Simple Symetrical Amplifier - Page 395 - 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 11th February 2013, 06:48 PM   #3941
PauloPT is offline PauloPT  Portugal
diyAudio Member
 
Join Date: Jan 2010
Location: Lisboa, Portugal
Send a message via MSN to PauloPT
For 7% Vin=35V, Vout should be 32.5V. Vout-Vin=2.5V . Is this right?
__________________
Kind Regards,
Paulo.
  Reply With Quote
Old 11th February 2013, 07:02 PM   #3942
diyAudio Member
 
Esperado's Avatar
 
Join Date: Jul 2011
Location: France
Quote:
Originally Posted by PauloPT View Post
For 7% Vin=35V, Vout should be 32.5V. Vout-Vin=2.5V . Is this right?
Please, look at the data sheet of the power transistor, to know the Collector/emitter saturation voltage, and add 2-4V for regulation margin. Better, tune-it in real life as indicated.
Please, as it is really out of topic, do-it by yourself or ask somewhere else.
__________________
Ultimate Protection and more.The Only Source of Knowledge is experience, everything else is just information” ©A. Einstein
  Reply With Quote
Old 11th February 2013, 07:32 PM   #3943
PauloPT is offline PauloPT  Portugal
diyAudio Member
 
Join Date: Jan 2010
Location: Lisboa, Portugal
Send a message via MSN to PauloPT
I apologize for the out of topic. I will look at the datasheets, thanks.
__________________
Kind Regards,
Paulo.
  Reply With Quote
Old 13th February 2013, 07:25 PM   #3944
PauloPT is offline PauloPT  Portugal
diyAudio Member
 
Join Date: Jan 2010
Location: Lisboa, Portugal
Send a message via MSN to PauloPT
Default Oscillations

Hi,

This is on topic, I promise!

My 2SJ162/2SK1058 arrived in the mail today. They look pretty and sound good.
But I'm dealing with an oscillation problem. I don't have a scope and I use the AM radio trick. The amp is oscillating (broadcasting?) at the begining of the AM band. I ear a whistle. The cause seems to be a long input cable. I use a 5m cable to connect the audio output of the pc motherboard to the amplifier. I'm not using an input coupling cap. Raising the VAS compensation seems to have no beneficial effect. I went up to 68pF. Soldering 100nF polyester caps between rails and ground (hopping the high ESR of polyester would damp the oscillation) also has no effect. What seems to have some effect is raising the input filter. I replaced the 20pF cap by a 680pF and the whistle became weaker but still there. What seems to kill the oscillation is using the 680pF cap and shorting the rails cable (from reservoir caps to amp board) to a minimum. But I need longer rails wires. I can't have the capacitor bank on top of the amp board!
Can you please help me on killing the oscillation? Thank you.
__________________
Kind Regards,
Paulo.
  Reply With Quote
Old 13th February 2013, 07:32 PM   #3945
diyAudio Member
 
keantoken's Avatar
 
Join Date: Aug 2006
Location: Texas
Blog Entries: 2
Try a 3.3k resistor in series with the 20pF cap. Some amps like to oscillate with inductive input, and this will keep you from regressing the amp by trying to stabilize it with the miller compensation when that is not really the problem. Of course if it's not an input oscillation problem, this may not be the correct solution.
  Reply With Quote
Old 13th February 2013, 09:23 PM   #3946
PauloPT is offline PauloPT  Portugal
diyAudio Member
 
Join Date: Jan 2010
Location: Lisboa, Portugal
Send a message via MSN to PauloPT
Quote:
Originally Posted by keantoken View Post
Try a 3.3k resistor in series with the 20pF cap. Some amps like to oscillate with inductive input, and this will keep you from regressing the amp by trying to stabilize it with the miller compensation when that is not really the problem. Of course if it's not an input oscillation problem, this may not be the correct solution.
I'm sorry Keantoken, it didn't work
I tried the 20pF in series with 3.3k and didn't make much of a diference.
I may have two issues at play: the lenght of the input cable (wich is really long) and the lenght of the power rails. If I disconnect the input cable the oscillation disappear. About the power rails: they are at bare minimum lenght. If I increase the lenght of the psu wires the oscillation gets worse.
I also tried a 1nF capacitor - which reduced the intensity of the whistle even further - but I don't want to lower the corner frequency of the input filter more.

Thanks any way for your help, keantoken.
__________________
Kind Regards,
Paulo.

Last edited by PauloPT; 13th February 2013 at 09:31 PM.
  Reply With Quote
Old 13th February 2013, 09:31 PM   #3947
diyAudio Member
 
keantoken's Avatar
 
Join Date: Aug 2006
Location: Texas
Blog Entries: 2
If you alter the root of the problem the oscillation frequency will change. So if you're just changing the strength then the problem could actually be your source oscillating. Or something else?
  Reply With Quote
Old 13th February 2013, 09:33 PM   #3948
PauloPT is offline PauloPT  Portugal
diyAudio Member
 
Join Date: Jan 2010
Location: Lisboa, Portugal
Send a message via MSN to PauloPT
Quote:
Originally Posted by keantoken View Post
If you alter the root of the problem the oscillation frequency will change. So if you're just changing the strength then the problem could actually be your source oscillating. Or something else?
The source is fine. It doesn't oscillate with others amplifiers. The frequency also changed but I wasn't paying much attention to the dial on the radio.
It's not a single whistle. It's several whistles at different frequencies. The stronger is at the beggining of the band.
__________________
Kind Regards,
Paulo.
  Reply With Quote
Old 13th February 2013, 10:36 PM   #3949
diyAudio Member
 
Esperado's Avatar
 
Join Date: Jul 2011
Location: France
Please, provide the exact schematic you used.
Did-you have decoupling film capacitors of power rails aboard ?
Did you used no inductive resistances everywhere ?
Are your power fets right on the board ?
__________________
Ultimate Protection and more.The Only Source of Knowledge is experience, everything else is just information” ©A. Einstein
  Reply With Quote
Old 14th February 2013, 05:09 AM   #3950
shaan is offline shaan  India
diyAudio Member
 
shaan's Avatar
 
Join Date: Mar 2009
Location: Near the Ganges
Hi paulo. Check the followin.

Do vas trannies share a common heatsink? If yes then the metal must be grounded. Same goes if the FETs share a common hs or even use different hs per device. Is there a zobel at the output? Check if it's soldered correctly. Shorten the psu wire as much as possible. Are the onboard decouple caps as close as possible to the FETs. Are the FETs directly on the board? If not then 100ohm stoppers at both ends of gate wire. Are the caps parallel to the zeners okay? Is the input 1k+100pF RC filter correctly installed(first the 1k then the parallel 100pF and 10k to ground, right from the joined input bases)? Is your 5m signal cable well shielded, it may be acting as a highly sensitive antenna. Shorten the cable to half meter and see if it helps.

shaan
__________________
The PeeCeeBee Thread
  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
Symetrical schematics are alike plague in Brazil, do you like them? destroyer X Solid State 151 1st July 2010 02:09 PM
Symetrical out low Zout karsten21 Tubes / Valves 5 1st February 2010 10:19 PM
going balanced/symetrical - what benefits? weissi Solid State 15 20th October 2007 08:06 AM
Symetrical field, is this? Raka Multi-Way 6 14th September 2003 01:21 PM
Non-symetrical SMPS output cm961 Parts 4 21st August 2003 10:27 PM


New To Site? Need Help?

All times are GMT. The time now is 08:54 AM.


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