Hello, this is my first post here on the forums. I will post pictures of my build in the gallery once I get everything back up and running.
Also this story is kind of long so please bear with me. I hope this does not come off as me being critical of the Crack kit I'm just having some problems that I can't figure out.
A month ago I built a Crack kit completely stock. I took my time at the build so as to not have any solder joints fail on me or other problems and that certainly paid off because the resistance and voltage checks all came out just as they should the first time around. Well the amp worked and sounded great for about a month but then about a week ago while I was looking for a different cd in my collection to listen to the amp (with no music playing at the time) started making some scratching and rustling noises through both channels. Realizing that the amp was making the sounds I took off my headphones in case anything worse happened. And it did. A loud pop ensued from the right channel followed by lots of tube microphonics and the tube heaters going dark. I turned the amp off for a while and then turned it back on but there was still no sound from the right channel once the tubes finally did light up again, the left one seemed unaffected by all of this once the tubes lit. So a couple days later I took the amp out of the system and turned it over to find out that one of the heater wires coming from terminal 4 of the transformer had come loose. So I soldered that back up and was back in businness minus the DT770 250 ohm headphones which didn't survive the blast. Well the next day I decided to take another look under the hood and reflow any dodgy looking joints just to be sure that everything was secured. I actually found 6 joints that had come loose even though I had put a fair amount of solder on them during the build. But when I plugged the amp back in I was now hearing what sounded like mains hum through both channels and the amp would make loud pops through the headphones (SR-80i this time) if I tapped on the wood base.
I did the resistance and voltage checks and everything checks out a-ok except for one test I read about in another thread. Putting the meter across terminals 4 and 5 of the transformer to measure the heater voltage results in a reading of about 2 volts AC instead of 6.3 like it should be.
Does this sound like a tube failed? I powered on the amp without the 12AU7 installed and still had the hum and pops. I'm using a NOS RCA 6080 that looks like it says it's from 1959. The 12AU7 is an Electro-Harmonix made in Russia in 2009. The 6080 does have a blackish sooty looking substance building up on the top of the tube on the inside. Being new to tubes I wouldn't know if this is normal or not.
I haven't been able to find any other electrical faults with the amp but maybe I'm not looking in the right places.
The other question I have is how can I protect my headphones from getting blown out if the amp developes faults in the future? I'm going to get another DT770 Pro or maybe a DT880 Pro 250 ohm. Unfortunately I feel like I'm taking a risk when I plug headphones into the amp now. Would protection relays right before the headphone jack work? I thought the output caps would protect the cans but apparently they couldn't stop this blast.
Thank you in advance. Advice on the is very much appreciated.
PS: I did use a Radioshack 30W iron and Radioshack lead free solder for this project. From other threads I've read that probably was a bad idea.
« Last Edit: June 05, 2011, 09:42:44 AM by Bipabew42 »
Chris Koenig
Gear: Crack OTL Headphone Amp - Carver SDA-390t Tube CD player - 1978 Yamaha CA-610II Integraded Amp
