Crack Problems - Help Needed

[sonodelirii]

Hi guys! Long time fan, recent Crack owner.

Just finished putting together the base kit (no speedball) and having an issue.

The resistances and voltages all came up ok however the sound levels are very low.

Works fine with low impedance ear buds but with Sennheiser HD650's very quiet (highs coming though ok, mids no so much and lows no existent).

The TRS connector on the HD650's got VERY hot. After listening for ~5min I pulled it out and it was too hot to hold for more then a second.

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Another issue I have might be unrelated but maybe not. I have a buzzing noise on both channels.

Now I also have this buzz on my active monitors as well. I switched source from my ASUS STX2 to smart phone and same problem so its not the source. The buzz is independent of volume level (except when the pot is next to zero on Crack, it gets a little louder).

I am thinking maybe the wiring in the house not great. I was told that could be an issue in older houses but this isn't a very old house. I have a wifi router but that's 2.4Ghz, should be too high to matter. There is a cell tower down the street but phones use 900MHz last I remember.

For the active monitors after talking to a few engineers I ordered something similar to a DI box that that helps reject common noise and has galvanic isolation via transformers for each channel (Radial J+4). Will report once it gets here if it helped.

But since the Crack doesn't have balanced inputs (unfortunately) I need another solution.

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[sonodelirii]

Small Update

Re-did the solder joints and took measurements again.

Everything still looks about right but the volume is still low, the headphone TRS  connector still heats up, and the buzzing noise is still present.

I should note that before re-solder job, at about 75% volume, I was getting weird distortion (sounded like harsh noisy clipping of signal that's too strong), even though the headphones were pretty quiet; but that's now gone after re-solder job.

I want to point out terminal 11 is reading a resistance even though its not connected to anything and is isolated from plate by non conducting stand off. On resistance check it reads 3-15 ohms depending on how steady your hands are. Now since its isolated it should act as extension of the probe and read 0L (no connection) right? Not sure if this is a sign of trouble.

The buzzing sound is still there, still on both channels. This noise is more or less independent of the volume pot position on the Crack or source volume.  I have a similar sounding noise on my active monitors. That noise is independent of the source volume as well.

 

[fullheadofnothing]

Can you post pictures of your build?

 

[Paul Birkeland]

The TRS jack should not get hot.  Please discontinue using headphones with this Crack until we get it sorted out.

Is this Crack 100% stock?  Can you confirm that the 100uF/160V capacitors are oriented correctly? 

If you have 0V at T6 and T10, but your TRS jack is getting hot, it's possible that the solder joint on the TRS jack with multiple black wires connecting to it is not solid.  I would reheat that joint, waiting for the solder to flow in and around all the connections there.

-PB

 

[sonodelirii]

Thanks for the tip!

First thing I did was re-flow the joint with the multiple black wires on the TRS jack. It seems to have fixed the volume levels, the noise problem and the headphones TRS connector heating up! Sounds amazing now!!

I only have one concern now, but maybe its normal operational conditions. After fixing that joint I listened for about 5 hours and the mounting plate heated up a lot. Not to an uncomfortable level and hottest around the tubes and the transformer. I know the tubes get hot but the transformer got pretty hot after 5 hours, is that normal? The headphone jack was also hot but not painfully, not nearly as much as before, and it took 5 hours. I am guessing by then everything got well heated by the transformer ans tubes. So is this normal? What heat levels should I expect from the Crack?

I also noticed I installed socket A same was as socket B, from the under side, vs from the top side like in manual. Hope this doesn't effect anything. From the look of it it shouldn't.

FYI the plate is painted black but I scraped off the paint in the spots where the ground screw and the two 5 terminal strips attach.

The caps are oriented correctly and this is 100% stock Crack. If this heating of the amp over hours is normal I will proceed to build the speedball.

Thanks again!

 

[Paul Birkeland]

I'm glad to hear that you were able to find the issue.  The Crack will run nice and warm, those 5 and 10 Watt resistors under the chassis produce a fair amount of heat, as do the tubes and power transformer, though they are able to radiate it up and away more easily.  If your voltages are correct, there is no concern for the heat the amplifier is generating.

-PB

 

[Strikkflypilot]

That is one good looking build!

 

[sonodelirii]

Thanks, I try.

UPDATE:

Built the speedball but not passing voltage checks. Ground and 170V seem to be reversed.

If someone can point out what could result in this I would really appreciate it.

For now I will try re-flowing the joins. Maybe replace large board with 3k resistors and see if I can narrow down the problem area.

 

[sonodelirii]

UPDATE:

Swapped large board for 3k resistors, voltages changed a bit but pretty much the same; problem still there.

LED's on small boards light up but much dimmer then the LED's on socket or large board (don't know if that is a sign of not enough current); that stayed the same as well after swap back to 3k resistors.

 

[sonodelirii]

UPDATE:

Swapped small boards out for resistors as well and still have the problem....

*wait I am a colossal idiot... stay tuned.

 

[sonodelirii]

UPDATE:

Turns out everything was fine (more or less), I was just measuring relative to 13 instead of 12 because I grab the resistor lead for convenience but having turned the body around was grabbing the lead going to 13 by mistake lol...

Rebuilt everything and voltages seem ok.

Only problem is on power up the voltage on the TRS (tip or ring) spikes to 20-21V before dying down to 0. Manual says significantly more then 9V is bad. Not sure if 10V is significant in this case.

 

[JamieMcC]

That's a nice looking Crack build congratulations. In the Cack thread sticky section the first post is

"Oops Moment" - easy mod to keep startup voltage on the output down 

Instructions here

http://bottlehead.com/smf/index.php?topic=2946.0

 

[grausch]

Just remember that if you do the "Oops moment" mod, your resistance at 6 & 10 will go to zero.

I had quite a "doh moment" figuring out why my resistances at 6 & 10 weren't working (with the help of DocB, PB and JH of course). You might want to write a note in your manual to avoid future trouble-shooting.

 

[Chris65]

Only problem is on power up the voltage on the TRS (tip or ring) spikes to 20-21V before dying down to 0. Manual says significantly more then 9V is bad. Not sure if 10V is significant in this case.

Not a problem, the TRS voltage spikes at bit higher with Speedball (not mentioned in the manual though). As long as it drops back to zero, it's good.
But worth doing the 'Oops moment' mod.