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A Very Compact Hybrid Amp - Page 140

post #2086 of 2213

You will find his direct email in this post http://www.head-fi.org/forum/thread/497255/exstata-boards#post_6711588

post #2087 of 2213

I put together a CTH and everything seems fine except for the relay circuit.  It cycles on and off even though there isn't DC offset (verified by checking L and R outputs from amp section to relay circuit).  Does anybody have operating voltages for the circuit? I checked pins 4, 6, and 7 on ICE and they seem to be inline.  This was from AMB's site.  The rest of his setup procedure isn't really relevant due to the change in circuit.  At the bottom it mentions that if R5-R8 are increased in value it could stop the relay from oscillating, but I see in the revised circuit the sensitivity has already been decreased. Any ideas?  I'll keep poking around and see if I can find anything.  Thanks.

post #2088 of 2213

When you say there isn't DC offset, do you mean its really low like < 10 mv ?   IOW, could you give a bit of specifics there, like its DC offset readings.

 

It's usual for cold CTH's to take 10 secs or more  to drop low enough to get relay latch.  Just curious if the amp is behaving as expected, e.g. you should see DC offset, even if in mV range, for a few secs from cold.     Also, do any of your parts vary from the BoM?


Edited by cfcubed - 10/17/10 at 4:32pm
post #2089 of 2213

Well there is while it's warming up, maybe like 15 seconds it'll kinda jump around, but after that it'll settle down to 1mV or less.  I left the amp on for a few minutes and the relay never stopped oscillating even after it sat for minutes.

 

I have a couple different resistors and caps in the power supply, but they're all the right values.  None of the transistors are changed and everything in the E12 circuit is from the BOM.

post #2090 of 2213

OK, your description of DC offset behavior sounds fine to me - Some moving around then settling down after 10-15 secs.

Edit:  I assume you've no load/no headphones attached during your tests, do you still get cycling with test headphones connected?

 

Don't think I can help much here, I've not run into problems w/CTH's e12 implementation latching that could not be traced to somewhere else in the amp.  We've had occasional trouble w/large C4s on long leads causing the e12 to cycle.  IIRC one theory was that the electronic "pulse" emanating from the relay latching action was being picked up & causing trips.  Not sure that theory panned out.  IIRC, properly fitting the C4s on shorter leads & steering clear of some large, esoteric C4s "solved" this.

 

I can only think double-checking e12 portion parts & orientation and considering swapping its semiconductors. And reporting any differences in expected setup readings:

http://cavalliaudio.com/cth/main.php?page=setup

 

Perhaps others have other ideas.


Edited by cfcubed - 10/18/10 at 7:06am
post #2091 of 2213

So i'm finally getting started with some case work, picked up a nice used drill press off craigslist this week.

 

Question - In reference to the Star Ground - How are you connecting it to the BOM case? 

 

Also, with the following diagram, looking at the pot, are those the pin outs with the pins straight up (looking at you) - Where 'top' is written throws me off

 

http://www.cavalliaudio.com/cth/images/CTHWiringDiagram.jpgCTHWiringDiagram.jpg


Edited by aphexii - 10/23/10 at 3:02pm
post #2092 of 2213

Re the Star ground question, I drilled a hole in the bottom of the case for a short screw about 3/4 inch from the back, and soldered a a wire to SG from the bottom, and put a spade lug on it. Make the wire long enough to give you some slack so you can slide the board forward (before putting on the front and back panels)  and tighten the spade lug down with the nut on the screw..  Slide the board forward and you are done.. 

post #2093 of 2213

Ahh that should work great, thanks! For now I have the SG taped tightly to the case which is sitting next to the board (figured it would be easier to test out of the case). Now time to troubleshoot following the instructions on Cavalli's site

 

Turned on the amp for 2 minutes, no smoke, both the green and red led's lit for e12, then the red led (LED2) turns off about 10-15 seconds in (normal?) However, i'm only measuring 3v across SG/OG, so i assume something must be shorting?


Edited by aphexii - 10/23/10 at 8:11pm
post #2094 of 2213

Did the amp work before case up?     You should test an amp on the bench before casing it up - its easier to do & it let's you know when any problems originated (e.g. worked pre-casing)

 

You will need to go through Setup & find all your Vs that deviate from it:

http://cavalliaudio.com/cth/main.php?page=setup

Be careful doing this, I tightly tape pins to my probes leaving only the very tips exposed.  Do this w/PCB out of case of course.

 

BTW one basic thing is OG is NOT =  SG (headphone must not be grounded to case...), so you may 1st want to make sure of this before pulling the board (OG-SG ohms) & checking all your setup measurements.

post #2095 of 2213
Quote:
Originally Posted by cfcubed View Post

Did the amp work before case up?     You should test an amp on the bench before casing it up - its easier to do & it let's you know when any problems originated (e.g. worked pre-casing)

 

You will need to go through Setup & find all your Vs that deviate from it:

http://cavalliaudio.com/cth/main.php?page=setup

Be careful doing this, I tightly tape pins to my probes leaving only the very tips exposed.  Do this w/PCB out of case of course.

 

BTW one basic thing is OG is NOT =  SG (headphone must not be grounded to case...), so you may 1st want to make sure of this before pulling the board (OG-SG ohms) & checking all your setup measurements.

 

 

Yep, i am testing the amp outside the case (just with SG grounded to the case).

 

Just noticed an incredibly stupid mistake though - I was testing AC voltage, not DC    <homer simpson> DOH! </homer simpson>

 

DC voltage shows a spot on 12.01v smily_headphones1.gif
 

post #2096 of 2213

hah!!..well post some pics man if you got it all cased up andworking. Been a long time coming this build.

post #2097 of 2213
Quote:
Originally Posted by sachu View Post

hah!!..well post some pics man if you got it all cased up andworking. Been a long time coming this build.


Will do! Gonna do my best to have it all cased up this afternoon, just need to drill through the case to mount the SG (as mentioned above). 

post #2098 of 2213

it lives!!! wow, this sounds absolutely amazing!!!! Currently running it with a 12BH7A with my ATH-ESW9's, have a few different tubes i'm gonna roll in tonight and see which i prefer. Thanks again for all the help everyone!!! Especially sachu and cfcubed for sending the extra parts, can't tell you how much i appreciate it!!

Pics coming soon, just need to screw on the endplates rather than use the plastic caps smily_headphones1.gif

 

BTW - Hope not to jinx it, but this is my FIRST build where everything worked after the first try without needing to do any tweaking/resoldering (6th or so build overall, MiniMAX, Mini3 and a few Cmoys)

EDIT: Noticing a very very slight buzzing on the left channel now that its all buttoned up when the volume over 50% on all the tubes, i have a feeling its something rubbing inside the case, there sure is very little room for everything to fit smily_headphones1.gif

 

Rolled in a RCA Clear Top 12UA7

photo 1.JPG

photo 2.JPG


Edited by aphexii - 10/24/10 at 7:46pm
post #2099 of 2213

Good to hear its working & glad you are liking it.

post #2100 of 2213

Hi-

 

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.

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