tropicalrips 0 Report post Posted February 23, 2004 (edited) i was feeling bored today so decided to try out this project that i had in my head for some time now its basically a volume control for my Cmoys that doesn't hav volume control, the pre-amp allows me to try out the amp using the line-out of any source its actually quite a simple project, just 2 stereo jacks , an Alps mini pot and a left-over casing which used to house my micro Cmoy. the knob is an aluminium one from RS. i thought of putting in my bass-enhanced cross feed circuit as there's still quite a lot of space left, but decided i didn't like the cross feed sound . i think i'll add an extra pair of RCA jacks and a switch for selecting 2 different source Edited February 26, 2004 by tropicalrips Share this post Link to post Share on other sites
Sipher 0 Report post Posted February 23, 2004 maybe u can add in some amplification (correct spelling?) circuit to make it function like a pre-amp found in speaker setup? Share this post Link to post Share on other sites
tropicalrips 0 Report post Posted February 23, 2004 i'm not sure ampping this unit is a good idea, cause the output is going into another amp Share this post Link to post Share on other sites
Sipher 0 Report post Posted February 23, 2004 i'm not too sure. just a suggestion. Share this post Link to post Share on other sites
hacknet 0 Report post Posted February 23, 2004 wow. cool work. where did you get the alps from? farnell? Share this post Link to post Share on other sites
tropicalrips 0 Report post Posted February 23, 2004 yes the mini alps are from farnell i had a tread here with the details mini alps Share this post Link to post Share on other sites
huangyong 0 Report post Posted February 24, 2004 (edited) hey, tropicalrips, i suggest you put a buffer(opamp buffer also can) in your pre-amp before the pot. i can see your cable is rather long, this can avoid fidelity loss. with the buffer, it will serve as a high impedance load to the output of your discman. and then send the signal to pot then to the amp. this a .2cent suggestion. Edited February 24, 2004 by huangyong Share this post Link to post Share on other sites
augustineRS 0 Report post Posted February 24, 2004 wah! like that machiam like MiniMe. I can forget bout getting it from Norm. Share this post Link to post Share on other sites
tropicalrips 0 Report post Posted February 24, 2004 (edited) huangyong : buffer will mean an extra battery rite? but the batt won't fit into this case i think maybe i'll built one more using the same mini Hammond case. do u hav ideas on how the circuit will be for a buffer/opamp buffer in the pre-amp? i'm also thinking of a third unit with nothing but buffers for current gain, making it into a 3 peice modular portable amp the power amp can work by itself, the other 2 units can be use to complement other amps, either as volume control or as current gain unit for low Z headphones the 3 units can come together to form a max-out version of the buffered cmoy it will be fun Edited February 24, 2004 by tropicalrips Share this post Link to post Share on other sites
huangyong 0 Report post Posted February 25, 2004 Oh, my GOD!!! you are going to carry these boxes around.LOL and call it 3 peices modular portable amp !?!!! why don't you put all in one box and make it modular.(or parts swappable)?? ok..ok... i will draw and post my circuit week after next.( after my test).and lets rock then... Share this post Link to post Share on other sites
tropicalrips 0 Report post Posted February 25, 2004 (edited) i was thinking the power amp alone can be used as a portable, and the other 2 units as modular add-ons for home use, making it into a max-out desktop amp the add-on units will also hav to be able to work with other portable amps, that should be the most important part of the design. it must be self contained, self powered, without need for any "special" stuff, just a mini to mini stereo cable to link all the modules together update on some changes to the pre-amp added 2 caps on the input side, according to most people over at Headwise, the caps will help reduce DC offset. i measure the dc voltage on the amp output at 0.2 - 0.7 mV , that should be quite safe for any headphones rite? Edited February 25, 2004 by tropicalrips Share this post Link to post Share on other sites
huangyong 0 Report post Posted February 26, 2004 (edited) ok . i've got wat you mean. the caps won't make any difference in DC offset, since you already have a input cap in your amp. may be the cap may help in reduce the induction effect by long cable.( think so, can't really sure, may be study in EMI) Edited February 26, 2004 by huangyong Share this post Link to post Share on other sites
hacknet 0 Report post Posted February 26, 2004 problem with puting caps in line with the signal is that the cap becomes a 1st order high pass filter. i don`t mean to discourage but i think its better to keep it simple as caps also tend to buger up the midrange. Share this post Link to post Share on other sites
huangyong 0 Report post Posted February 26, 2004 hacknet, put caps in series means decreasing the capacitance. as in series: C= 1(1/C1 + 1/C2) which means increase the roll off freq. it's that wat you mean by buger up the midrange?? Share this post Link to post Share on other sites
Firefox 0 Report post Posted February 26, 2004 If you put your "pre-amp" before the cmoy, it'd be fine. It's akin to having a volume pot in the cmoy. I do hope your coupling cap is placed after the pot and before the output though. Otherwise, you'll run into some frequency filter issues. Also, tantalum caps are a no-no in the signal path. Share this post Link to post Share on other sites
