Another buzzing thread

[xavhan]

Hey guys, I finally finished to mount my crack.
I had a little bit of panic when i plugged it for the first time,  the transformator was smoking and i found that i did not solder the right way the 2 diodes in 20 & 21. My bad :s

Now everything seems great, the resistance and voltage check are all good but i have somekind of a buzz.

When i turn the crack on i have no noise, and it appears 5 seconds after when the tubes are warm. When i turn the potentiometer clock wise, at 9 oclock i begin to hear a higher buzz coming, at 12 oclock i hear both of them at 3 a clock i hear a very high pitched buzz. When i turn the volume button the amplitude of the buzz doesnt change, just the frequency.

Do you have an idea of what it could be / come from?

I can take pictures of specific area of the amp if it helps or record the buzz.

I forgot to add that when i plug a source and play a song that i can hear the sound but it's really messy and covered by the buzz sound

[Doc B.]

The first buzz may be from a bad solder joint. I would suggest going over the solder joints again. The second buzz that changes pitch might be an interaction with your interconnect cables. Try removing the interconnects and see if the higher pitched buzz goes away, or changes.

[xavhan]

I am going to check the solder joints again.

I have the pitched buzz even if i have no cable pluged.


I was reading the thread on ground path and i was noticing that i have no ground on transformator 4 (red note on page 19) is it relevant in this case?

[Paul Birkeland]

I was reading the thread on ground path and i was noticing that i have no ground on transformator 4 (red note on page 19) is it relevant in this case?

No ground with a meter, or no extra black wire connecting to power transformer terminal 4?

If you have no ground path, you can move that connection to 16U pretty easily.

-PB

[xavhan]

So I redid and rechecked my soldering. I lost the buzz who pitched high when i turned up the volume. I can hear the sound of my music, and its great but i still have that low pitched buzz. It does not change when i turn the volume up or down.

I did the ground thing you told me soldering a wire between transfo4 and 16U. And the little tweek with the 2 jumpers on the jack.

I took some pictures, maybe something will pop out to you eyes that i did not see.

It's really frustrating feeling the good sound and still having that buzz

pictures here : http:///imgur.com/a/PBZJN#0

[Paul Birkeland]

Photo 1: Remove that extra black wire going to 22.  You can make a ground loop by making that connection, which will make your amp noisy.

Photo 2: Are those power supply diodes pre or post-diode repair?  Try your best to bend them to look like what's in the manual, otherwise you risk creating a shorted power supply. 

Photo 4: The braided input wiring is right next to the red/black heater wiring.  These need to be moved apart.

Photo 7:  Same as above.  You want the braided wire as close to the edge of the chassis as possible.

How are your voltage readings?

[xavhan]

Oh yeah! That did the trick! I removed the extra black wire and moved the 2 braided cables apart and it worked! Thanks a lot for that precious help.

I still have a question about the diodes i misplaced before. Could they be damaged even if it works right now? Do I have a way to test them?


Can't wait to install the speedball now!

[Paul Birkeland]

If you pass the voltage checks, I don't believe you need to worry about the diodes.

-PB

[xavhan]

Hello again, problems are back but different this time.

I had some issues because i lost the sound in my right speaker
At first it was looking like a false contact in my jack and the problem was a bit of random.
I redid some soldering there and there and the problem seems to have stabilised.

Now i have perfect sound in my left ear. In the right one its another thing, the sound is really low and doesnt goes up when i turn the volume knob up but i can hear some scratching sound when i turn it (only in the right ear).

Where should i look into to fix this problem ?

[Strikkflypilot]

First do a voltage check.

[xavhan]

I did my voltage checks but it seems ok :
term      expected   real measure
1      75-90   73,7
2      170      162
3      0      0
4      170      161
5      75-90   71,2
6      0      0
7      100      97,4
8      0      0
9      100      94
10      0      0
11      0      0
12      0      0
13      170      161
14      0      0
15      185      179,5
20      0      0
21      206      200

[Strikkflypilot]

Your voltages look great.
I take it all diodes and both sides of both tubes light up.
I had a black beauty (Alps potentiometer), that had a bad contact causing what You are experiencing.
Not to say that has to be it, but have You tested restistance between in out on both channels on the pot meter itself?  It could be shot.

[xavhan]

Yeah that make sense that the potentiometer must be damaged.
The Five positions are :
- fully closed
- knob at 9 'o clock
- knob at 12
- knob at 3
- fully open

on the right channel between the 2 red wires i can read :
89,2      84,4      76      30      0
on the left channel between the 2 white wires i can read :
95      90      81,5      36,5      0

First of all it seems that it's poorly balanced.
Would you advise me to change it ?

[Strikkflypilot]

Hi.

This looks slightly poor balanced but the values are not completely off as in 0 or infinity.
I recall that my pot was broken at the same time that I had i bad connection on my 12Au7, I believe A3. Check those connectors on the 12AU7 too.

[Paul Birkeland]

on the right channel between the 2 red wires i can read :
89,2      84,4      76      30      0
on the left channel between the 2 white wires i can read :
95      90      81,5      36,5      0

First of all it seems that it's poorly balanced.

It's a very bad idea to call a pot poorly balanced because the resistances numbers aren't identical, as that's such a small part of what's going on.  I will translate these to dB so you can see what I mean.

Right channel is 89.2K total resistance.  Your steps are:
0db, -0.48 dB, -1.4dB and -9.5dB
Left channel is 95K total resistance.  Your steps are:
0dB, -0.46 dB, -1.3dB, and -8.3dB

The 1dB difference on the last step will be a little audible, the rest of those settings are very tightly matched.