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Bottlehead Kits => Crack => Topic started by: Colonl_Charisma on July 22, 2021, 09:29:02 PM

Title: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Colonl_Charisma on July 22, 2021, 09:29:02 PM
Hi all,

I am experiencing some channel imbalance in my Crack amp again where the left channel is noticeably louder and clearer than the right. This seems to be a recurring issue (or one that I haven’t ever fully resolved). I’ve seen a bunch of posts where a 60 Hz sine wave is played through the Crack and voltages are measured. This is a test that I’d like to carry out because it might help me in diagnosing what is causing my issue. I just don’t know how to perform the test.

I was able to rule out my headphones. I plugged them into another amp recently where they sounded perfectly normal. This is what alerted me to having a channel imbalance. Now, I cannot unhear it haha.

As always, I appreciate any help that is given.
Title: Re: Measuring voltages while playing a 60 Hz sine wave.
Post by: Paul Birkeland on July 23, 2021, 05:29:50 AM
The first thing to do is to take a 1/8" TRS to RCA cable and download a signal generator onto your phone, then see if your meter is able to measure the 60Hz tone coming out of the RCA cables.
Title: Re: Measuring voltages while playing a 60 Hz sine wave.
Post by: Colonl_Charisma on July 23, 2021, 07:00:08 AM
Thanks, PB! Just to confirm, this is the cable that I would need, right? Also, could I do this from my laptop? I have an iPhone so I would have to pick up an adapter for the cable too haha.

https://www.amazon.com/AmazonBasics-3-5mm-2-Male-Adapter-Stereo/dp/B01D5H8JW0/ref=sr_1_1_sspa?dchild=1&keywords=8th%2Binch%2Bto%2Brca&qid=1627059133&sr=8-1-spons&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUExVTFFVFE1WlIwTkNFJmVuY3J5cHRlZElkPUEwNjczNDQ0MlRCMVRWQUtaT1hQUyZlbmNyeXB0ZWRBZElkPUEwNTg4NjY5MVI5WFlWV0VVRUZVOSZ3aWRnZXROYW1lPXNwX2F0ZiZhY3Rpb249Y2xpY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU&th=1
Title: Re: Measuring voltages while playing a 60 Hz sine wave.
Post by: Paul Birkeland on July 23, 2021, 07:07:01 AM
Sure, a laptop will work.  Yes, that is the cable you need.

Your meter will need a 2V AC scale or a mV scale to resolve these readings.  If you have a meter that has something like a 200V and 500V AC scale, that won't do the job.
Title: Re: Measuring voltages while playing a 60 Hz sine wave.
Post by: Colonl_Charisma on July 23, 2021, 07:53:39 AM
I have a Crenova MS8233D Digital Multi Meter. I looked up the online manual, and I believe it should be able to resolve those readings.

https://www.crenova.net/Uploads/Product/Manual/5afce34f0db0f.pdf
Title: Re: Measuring voltages while playing a 60 Hz sine wave.
Post by: Paul Birkeland on July 23, 2021, 09:38:46 AM
Yes that should work.
Title: Re: Measuring voltages while playing a 60 Hz sine wave.
Post by: Colonl_Charisma on July 23, 2021, 10:32:18 AM
Perfect! I may try this tonight. Can I go computer —> dac —> amp (normal setup) or should it be computer —> amp (this using the trs cable to connect the devices).

When I play the 60 Hz sine wave through the amp, is the amp on or off and do I have headphones plugged in?

I appreciate your help!
Title: Re: Measuring voltages while playing a 60 Hz sine wave.
Post by: Paul Birkeland on July 23, 2021, 10:44:14 AM
That is up to you.

The first tests would be with the amp off and measuring the AC voltage at the center pin of each RCA jack and the center lug of each level of the volume pot with the pot turned up half way.
Title: Re: Measuring voltages while playing a 60 Hz sine wave.
Post by: Colonl_Charisma on July 23, 2021, 11:13:33 AM
Sounds good! Once I’m at my workbench later this evening, I’ll take those measurements and report back.

