[hatfi]

I am bored. Can anyone recommend an easy circuit for me to start on this weekend? A pocket amp or something. Must be something that I can get all parts for at Radioshack. I am new to this, so I am going to need a link to fairly comprehensive instructions. Sorry for being lazy and impatient.

 

[Polaris111688]

http://tangentsoft.net/audio/cmoy-tutorial/

CMoy amp. Simple DIY project for starters.

 

[picklgreen]

I smell another candidate for a CMOY!!!! Welcome aboard buddy!

Just know that everything is available at Rat Shack for the CMOY but tha opamp they sell sounds kinda crappy, so if you get it built with everything but a decent opamp let me know....

 

[hatfi]

I have a few LM4562s on the way. Would it be possible to build an amp from RShack parts and then swap over the 4562? Forgive any ignorance.

I originally was going to use the 4562 in my 203.2, but I then learned that it was not a simple plug in operation.

 

[picklgreen]

yes. just make sure u put it in correctly! and use an opamp socket!!!

 

[Ace o' Spades]

Try to stray away from using the Ratshack socket, it is really terrible compared to the ones from Digikey that Tangent reccomends on his site.

 

[tomb]

I kind of disagree with that - the little RatShack socket is fine the first time out. It's easier to just order an opamp and not worry about 10,000 part numbers for other things on the first go-round. Ordering from Mouser and DigiKey is the one of the most difficult things in this hobby, IMHO (to get right).

The LM4562 looks to be a good prospect. I've already heard good reports. It may be a little weak on the current, so I'd keep that in mind. The canonical OPA2132/4 will put out about twice as much current. That's not as important if you have high-impedance phones. IOW, it will work great with your KSC75's, but the Grados may lack a little oomph.

Built properly, it will most likely sound better than your PA2V2.

 

[hatfi]

Thank you Ace and Tomb. I'll probably go for the Ratshack socket because I absolutely have to do something this holiday w/e, I have 4 days to fritter away.

 

[hatfi]

OK. Built it. Used the only opamp in Rshack - tl082.
Sounds terrible, here are the details:
Really scratchy and distorted in both channels.
Source is ok.
Test headphones are ok.
No improvement with 2x9v
PS circuit tested ok. +4.43 -4.44
Checked grounding of input and output - looks ok
Distortion same whether input is high or low.
No change after running for 10 min,

I will befriend the search engine later this afternoon. I need to take my wife to lunch now as she is getting jealous of the Cmoy.
In the meantime, any thoughts would be appreciated.

 

[kipman725]

Im having trouble with mine aswell..

One channel works perfectly yet the other plays through sides of the headphones and when both left and right channels are connected to the source one side of the headphones has major distortion wheras the other sounds fine. Very weird as I would have thought both channels would be effected when pluggged in individualy. I haven't followed tangents layout as I just had strip proto board on hand so I devised my own layout as such the layout may be defective but there is nothing I can see wrong with it.

I am using 2x9v and the powersupply section gives out the right voltages so that isn't the problem. It also worked fine on breadboard so I don't think any components are defective.

any ideas?

 

[hatfi]

Quote:

OK. Built it. Used the only opamp in Rshack - tl082. Sounds terrible, here are the details: Really scratchy and distorted in both channels. Source is ok. Test headphones are ok. No improvement with 2x9v PS circuit tested ok. +4.43 -4.44 Checked grounding of input and output - looks ok Distortion same whether input is high or low. No change after running for 10 min, I will befriend the search engine later this afternoon. I need to take my wife to lunch now as she is getting jealous of the Cmoy. In the meantime, any thoughts would be appreciated.

Further details:
Board cleaned up and checked for bridges: ok
Disconnected I and O, RandL one at a time. No improvement.
Opamp remains at room temp. No significant heating.
Sound is amplified.
No R5 on circuit as recommended by Tangent.

Help. Help. This was meant to be the Holiday of Cmoy Love.

Will continue to search forums and maybe try some different headphones.

 

[Ace o' Spades]

It could just be the OPamp, but the symptoms seem too severe for just a bad sounding opamp.

Can you post any pictures of the top and bottom of the board? It would help a lot

EDIT: I take that back. From tangents guide:

Quote:

Bottom line, this chip does not like to drive low impedances. I've heard members of this op-amp family distort even at the chip's full operating voltage of 30V. I'm not talking about minor problems here — I'm talking about crunchy, ugly, obvious distortion.

What headphones are you driving?

 

[picklgreen]

Check your voltages with a volt meter. Its important to check the outout DC dc voltage. This amount should be in the very small millivolt range. (o volts DC is what you really want). Next check the power supply voltages. With 2 9 volt batteries you should be getting 9 volts plus and minus from both each side of the power supply caps. Next try chanigng the value of R3. Default is 1K which sets the gain at 11. I use a gain of 4 (R3 is 3.3K). Most common cause of distortion is powersupply problems, or too much gain. Also increasing the size of your powersupply caps can help if your headphones are high imendance. With low impendance bud types this usually isnt an issue, but high impendance headphones require more current from your batteries, so increasing the power caps helps here (i use 1000uf caps). Just make sure they are rated for the right voltage. Use 10V with 1 9V and 20V caps if you are using 2 9V's. You should also check all your jack connections! It is very easy to over heat those small jacks and create a short at the jacks themselves. Use an OHM meter and check for shorts (The meter will read 0 resistance if there is a short, infinite resistance means an open circuit).

The opamp you are using will distort very easily and if all your voltages are fine and no shorts, etc, simply swapping in an OPA2227PA or a OPA2132/4 will make the distortion go away!

 

[picklgreen]

Quote:

Originally Posted by kipman725 /img/forum/go_quote.gif Im having trouble with mine aswell.. One channel works perfectly yet the other plays through sides of the headphones and when both left and right channels are connected to the source one side of the headphones has major distortion wheras the other sounds fine.

Check your connections going from the in/out jacks to the board. Sounds like you have a bad connection here someone. Start at the jack from the bad channel and move to each connection all the way to the opamp, going one component at a time. Also temporarily disconnect the connection to the LED if you are using one. If you are draining too much current from the powersupply this can cause an imbalance in the powersupply, causing one channel to be louder and/or distort. You are using 4.7K for R1+/R1- right?

 

[hatfi]

The plot thickens.
Without changing anything else:
Original test phones: MDRWO8s - Terrible distortion

New test phones: KSC75s - much better; sounds like real music now. Input of 50% from muvo sounds ok. Increasing from this give proportional distortion (clipping).

SR60s sound like the original scratchy headphones.

Must be an impedance issue.

I am awaiting delivery of LM4562s soon. Maybe this will solve all my problems and I need not troubleshoot my board anymore.