Odd "charging" noise in guitar preamp - Page 2 - 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 7th January 2013, 12:58 AM   #11
benb is offline benb  United States
diyAudio Member
 
Join Date: Apr 2010
Quote:
Originally Posted by audiostrat View Post
Well, thanks for both answers! It seems to be a logical explanation that the behaviour becomes unpredictable until the 3V are reached, but I tried the instant rise by removing the 220u, and the situation changed, but not the way I wanted (see my first post).
Quote:
discarded the 220u cap - the noise became louder but shorter
I'm thinking the noise became louder because there was plenty of feedback through the unbypassed "ground" connection.

Looking again, it still happened because the 470 ohm and 1,000uF in the power supply slow down the power supply rise time substantially, to a large fraction of a second. Short out that resistor, and toss out the 1,000uF as well. The regulator will reject the ripple voltage very well on its own, and there's not much current (thus not much ripple voltage) in this circuit to begin with.
  Reply With Quote
Old 7th January 2013, 06:51 PM   #12
diyAudio Member
 
Join Date: Dec 2012
Location: Athens
Trying to respond to everyone:

jaycee: I have already responded to that! I was meant to make an extremely simple design that could simply work - not build a superior amp. I don't mean this regular supply you suggest is rocket science, but was rejected for personal reasons, if you wish! Thus, you have the right to completely disagree. But I don't think it is immediately visible that it could have that flaw - even though it seems annoying as a scheme. I posted it again: the build was mainly for educational purpose. Now I think I have learned I should always seek for symmetrical supplies. In the real world, though.

nigelwright7557: I think you are not mistaken, but seems like I did not put it exactly the way I wanted: I want to learn how to build things the right way. Even if it won't matter sometimes - there will be an occasion that it could matter.

benb: I see what you mean, and it seems logical. By the way, there is more current drawn from the 2200u, since it is there where I connect the power supply of the power amp - yet, you could not know that! Even though it may cause negligible ripple too. But I will try this amendment, and should it cure the problem maybe try a shorter time constant!

Soon I will be able to play with it again.
  Reply With Quote
Old 8th January 2013, 08:03 AM   #13
jaycee is offline jaycee  United Kingdom
diyAudio Member
 
Join Date: Apr 2004
Location: Norwich, UK
I guess I didn't phrase my post very well... sorry.

You might get quicker startup by replacing the two resistors/capacitor with a 7815 regulator. You should be able to retrofit it to an existing layout too.

There are a couple of alternatives - one is a symmetric supply. All this really requires is a transformer with either dual secondaries, or a centre tapped transformer. You can even make it with a single secondary, using half wave rectification which is good enough for a few opamps. Often you can get a plugpack supply with an AC output and use that.

Another is a virtual ground - this is similar to what you are doing, but usually with an active source such as a regular, or an opamp to create VCC/2.
  Reply With Quote
Old 9th January 2013, 09:22 AM   #14
diyAudio Member
 
Join Date: Dec 2012
Location: Athens
Quote:
Originally Posted by jaycee View Post
I guess I didn't phrase my post very well... sorry.

You might get quicker startup by replacing the two resistors/capacitor with a 7815 regulator. You should be able to retrofit it to an existing layout too.

There are a couple of alternatives - one is a symmetric supply. All this really requires is a transformer with either dual secondaries, or a centre tapped transformer. You can even make it with a single secondary, using half wave rectification which is good enough for a few opamps. Often you can get a plugpack supply with an AC output and use that.

Another is a virtual ground - this is similar to what you are doing, but usually with an active source such as a regular, or an opamp to create VCC/2.
Well, using an opamp to deliver VCC/2 was my initial thought to be honest! Just discarded the option out of laziness of putting another IC on the layout.

I am also considering the 7815 regulator. Thanks for the advice! I hope I will have syfficient room, as you say.
  Reply With Quote
Old 9th January 2013, 02:55 PM   #15
diyAudio Member
 
Join Date: Dec 2012
Location: Athens
I short-circuited the 470R resistor, but the noise did not go. Now I am going to try the regulator solution!
  Reply With Quote
Old 10th January 2013, 03:13 PM   #16
diyAudio Member
 
Join Date: Dec 2012
Location: Athens
Tried the regulator solution, and it seems to be working flawlessly.

