"Disappointing" DC-300a power measurements - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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 19th February 2016, 10:09 PM   #1
diyAudio Member
 
Michael F's Avatar
 
Join Date: Apr 2008
Location: Montreal Canada
Default "Disappointing" DC-300a power measurements

Picked up a `76 vintage IOC equipped Crown the other day, I find the power measurements to be a little on the anemic side.
I`m getting 163@8, 1khz single channel driven and 512@8 1khz mono.
DC offsets are normal, line voltage at 118. Supply rails 60vDC.

Every other 300a I recall measuring would easily do 180+ all day long.
Hmmm.......
  Reply With Quote
Old 19th February 2016, 10:47 PM   #2
badman is offline badman  United States
Custom Title
diyAudio Member
 
badman's Avatar
 
Join Date: Sep 2003
Location: Sunny Tustin, SoCal
Leaky caps perhaps?
__________________
"The dawn of Bose created the "Man Cave" and reduced testoterone levels worldwide by 18.5 per cent" Peteleoni
  Reply With Quote
Old 19th February 2016, 10:58 PM   #3
infinia is offline infinia  United States
diyAudio Member
 
infinia's Avatar
 
Join Date: May 2005
Location: Californication
how did you measure it?
@1% THD or observed clipping on a scope
IMO seems within some meas. accuracy bounds perhaps excess ripple or unexpected drop on supply side. I couldn't hear the difference (180-163)/180 ~9%
__________________
like four million tons of hydrogen exploding on the sun
like the whisper of the termites building castles in the dust
  Reply With Quote
Old 19th February 2016, 11:08 PM   #4
diyAudio Member
 
Michael F's Avatar
 
Join Date: Apr 2008
Location: Montreal Canada
Quote:
Originally Posted by infinia View Post
how did you measure it?
@1% THD or observed clipping on a scope
IMO seems within some meas. accuracy bounds perhaps excess ripple or unexpected drop on supply side. I couldn't hear the difference (180-163)/180 ~9%
At the onset of waveform clipping and IOC illumination. It`s worth mentioning that the negative cycle will clip around 3 volts before the positive. What would cause such asymmetry?
  Reply With Quote
Old 20th February 2016, 01:24 AM   #5
infinia is offline infinia  United States
diyAudio Member
 
infinia's Avatar
 
Join Date: May 2005
Location: Californication
Quote:
Originally Posted by Michael F View Post
At the onset of waveform clipping and IOC illumination. It`s worth mentioning that the negative cycle will clip around 3 volts before the positive. What would cause such asymmetry?
PNP/ P channel side ?
__________________
like four million tons of hydrogen exploding on the sun
like the whisper of the termites building castles in the dust
  Reply With Quote
Old 20th February 2016, 02:03 AM   #6
diyAudio Member
 
Michael F's Avatar
 
Join Date: Apr 2008
Location: Montreal Canada
Quote:
Originally Posted by infinia View Post
PNP/ P channel side ?
NPN, quasi complementary.
  Reply With Quote
Old 20th February 2016, 03:23 AM   #7
GoatGuy is offline GoatGuy  United States
diyAudio Member
 
GoatGuy's Avatar
 
Join Date: Dec 2012
Location: SF Bay Area
Dunno… you're looking at a 1.1 volt peak drop from the 1970s measurements. You're also looking at a 0.47 dB max-amplitude headroom loss. I'd call that “perfectly reasonable”, as long as it is stabile. Most likely “something” has drifted internally. But “back in the day” the rail voltage was NOT regulated. Filtered, yes. Regulated, no. Could have been running the things off hotter mains back then.

Just saying. i don't think I share the disappointment.

GoatGuy
__________________
John Curl's Golden Rule…: 100 kHz bandwidth, 3 μs risetime, 100 W mean output, 100 V/μs slew rate, 2 Ω dynamic load, 20 amp min current source/sink
  Reply With Quote
Old 20th February 2016, 05:01 AM   #8
JMFahey is offline JMFahey  Argentina
diyAudio Member
 
JMFahey's Avatar
 
Join Date: Mar 2009
Location: Buenos Aires - Argentina
Me neither.
We are talking almost unmeasurable, definitely impossible to hear with any certainty 0.47dB as stated above.

And not only wall voltage may change, **measuring instruments** too, how do you know the test instruments used 40 years ago were better than 5% accurate?

Were they digital or needle meters?

and so on.
__________________
Design/make/service musical stuff in Buenos Aires, Argentina, since 1969.
  Reply With Quote
Old 20th February 2016, 05:23 AM   #9
Enzo is offline Enzo  United States
diyAudio Member
 
Join Date: Sep 2004
Location: Lansing, Michigan
I have a couple pieces of Crown gear I bought new, geez, 45 years ago? A DC150A and an IC150. Both came with individual response curves drawn out for both units, on what test gear I know not, plus an evaluation sheet with all the 0.l% and so on distortion figures. Pretty thorough, and at least Crown thought the test stuff was pretty good.
  Reply With Quote
Old 20th February 2016, 05:43 AM   #10
diyAudio Member
 
Michael F's Avatar
 
Join Date: Apr 2008
Location: Montreal Canada
Default The plot thickens

As it turns out, this is not a bone stock DC300a but one modified by Solotech, a local sound company which performed this mod on their entire arsenal of 300a`s.
What they did was use the 100 volt primary tap rather than the 120 and a limiter circuit was installed in, I`m guessing here, the feedback loop.
I`m sure Crown didnt endorse such a mod but they ran those amps that way for many many years.
For some reason, this particular amp had the limiters installed but the primary was set to 120 rather than 100.
The limiter circuit is mounted immediately above the 5 way binding posts. There is a red LED and 3 wires coming from the epoxy encapsulated board, two wires going to the output terminals and one to 4uf/50vNP cap and onto R210 on the driver board.

It didnt seem anything was added so I just removed them and crossed my fingers

This is what I`m getting now:
176@8 on each channel single channel driven @ 1khz,
356@3 under same conditions
531@8 mono
600@6 mono

Thats more like it.
Attached Images
File Type: jpg Limiter.jpg (913.8 KB, 195 views)
File Type: jpg Limiter 2.jpg (703.3 KB, 187 views)
File Type: jpg subject.jpg (558.8 KB, 184 views)
  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
Capacitor on "ground" interconnection to block "ground" DC voltage wwenze Analog Line Level 2 14th March 2015 06:00 PM
"WTB" "The Wire AMP" Class A/AB Power Amplifier based on the LME49830 with Lateral enantra Swap Meet 3 23rd December 2012 07:36 PM
What Does Fostex "Rated Input" and "Music Power" mark02131 Full Range 5 13th October 2012 06:18 AM
UCD "dc" & "on" Moby Class D 5 28th October 2007 02:55 PM
Fostex "rated input" and "music power" hugz Full Range 12 16th March 2006 05:33 PM


New To Site? Need Help?

All times are GMT. The time now is 10:08 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2016 DragonByte Technologies Ltd.
Copyright ©1999-2016 diyAudio

Content Relevant URLs by vBSEO 3.3.2
Wiki