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A Very Compact Hybrid Amp - Page 141

post #2101 of 2213

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...

post #2102 of 2213

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:

 

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

 

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.

 

Quote:

Originally Posted by laduq View Post

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
post #2103 of 2213

Quick Question - Does anyone else get a pop/click in their headphones when shutting the amp off? I can see the headphone protection circuit come on for a split second before the power dies, but is the pop normal?

post #2104 of 2213
Quote:
Originally Posted by aphexii View Post

Quick Question - Does anyone else get a pop/click in their headphones when shutting the amp off? I can see the headphone protection circuit come on for a split second before the power dies, but is the pop normal?


Yes, quite normal.

post #2105 of 2213

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:

http://www.head-fi.org/forum/thread/417322/cavalli-compact-tube-hybrid-cth-tube-tweak-thread/555#post_7026098

)

Quote:
Originally Posted by aphexii View Post

Quick Question - Does anyone else get a pop/click in their headphones when shutting the amp off?


Edited by cfcubed - 11/5/10 at 4:13am
post #2106 of 2213

Hi all,

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.

 

Bob

post #2107 of 2213

After today's NYC meet I can take a look for the BC337s... I probably have them.  Could then get a care package w/a spare tube out to you:)

post #2108 of 2213

Cfcubed you rock!

Let me know if you had any success with the npn's and I will shoot you my address.

Plus let me know what I can pay you for them.

 

Thanks,

Bob

post #2109 of 2213

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.

post #2110 of 2213

PM sent.

Thanks again.

 

For tubes on ebay, what are some of the favorites and what is the typical price range?

 

Thanks for all the help.

post #2111 of 2213

Sorry if this is a dumb question, but I can't figure out for the life of me where to find the PCB for sale.  All I can find is "Boards for the CTH are available from Cavalli Audio" on its homepage.

 

Thanks,

Mike

post #2112 of 2213
Quote:
Originally Posted by mikelikespie View Post

Sorry if this is a dumb question, but I can't figure out for the life of me where to find the PCB for sale.  All I can find is "Boards for the CTH are available from Cavalli Audio" on its homepage.

 

Thanks,

Mike



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.

post #2113 of 2213
Quote:
Originally Posted by laduq View Post

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...



Are you still having problems, laduq?

post #2114 of 2213

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

 

Any Ideas?

post #2115 of 2213

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.

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