Would I set my multimeter to the mA setting to record these first measurements?
Title: Re: Measuring voltages while playing a 60 Hz sine wave.
Post by: Paul Joppa on July 23, 2021, 11:39:02 AM
Set it to the AC voltage scale, marked "~V" according to the manual.

 mA is milli-amperes, which is a current - you want to see voltage for this measurement.
Title: Re: Measuring voltages while playing a 60 Hz sine wave.
Post by: Colonl_Charisma on July 23, 2021, 11:52:48 AM
Thanks, PJ!
Title: Re: Measuring voltages while playing a 60 Hz sine wave.
Post by: Colonl_Charisma on July 23, 2021, 02:06:41 PM
Okay, so here is how I performed my 60 Hz sine wave test:

1) Amp is off.
2) Sine wave is coming from an online generator (Laptop --> DAC --> Crack).
3) I have 6080 and 6SN7 tubes in the amp. I did test whether or not tubes were the issue. I tried different combos, and the channel imbalance was still present.
4) No headphones are plugged into the amp.
5) I'm measuring from 12U
6) Volume knob turned halfway.

Voltages:
RCA left center pin = 1.488 V
RCA right center pin = 1.358 V

Top center lug of volume pot = 0.027 V
Bottom center lug of volume pot = 0.024 V
Title: Re: Measuring voltages while playing a 60 Hz sine wave.
Post by: Paul Birkeland on July 23, 2021, 02:29:14 PM
You have about 1dB of difference at the RCA jacks; I wouldn't consider that normal!

Your pot is turned almost all the way down, so the output voltages are a bit low, but they are also off by 1dB. 

Pull the RCA plugs out of the Crack and check the AC voltage across each RCA plug.
Title: Re: Measuring voltages while playing a 60 Hz sine wave.
Post by: Colonl_Charisma on July 23, 2021, 03:55:28 PM
Yeah, it’s a noticeable difference haha. How do I measure the voltage of the RCA plugs?
Title: Re: Measuring voltages while playing a 60 Hz sine wave.
Post by: Paul Birkeland on July 23, 2021, 04:07:38 PM
One probe on the pin, one probe on the shell.
Title: Re: Measuring voltages while playing a 60 Hz sine wave.
Post by: Colonl_Charisma on July 23, 2021, 04:14:27 PM
Thanks! This is with the 60 Hz wave playing.

Left channel RCA plug: 1.488 V
Right channel RCA plug: 1.487 V
Title: Re: Measuring voltages while playing a 60 Hz sine wave.
Post by: Paul Birkeland on July 23, 2021, 04:20:11 PM
OK, this is helpful information.  That's 0.005dB.

What DC resistance do you get from center pin to shell on each RCA jack on your Crack with nothing plugged in?
Title: Re: Measuring voltages while playing a 60 Hz sine wave.
Post by: Colonl_Charisma on July 23, 2021, 04:34:36 PM
RCA left = 99.3 k ohms
RCA right = 99.4 k ohms

Nothing was plugged in.
Title: Re: Measuring voltages while playing a 60 Hz sine wave.
Post by: Paul Birkeland on July 24, 2021, 05:23:50 AM
Something isn't adding up.  To get an imbalance when you plug in your RCA cables, you'd need to load down the DAC, which would show as low impedance across the RCA jacks.  Consequently I would question the measured AC voltages.
Title: Re: Measuring voltages while playing a 60 Hz sine wave.
Post by: Colonl_Charisma on July 24, 2021, 06:29:45 AM
When I get home, I’ll re-measure everything. I’ll also bend the RCA cables in the angle that they are plugged in at. I have had some issue with this RCA cable in the past with the right channel.
Title: Re: Measuring voltages while playing a 60 Hz sine wave.
Post by: Colonl_Charisma on July 24, 2021, 09:12:24 AM
Quick update! I picked up a new RCA cable, and I took two new readings with a 60 Hz wave playing.

