First Pass Build. F5. General Help Needed. - Page 2 - diyAudio
Go Back   Home > Forums > Amplifiers > Pass Labs

Pass Labs This forum is dedicated to Pass Labs discussion.

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 12th February 2013, 08:03 PM   #11
diyAudio Member
 
Join Date: Feb 2012
I finished my F5. It biased nicely and all measurements seem to be within spec. I am having a problem though. When both RCA cables are connected, I am getting some low level hum. It is not volume dependent. Music is playing but there is hum in the background. But when only one is connected, that channel is crisp and clear with no audible hum whatsoever. Here is the source:

Squeezebox Touch=>
Cambridge Audio DacMagic Plus=>
Grounded Grid Preamplifier (Tube)=>
F5

This configuration works like a charm when powered by my 125W KT120 Tube Monoblocks. Is this some sort of grounding issue. Impedance problem? Any direction would be great because I am at the end of the road with this build and i am extremely excited to listen to some tunes.

I am in the process of ordering parts for a DCB1 build to match the F5.

Thanks in advance..
  Reply With Quote
Old 12th February 2013, 08:32 PM   #12
Zen Mod is offline Zen Mod  Serbia
diyAudio Member
 
Zen Mod's Avatar
 
Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
give me pics and few words about concept - stereo amp with one PSU, monoblocks in one case , ........ yukyuk ?
__________________
my Papa is smarter than your Nelson !
clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa... by Mighty ZM
  Reply With Quote
Old 12th February 2013, 10:02 PM   #13
diyAudio Member
 
Join Date: Feb 2012
400V Antek AS-4218 - Dual 18V Secondary

(4X22K Capacitors) X 2 = 166K Total Capacitance

(4) 68A 600V IXYS Bridge Rectifiers

I believe this hum to be some sort of grounding issue. Right now i have each PSU grounded through its own NTC (1 per side) and then connected to a common ground point. Earth ground also meets in this point. Along with the purple "Shield" wire from the transformer. PSU and amp boards are connected through V+, V-, and ground.

I tried connecting a wire between the RCA input ground on both sides. I did this on the actual RCA jack side of the wire, not PCB side. This cut the hum in half. This is not shown in the photos by the way.

Any ideas on what else this could be. I have the hum down from where i started and it is quite faint. It can only be heard when music is at low volume or off. The hum does not increase with volume.

As i said earlier, while only one RCA cable is connected, that channel has absolutely zero hum.

Any suggestions on some grounding schemes would be great.

I am a beginner (maybe an intermediate) and this is my first build that wasn't purchased as a kit.

I must say that when music began to play (even know there is this slight hum), i felt a profound sense of accomplishment. This is a great hobby and i have learned very much from this forum (mostly reading though).

Thanks in advance Click the image to open in full size.
Attached Images
File Type: jpg DSC_0005.jpg (670.8 KB, 68 views)
File Type: jpg DSC_0006.jpg (766.1 KB, 88 views)
File Type: jpg DSC_0014.jpg (667.1 KB, 85 views)
File Type: jpg DSC_0012.jpg (835.8 KB, 90 views)
File Type: jpg DSC_0015.jpg (510.6 KB, 79 views)
File Type: jpg DSC_0016.jpg (594.0 KB, 65 views)
File Type: jpg DSC_0013.jpg (419.2 KB, 64 views)
  Reply With Quote
Old 12th February 2013, 10:04 PM   #14
diyAudio Member
 
Join Date: Feb 2012
Oh yeah, and the LEDs on the AMP boards are not lighting up.. I am almost 100% positive i put them in the correct way. Maybe i will remove them and insert new ones. I checked everything like three times before soldering though.
  Reply With Quote
Old 12th February 2013, 10:11 PM   #15
diyAudio Member
 
Join Date: Feb 2012
Biased at .59V with almost zero DC offset. Power supply rails are +25V/-25V
  Reply With Quote
Old 13th February 2013, 12:08 AM   #16
Zen Mod is offline Zen Mod  Serbia
diyAudio Member
 
Zen Mod's Avatar
 
Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
trick No.1 - put 10-15R resistor in series with one black wire on one RCA

trick No.2 - solder fat (shortest you can manage ) wire bridge between two central gnd points - those gnd points on pcb(s) , left up of P1

No.1 or/and No.2 will solve ground loop problem
__________________
my Papa is smarter than your Nelson !
clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa... by Mighty ZM
  Reply With Quote
Old 15th February 2013, 12:52 AM   #17
diyAudio Member
 
Join Date: Feb 2012
Ok great thanks for the advice. I chose option two and connected a 14 gauge wire from ground to ground on the amp pcb's. This solved my problem. The amp is almost totally silent now. I have extremely high efficiency horn speakers and the amp is still quite silent.

I have ooooone more question and ill leave you alone (for now). I have been regularly checking voltages to make sure everything remains constant. The bias is not fluctuating at all and has remained pretty much constant at .59VDC. Anyway, i have noticed that the power supply voltage has lowered evenly from the previous +/-25VDC to around +/-22.9VDC. The AC voltage from the wall has remained the same at 119VAC and i have checked the secondaries to be constant at 18/18V. Was this caused by the ground connection i made? This is the only change i have made.

Just want to be sure these voltages are OK and wondering was may have caused it..

Thanks in advance

-Madison

Last edited by madisonroberts; 15th February 2013 at 12:55 AM.
  Reply With Quote
Old 15th February 2013, 02:32 AM   #18
Zen Mod is offline Zen Mod  Serbia
diyAudio Member
 
Zen Mod's Avatar
 
Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
just chill

22V9dc is what you can and must expect from 18Vac , when loaded with standard FW Iq (between 1A5 and 2A)
__________________
my Papa is smarter than your Nelson !
clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa... by Mighty ZM
  Reply With Quote

Reply


Hide 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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Wattage of Pass F5 pdhanwada Pass Labs 132 28th January 2013 04:14 PM
Pass F5 Pair (Spuds) Spuds Pass Labs 14 20th November 2012 05:43 PM
Building my perfect speakers. General advise needed. running123 Multi-Way 10 30th November 2011 02:22 AM
Pass F5 Help Needed vdi_nenna Pass Labs 28 18th August 2009 01:06 PM


New To Site? Need Help?

All times are GMT. The time now is 09:57 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2