Right Channel Not As Loud, Seems Less Crisp Than Left [resolved]

[jtori]

This question may be premature, but here goes.

Just completed the Mainline and am in the first hour of listening.  Immediately, I noticed music appears to be biased toward the left channel; it is consistently louder and crisper sounding than the right.  All voltages and resistances checked out, and the LEDs are all lit.  The amp was properly biased.  Visual inspection shows all connections soldered (none cold).

For reference, I've compared the newly built Mainline to my Speedballed Crack.  The Crack is more equally balanced.

Might this improve with a little time, or is there something else I should be looking at?

Thanks,

Joe.

 

[Paul Birkeland]

You can try switching around the 6C45P tubes to see if that issue follows a tube, though I doubt that will be the case.

What you're describing could be an issue with attenuator wiring or output transformer winding. 

To check on all of this, play a 60Hz sin wave tone into your Mainline from your phone and turn the attenuator all the way up.  Set your meter to AC volts (on the 2V range if your meter is not auto-ranging).  Check the AC voltage between ground and the center post of each 6C45P socket.  Let us know what you measure (this can be done with the amp off).

If those voltages look to be matched, then measure the AC voltage on the left side of each 10uF cap (the side that is wired to the output transformer).  Let us know what you see there.

A lot of information will be provided by these simple measurements.

 

[Rocketman248]

It's a long shot, but your symptoms are very similar to what I experienced once.  Try gently wiggling the attenuator knobs while listening.  I had an attenuator switch that had a little bit of play, and it would cause a channel imbalance. 

 

[jtori]

You can try switching around the 6C45P tubes to see if that issue follows a tube, though I doubt that will be the case.

What you're describing could be an issue with attenuator wiring or output transformer winding. 

To check on all of this, play a 60Hz sin wave tone into your Mainline from your phone and turn the attenuator all the way up.  Set your meter to AC volts (on the 2V range if your meter is not auto-ranging).  Check the AC voltage between ground and the center post of each 6C45P socket.  Let us know what you measure (this can be done with the amp off).

If those voltages look to be matched, then measure the AC voltage on the left side of each 10uF cap (the side that is wired to the output transformer).  Let us know what you see there.

A lot of information will be provided by these simple measurements.

Hello Paul, and thank you for your reply. 

I've followed your recommendations.  Here are the test results:

- Swapped the 6C45P tubes and rebiased after 20-30 mins. -- No change, as predicted.

- Ran a 60Hz sine wave and checked AC volts at the 6C45P center taps -- A side = 0.307 V; B side = 0.306 V

- Checked AC volts at the left side of 10 uF capacitors (amp on) -- Both read 0 V.

Also, I need to amend my previous observation.  I wouldn't say the right channel is muffled, just lower in volume.

A quick note:  Since no direction was specified, I installed the 10 uF capacitors in opposite orientations (not deliberately).  Also, I accidentally nipped off one of the leads on one of these capacitors while straightening it; I resoldered the nipped-off piece to the 1/2" remaining; all pre-check measurements were unaffected.  If advised, I can install a fresh one.

Thanks for your guidance.

Best regards,

Joe.

 

[Paul Birkeland]

The amp will need to be running to do the measurement on the 10uF caps. 

 

[jtori]

The amp will need to be running to do the measurement on the 10uF caps.

Hi Paul,

The amp was on, with both attenuators at 0 dB.  Have I missed something?

Thanks,

Joe.

 

[Paul Birkeland]

There should be considerable AC voltage at the output of each 10uF cap.  0V AC is no signal coming out of either channel.

 

[jtori]

It's a long shot, but your symptoms are very similar to what I experienced once.  Try gently wiggling the attenuator knobs while listening.  I had an attenuator switch that had a little bit of play, and it would cause a channel imbalance.

Hi Nick,

Thanks for the suggestion.  Neither of my attenuators exhibits any play.  I did exercise the attenuators to remove oxidation, however, this has not helped.

Best,

Joe.

 

[jtori]

Paul,

If those voltages look to be matched, then measure the AC voltage on the left side of each 10uF cap (the side that is wired to the output transformer).  Let us know what you see there.

Voltages at the output side of the capacitors (the side not connected to the output transformer) are as follows:

- A side -- 319 VAC
- C side -- 311 VAC

Please let me know if this is the information you are looking for.

Thanks,

Joe.

 

[Paul Birkeland]

Voltages at the output side of the capacitors (the side not connected to the output transformer) are as follows:

That's the side connected to the plate of the 6C45P, and your meter is likely reading AC on top of DC and giving you those high numbers.  You should get a straight AC voltage number on the side of each cap connected to each output transformer.

 

[jtori]

That's the side connected to the plate of the 6C45P, and your meter is likely reading AC on top of DC and giving you those high numbers.  You should get a straight AC voltage number on the side of each cap connected to each output transformer.

Got it.  I double checked and the side connected to the output transformer is reading 0 VAC on both sides.  What do you suggest?

 

[jtori]

That's the side connected to the plate of the 6C45P, and your meter is likely reading AC on top of DC and giving you those high numbers.  You should get a straight AC voltage number on the side of each cap connected to each output transformer.

Just shut down the amp.  Interestingly, both output transformers are cool to the touch.  Going back through the instructions to see if I missed something. 

 

[Paul Birkeland]

I don't really have a suggestion beyond that.  If you plug headphones in and you hear the 60Hz tone, then there's a 60Hz AC signal sitting on the transformer side of that capacitor that should be very easy to read. 

Are you sure your meter isn't showing "OL" for "Over Limit"?  If the meter is not auto ranging, you may need to go up one range to see the AC voltage value that will be present there.

Both output transformers will remain very cool to the touch during normal operation, that's not abnormal at all.

 

[jtori]

I don't really have a suggestion beyond that.  If you plug headphones in and you hear the 60Hz tone, then there's a 60Hz AC signal sitting on the transformer side of that capacitor that should be very easy to read. 

Are you sure your meter isn't showing "OL" for "Over Limit"?  If the meter is not auto ranging, you may need to go up one range to see the AC voltage value that will be present there.

Both output transformers will remain very cool to the touch during normal operation, that's not abnormal at all.

I have been walking through the build instructions and found that I miswired one connection: I wired the white lead that passes from the lower front terminal on the fine attenuator to the lower rear terminal on the coarse attenuator.  It should connect to terminal 1 on the coarse attenuator. [top of p. 43 in build instructions; first instruction]

 

[jtori]

I have been walking through the build instructions and found that I miswired one connection: I wired the white lead that passes from the lower front terminal on the fine attenuator to the lower rear terminal on the coarse attenuator.  It should connect to terminal 1 on the coarse attenuator. [top of p. 43 in build instructions; first instruction]

Correcting the miswiring seems to have done the trick.  Still perplexed by the 0 VAC on the OT sides of the 10 uF capacitors.  I've employed two meters (an old auto-ranging Micronta and a Wavetech Meterman 10XL) with the same results.  Should I be concerned?

 

[Paul Birkeland]

If you hear sound coming out of the amp, the AC voltage is there and there isn't really anything to be worried about. 

 

[jtori]

If you hear sound coming out of the amp, the AC voltage is there and there isn't really anything to be worried about.

Thank you, Paul, for your sage guidance, nearly immediate responses and extraordinary patience!  A value simply can't be placed on the manner in which you and Bottlehead support DIY'ers such as me.

Best,

Joe.