Old RCA cable measurements:
RCA left center pin = 1.487 V
RCA right center pin = 1.368 V

New RCA cable measurements:
RCA left center pin = 1.489 V
RCA right center pin = 1.488 V
Title: Re: Measuring voltages while playing a 60 Hz sine wave.
Post by: Paul Birkeland on July 24, 2021, 10:04:27 AM
Time to junk that old cable.
Title: Re: Measuring voltages while playing a 60 Hz sine wave.
Post by: Colonl_Charisma on July 24, 2021, 11:17:41 AM
Definitely haha. I'll listen for the rest of the day with the new cable, and I'll see if anything sounds off.
Title: Re: Measuring voltages while playing a 60 Hz sine wave.
Post by: Colonl_Charisma on July 26, 2021, 02:34:51 PM
Hi, PB! I think you can mark this thread as resolved. I've been listening to my Crack for awhile now since switching out RCA cables, and I do not perceive any channel imbalance. What I was experiencing was pretty distinct.

Thanks for your help!
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Colonl_Charisma on August 04, 2021, 06:43:23 AM
I'm back with some new measurements. Turns out my channel imbalance seems to still be present. My headphones sound balanced when just plugging them straight into my computer, but the right channel sounds quieter than my left channel when plugged into my Crack.

I followed the measurement instructions on this thread https://forum.bottlehead.com/index.php?topic=7788.15

My RCA jack measurements, middle lugs on potentiometer, and A2 and A7 were more or less equal. However, I seem to have a discrepancy when measuring AC voltage on terminals 1 and 5.

AC voltage with amp on and volume pot turned all the way up.
Terminal 1: 6.51
Terminal 5: 6.92
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Paul Birkeland on August 04, 2021, 06:53:40 AM
That's half a dB, which is audible but not horrible.  What is the DCR of each headphone driver? 

You may find that tube rolling could yield more equal balance, or you could fit a balance control if you prefer.
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Colonl_Charisma on August 04, 2021, 06:58:25 AM
I agree. It isn't as bad as what I was experiencing with the bad RCA cable, but I still notice it.

What does DCR mean? I am unfamiliar with the acronym haha.
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Paul Birkeland on August 04, 2021, 07:00:07 AM
DC resistance.  You can use your meter to measure the resistance of each driver, though at 60Hz that measurement may not be so useful.
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Colonl_Charisma on August 04, 2021, 07:02:47 AM
I can take the measurement now. Do I need to disassemble my HD600 to get to the driver?
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Paul Birkeland on August 04, 2021, 07:05:04 AM
No, you can measure across the headphone plug.  The tip is L+, the ring is R+, and the sleeve is common.
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Colonl_Charisma on August 04, 2021, 07:25:54 AM
Thanks for your help, PB! I am unable to post pictures (site not allowing it). Do I measure across the plugs that connect to the left and right sides of the HD600 while the headphone is plugged into the Crack with the 60hz sine wave playing?
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Paul Birkeland on August 04, 2021, 07:26:40 AM
No, you unplug the headphones from the Crack and measure across the plug on the headphones.
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Colonl_Charisma on August 04, 2021, 07:33:00 AM
My bad haha. Got those measurements for you!

L headphone DCR = 0.303 K ohms
R headphone DCR= 0.302 K ohms
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Paul Birkeland on August 04, 2021, 07:53:04 AM
Yeah, I think you could try some different tube combinations to tighten up the channel balance.
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Colonl_Charisma on August 04, 2021, 08:00:42 AM
Thanks, will do! The channel imbalance does seem less noticeable when using a 12AU7 tube compared to a 6SN7. I have a new problem now though haha. I opened up a new thread.
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Doc B. on August 04, 2021, 08:03:11 AM
Quote
That's half a dB, which is audible but not horrible

It's audible by a few with a lot of ear training, but not many.
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Paul Birkeland on August 04, 2021, 08:06:27 AM
Doc brings up a good point, I'm not sure I would readily pick up on half a dB myself!
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Colonl_Charisma on August 04, 2021, 08:26:11 AM
Right on! Doc B and Paul, it could easily be my mind playing tricks on me haha.
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Colonl_Charisma on August 05, 2021, 04:24:04 AM
That's half a dB, which is audible but not horrible.  What is the DCR of each headphone driver? 

