Mine aren't exact neither. There are tolerances in everything. It could be part variations. It could also be your DMM, since most everything reads low except for the 0.6V test.
Cavalli EHHA Embedded Hybrid Headphone Amp - Page 118
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Horio, one thing to check would be the resistor values over R5 and R7 if your parts came from GJA kit. My supplied kit as well as some others here came with 47.5k when the schematic/parts on Alex’s is listing it as 47ohm.
...just in case.
Thanks for the suggestion guys. I checked the resistors at R5 and R7, and I have 47.5ohm resistors in those spots. I've been using my new Fluke 287 DVM, but I'll try my old Fluke 117 to see if it gives similar numbers.
I did try turning up the quiescent current to 0.22V across R32 and R33. One thing I noticed was the left sink (Q8M) definitely gets pretty warm, while the right sink (Q9M0) stays cooler in comparison. Even after only a couple of minutes the Q8M heatsink gets pretty hot. I can hold my hand on there for about 5-10 seconds, before it gets uncomfortable. Have you guys noticed this same behavior.
So what would be the effect on the amp if I ran it at these lower values (across R4, R10, etc)? Will it have a significant effect on performance or reliability?
Thanks for the help guys, I'll keep trying things and studying the schematic.
I did not match my transistors, so I get the same effect...it's why I bought a kit, so I could be lazy. If I did it again, I would buy a bunch of parts and match it myself. One thing I did wish I would do was to center R6 via a DMM instead of by the number of turns.
The bias is different between top and bottom on the PP section, so yes I have the same issue but not to the degree you state. It's not horribly off, just a bit. I believe my readings on the initial setup was closer to your first post than the 2nd. I don't have other tubes to try though.
I had a mishap with my EHHA, it still works and sounds good... but stupidly forgot to turn the heater supply on the last night. I had the amp on for an hour to warm up and noticed my mistake!
There’s something to be said for automatic delays... anyways with the filaments dead cold for an hour or so with the amp on what the chances I’ve ruined my set of quad tele’s?
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At least based upon my understanding how a tube works. I could most certainly be wrong.
Horio, i dont really get the conundrum of switching pin 1 on your XLR inputs i personally wouldnt bother, these are shields, they should be all directly connected to the chassis at a single point, what purpose would switching them serve? or are you running a redundant signal ground on pin 1? if so i recommend deleting it, it serves no purpose other than providing a path for possible ground loops. or are you running some sort of dual single ended input (mutton dressed as lamb :D) rather than your balanced dac? imo best thing to do is draw out your signal inputs and see if any return currents are actually flowing on pin 1, if not, delete them.
Edited by qusp - 8/4/11 at 12:25am
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So I am getting ready to start another amp build project and looking for some input.
Bijou, EHHA, or EHHA rev A? (I realize I might be asking this in a slightly biased thread)
My first build was the SOHA II (Below) I simply love it - its used several hours a day at work each week.
I'm still working my way through the EHHA and EHHA rev A threads (there is a TON of info here!) but thought some of you more experienced builders (and listeners) might be able to offer some insightful knowledge.
EHHA vs EHHA Rev A: the costs are about the same except for the additional enclosure - housing the PS separately is attractive from a noise standpoint but has that been an issue at all in the rev As?
Bijou is only slightly cheaper for the glass jar kit but I am not a big fan of the electrolytic in the output although from what I have read everyone who builds one seems to love it...
Can anyone offer any suggestions or insight?