ic preamp circuit & ipod

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ic preamp circuit & ipod

Posted by: andrew ()

Date: August 15, 2006 08:59PM

here's the first email i'm posting, any comments/guidance is appreciated::
-----------------
from ehiunno

Quote

I see the preamp is labeled for use with an electret microphone, but the application im working on requires the amplication of a low-level source(namely, an ipod) a small amount as the headphone out doesnt put out at line-level. Could i use this pre-amp in this application?

It aslo seems to me that the circuit might create a high pass-filter with a cutoff frequency well above where i would want it (created by C1 and R2) but i may be missing something or doing incorrect math as i couldnt imagine why you would want to filter out such high fequencies for a mic. Do you have the theoretical cutoffs of any of the filters in the preamp? I need something that will amplify the entire audio spectrum.

thanks a lot,
Brielin

---------------------
my response:

Quote

hey, sorry for the delay in getting back to you.

well, firstly the forum you emailed me through is deprecated (i need to take it down and fwd. all traffic to the new forum at [www.reconnsworld.com])

looking at the circuit, I'm not sure which section you think will create a high-pass filter.. (r1 & c1? r5 & c2?)

meanwhile this schematic looks very similar to a reference audio amplifier design that national semiconductor has on their website:
[webench.national.com]

so i imagine it works well. the main difference seems to be the r1 supplying voltage to the electret microphone, which in your case you don't need. in your case you would need to remove r1 and feed directly into the pin on c1.

wikipedia (http://en.wikipedia.org/wiki/Line_level) has line voltage at about 1.228vrms which would be 1.228v*(2*sqrt(2)) = 3.47v peak-to-peak
audio electronics really isn't my thing, and I can't seem to find a definitive source about 'what voltage does the ipod run the headphones', is it larger/smaller than 3.47?

meanwhile, if you're interested in a circuit that should definitely meet your specs you should check out national semi's website. they have a tool called 'my webench' which allows you to design circuits, on the website, and simulate them to make sure they operate to your spec.

check it out at
[www.national.com]

i followed the 'audio' link under the 'design' section. meanwhile they do have samples available for some of their chips, so that may help your project out.

let me know if that works for you -- also i'd appreciate if you gave me your opinion of the new forum vs. old forum

thanks,
andrew

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			Home Forum!! *Robotics Projects:* Smallbot *Electronics Projects:* SMT Reflow Serial Multiplexer *Project Log:* Current Projects My Bench Equipment				E-mail Bag : Reconn's World Forum Attention! If you would like to post, but don't want to create your own account, use login:guest password:rw -- Enjoy! Goto Topic: Previous•Next Goto: Forum List•Message List•New Topic•Search•Log In•Print View ic preamp circuit & ipod Posted by: andrew () Date: August 15, 2006 08:59PM here's the first email i'm posting, any comments/guidance is appreciated:: ----------------- from ehiunno Quote I see the preamp is labeled for use with an electret microphone, but the application im working on requires the amplication of a low-level source(namely, an ipod) a small amount as the headphone out doesnt put out at line-level. Could i use this pre-amp in this application? It aslo seems to me that the circuit might create a high pass-filter with a cutoff frequency well above where i would want it (created by C1 and R2) but i may be missing something or doing incorrect math as i couldnt imagine why you would want to filter out such high fequencies for a mic. Do you have the theoretical cutoffs of any of the filters in the preamp? I need something that will amplify the entire audio spectrum. thanks a lot, Brielin --------------------- my response: Quote hey, sorry for the delay in getting back to you. well, firstly the forum you emailed me through is deprecated (i need to take it down and fwd. all traffic to the new forum at [www.reconnsworld.com]) looking at the circuit, I'm not sure which section you think will create a high-pass filter.. (r1 & c1? r5 & c2?) meanwhile this schematic looks very similar to a reference audio amplifier design that national semiconductor has on their website: [webench.national.com] so i imagine it works well. the main difference seems to be the r1 supplying voltage to the electret microphone, which in your case you don't need. in your case you would need to remove r1 and feed directly into the pin on c1. wikipedia (http://en.wikipedia.org/wiki/Line_level) has line voltage at about 1.228vrms which would be 1.228v(2sqrt(2)) = 3.47v peak-to-peak audio electronics really isn't my thing, and I can't seem to find a definitive source about 'what voltage does the ipod run the headphones', is it larger/smaller than 3.47? meanwhile, if you're interested in a circuit that should definitely meet your specs you should check out national semi's website. they have a tool called 'my webench' which allows you to design circuits, on the website, and simulate them to make sure they operate to your spec. check it out at [www.national.com] i followed the 'audio' link under the 'design' section. meanwhile they do have samples available for some of their chips, so that may help your project out. let me know if that works for you -- also i'd appreciate if you gave me your opinion of the new forum vs. old forum thanks, andrew Options: Reply•Quote Goto: Forum List•Message List•Search•Log In Array Sorry, only registered users may post in this forum. Click here to login This forum powered by Phorum.