I've found that if I turn the sound up very loud, I do have some sound coming through the right headphone, which I thought was completely dead. It's low but it is present. I'm not sure if I should look for a bad component, or a bad ground...
A Very Compact Hybrid Amp - Page 141
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At one time I knew a bit more about this, and others (e.g. runeight) would be better to assist w/HV issues in this amp, but here's my thoughts...
The difference in your plate voltages is not good. AFAIK they should be within a couple/few volts of one another & around 80V-85V. Not up around 100V (B+ / TB+ which I guess is measuring 99.3V for you).
This problem may be contributing to the lack of sound in one channel as well. When we look at the input stage schematic:
We see that D1L & D1R in conjunction with cathode parts (R3s, R4s, ICL/ICR) should make your plate Vs in the desired 80s range (pins #1 & #6). You should review the solder joints, parts, parts orientation, etc, e.g. reflow joints in the faulty input stage. Comparing resistances at like points between your L & R stages, with amp powered off, may show something. Could try swapping tubes too as part of this just for kicks.
I've just completed putting the CTH board together, and I've got two separate problems. In finishing the setup tests, all pass except going between pin 1 of the tube and the star ground, which is 99.3 volts. The voltage between pin 6 and star ground is 83.6 volts. I'm not sure how big of an issue this is.
The bigger issue is that I'm only getting sound through the left channel, I get no sound through the right channel. Any suggestions on debugging this? The one channel sounds great, but I think I want them both.
Edited by cfcubed - 11/3/10 at 7:17am
- 306 Posts. Joined 1/2008
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Yes, quite normal.
Yes, the pwr-off click/pop is normal for CTH. It's been talked about here, somewhat irritating but should be harmless. I just remove cans from my head before pwroff (on CTHs other than ones w/the mod talked about here:
Edited by cfcubed - 11/5/10 at 4:13am
I got my board and have ordered and received most of the parts. There is one transistor though that is back ordered on Mouser as well as Digikey. Does anyone know of a possible other source?
The part is this one, the Fairchild BC33725BU, NPN, according to the BOM, 5 of them.
I am a newbie as far as tubes go too, so was wondering what are the best options for acquiring a couple of tubes to try with the amp when I finally get it built. I bid on a couple on ebay, but not knowing the worth of them bailed on the auction at the last minute. A friend suggested trying Audigon. Your help in this region is greatly appreciated.
Thanks ahead of time.
I've 5 spare BC337s and a 12au7 I don't need (if you need one for testing). PM me your address & I'll get 'em out to you gratis.
The tube isn't one of the favorites from Tube & Tweak thread, for those I use ebay, but it works fine & should give you a taste of the amp.
that's not a dumb question, there's no contact link i could find neither. Send runeight an email via head-fi. runeight is Alex Cavalli.
Are you still having problems, laduq?
- 166 Posts. Joined 2/2008
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So, Finally its my turn to come back to this forum for help, it's been a long while and I've had a busy summer with cycling.
Heres the story, a few weeks ago I got my hands on some Shure E2C iem's, I was listening with my CTH and noticed some hum, so I figured now would be a good time to change that Cap (C3H). At the same time I also changed the output resistors (R18R, R18L) to 100ohm. The only 330uf 50v capacitor I could find was a little large so I left the leads a little long, all went well. Powered it on and it seemed like all was fine and dandy, the hum was basically gone. I listened to it for a few hours that night (this was saturday) I listened a bit more on sunday and the amp was basically on for 10 hours yesterday, no problems! Today I plug in the amp and FLASH! the red LED flashes and goes out, the e12 never switches... I swap out the dual LED for one green and one red, still nothing. I tried a different tube, still nothing.
TB+ - 129.7v
PIN1 - 47.9v
PIN6 - 45.7v
OG - 0.109v
Wow, long time no hear from Mr. CTH Proto PCB #2 :)
When you say FLASH do you mean SPARK (e.g. fireworks of some kind)? Think there was a short?
All those Vs seem off to me (not close to setup Vs below). All of these are WRT SG right?
How about crawling though Alex's setup measurements http://www.cavalliaudio.com/cth/main.php?page=setup and listing your results here.
The basics of which are trying to do these things:
1) check your LV 24VDC supply - you can do this on the output pin of the 24V reg (between middle pin & pin labeled "O" here: http://www.cavalliaudio.com/cth/main.php?page=boards)
2) check the rail splitter is creating a virtual ground @ 1/2 of LV (12V OG-SG difference)
3) check that your HV - approx 100V TB+ is being brought down to approx 80V on plates
What A/C reading are you getting at the wallwart in? I ask because your TB+ of 130V is about 25% higher than expected.
Be very careful making these measurements (e.g. pins taped to probes). I blew an OB once by shorting while taking measurements.