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A Very Compact Hybrid Amp - Page 133

post #1981 of 2213
I'm confused and in need of help. I built my CTH a while ago, it worked perfectly. I lent it to my dad, he accidentally plugged a γ1 into the output jack and nothing in the input jack and powered it on. It let out a puff of smoke and I assumed it was done (I found out later that the fuse wasn't blown though). Recently I've got some spare time; I figure what's the worst that can happen and run through the initial setup on the amp, and everything checks out. Questioning my sanity, I plugged a pair of tester headphones in and lo and behold, it works fine; no distortion, no channel imbalances, sounds just like it used to.

But here's the rub; the darn thing still smells like smoke and I can't shake the feeling something's broken. The smell's only coming from the power supply section, and it seems like it might be getting warmer than it used to? It doesn't smell like burned rubber and not quite like burned semiconductor, but I understand that bits of wire can cause problems? This could very well be a case of me thinking too much about things.

My two questions are:
1. Could the amp have actually given up the ghost from what my dad did?
2. Does anyone know a good way to remove smoke smell from an enclosure?
post #1982 of 2213
Quote:
Originally Posted by suicidal_orange View Post
Thanks again Devast, expert or not your help and encouragement are much appreciated

So I measured pin 3 to SG at just 2.7V. Removed the 7824 and pin 1 to SG reads 35.7V so that's where my problem is. So in your inexpert opinion do I buy a 7824 or 3 of them, expecting it to blow again?

EDIT: TAIWAN SEMICONDUCTOR|TS7824CZ|V REG +24V, 7824, TO-220-3 | Farnell United Kingdom <-This one looks to be suitable?
Yup, thats it. Or if you have any local electronic parts store i'm pretty sure they have 7824 regulators for pretty cheap. Don't forget the insulation
post #1983 of 2213
Quote:
Originally Posted by devast View Post
Can someone do the following: do not plug headphones into the cth, set the volume pot to max, and start playing something.
I'd like to bump this question. After replacing q8l and q8r the the tripping happens at 14 o'clock, before it happened at 10. I don't know if this is normal. How much is the maximum DC offset of a properly functioning cth?
post #1984 of 2213
devast - I assume the query in the quote (vol max, no cans then play) is whether it trips CTH e12 (as well as the 14 o'clock question). I can try those in a day or two but what is your source?.. E.g. powering on or bringing an attached iPod out of "sleep" almost always caused trips for me. And tube choice, maybe even TO92 variances, can make subtle differences in tripping behavior... E.g. AFAIR for a couple non-12au7s/non-6922s I have to have cans plugged in to get e12 latch.

But you should not get nuisance tripping under normal usage (proper tubes, cans attached, source playing, sane listenting levels)... I don't for any of my CTHs across any of my cans & sources.

WRT DC offset before trip - IIRC, which I may very well not, it was tuned for around 90mV or so. AFAIR reasons for somewhat elevated & de-sensitized settings were due to component limits on 3x5 PCB involving the OB. But if you watch the offset behavior ( http://s2.photobucket.com/albums/y33...t=35a37920.flv ), once things settle down then tend to stay much below the tripping limits.
Again, you can solder wires to relay input & watch offset WRT OG & let us know what you see.
post #1985 of 2213
Quote:
Originally Posted by cfcubed View Post
Again, you can solder wires to relay input & watch offset WRT OG & let us know what you see.
Did that, when volume is maxed i get a jumping value between -2 and 2 volts(no cans connected). My source is my notebook with volume maxed. On tuesday i'll check out with my dac, at least i know that has 2.1Vpp line out. When using my mobile phones headphone out, i have to max the volume on the CTH to get enough level, of course that way it wont trip.
I checked out the video you linked, you get those value regardless of volume ?
At low volume i get the same results, when i turn it up, it increases and after a point it trips. You think i feed too high signal to it and it simply trips before it starts clipping ?
post #1986 of 2213
My DC offset measurements were done how we normally do them, with no source connected & thus regardless of volume setting.
I think you may be talking common line-level / signal AC peak-to-peak levels (e.g. 2Vpp). CTH's e12 should/would trip on the DC component of its output... E.g. I'd expect 100mv DC or so to trip it.
Edit: But "speed"/reaction time of CTH e12 to DC comes into play as well & as you can see the cheapo meters I used for DC offset measurements are not too fast.
post #1987 of 2213
Quote:
Originally Posted by cfcubed View Post
My DC offset measurements were done how we normally do them, with no source connected & thus regardless of volume setting.
I was measuring the dc offset while the music is playing. Btw from this point on this test i mentioned before is just for me verifying that everything is fine, and working as intended. I can't reproduce e12 tripping with my cans connected (i don't want to endanger them, so at 13 o'clock max volume or so with my source). Thanks for you continous support!
edit: came back to the dorms, still tripping with my dac. Looks like it's heavily dependant on the source.
edit2: i also realized, that i cant measure DC offset while the music is playing.
post #1988 of 2213
Hi all,
I have nearly finished my CTH but I could only get a 100K alps pot. Does it affect sound quality? my source is a y2.
post #1989 of 2213
Double post
post #1990 of 2213
> I could only get a 100K alps pot. Does it affect sound quality?

Not as long as you have enough rotation for your listening volume(s). IOW, as long as it doesn't limit your use of the pot rotation too much, given the lowest portion of rotation is least desirable. And 150R is the max we'd like to see for the output resistors (R18s).
post #1991 of 2213
Why the limit on R18? Any other techniques for lowering the overall gain of the amp for low Z headphones?
post #1992 of 2213
Quote:
Originally Posted by stringgz301 View Post
Why the limit on R18? Any other techniques for lowering the overall gain of the amp for low Z headphones?
Don't recall why raising R18s above about 150R was seen as non-ideal... Maybe search this thread of "150R"? Makes sense tho that one would want to use the min resistance here that makes the amp usable for them.

Another way of lowering gain is try to stick w/the lower-gain tubes the amps supports. But in the end whatever works & sound best for you is the way to go of course
post #1993 of 2213
What about changing to a 10k pot? (sorry if this is a dumb question)
post #1994 of 2213
Quote:
Originally Posted by stringgz301 View Post
What about changing to a 10k pot? (sorry if this is a dumb question)
I could, but I've already paid 20 dollars for the 100k pot.

When I ordered all the parts for the CTH the relay was out of stock with a 7 week lead time, so I ordered a different one. But it doesn't fit. Does anyone have a spare that they're willing to sell me?
post #1995 of 2213
Seems I have a spare CTH relay... Fire me a PM w/your address, preferred shipping method, etc.
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