I discarded the 2x100k, 220u network and replaced them with a 78L15 regulator, putting in series with its input a 1k8 resistor to drop the voltage. I added 10u at the 15 volt stabilised output, in parallel with a 4k7 resistor to draw some current. Eventually it will not be needed, since about 2,5-3 milliamperes are already drawn.

So, no "charging noise"! I did receive a second pop on turn-up, coming from the preamp - sharper than the pop coming from the output stage, which is smoother. I removed the LF353 from the circuit to check it came from the preamp's new supply and was not a remaining of the old problem, and it was still there.

So, problem fixed for the time being! I am going to try fitting a soft starter to get rid of these pops. By the way, I am leaning towards using a simple soft starter published in Elektror Electronics - using a bridge and RC networks.

Many thanks for all of your answers!
  Reply With Quote
Old 10th January 2013, 03:45 PM   #17
diyAudio Member
 
Join Date: Apr 2010
Location: Coffs Harbour
Default a soft starter?

A soft starter dulls just the enormous inrush current for a few 100 milliseconds - It is meant to protect the transformer, switch and fuse from the first extreme peak start-up current. This usually doesn't stop clicks and pops when the rail voltages eventually rise and amplifiers begin to settle - when thumps and pops occur.

You use a muting circuit to kill the input to the amplifier at turn-on for what you require. Domestic amplifiers use the speaker relay for the same purpose.
__________________
regards
  Reply With Quote
Old 10th January 2013, 03:55 PM   #18
diyAudio Member
 
Join Date: Dec 2012
Location: Athens
Quote:
Originally Posted by Ian Finch View Post
A soft starter dulls just the enormous inrush current for a few 100 milliseconds - It is meant to protect the transformer, switch and fuse from the first extreme peak start-up current. This usually doesn't stop clicks and pops when the rail voltages eventually rise and amplifiers begin to settle - when thumps and pops occur.

You use a muting circuit to kill the input to the amplifier at turn-on for what you require. Domestic amplifiers use the speaker relay for the same purpose.
I am aware of that and these uses - speaking of the soft starter. I just supposed this would help, because in the first place, when the 15 volt rail was slowly raised, no such pop existed.

Anyway, I just want to experiment a bit. Speaking of muting circuits, by the way, I don't know anything at all. Could you point me towards a simple circuit used for muting? Based on your experience.

Thanks for the input!
  Reply With Quote
Old 10th January 2013, 04:24 PM   #19
diyAudio Member
 
Join Date: Apr 2010
Location: Coffs Harbour
Here is a comprehensive design with multiple features from which you can experiment and learn. Really, there is no
substitute for the text references of the article or even Self's newer "Small Signal Audio Design" book.
__________________
regards
  Reply With Quote
Old 10th January 2013, 04:26 PM   #20
jaycee is offline jaycee  United Kingdom
diyAudio Member
 
Join Date: Apr 2004
Location: Norwich, UK
The popping thats left will be from signal coupling capacitors charging. This is another reason why a symmetric supply is preferred - just so you know

A muting circuit can be as simple as a time delay of some kind (an R-C delay, or even a 555 timer) which will eg engage a relay to connect the signal after a short time delay. This allows the circuit time to stabilise
  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
Frugal Mono Full-range, Solar-Charging, Battery-Powered "Ashiko" Speaker xpheolix Construction Tips 2 13th June 2012 02:51 PM
Simple Idea of "Fully" Digital Microphone and Guitar StevenStanleyBayes Instruments and Amps 111 26th March 2012 06:14 PM
"REPLACE YOUR GUITAR AMP TUBES WITH THD "Yellow Jackets" NO REBIAS NEEDED. JUST PLUG cbdb Instruments and Amps 2 14th March 2012 05:49 PM
Achieving "Vintage Sound" with Mini-LM386 Guitar Amp? TheLaw117 Full Range 8 3rd January 2012 10:28 AM
2chanell PCL86-PP "tube buster" for guitar davorin Tubes / Valves 6 30th November 2009 04:21 AM


New To Site? Need Help?

All times are GMT. The time now is 04:35 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