You may find that tube rolling could yield more equal balance, or you could fit a balance control if you prefer.

PB, you mentioned that I could try fitting a balance control. I am all about modding my Crack. How much space would be required to add one? I believe space to be my limiting factor.
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Paul Birkeland on August 05, 2021, 06:26:53 AM
You'd need to fit the 100K linear version of the volume pot we supply, and you'd want it close to the volume pot itself.
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Colonl_Charisma on August 05, 2021, 06:53:11 AM
Cool! Do you have the dimensions by any chance? I can take a look at my amp to see if it would be worth the trouble. It would be a fun addition to my build.
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Paul Birkeland on August 05, 2021, 07:16:54 AM
You have the dimensions, it's exactly the same as the stock pot but just has a different part number.
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Colonl_Charisma on August 05, 2021, 07:25:09 AM
Oh haha. I'll look into this on my end, and see if I can implement this into my amp.
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Colonl_Charisma on August 17, 2021, 06:54:42 AM
Hi, PB! So, after looking at my amp, I think I will be able to install another potentiometer for balance control. Can I  order the pot off of DigiKey or Mouser?
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Paul Birkeland on August 17, 2021, 06:59:32 AM
Mouser has it.  We provide RV24BF-10-15R1-B100K-LA as a balance pot with our kits.  You'd need a pair of 33K resistors as well.
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Colonl_Charisma on August 17, 2021, 10:41:16 AM
Thanks! What kind of wires do you use for the Crack? I would like to pick up some extra to have on deck.

I’ll get those ordered, and I guess we can come back to the wiring once everything arrives.

edit:

Are these 100K resistors fine?

https://www.mouser.com/ProductDetail/Vishay-Dale/CCF02100KJKE36?qs=sGAEpiMZZMsPqMdJzcrNwncUUYJvQsyPlLH02FNSk8g%3D
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Paul Birkeland on August 18, 2021, 07:01:23 AM
You want 20-22 gauge solid core tinned copper wire.  Be sure it's tinned and be sure it's not stranded.
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Colonl_Charisma on August 18, 2021, 07:33:19 AM
Thanks for the info, PB. I will be sure to order that type of wire.

How do those resistors look? Does the power rating or tolerance matter for what I will be doing?
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Paul Birkeland on August 18, 2021, 09:23:17 AM
Sorry, you want 33K resistors.

I would not use 2W resistors in that position, that's overkill and just too big in general.
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Colonl_Charisma on August 18, 2021, 02:32:42 PM
All good! I actually have two 33K resistors that are 1/8 W. I used these on my volume pot to pad it.
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Paul Birkeland on August 18, 2021, 02:51:18 PM
If you're ordering a pot, I would order more.  It helps if they are a bit longer.
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Colonl_Charisma on August 18, 2021, 03:14:12 PM
Will do! I'll get all this ordered tonight.
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Colonl_Charisma on August 21, 2021, 01:56:57 PM
I should have everything in on Monday. How close should the balance pot be to the volume pot? I am going to go ahead and drill a hole in the chassis for the new pot.
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Paul Birkeland on August 21, 2021, 04:38:03 PM
2"-3" is about enough.

I've made a crude image that shows the proper perspective if you're looking from the back of the chassis.  Be sure this is adequately clear before drilling holes or anything.
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Colonl_Charisma on August 22, 2021, 08:04:29 AM
Thanks, PB! Should I desolder all of the old wire, or could I just clip the wires that I currently have and reattach them to the balance pot?
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Paul Birkeland on August 22, 2021, 08:46:16 AM
That is up to you.  I've never done what you're doing, so you'll have to slog through it and figure some of this out on your own.
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Colonl_Charisma on August 22, 2021, 01:00:41 PM
No problem. This will be an interesting experiment haha. I do have my extra wire (and plenty of it), so if I need to redo my wiring it shouldn’t be a problem.

As far as the actual wiring goes, left and right rca jacks to the balance pot, and the balance pot to the volume pot, what is that looking like? Or is that something we will need to work through?

