Crack with Speedball - Loud Humming Help [resolved]

[alihill77]

I built the amp with the speedball around a year ago. Recently I noticed that there was a faint humming and decided to reflow all of the solder joints. Since then there has been a loud humming coming from the amp. The humming/buzzing inceases the more the volume is turned up but is obviously noticeable at low volumes too.

Weirdly if I plug the RCA jacks directly into my computer there is no humming but if I plug the RCA jacks into nothing, a phone or my dac there is humming. I thought there might be a grounding issue but I checked every ground point they seem ok. My resistances and voltages seem fine too. My voltages are:

T1 - 74
T2 - 183
T3 - 0
T4 - 183
T5 - 72
T6 - 0
T7 - 107
T8 - 0
T9 - 110
T10 -0
T11 - 0
T12 - 0
T13 - 183
T14 - 0
T15 - 202
T16 - 0
T17 - 0
T18 - 91
T19 - 91
T20 - 0
T21 - 222
T22 - 0

A1 - 71
A2 -0
A3 - 1.5
A4 - 0.01
A5 - 0.01
A6 - 73
A7 - 0
A8 - 1.5
A9 - 0

B1 -  73
B2 - 182
B3 - 107
B4 - 72
B5 - 182
B6 - 110
B7 - 0
B8 - 0

SMALL CURCUIT
OA - 73
IA - 182
B-A/B - 0
IB - 182
OB - 72

BIG CIRCUIT
G - 0
OB - 107
B+ - 182
OA - 110

 

[Paul Birkeland]

Weirdly if I plug the RCA jacks directly into my computer there is no humming

This is likely to not be an issue.  Is there any hum with the volume pot turned all the way down and nothing plugged in?

 

[alihill77]

With nothing plugged in I can only hear a buzzing when I turn the volume up a quarter of the way or more.

With the rca shorted I can start hearing the buzzing from turning the volume up an 8th of the way.

This is a problem because the buzzing is louder then the music when I plug the amp into my dac.

Also it sounds like a techno beat is coming from my computer when I plug it in now.

 

[alihill77]

Also if I touch the rca jack with my finger I can hear buzzing in the relevant ear.

 

[Paul Birkeland]

With nothing plugged in I can only hear a buzzing when I turn the volume up a quarter of the way or more.

That's very likely normal.

With the rca shorted I can start hearing the buzzing from turning the volume up an 8th of the way.

There shouldn't be any buzzing with the RCA jacks shorted.  What are you using as the short?

This is a problem because the buzzing is louder then the music when I plug the amp into my dac.

What're you using for a DAC.

Also it sounds like a techno beat is coming from my computer when I plug it in now.

Can you try using just an 1/8" to RCA cable to connect the Crack to your phone.  What issues (if any) are present under these conditions?

 

[alihill77]

My DAC is a modi 2 uber which is plugged in to the wall.

I get buzzing with heavy distortion on the music when plugged into my phone as well as my dac.

The buzzing is a lot quieter when shorted I just plug the + and - of an rca cable into the amp.

 

[Paul Birkeland]

OK, the distortion is definitely an issue.

Can you post some photos of your build?  I'd be interested in seeing the power supply wiring, headphone jack wiring, and each socket.

-PB

 

[alihill77]

Here are some images I have just taken: https://drive.google.com/drive/folders/1NsMXJbQKXy6rDGqEzuT6w1vEd_q3OZTS?usp=sharing

 

[Paul Birkeland]

Was this issue present before you installed the Speedball?

You have many, many connections in that amp that are just the stripped wire passing through a terminal with a little solder on it.  I would recommend going back and bending all those wires up against the terminals they are passing through (this is the "attach' part of the instructions), then reheat the solder joint and flow a little solder between each wire and terminal where the wire is resting against said terminal.

There are also some leads that aren't well trimmed that may cause some problems.  Specifically the area around the 220uF cap by the UF4007 diodes is concerning.  If you lay down two of the three power supply caps like we show in the manual and take new photos, I could see much more of the build under there.

I would suspect that the noise you are hearing is related to a power supply capacitor that isn't well connected/soldered.  The distortion is most likely a poor solder joint making itself audible.

 

[alihill77]

No my speedball worked before with a light hum at low volumes that I could usually remove by hitting the amp with my hand. This louder hum and distortion that I am getting now has only happened since I tried to fix the light hum by reflowing solder joints.

 

[alihill77]

Did you want picture like this?

I added two more angles to the shared folder

 

[Paul Birkeland]

Yeah, you need to bend the leads up against the terminal strips and then reflow the solder joints.  I've circled potential issues in that photo; I wouldn't ignore any of these.

 

[alihill77]

I did the "chhopstick test" and when I pushed the capicitors there was a crackle and pop when I touched any of the capitors.

I have reflowed all of the joints you have circled and now none of the capicitors crackle and pop but the buzzing is still there.

 

[Doc B]

Just reflow every joint. That is the first thing we would do if you sent it to us for repair.

 

[alihill77]

I tried reflowing all the joints and the buzzing still persists. 'll get my friend to look at it and see if he can see any bad solder joints.

 

[Paul Birkeland]

Can you post updated photos of your amp?

 

[alihill77]

Here is a folder with some updated pictures: https://drive.google.com/drive/folders/1WvB65H1B09iLaMLstBxhV_yOqtW_AzUq?usp=sharing

 

[Paul Birkeland]

There are still many, many leads that need to be trimmed and resoldered. 

A hum that is resolved by hitting the amp with your hand is a loose connection. 

 

[Paul Birkeland]

The circles in green are connections that could make for noise issues.  Those in red are more of a safety concern.

The circle around the headphone jack is the red wire not looking lit it was wrapped/soldered in another photo.

 

[alihill77]

Thanks for all your help. It is 10pm for me so I'll give this another go tomorrow and get back to you with the results.