Crack Speedball hpjun's trouble shooting thread [resolved]

[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.

 

[Doc B]

Are the tube pins nice and clean? Is there any damage to a capacitor?

 

[hpjun]

The Caps don't look damaged, it only starts to ring when I have the crack on for a long time and when I turn it off it goes away. I'll inspect the pins and clean it if it looks dirty.

I also want to know what type of 12au7 I have. It says 12au7a and has no logo on it and doesn't have any indication of a brand name it seems like its just unbranded.

I am thinking of getting a telefunken or gold lion 12au7 to test out later on.

edit: attached picture to help identify my 12au7a, also the pins look dirty going to clean them.

 

[hpjun]

I cleaned the 12au7a and it sounded better not sure what channged but subjectively it sounded better, it could be bias. So I went ahead and cleaned the power tube as well. I might even get some small pipe cleaners for the sockets as well. I don't have an hour at this time to listen to the ringing but when post again if hear it later on.

edit:
Ok I hear that faint ringing now and it doesn't take an hour of warm up to hear it. It sounds like it might be from the power supply area or the capacitors.

 

[Paul Birkeland]

I also want to know what type of 12au7 I have. It says 12au7a and has no logo on it and doesn't have any indication of a brand name it seems like its just unbranded.

That's an RCA 12AU7.

Does the amp ring when powered up with no tubes in?

 

[hpjun]

I just removed both tubes and powered it on and it was silent.

It's safe to do this right? the speedball board doesn't light up with no tubes in.

When I tested earlier with the tubes in I put my ear close to the 12au7 and it was the noisy one. I hear a hissing, ringing and sometimes emi noise.

I think the problem might be the 12au7 tube.

I am going to get a telefunken tube.

 

[hpjun]

When I tap on the big power tube the ringing noise stops and then comes back later on. yep it's the power tube not the 12au7. but once it resonates the little 12au7 picks up on it and will resonate also.

edit: taping on the 12au7 also stop it from ringing but tapping the on big one is key though.

 

[Deluk]

Some people find that a silicone ring or two will solve the problem but a new 6080 is inexpensive and I'd go down that route first. If you can get another 12au7 from the same vendor at the same time that won't up the bill very much and you'll save on postage.

 

[hpjun]

Yesterday I decided to rewire the AC heater wire to the first power tube for optimal results, (I wanted a balanced and tight winding to lower the ac hum further).

I thought I did a good job so I turned it on (my mistake for not performing resistance check). none of the boards lighted up and one of the resistors was smoking so I turned it off really quick.

I did some measurements and got infinite ohms for terminal 7 and 9.

I checked resistance between terminal 4 and 5 was at 0 ohms (one probe on 4 and other on 5). I was wondering is terminal 4 and 5 supposed to be bridged? or did I do something wrong? I know I messed with the AC heater wires so the problem is around that area.

Edit: I think terminals 7 and 9 becomes infinite ohms when speedball is installed right? What about terminal 4 to 5 when probed I got 0 ohms. I don't want to risk turning on my crack for voltage checks, last time the 270k ohm resistors got really hot and smoked the wires (good clue for what's going on) and none of the boards lighted up. Not sure how to continue the resistance checks for speedball.

 

[hpjun]

bump, I'd like to get help on this.

 

[Doc B]

How exactly did you proceed when you rewired the AC heater wiring, meaning what wires did you disconnect and reconnect? This could be multiple issues as it sounds like you have a shorted front Speedball board and that may have happened due to a miswire of the redone heater wiring. Was the kit working with the Speedball before you redid the heater wiring?