dreamie 0 Report post Posted November 2, 2004 (edited) Hi all, this is the AD8610 based pre/head-amp I did up last week, after letting the components collect dust for more than a year ... Resistors used are Holco 0.1%s... power supply caps are Panasonic FCs (1800uF per rail on virtual ground divider board, 220uF per rail per channel on signal board), 1uF stacked film across the +ve and -ve rails on signal board... rectifier diodes are OnSemi MUR860s encapsulated PCB mount trannies are bought during my last trip to Shanghai... no capacitors are used in the signal path... this is the overall pic... no casing yet... Edited November 2, 2004 by dreamie Share this post Link to post Share on other sites
dreamie 0 Report post Posted November 2, 2004 the signal board... Share this post Link to post Share on other sites
dreamie 0 Report post Posted November 2, 2004 a closer view... Share this post Link to post Share on other sites
dreamie 0 Report post Posted November 2, 2004 the underside of the signal board... a 1uF cap is soldered directly across +ve and -ve. the feedback resistor is concealed by the 1uF cap... Share this post Link to post Share on other sites
dreamie 0 Report post Posted November 2, 2004 lastly... the virtual ground divider... the TO220 package is the BUF634 and the TO3 package is the TLE2426... no passive components other than the 2 caps were used for virtual grounding... Share this post Link to post Share on other sites
bpribadi 0 Report post Posted November 2, 2004 Dreamie, what is your gain setting? And why you seperated those small boards, why not put them in one board? Share this post Link to post Share on other sites
Q00 0 Report post Posted November 2, 2004 Maybe trying to fit it into the 'dog in the xmas hat' package with the candy? Share this post Link to post Share on other sites
digi01 0 Report post Posted November 2, 2004 wow,good do you have using the pcb mounting transformer made in BEIJING? Share this post Link to post Share on other sites
dreamie 0 Report post Posted November 2, 2004 bpribadi, The gain is 2.7, inverting configuration. Used separates for the 'modular' design. Can swap the signal board easily if i one day decide to change it. Or i could also change the virtual ground driver board with something better (perhaps higher output for a more demanding signal board?). The power supply can also be changed. My previous power supply uses 2 trannie, 16 MUR860 diodes and 4 Panasonic FCs. Ripped that up and now I can make 2 power supplies. Q00, That's an evil sheep wearing Santa's hat. It's actually a jellybean dispenser.. the jellybean's dispensed out of the backside... notice that the jellybeans in that package are all brown... hehe.. but I have run out of jellybeans... digi01, Thanks! I think the transformers are made in Shanghai, not Beijing. Have not been to Beijing before... Share this post Link to post Share on other sites
huangyong 0 Report post Posted November 2, 2004 dreamie, nice head/pre-amp. what is the output resistance when it works in preamp mode? i made one preamp using opa627 recently too, and i need advice to refine it. may be can share your experience. Share this post Link to post Share on other sites
dreamie 0 Report post Posted November 2, 2004 dreamie, nice head/pre-amp. what is the output resistance when it works in preamp mode? i made one preamp using opa627 recently too, and i need advice to refine it. may be can share your experience. huangyong, What do you mean by output resistance? I don't have much experience to talk about.. hehe... regarding the OPA627, I recently swapped that out of my phono stage and changed it to a OPA2228... nice sweet sound! Intend to keep the OPA2228 in the phono stage. Share this post Link to post Share on other sites
huangyong 0 Report post Posted November 2, 2004 The input impedance of the power amp ( or any other load ) is usually very high and not much current is needed. Normally, preamp has the output resistance to reduce the current. That's what i observe in most preamp circuit. Share this post Link to post Share on other sites
bpribadi 0 Report post Posted November 3, 2004 The gain is 2.7, inverting configuration. That's pretty low gain for a pre amp Why inverting? The common mode / non-inverting mode is better right? The inverting mode ussually has noise gain 4 times or more of the common mode. Share this post Link to post Share on other sites
huangyong 0 Report post Posted November 3, 2004 dreamie. do you think virtual ground is good for preamp?? what is the advantage over real ground? Share this post Link to post Share on other sites
bpribadi 0 Report post Posted November 3, 2004 I prefer to use Transformer with CT (centre tap) for 'real' ground. It is cheaper than the BUF634, and the current limit is equal to the PS transformer. I see there is only one bridge (4x MUR860), that's why dreamie use the BUF634 for the 'virtual' ground. In case you want to isolate the source ground, you can use 1 high speed op-amp with output connected to the 'real' ground of the transformer CT. Share this post Link to post Share on other sites
