[rokk]

Hi,
i recently built a cmoy amp for just daily use with my headphones.
It worked just fine until i today decided to replace the C2 cap with some higher quality ones, plus redoing some less beutiful solderings. Now it seems the amp sounds distorted on the last 20% of the volume-knob, i have a gain or 3,5 set, so it's not really that loud.

Earlier i has a small distortion on the last, say 10% which just lasted for like half a second when the knob went up. I tried a few different powersources, such as 2 different Powersupplys as well as a 9V battery with no luck, also tried different sources. I planning on trying ti switch back to the old caps, but the new ones sounds better in the bass and less hissy in the upper ends.

Input caps not couping up due to some reason, new caps are not working correctly, or damaged opamp?

I'm using a OPA2134PA and the 2 new caps are metallized polypropylene 0.1 µF 250V precision capacitors. The old caps were wima metallized polyester 0.1 µF caps.

Oh, and the C1 caps for the power is 560µF 35V electrolytics, i oversized a little bit to be on the safe side.

I'm going to try to switch back to the old caps and see, but suggestions what may be causing this is welcome.

Thanks in advance!

// rokk

 

[tomb]

Sometimes intermittent distortion is nothing more than just the pot. It's possible that your cap change is just a coincidence, or it stirred up some dirt in the pot.

 

[rokk]

Quote:

Originally Posted by tomb Sometimes intermittent distortion is nothing more than just the pot. It's possible that your cap change is just a coincidence, or it stirred up some dirt in the pot.

Thanks for your reply...
Actually, i'm hoping it's the pot... anyhow, i soldered my old caps back and it sounds even worse (Yuck!). So i guess it's not that...

I guess i just can bypass the pot and see how it sounds to see if it's just the pot?

By the way, my new caps should do the job just fine, right?

 

[tomb]

Look closely at your pot and see if you can see any flux residue that could've dripped down inside at the leads. Your recent re-soldering would make this worse.

It happened to mine after I first finished. I dripped some tape head cleaner through the pot to "rinse" out the flux. It's been dead quiet ever since, all the way to WFO.

 

[rokk]

i just tried to bypass the pot by simply giving the current a shorter way rather than through the pot and it sounded fine in both channels at maximum volume... yey a dead pot, sigh.

Thanks alot, i guess i'm somewhat relieved it's 'just' the pot

By the way, you got any recommendations for improving my cmoy sound?

EDIT: Yeeey, not i can continue to work on my grado-modding!

 

[tomb]

Personally, 2 high-current NiMH 9V batteries made a bigger difference in mine than anything else. Standard alkalines suck by comparison.

 

[thomasmiller]

tomb, where'd you get those?

and what are the specs on your charger? (thinking I could maybe build with one of these old wallwarts hanging around)

thanks
--tm

 

[tomb]

Circuit Specialists has some real cheap NiMH 9V's, and then there's Thomas Distributing, the end-all to re-chargeable batteries. However, it seemed like none of them had a "cheap" charger. After all, in most cases we're talking a trickle charger that's nothing more than a backup. More sophisticated DIY designs almost always include a charger in the amp. Radio Shack has some pretty cheap ones - especially the all-one-unit walwart plug-in unit. Unfortunately, their batteries are all below 200mah, and are over $10.

I finally went the e-bay route with no regrets. I got the little charger combo with two batteries, and then ordered four more batteries (250mah) from this guy (Shoreline Market):
http://cgi.ebay.com/V228-Charger-2-9...QQcmdZViewItem

Everything works great - highly recommended.

 

[rokk]

I tried adding a bypass cap, but i have not been able to sit down and see the diff yet, but i will later, also shortened the distance between the components and added better cabling. At the moment i'm using a 14V Linear Regulated Powersupply, it seems to do the job for now. I'm not really that fond of batteries...

Again, thanks alot for the help!