Forums :: NEW! Web Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Oct Thu 21, 2021 12:37 am


All times are UTC [ DST ]





Post New Topic Post Reply  [ 5 posts ] 
Author Message
 Post subject: SOLVED Help please with understanding this circuit
PostPosted: Aug Sat 21, 2021 3:03 am 
Member
User avatar

Joined: Dec Sun 25, 2016 5:53 am
Posts: 339
Attachment:
SANSUI 3300 PS 01.png
SANSUI 3300 PS 01.png [ 163.81 KiB | Viewed 392 times ]
Greetings
I have been doing some testing on the power supplies of my 41 year old Sansui 3300 receiver. Looking at this element
made me recall an email conversation I had with Mr. Conrad Hoffman a couple of years ago. I had referred to this circuit as a series pass regulator, but he wrote that it might be some sort of turn on anti-thump scheme.
The reason that I am not certain about this possibility is: The output at terminal 0B and power path 20 is the only VCC connection to the power amp section's Driver Board (F-1180f), which contains all the circuitry of the power stages of both channels, except for the output transistors and output coupling caps. So the operation of the driver circuits is dependent on the output of this circuit. This Vcc, as far as I can surmise, should be regulated.
The input at terminal 0A is from the output of a full wave bridge and a 3300 uF / 100 DC wv cap to ground.
I am somewhat familiar with series pass regulators, however the 100 uf from the base of the 2SC1124 transistor to ground, versus having a zener or another reference voltage from another stage in the base leg is a configuration I am not familiar with. Rather than reaching an incorrect conclusion about this circuit's operation I am asking of those here with a more thorough understanding of it. Thanks.

_________________
1970's Avionics Tech, USN Attack Squadron 147, "ARGONAUTS" A-7E A/C


Last edited by COM-NAV-ECM on Aug Wed 25, 2021 10:22 am, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: Help please with understanding this circuit
PostPosted: Aug Sat 21, 2021 5:26 am 
Member
User avatar

Joined: Feb Sun 05, 2012 5:12 pm
Posts: 1166
Location: North Syracuse NY 13212
With such a large value resistor, I would say it's a turn-on delay.
The circuit is identical to a capacitance multiplier which is used to improve power supply filtering.
The difference is in the value of the resistor and capacitor.

There is no regulation because the output is not sensed, and there is no feedback to the transistor.

Bob

_________________
Life is too short to be serious all the time.


Top
 Profile  
 
 Post subject: Re: Help please with understanding this circuit
PostPosted: Aug Sat 21, 2021 5:39 am 
Member
User avatar

Joined: Jan Fri 06, 2012 8:47 pm
Posts: 7479
Elvirafan wrote:
With such a large value resistor, I would say it's a turn-on delay.
Agreed. They probably wanted to make sure the power input was stable before it connected to everything else.

If there was a zener between the base and ground it would have provided some regulation. but there is none so it doesn't.

Curtis Eickerman

_________________
http://curtiseickerman.weebly.com


Top
 Profile  
 
 Post subject: Re: Help please with understanding this circuit
PostPosted: Aug Tue 24, 2021 3:46 am 
Member
User avatar

Joined: Jul Mon 08, 2013 2:48 pm
Posts: 795
Although this circuit will create some turn on delay I don't think it was his main purpose. This very simple circuit is called a capacitance multiplier (because in the emitter-follower configuration the capacitance connected to the base will be roughly multiplied by the current gain of the transistor). This is not a voltage regulator but a "super ripple smoother" to supply low level sensitive stages, and cheaper (and smaller) than a big electrolytic reservoir cap.
It's a very common circuit I've seen many times in Hi-Fi audio equipment.

More detailed info's about this circuit can be found here:

https://www.electronics-notes.com/artic ... ircuit.php


Top
 Profile  
 
 Post subject: Re: Help please with understanding this circuit
PostPosted: Aug Tue 24, 2021 5:46 am 
Member
User avatar

Joined: Dec Sun 25, 2016 5:53 am
Posts: 339
Tubologic wrote:
Although this circuit will create some turn on delay I don't think it was his main purpose. This very simple circuit is called a capacitance multiplier (because in the emitter-follower configuration the capacitance connected to the base will be roughly multiplied by the current gain of the transistor). This is not a voltage regulator but a "super ripple smoother" to supply low level sensitive stages, and cheaper (and smaller) than a big electrolytic reservoir cap.
It's a very common circuit I've seen many times in Hi-Fi audio equipment.

More detailed info's about this circuit can be found here:

https://www.electronics-notes.com/artic ... ircuit.php


OK, thanks. Almost sort of an active filter? (?)
The multiplied capacitance is "felt" at the collector, then?
Is its response in dealing with the ripple faster than just having just an electrolytic in place after the bridge?

This circuit supplies only the driver stages. The low-level tuner and preamp sections' VCCs are filtered conventionally, with caps and resistors. Would the choice of a capacitance multiplier possibly have anything to do with the current required by the driver stages?
Thanks again, now I can put my curiosity about its basic function to rest.
Thanks for the link.

_________________
1970's Avionics Tech, USN Attack Squadron 147, "ARGONAUTS" A-7E A/C


Top
 Profile  
 
Post New Topic Post Reply  [ 5 posts ] 

All times are UTC [ DST ]


Who is online

Users browsing this forum: Barry H Bennett, J. Hill and 6 guests



Search for:
Jump to:  


































Privacy Policy :: Powered by phpBB