I really appreciate your help.
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Karl5150 on August 23, 2021, 03:02:47 AM
Ross,
If space is tight and you haven't drilled yet, I was able to get the CtoC on the Vol/Bal pots down to 1.75" as per the photo Paul  attached and 1.5" sitting side by side with the terminals pointing to the same side. 
Another simple fix for the imbalance is dual-mono volume pots.
Good luck on your mods,
Karl
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Colonl_Charisma on August 23, 2021, 08:45:46 AM
Hi Karl,

I have not done any drilling yet. Would you mind posting a pic of your build? I'd like to see a longview of the wiring. The closeup view that Paul provided helps a lot, but I'd like to see the full view (I also realize that Paul's pic is not a Crack so a larger view of that one would probably not help me out much).

I appreciate the kind words! I believe this mod will go smoothly once I get going.
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Colonl_Charisma on August 25, 2021, 07:53:46 AM
I got my holes drilled and my new potentiometer place inside my Crack. So far, so good. I am going to solder the connections as they are shown in the above image. I'll also try to post some pics later tonight of how it is looking after I solder the connections.
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Colonl_Charisma on August 25, 2021, 07:01:02 PM
Okay, I believe that I got the wiring figured out! Let me know what you think PB.
Looking from the back of the chassis here are the connections that I made to the balance pot.

RCA to balance pot:
Left RCA --> top left lug balance pot
Right RCA --> bottom right lug balance pot
Right RCA ground -- > top right lug balance pot
Left RCA ground --> bottom left lug balance pot

Balance pot to volume pot (I just went off the picture for these connections):
Ground wire --> between bottom left lug of balance pot and bottom right of volume pot.
Ground wire --> between top right lug of balance pot and top right of volume pot.
Left input --> between top middle lug of balance pot and top left of volume pot.
Right input --> between bottom middle lug of balance pot and bottom left of volume pot.
33K resistors between top left of balance pot and top left of volume pot + bottom right of balance pot and bottom left of volume pot.
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Paul Birkeland on August 26, 2021, 05:34:16 AM
Let me know what you think PB.
Does it work?
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Colonl_Charisma on August 26, 2021, 08:14:57 AM
I'm letting some standoffs settle into epoxy under the chassis. I had to raise one of my film caps up to get it out of the way. Once the standoffs get settled and I solder the film cap connections, I will turn the amp on and see if everything works.
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Colonl_Charisma on August 31, 2021, 12:25:04 PM
Hi PB! I confirm that the balance pot works, and my Crack amp is up and running just fine. I've been listening for about 30 minutes with no issues.

The balance pot clearly changes the prominence between the left and right channels. For instance, when I crank the balance pot all the way to the right, the right channel becomes more prominent with sound still coming from the left channel. My volume pot is working just fine too.

I threw on some mono tracks to test everything out.

If any issues arise, I will post them here. I really appreciate all of your help! This is a very cool mod.
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Colonl_Charisma on September 02, 2021, 06:58:41 AM
I have noticed a couple semi-issues.

1) When I turn my amp on with my volume knob not in the zero position, I get really loud buzzing coming from my headphones. It only lasts for like a minute or so before going away. However, semi-issue #2...

2) When I turn my volume knob there are occasional loud scratching and popping noises. Much louder than what I have heard pots generate. Loud, as in I need to take my headphones off to turn the volume knob.

None of these issues occur with the turning of the balance pot. Other than these two things, everything sound great!
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Paul Birkeland on September 02, 2021, 07:07:10 AM
You can spray some electronics cleaner into the pot if you'd like, as the pots we provide are open and debris can get in there.
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Colonl_Charisma on September 02, 2021, 07:17:25 AM
I have a PEC pot that is closed. I would get some scratching before, but never any pops when turning the volume pot.  The scratching is also super loud. Do you think I can do anything about it?
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Paul Birkeland on September 02, 2021, 08:13:42 AM
Just be sure that all your solder joints are solid.
Title: Re: Measuring voltages while playing a 60 Hz sine wave. [resolved]
Post by: Colonl_Charisma on September 02, 2021, 10:52:08 AM
Thanks, PB, and I’ll double check all my solder joints. The buzzing at start up is weird. No idea why that is occurring.