Username 0 Report post Posted April 28, 2005 Thanks heady: I just realised that I have got a problem. I forgot to buy the C1 cap (supposed to be 0.22uF 63V) but I am too lazy to go down to SLS again. But I have a 0.1uF 100V cap, can I use what I have in place of the original spec c1? Sry for being such a bonehead. Share this post Link to post Share on other sites
heady 0 Report post Posted April 28, 2005 hi username, I omitted C1 from my Pimeta. This is necessary only if your source has DC offset. Which you can check by measuring the voltage from left channel to signal ground and the right channel to signal ground. It is usually less than 20 mV (according to the experts, I am just repeating). Unless the DC offset is more than 20mV, you don't need C1. Believe me, the Pimeta will sound better without it. BTW, my sources never have more than 0mV offset. PS - if forgetting a component is being bonehead, then my head is solid bone. Share this post Link to post Share on other sites
Username 0 Report post Posted April 28, 2005 To measure DC offset do I minus the right-gnd with left-gnd reading? does 20mV include the gain multiplication already? Share this post Link to post Share on other sites
heady 0 Report post Posted April 28, 2005 To measure DC offset do I minus the right-gnd with left-gnd reading? does 20mV include the gain multiplication already? No, each measurement is separate. You just state for left channel, DC offset is so much and right channel is so much. You will have to measure this too on the output after the amp is finished, to ensure it is safe to plug your headphones in. You can read a better explanation in Tangent's site. http://www.tangentsoft.net/audio/input-cap.html Sorry, my mistake, the 20mV figure refers to the output DC offset acceptable to headphones, not the input DC offset. Anyway, I am not sure of the exact figure. Usually there is very little offset. Share this post Link to post Share on other sites
Username 0 Report post Posted May 3, 2005 Question: I am wondering if I should connect the power supply (2 9-volts) in parallel or series. I know that in series, the voltage will increase thus giving the amp more power, but I don't need so much voltage knowing that I'll prolly power only low-impedence Grados. So will putting the batteries in parallel help improve the battery life? Another question: Are there any reccomended brands for rechargable 9-volts. Share this post Link to post Share on other sites
huangyong 0 Report post Posted May 3, 2005 Username, may i know what opamp you use? general opamp dislike to operate in low voltage condition. Putting in parrallel might improve the battery life. just my 2cent. Share this post Link to post Share on other sites
Username 0 Report post Posted May 3, 2005 hello: I ordered a OPA2227 and OPA227 in my Pimeta. But if I have the money I will purchase the OPA2107 later Share this post Link to post Share on other sites
