Rod Elliot P.68 Phase? - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 27th June 2010, 02:51 PM   #1
diyAudio Member
 
Join Date: Jun 2010
Default Rod Elliot P.68 Phase?

Hi all,

Having read numerous posts on the forum I have come to learn the importance of linear phase response and would like to take the audiophile route through my system.

I recently realised upon testing with a scope my cheapish subwoofer amplifier has very poor phase response deviating to almost 90 degrees at 120hz even if dc coupled. I found the capacitors which cause the problems but they are required for the amps stability and as the amp has had numerous faults and is running on virtually 0 bias current, I was looking into Rod's design substituting the MJ transistors with 2sc's.

I have emailed Rod but received no reply, could anyone advise from the design if it has a reasonably linear phase response with minimal deviation from 0 degrees (if anyone is able to deduce such information)?


Thanks

300/500W Subwoofer Power Amplifier
Attached Images
File Type: gif p68-f1.gif (9.2 KB, 534 views)
  Reply With Quote
Old 27th June 2010, 03:15 PM   #2
diyAudio Member
 
Join Date: Nov 2008
Location: Brazil
Quote:
Originally Posted by samutacaratti View Post
Hi all,

Having read numerous posts on the forum I have come to learn the importance of linear phase response and would like to take the audiophile route through my system.

I recently realised upon testing with a scope my cheapish subwoofer amplifier has very poor phase response deviating to almost 90 degrees at 120hz even if dc coupled.
Your subwoofer amplifier must have a crossover, the phase shift is normal.
  Reply With Quote
Old 27th June 2010, 03:17 PM   #3
diyAudio Member
 
Join Date: Jun 2010
There is no crossover as I have stripped down the sub to the bare amp to use it with an PC based XO with a routed soundcard.
  Reply With Quote
Old 27th June 2010, 04:09 PM   #4
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
There must be a fault with the amp then. Any reasonable amp will have no phase shift to worry about in the audio band. The P68 will be fine and you can work out the phase shift points from the feedback network and input stage if it bothers you.
__________________
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more.
  Reply With Quote
Old 27th June 2010, 04:17 PM   #5
diyAudio Member
 
Join Date: Jun 2010
Attached is a schematic of the stripped amp in use with the phase shift. The caps causing the big shift are circled in red. When removed the amp distorts heavily and is unstable.

Could anyone shine any light on this?

Thanks alot
Attached Images
File Type: jpg amp.JPG (69.8 KB, 515 views)
  Reply With Quote
Old 27th June 2010, 04:24 PM   #6
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
the input high pass filter 4u7F & {2k2+22k} is sufficiently low to allow all your bass and sub-bass signals to pass and yet still block DC and ultra low frequency.

The high pass built into the Negative FeedBack route cuts off a little higher. This should be lower than the input filter, change C4 to 180uF or 220uF.
Similarly C5 could usefully be a bit bigger, maybe 150uF.
__________________
regards Andrew T.
  Reply With Quote
Old 27th June 2010, 04:29 PM   #7
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
what happened to ESP's P68?

Your new post shows the opamp with three caps directly connected to the -IN pin.
Many opamps become unstable with these in place. Maybe this amp has used these as compensation caps.
__________________
regards Andrew T.
  Reply With Quote
Old 27th June 2010, 04:36 PM   #8
diyAudio Member
 
Join Date: Jun 2010
Thanks for the advice with Rods design, from what people have said I gather Rods design will definitely have a linear phase response for atlest the lower frequency band (all "bass")?

My latest post was just to show the current manufactured design as Richie said it may be faulty - if the phase shift problem could be fixed I may put off building rods design for a while, ie if anyone can spot a flaw causing the phase shift in the original design that would be great I was resigned to having to totally make a new amp.

Thanks alot
  Reply With Quote
Old 27th June 2010, 04:48 PM   #9
diyAudio Member
 
Join Date: Nov 2008
Location: Brazil
How you measured the phase shift in your amp?
  Reply With Quote
Old 27th June 2010, 05:26 PM   #10
wahab is offline wahab  Algeria
diyAudio Member
 
Join Date: Nov 2009
Location: algeria/france
Increase C1 up to 68uF.
Increase C4 to 220 to 330uF.
C5 has a good value, increasing it bring no
improvement, quite the contrary.

Other than that, since it s a basses amp,
use a beefy power supply.
  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
Rod Elliot P37? roger-k Solid State 21 7th October 2006 07:37 PM
Rod Elliot P101 amplifier for sale supernet Swap Meet 2 26th January 2006 04:58 PM
Parts for Rod Elliot ESP88 kestrel200 Solid State 9 8th March 2005 05:18 AM
Rod Elliot P68-2 PSU Recomendations BeanAnimal Solid State 10 17th January 2005 03:57 PM
Another new Rod Elliot amp! p3B! Mattyo5 Solid State 20 27th January 2004 11:45 AM


New To Site? Need Help?

All times are GMT. The time now is 05:51 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