heady 0 Report post Posted February 13, 2005 Hi guys, I made this amp using the 74HCU04 chip and the schematic from Sijosae's site. The power supply is just two AA batteries and a electrolytic cap. I stacked two 74HCU04 chips together for more current output. My built has a gain of 6. The sound is quite strange. Thru my Grado SR60, it is very dark, worse than the Burr-Brown OPA2134 in a CMOY. However thru my DT880, it sounds quite acceptable albeit still a little dark. It was mentioned in HeadFi that this chip is not suitable for Grados, so it must be true. I think this headamp is easier to built than a CMOY and it is much less power hungry. I am still using a pair of rechargeable AAs for almost 48 hours continuous running now and it's still going. Not bad. Share this post Link to post Share on other sites
Q00 0 Report post Posted February 13, 2005 Would this mean that this amp is not suitable for low impedance cans? Nice to see new amps in the forum! Share this post Link to post Share on other sites
Firefox 0 Report post Posted February 13, 2005 Ditch the Evox caps and put a pair of 1uF Solens in instead. That will brighten up the sound. Share this post Link to post Share on other sites
heady 0 Report post Posted February 13, 2005 Q00 - yes, it is stated in the discussion in HeadFi that it won't drive low impedence phones well. On my Grado, the details are just missing. Firefox - thanks for the tip, I will try it! Share this post Link to post Share on other sites
Firefox 0 Report post Posted February 13, 2005 It doesn't have very high current output to begin with.. Also, I recommend that you use at least a 1000uF cap on the output if you wish to drive 32ohms or lower impedance cans. Otherwise, there will be attenuation of signals. Share this post Link to post Share on other sites
heady 0 Report post Posted February 13, 2005 Thanks Firefox, wah, 1000uF must be quite a big cap. I can try increase the current output by stacking one more chip before it gets too high. BTW, where is best place for Solen caps? Thanks again. I was listening to this amp with a very old pair of Senns HD450 and it sounded pretty good for a portable amp. Source was an old Creative MP3 player. The advantage to me is its very low power consumption which means less battery charging. I gave up my portable Pimeta and converted it to run off a wall wart. It was drinking up 9v batteries, the re-chargeable 9v are worst as they are small in capacity. Share this post Link to post Share on other sites
bpribadi 0 Report post Posted February 13, 2005 Interesting Heady! Congrats for another tin can amp So the ps is +3V-0 or +1.5V-0-(-1.5V) ? Share this post Link to post Share on other sites
heady 0 Report post Posted February 14, 2005 Thanks bpribadi. You know me, I like sweets too much. The power is single +3V-0. Share this post Link to post Share on other sites
Firefox 0 Report post Posted February 14, 2005 Thanks bpribadi. You know me, I like sweets too much. The power is single +3V-0. It's actually 2.4v.. Try Well Audio Labs for Solens. Note that the Solens are quite a bit bigger than the Rifa's. The voltage for the 1,000uF cap can be as low as 3.3v or 4v if you do not intend to up the supply voltage beyond 3v (Obtainable with normal batteries). That will bring the size down. In fact, Koba has 820uF/ 4v Oscons if you intend to stick by them. Share this post Link to post Share on other sites
heady 0 Report post Posted February 15, 2005 Thanks Firefox, got the Solens from Wells Audio. Next time I get to Koba will look for the 1000uF caps. Wells sells them but the expensive variety. Share this post Link to post Share on other sites
digi01 0 Report post Posted February 16, 2005 Hi heady,I am glad to see another good amp you have maked where did you get the chip? Share this post Link to post Share on other sites
heady 0 Report post Posted February 16, 2005 Thanks digi01, I got the chip from Farnell in Singapore, costs about 90cents each!! The passives cost more. Share this post Link to post Share on other sites
heady 0 Report post Posted February 16, 2005 Hi, I checked Sijosae's site again and found he actually uses a dual battery supply(1.2-0-1.2V) while I used a single power supply (2.4V-0). But my amp still work and sounds ok. Are there any advantageous in going for the dual supply? Gurus? Thanks. Share this post Link to post Share on other sites
bpribadi 0 Report post Posted February 17, 2005 Not to sure with the 74HCU04 circuit, but setting the ground in the middle of the supply voltage is good to avoid capacitor in the audio line Share this post Link to post Share on other sites
heady 0 Report post Posted February 17, 2005 Thanks bpribadi. It was your post asking about the power supply which got me thinking and checking Sijosae's site again. When I looked closely at his circuit board, I realised it was dual supply, with one additional wire going to the connector between the two battery. Anyway, I modified my amp for the dual supply last night and I must say it makes a difference to the sound. It is much more detailed. Even my Grado SR60 sound ok with it now. Really puzzling to me since I am not EE trained. Seems this is a good amp to make if just want a quick and easy amp for MP3 players. I am making another and will take pics of the progress. Maybe I will put it here as a guide for others to try. Share this post Link to post Share on other sites