M3.  The M3 incorporates an active ground channel and an option for a bass-boost, among other improvements over the original design.  It's still a top-flight amp and continues to be sold and supported by AMB.

 

Unfortunately, those facts seem to cause a great conflict with a few people who frequent the forum these days.  Anyway, here's the history on the M3 development from the SDS labs headphone amplifier:

http://www.amb.org/audio/mmm/history.html
 

 


Edited by tomb - 2/6/12 at 8:27pm
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post #4 of 5
2/7/12 at 10:31am
Thread Starter 

Thanks Guys,

 

I was beginning to feel I must have insulted everybody !

 

I've been getting some inspiration for the enclosure from the DIY Enclosure thread (love the SOHA II build) and am planning on buying a pillar drill this weekend and collect the few bits needed to complete it.

 

I'll post pictures when it's complete.

 

thanks.

 

DMC.


Edited by DudeMyCans - 2/7/12 at 3:12pm
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post #5 of 5
2/7/12 at 11:22am

I have been "working" on an amp for about 2 years. The one before took about the same amount of time.

 

I rate a drillpress (pillar drill) pretty high on the list of things that will make your work SO much easier and get better results. It is very well worth its cost.

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