Left Channel is slightly louder than the Right [resolved]

[undertowogt]

Hello,

I have had my reduction for a while and always noticed the Left Channel is slightly louder than the Right. I ran signal through my audio interface and digitized it and it is about 2 db difference. Even when I move Tubes around to troubleshoot, the left channel is louder .Vocals always seems to be shifted to the Left. The problem is surly coming from the reduction as I have trouble shot cables, amp and everything else including my cart and turntable setup. If it is NOT the Tubes what could it be.........any thoughts. I am going to do A voltage check tonight.

 

[Paul Birkeland]

This is very, very, very, very likely to be bad solder joints.  I would go through the Reduction and reflow all of them.

You can generate a 60Hz tone and feed it through the amp to check for signal levels in various spots, but I wouldn't go to this just yet.  I'm pretty sure you have some grounds that aren't well grounded.

 

[undertowogt]

Solder will be flowing after the kids are in bed tonight. I will update later,

Thanks

Update: So I re flowed solder last night and did improve on some solder joints. Unfortunately the problem still exists. I did another signal capture with my audio interface to be 100 percent sure. When capturing I add no gain on the channels of the audio interface to be sure the signal is direct from the phono preamp. My Captured Waveform is consistently off balance by about 2db. I can see this is the Phase analysis and the Freq analysis and the waveform itself as well as hear it shifted in the sound stage.

The capture is: Record Player> Reduction>Audio Interface>Capture computer.

 

[undertowogt]

How hard is it to pump signal into the reductions to check for signal levels in various spots as you suggested?

 

[Paul Birkeland]

If you have a cell phone and an 1/8" mini to RCA adapter, you can download a signal generator app and send a 60Hz sine wave tone into the Reduction.  You want to be careful to have the volume at the lowest possible setting on your phone though (one up from muted).

-PB

 

[undertowogt]

Hi PB,

I have a 60hz tone and all, thats the easy part for me. Unfortunately I am not an electronics wizard like a lot of DIYers out there and I dont understand how to go about checking signal levels in Various spots. Is this done with a multi meter?

Would I be correct in saying that I should be trouble shooting the Lower Channel and NOT the higher volume channel?

 

[Paul Birkeland]

You should troubleshoot both channels!  In a phono preamp, the EQ pulls the signal down significantly everywhere except the low bass, so while my opinion is that you have a flaky solder joint on a ground wire in the offending channel, you could also have a bad EQ connection in the channel that seems to be good.

To measure the signal voltage, you will need a meter set to AC volts.  Your meter will need an AC volt scale that's pretty low, most of them will have a 2V setting or a setting that looks like mV~.  If you meter only has something like a 200V and 500V (or 200V and 700V) scale, then it won't quite get the job done.  The $25-ish meter at Harbor Freight is perfectly adequate for this job.

To get your bearings, you can hook your phone up playing a 60Hz tone to the Reduction with the Reduction powered off, then crank the volume up all the way on the phone and measure AC voltage between the center pin and ground on each input jack.  For most phones, this will be about 0.3V (300mV).  For the remainder of the tests, you'll want to turn your phone down so it's at 10mV or less.

 

[undertowogt]

It could be an EQ issue as you say. The Channels differ slightly in EQ. The right channel is slightly thinner sounding and the Left Channel has a tiny bit more bass. This may also bring the signal level down or up slightly I would think as EQs do.

Where exactly is the EQ section of the reduction. I will take an even closer look. Ok , thanks for the tips.

 

[Paul Birkeland]

Another possibility is that you have a 47K and a 475K resistor swapped.

The EQ is the 75K, 10.7K, and all the 0.01uF caps. 

 

[undertowogt]

I looked at the resistors, They are in the correct position. I also checked the grounds again and they look solid. I am kinda of stumped now. I will do a Voltage check later and update.

 

[undertowogt]

After closer inspection I noticed that the red wire attached to a tube pin with the 1 .0μF 50V (Z5U) capacitor was lose. It was still touching with pressure so the reduction was still working, maybe it recently came lose. I soldered it on correctly and plug the unit in to test. Unfortunately, Now I have a new problem........ both channels distorting significantly. So I pretty much made things much worse. I think the channel are balanced now ( somewhat hard to tell with the distortion though)
I am away for a few days and will have to take a closer look when I return.

 

[Paul Birkeland]

Go back and recheck your voltages.

 

[undertowogt]

Go back and recheck your voltages.

I checked Voltages. Some seem a little lower then they are supposed to be?:



Terminal Voltage (DC)
1
2      68.2
3
4    147.2
5
6
7      72.7
8
9
10
11
12
13    67.0
14    67.6
15
16
17
18    67.3
19    62.5

20    61.9
21
22
23
24
25
26    67.2
27
28
29    146.9
30
31    71.5
32
33    5.6
34
35
36
37    5.6
38    9.7
39    3.5
40
41    3.7
42    9.7
43
44    181.6
45
46
47
48
49
50    164.1
51    164.1
52    181
53    181.3
54
55
56    146.8
57    146.8
58
59    164.3
60    164.3
61
62

 

[Paul Birkeland]

The 5.6s are concerning.  Can you post photos of the two 5 lug terminal strips where the axial blue capacitor is mounted?

 

[undertowogt]

Pic Doc

 

[Paul Birkeland]

If you pull the tubes out, what voltages do you get at 38, 42, 33, and 37?  What is your incoming AC line voltage?

 

[undertowogt]

With Both Tubes removed:

38 - 10.3
42- 10.3

33 - 5.9
37 - 5.9

120 Volts into my house if that what you are referring to ( or are you taking about the Reduction AC line Voltage?)

 

[Paul Birkeland]

I would double check that you get 5.6V with the tubes plugged in.  This voltage shouldn't change much, and it certainly shouldn't drop that low.  It could happen if a 22 ohm resistor or one of the 1N5818 diodes isn't well installed.

 

[undertowogt]

I would double check that you get 5.6V with the tubes plugged in.  This voltage shouldn't change much, and it certainly shouldn't drop that low.  It could happen if a 22 ohm resistor or one of the 1N5818 diodes isn't well installed.

OK,

I will look tonight. thank you for your time

 

[Paul Birkeland]

My thinking with this is that at 5.6V, the functionality of the 6922 in the circuit will start to become more dependent on the tube itself, as you aren't heating the tube all the way.  Of course if you end up measuring 5.9V there, all is well and I wouldn't worry about that.