Crack Speedball hpjun's trouble shooting thread [resolved]

[Doc B.]

You might try tightening up the power transformer mounting screws a bit. Sometimes that will eliminate the kind of mechanical buzz you hear.

[hpjun]

I tightened up the power supply to the chassis and noticed a small improvement. Before i had to turn it up to about half way 6 o clock to hear a buzz, now I need turn it up to about 7 o clock to hear the buzz. The nuts are really hard for me to reach and tighten since I don't have the tool for that size nut but I will keep trying and I'll buy some tools tomorrow.

[hpjun]

It was those long wires that ran from the rca input to the potentiometer! I noticed a good reduction in noise when I manually moved those wires farther away from the noisy powersupply. Is the powersupply supposed to be this noisy? Having the RCA inputs near the powersupply isn't an optimal design. I didn't do that good of a job braiding those wires though and probably would have made a difference. Knowing how bad the power supply can interfere with the sound just doesn't sit well with me. I feel like rerouting all wires carrying audio signals as far away as possible from the powersupply. Maybe I will drill 2 holes and install the rca near the potentiometer and away from the powersupply. Are there good ways of isolating the power supply noise?

[JamieMcC]

Rather than moving your RCA sockets you could replace the stock red white and black wires that run from them to the potentiometer with some high quality four core screened cable from Belden or Mogami as a number of other Crack builders have your only going to need a short length.

Or just re braid what you have and save some cash its dead easy to get a nice braid.

[mcandmar]

The braided input wiring, and the tightly twisted filament heater wiring is done to reduce noise.  If built exactly as shown in the manual the amp will be completely silent.  Shielded input cabling is better again, but fine multi stranded cable like that is much more difficult to work with than the solid core wire supplied.

[Doc B.]

Don't buy a different horse just because your stirrups are too long. Try braiding and positioning the wire as close as possible to the way shown in the manual before you decide to redesign the amp. Wire dress and solder joint integrity are very important to noise rejection.

[hpjun]

I'll try braiding them and then wrapping some grounded aluminum foil around the wires as a faraday shield.

[Doc B.]

If it's magnetic field interference as you suggest, aluminum foil is not going to do much good. The braiding and proper wire dress and solder joints will have more influence.

[hpjun]

Ok doc, I am going to need a longer wire as tightly braiding them made it too short, going to radio shack later today.

[hpjun]

I bought some nice solid core copper wires from radioshack and did a really tight braid. I added aluminum foil shielding (see attached photo lol) not sure if it made a difference maybe I'll take off the aluminum and test someday. At max volume it's dead quiet, though I can feel a hint of 60hz harmonic hum, maybe I am hearing the phase or something but it's actually nothing, it would take measuring equipment to pick up on it.

I am currently happy with my crack, but the crack has gotten me addicted. I want to improve it further so do I upgrade the output capacitor? stepped pot? add a choke? tubes? Crackatwoa? What's the best upgrade path to take?

[Doc B.]

What's the best upgrade path to take?

Once you price out some of the boutique part upgrades that some Crack builders do you might find that upgrading to a Crackatwoa kit is not that unreasonable. The circuit upgrades in the Twoa are some that you can't do to a stock Crack, and the improvement is significant. We will be hosting a Head Fi meet in late April and we plan to have a "tricked out" Crack and a Crackatwoa side by side for attendees to compare for themselves.

[hpjun]

Oh you guys should exhibit at canjam socal I am going there in two weeks.

Also my left and right channel voltages are a little off, is it because of tubes or is it my soldier connections? Should I buy an 12au7 tube just to check?

[JamieMcC]

I had a lot of enjoyment experimenting modding my Crack with bargain finds from ebay. You don't need to use expensive boutique parts.

£13 5x Film caps for output and last power supply (these look worth a try I've had good results with Epcos in the past)
£12 Triad C7X choke (cheaper on mouser)
£19 Valab 23 Step Ladder Type Attenuator Potentiometer 100K Log Stereo
£6   Teflon capacitors for bypassing the output caps

http://www.ebay.co.uk/itm/262044284465?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT
http://www.ebay.co.uk/itm/Triad-C7X-10H-90mA-smoothing-choke-/171093411086?hash=item27d5f6450e:g:2pUAAOxyYSJR-35Y
http://www.ebay.co.uk/itm/Valab-23-Step-Ladder-Type-Attenuator-Potentiometer-100K-Log-Stereo-/252309543160?hash=item3abed218f8:m:msNfZ0JQ0HBEYro_BkTZXtg
http://www.ebay.co.uk/itm/0-047uF-500V-Matched-Pair-AUDIO-teflon-capacitors-K72P-6-/331575835775?hash=item4d3375bc7f:g:gi4AAOSwNSxVcwQV

Boutique version

£150 Caps Mundorf (their budget MKP range)
£12 Triad C7X choke (cheaper on mouser)
£125 48 step Khozmo stepped attenuator
£160 V-cap Teflon bypass capacitors

£447 for the Boutique parts vrs £50 for the budget option.

[Paul Birkeland]

Just about every Crack that I have fixed that was buzzing either had a loose capacitor or a loose ground wire.  A loose cap won't change any of the voltages, but the low AC impedance that the cap provides is lost, which brings the noise floor way up.

The most common ground joint to give folks problems is where the black wires meet on the headphone jack.

-PB

[hpjun]

I noticed some faint ringing sound when I have the crack on for longer amounts of time. I start noticing the ringing sound for about an hour (could be earlier). I can even hear it without headphones, it's coming from the chasis, I lifted the board and put my ears closer to hear where it's coming from and it sounds like it's coming from either the volume pot or the speedball or the 12au7 area. It's very faint but it sounds like the type of sound a capacitor might produce when it discharges.