Sudden distortion in Reduction (+ Integration upgrade)

[jasperd84]

Hi all,

Built my Reduction pre-amp about a month ago and it worked like a dream, sounded fantastic. Added the Integration upgrade a few weeks ago, also worked like a dream.
Yesterday though, all of a sudden music started to sound very distorted. Checked all cables for damage but all seem ok.

Any thoughts as to where I should start to troubleshoot? Did a visual inspection and couldn't find anything out of the ordinary. I plan on running all resistance and voltage checks from the manual when I have time this weekend.

Thanks,
Jasper

[Paul Birkeland]

I would run resistance and voltage checks.

Space is pretty tight in the Reduction, and the repairs I have gotten usually have a missed solder joint or two.

[jasperd84]

Thanks Paul! Will def run all checks again.

Is it worth mentioning that the amp work perfectly up until it suddenly started to sound distorted? This would rule out missed solder joints.
Could it be a component that failed? Or a tube? Distortion is present on both left and right channels.

[Paul Birkeland]

This would rule out missed solder joints.

It does not.  I've found problematic missed solder joints on vintage receivers built in the 1960s that didn't get discovered until recently.

Distortion is present on both left and right channels.

That would tend to suggest an issue with a common ground joint or an issue in the power supply potentially.

A failed component will usually produce a DC voltage that isn't correct.

[jasperd84]

Little update after measuring.

• points 38 and 42 measure 0 Ohm to start with and it slowly climbs to about 7-8 Ohms - this value should be *
• points 39 and 41 measure about 1k Ohms - this value should also be *

I haven't been able to see any solder joints that look really bad or miswires. I might reflow some that aren't as good as they can be.

I can confirm the power transformer makes good contact with the aluminum plate and ground post. All LEDs (both on Reduction and Integration side) light up.

I've included some photos of the area with the Integration PCBs out of the way.

Any thoughts?

Many thanks,
Jasper

[Paul Birkeland]

What DC voltages do you get at 33 and 37?

[jasperd84]

Both get 6.00 V

[Paul Birkeland]

I would suggest turning the temperature of your iron up all the way and adding a little more solder to most of those joints.

Also when a lead passes through a terminal, it should at minimum be bent up 90 degrees against the terminal.  If the lead just passes straight through and isn't bent, things can come apart more easily and the solder has less to grab onto.

[jasperd84]

Got it. Will do that and repot back

Thanks!

[jasperd84]

For what it's worth, just did a DC check on all other points and found some values that were off:

• points 4 and 29 are at 109 V DC - these should be 145-155V
• point 51 is at 0V DC - this should be 165 V
• point 59 is at 150V DC - this should be 0 V

Any thoughts on the above?

[Paul Birkeland]

4 and 29 change when you install the integration.  The others I believe are a typo in an older version of the manual.

[jasperd84]

Had time to reflow all points around the power supply area.
I still measured the same wrong resistances on 38/42 and 39/41 but the distortion is gone and the amp sounds the way it did again.

Been playing now for 30mins or so and things seem stable