Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Pass Labs This forum is dedicated to Pass Labs discussion.

F6 Illustrated Build Guide
F6 Illustrated Build Guide
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 17th March 2018, 11:44 PM   #1101
Salas is offline Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
F6 Illustrated Build Guide
@silasmellor

Start from simple things like do the input signal's wiring in shielded coax if its not. First see it best dressed away from any AC power wiring. Its not only the AC inlet primary side. The secondary exit points and wires can be throwing quite a field no matter if the toroid has some form of magnetic screening for its most part. If rotated and the harmonic noise changes in FFT then there is a gotcha.

On the other hand if its simply due to high PSU ripple, just try measure it on the rails with a DMM in ACV mode. A CRC or a CLC or a capacitance multiplier could solve it.

Then again if its mainly due to some low intensity ground loop in the build itself or in its interfacing with the rest of the system... it will take enough conceptual guessing and experimental investigation.
  Reply With Quote
Old 18th March 2018, 12:31 AM   #1102
silasmellor is online now silasmellor  Denmark
diyAudio Member
 
Join Date: Nov 2016
Location: Denmark
F6 Illustrated Build Guide
@2picodumbs,
Yeah I suppose more filtering probably wouldn't hurt!

@wdecho
You are absolutely right, this buzz is totally irrelevant to the listening experience, and since upgrading from a naim nap 155xs I couldn’t be happier – it sounds fantastic! The only reason I am chasing it is to try and understand the issue and learn something new

@Salas
Thank you for those suggestions. Tonight I spent some time rearranging the AC side, mainly to improve safety in case of bad luck and loose screws, but I also reouted the inlet AC line further away from the business end, without any visible change in the FFT. The input wires are mogami coax, routed as far from the AC side as possible (4U deluxe case) – essentially like shown in 6L6’s illustrations. I actually also rotated the toroidal a bit (about 30 degrees) during this process, but I don’t see any obvious change. I don’t know if that is enough of a rotation to warrant anything though.
My DMM measuring AC on the outputs with no signal is varies between 0-1 mV, I don’t think it is sensitive enough to pick up anything major. Though 2pD also suggested more filtering, and I am on the low side of the recommended specs with 4x15mF/rail, I lean towards keeping that in mind for my next build and being happy with what I have now

Thanks for the feedback and suggestions, and for making diyaudio such an awesome place!

Last edited by silasmellor; 18th March 2018 at 12:37 AM.
  Reply With Quote
Old 18th March 2018, 02:12 AM   #1103
Salas is offline Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
F6 Illustrated Build Guide
Rectification ripple got to be measured on the DC power rails themselves.

Getting rid of harmonic noise, especially when including substantial FFT needles up to the mid range or higher, its worthwhile. Even if not easily noticeable at couple of meters away from the speakers. A bit of finer & softer resolution plus little better depth perspective can be usually observed. Its only after a tiny nuisance goes away we have a chance to grasp any tiny signal details it obscured. Given the transducers (speakers, headphones) are resolute enough.

Can that input signal transformer benefit from some screening test I would have also wondered...
  Reply With Quote
Old 18th March 2018, 04:50 AM   #1104
trobbins is offline trobbins  Australia
diyAudio Member
 
trobbins's Avatar
 
Join Date: Feb 2009
Location: Melbourne, Oz
What is spectrum with power amp off (but plugged in to power etc) and no input - as a benchmark for the probing and hardware and environment setup you are using with REW ?

Last edited by trobbins; 18th March 2018 at 04:53 AM.
  Reply With Quote
Old 18th March 2018, 05:05 PM   #1105
silasmellor is online now silasmellor  Denmark
diyAudio Member
 
Join Date: Nov 2016
Location: Denmark
F6 Illustrated Build Guide
@Salas
With my DMM set to AC i measure 30mV on +ve and -ve rails (each with respect to gnd) at the PSU output. Maybe the simplest solution is simply more filtering?

Transformer screening sounds like a good idea to try as well, i will have to read up on how that is bets achieved. I have mounted the toroidal power transformer at the front of the chassis, as far from the input transformers as possible - as per 6L6's illustrations again, but mounted to the baseplate directly, not on an angled bracket.

@trobbins
Power amp off
F6 Illustrated Build Guide-6-amp-png

and the noise of the interface itself (interface out plugged directly to in)
F6 Illustrated Build Guide-7-interface-out1-in1-loop-png

Looks like the 50hz could be a ground loop with the interface?
Attached Images
File Type: png 6 amp off.png (50.7 KB, 705 views)
File Type: png 7 interface out1 to in1 loop.png (69.3 KB, 687 views)
  Reply With Quote
Old 18th March 2018, 11:48 PM   #1106
trobbins is offline trobbins  Australia
diyAudio Member
 
trobbins's Avatar
 
Join Date: Feb 2009
Location: Melbourne, Oz
Quote:
Originally Posted by silasmellor View Post
Looks like the 50hz could be a ground loop with the interface?
If the mains frequency bump goes away with the amp power cable disconnected then that would certainly indicate a mains lead related loop with your measurement system.

