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Posts by ffivaz

 Could it be source related if you had it with previous amps? I would try to run the Crack without any source connected and using a shorting plug (a RCA jack with an around 500 Ohms resistor connecting ground to center). If it's dead quiet with a shorting plug, then it's your source (without shorting plugs and no source, there should or could be some humming). If it's not quiet, then I would try to move the Crack around, remove RFI source around and finally ask help at...
 The stock Crack is musical. It's warm but not laid back or "tubey". The HD 650 are also on the warm side of headphones. Don't get me wrong : that is nice, I can listen to them for hours without any fatigue (like I get with, say, grados). So IMHO, I think you can get a clinical or analytical DAC. Now for the SB, I don't think it changed the sound signature of the Crack, only everything the Crack did well was even better : tight bass, excellent mids and precise trebble!
ODAC... And spend the rest on a speedball!
 Yeah, you could lower the impedance of the output tubes by adding some transformers. But then, it wouldn't be a Output Transformer Less design anymore. S.E.X. has transformers and drives about any headphone you can throw at. Now you have to live with the output tube impedance and choose carefully some really nice sounding, high impedance headphones : Beyerdynamics in the 250 to 600 Ohms (T1, 990, 880, 770), Senns : the HD650, 600 (300 Ohms) and of course the flagship...
 You can replace the crack pot with 100 kOhms resistors. That would sure improve the sound. I think, you can just connect wires white to white, red to red, black to black and put a 100 kOhms resistor between the ground lugs and center of each RCA... It could be also interesting to reduce the length of signal path by putting the RCAs closer to the front of the Crack.
 I'm not sure solid core is the best for a headphone cable since it's rigid and quite fragile if bent.
I had the experience two weeks ago. I forgot to bridge the two grounds on a new pot. My resistance went haywire, and I still decided I could start the Crack. Bad move. Even after shutdown and power cable removal, I got snapped when touching something inside. Something I never experienced before : the resistors (the 270R in the PS I think) work fine and discharge the caps in a couple of seconds (if your grounding is correct!).
 +1 Don't forget to connect the two grounds when you rewire you new pot. If you don't, your Crack will go crazy and become potentially dangerous (some caps aren't discharging anymore at shutdown). half of the Crack's grounding is done through the small wire on Jamies's pot.
 Just to correct one thing. I think that all Bottlehead products never drift out of class A. Crack, S.E.X. and mainline are all Single Ended "Class A" designs, as opposed to other classes that use push pull design for higher output power. You have a maximum output voltage before clipping, which many find less harsh with tubes.
 You would receive better inputs if you posted your problems on the Bottlehead forum. Back there, you would be asked if your resistance checks and voltage checks were fine. Were they ? If the noise is only in one channel, then you have a cold solder joint in the signal path of this channel, or sometimes (but it's a rare sometimes) a bad tube. You could try the chopstick test : the test for the hardcore diy guys. Take a wooden stick (wooden, nothing else) and try to poke...
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