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A Very Compact Hybrid Amp - Page 130

post #1936 of 2213
So I finally got my case and installed the CTH in it. First, there's noise now thats not really a hum but a sharper buzz sound. Secondly, I blew a couple fuses before realizing that my case which has not yet been grounded is 12.4ish volts above ground. This is not the output ground voltage which is just under 12 volts. As long as the case isn't grounded, it works fine except for the buzzing. I checked all the obvious points (e.g. power, different signals, grounds) to chassis and they're not shorting. Any ideas? Maybe some part of the heater supply is hitting it causing the buzzing?
post #1937 of 2213
check wiring on the pot, are the grounds connected?
post #1938 of 2213
Turns out the AC input jack was no insulated and it was shorting to the case if the power cable was turned a particular way. I need to order an insulating one. In the meantime, the buzz is gone since there isn't AC flowing around the input RCAs.

Another build note: I mounted my board to the case using screws with hex nuts and the nuts in several places were too close to components and wouldn't turn. It'd be nice if in the next generation of CTH boards the mounting holes had a little more room around them.
post #1939 of 2213
Well, off and on building over the past few months, and a CTH is alive! I (of course) have a problem.
I'm not pretty sure I've been running my tubes at the wrong voltage. I started with a 6gu7, it got hot, filaments turned red, and not knowing any better I used it like that for hours. Moved to a 6n6p, same story. Tried a 12au7, switching to "12" volts and it sorta worked, but one channel was much quieter than the other. Together I probably ran each 6 volt tube for 6-7 hours each over the past couple days.
Today I tried the 12 volt in "6" volts and it worked! Tried a 6 volt tube at "12" volts and it also worked, but without the glowing filaments.
I'm going to take a multimeter to work tomorrow and verify the voltages across pins 4/5, but right now I'm assuming I screwed up. The real question here is how likely is it I did any permanent damage to the amp it's self, especially running the 6n6p at 12 volts. Everything seems to be fine currently for what it's worth.
post #1940 of 2213
post #1941 of 2213
The heater switch is "open" for 12.6V & "closed"(0 ohms) for 6.3v.

Think the amp will cope w/this fine, but not sure about tubes (e.g. tube life, etc.). If you could find a tube tester somewhere you could test 'em, otherwise let your ears be the judge.

If you look @ CTH Tube & tweak thread you'd see you are not alone mistakenly running 6.3v heated tubes @ 12.6v. Most of these heaters should not glow too brightly & are often hard to spot in normal lighting. And quiet/low gain for a 12.6v tube could indicate its running @ 6.3v.
post #1942 of 2213
Thanks for the input. I had done some searching in this thread, but didn't think to look through the tweak thread. There is definitely some discoloration on both tubes, especially the 6N6P tube. We'll see tomorrow how well they coped. Hopefully this als explains the low hum. Even with running the tubes at the wrong voltage I've loved every second so far with this amp. Time to compile a list and hit up a local electronic's place. A quick look through their mess of tubes revealed a few 12au7's and a 6gu7(which I guess I'll get now) so I'm hopeful to find some more.
post #1943 of 2213

Part equivalences

Hello. First of all please excuse my ignorance with electronics. I'm nearly done ordering the parts to build the amp, but I can't find equivalences for these mouser references:

I'm also going to make orders to digikey and farnell so I don't care if these missing parts come from any of them.

Hope you can help. Thank you!
post #1944 of 2213
> but I can't find equivalences for these mouser references.

As you are asking, would have to defer to any others that might have build up CTHs with parts other than those from Mouser.... And of course not those that used wiatrob's kits (btw, he may still have some CTH parts around - not sure & not sure if he'd do int'l on 'em).

I suppose you've looked for any pin- & value-equivalents that meet or exceed ratings & stay close to size constraints (based on datasheets of the parts you listed). IOW, you may be able to squeeze in slightly larger parts for some of them (print scale PDF & search for populated PCB pics, etc.).
post #1945 of 2213
Has anyone played with larger values for C4? This appears to be the interstage coupling cap and so would have a significant effect, especially on low frequencies. I'm using the CTH with Grado's, a low impedance phone (32 ohm), which in theory would make them more sensitive to the value of this cap. I've been playing around with bypassing C4 and was very surprised with the effect of adding a .022mF bypass to the .22mF recommended cap. The amount of very low end went up significantly, which seems surprising given that I only added 10% overall capacitance.

post #1946 of 2213
Originally Posted by stringgz301 View Post
Has anyone played with larger values for C4?
I asked about using larger values early on and was told that the roll-off point was so low that larger cap values would have no audible difference, so have only experimented with different cap brands and not values. Have read that cap bypassing can have very mixed results depending on the combo used, some work and some don't. Sounds like you have hit on a combo that work well together.

What caps are you using and how have you mounted them? Its a tight fit to get one cap in for each C4, let alone two.
post #1947 of 2213
I'm in the middle of building mine, from wiatrobs kit. I've got a question: There's one heatsink included in the kit. Should i use that for 7824 regulator, or the lm2595 ? I could fit that on either of them.
post #1948 of 2213
Originally Posted by devast View Post
I've got a question: There's one heatsink included in the kit. Should i use that for 7824 regulator, or the lm2595 ?

The heatsink is for ICP, the 24V regulator(7824).
post #1949 of 2213
There is a kit that is possible buy for build this amp??
post #1950 of 2213
Originally Posted by netsky3 View Post
There is a kit that is possible buy for build this amp??
There was. Bill stopped selling it 3-4 months ago. I'm too busy nowdays, so i did not have any free time to build mine, even though i had it for months.
For the build:
I switched c5p and c10p so my 1000uf 50V capacitor emitted some smoke and died peacefully
I'll get a new cap tuesday, and i hope nothing else died there
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