If the bump remained, then that would indicated pickup from the local environment, given you would have a signal connection going to a dummy load that has cabling back in to the amp, as well as the probe and interface to the soundcard may be a bit susceptible to nearby mains wiring or equipment.

I have to turn one bench light off to remove some noise artifacts I get, and I insert a USB isolator when using cheap soundcards to attenuate mains earth related loops.

If the amp power supply rails hold up for a few seconds when mains is turned off, then you may be able confirm any influence (or not) of a mains cable loop from your 'amp on' spectrum mains harmonic bumps.

The 1W spectrum should allow you to calculate the nominal rms voltage of those harmonics, as an indicator of how 'measureable' they would be with a meter.
  Reply With Quote
Old 19th March 2018, 03:53 PM   #1107
Russellc is offline Russellc  United States
diyAudio Member
 
Join Date: Mar 2003
Location: midwest
F6 Illustrated Build Guide
Many of these mystery hums have been the transformer it self. Easy enough to find out, remove it from the chassis box. If it then goes away, a different transformer may cure it, as others have found out. Or a remote box to house the transformer/power supply.

Russellc
__________________
Pass B-1 preamp, Pass BA3 preamp, Pass F-5 Amp, Pass F-6 Amp, Pass BA-3 Amp, Pass M-2 amp, Pass Aleph J amp, Pass Pearl 2 Phono pre Tekton Enzo, Altec A7, Econowave JBL 2235H & B&C CD

Last edited by Russellc; 19th March 2018 at 04:20 PM.
  Reply With Quote
Old 20th March 2018, 11:45 AM   #1108
silasmellor is online now silasmellor  Denmark
diyAudio Member
 
Join Date: Nov 2016
Location: Denmark
F6 Illustrated Build Guide
@trobbins, i will have another look and see if i cant calculate the expected ripple V and check with cable unplugged. Any idea if REW can output the numbers from the FFT into a format that i can work with in excel?

@russelc, i suspect you may be right. There isn't much wriggle room with the toroid im using, but i've bought an L-bracket, so will see if mounting the toroid vertical has any effect.
  Reply With Quote
Old 20th March 2018, 12:22 PM   #1109
trobbins is offline trobbins  Australia
diyAudio Member
 
trobbins's Avatar
 
Join Date: Feb 2009
Location: Melbourne, Oz
Russellc points out another coupling risk with the measurement technique, as some hum from a transformer could also be coupling in to the measurement resistor probe circuit, and that form of bump would stop immediately that power from the amp was turned off.

I haven't looked at logging measured values from REW - I just screen capture or use snipping tool to save a spectrum result during amp measurements. REW does have an excellent forum that I've used a few times to post queries.

I think it is worthwhile trying to confirm spectrum results mean what you think they mean. One hassle is that soundcards can identify very low signal levels, which would require a lab grade meter to independently measure - and I guess you are getting down in to that territory.

If ripple on the power supply output is the concern you are chasing, then changing filter part values is one way to characterise the issue, along with ripple voltage measurements at the filter itself.
  Reply With Quote
Old 20th March 2018, 12:33 PM   #1110
silasmellor is online now silasmellor  Denmark
diyAudio Member
 
Join Date: Nov 2016
Location: Denmark
F6 Illustrated Build Guide
I guess i might be biting off more than i can chew I will have to check how it behaves upon shutdown. When it starts up i observed that the 50 hZ hum occurs immediately - which fits with the above ffts - but the remaining 100hz and up peaks gradually rise from the noise floor after a little while, 30s-1min.

The distance between the mbox i use to record and the toroid is probably around 30-40cm. Is that a distance you would reasonably expect the field of the toroid to extend to?

I measured 30mV AC with my cheap-o DMM at the +/gnd and -/gnd outputs of the PSU. I measure 0mV AC at the speaker outputs though...
  Reply With Quote

Reply


F6 Illustrated Build GuideHide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
diyAudio Power Supply Circuit Board v3 illustrated build guide 6L6 Power Supplies 702 Today 06:02 AM
F5Turbo Illustrated Build Guide 6L6 Pass Labs 471 24th September 2018 09:19 PM
Aleph J illustrated build guide 6L6 Pass Labs 2868 24th September 2018 02:31 PM
ACA illustrated build guide 6L6 Pass Labs 145 21st September 2018 05:09 PM
BA-3 Amplifier illustrated build guide 6L6 Pass Labs 155 21st September 2018 12:30 PM


New To Site? Need Help?

All times are GMT. The time now is 09:07 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki