Protecting my amp during circuit tests - diyAudio
Go Back   Home > Forums > Source & Line > Analog Line Level

Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

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 12th March 2012, 09:25 AM   #1
diyAudio Member
 
Join Date: Jun 2011
Location: Hobart Australia
Default Protecting my amp during circuit tests

Hi all,

I am very much a Novice I have been entertaining the idea of experimenting with a couple of simple guitar pedal circuits one runs at 9v the other at +/-15v I only have a multimeter and an amp with which to test.

The amp I would like to protect from damage.

Is this a real concern? If so how can I protect the amp?

If there are other things I must consider please let me know.

Cheers
  Reply With Quote
Old 12th March 2012, 10:18 AM   #2
diyAudio Member
 
Join Date: Sep 2004
Location: hobart tasmania
Quote:
Originally Posted by magnetman View Post
Hi all,

I am very much a Novice I have been entertaining the idea of experimenting with a couple of simple guitar pedal circuits one runs at 9v the other at +/-15v I only have a multimeter and an amp with which to test.

The amp I would like to protect from damage.

Is this a real concern? If so how can I protect the amp?

If there are other things I must consider please let me know.

Cheers
Hi magnetman
Your best resource for attempting work on any circuit is to know how it connects, this is usually drawn as a schematic. The schematic will show, or should show well thought out plan of all the components. You have described power supplies of 9v and +-15v.

Its great to peer into circuitry and a few hours study here at diy audio forum will find many good ideas. Your pedal you can be fairly certain is a variable resistor with lots of emphasis on mechanical strength. Capacitors may be used for cutting off or narrowing frequency, and resistors used for defining current to components.

Commercial made gear usually follow very known recipes of schematic, so another way of saying this is that they are proven designs. So to modify these circuits you sort of place yourself as knowing something more than the designer. Anything is possible, but study first.

Here is info on a famous modifier of pedals who worked with Hendrix.
http://en.wikipedia.org/wiki/Roger_Mayer_(engineer)

Cheers / Chris
  Reply With Quote
Old 12th March 2012, 10:47 AM   #3
diyAudio Member
 
Join Date: Jun 2011
Location: Hobart Australia
Hi Chris,
thanks for that reply, I really like your description of component function.

The two schematics are the Arbiter fuzz face, the first on this page Fuzz Central -- Arbiter Fuzz Face
it seems to be a simple potentially cool sounding circuit.

The second is a spring reverb driver and recovery circuit provided buy this web site Spring Reverb
I like this because it has been explained so well the supply boards, but i will probably make my own. If I can make it work that is.

I am trying the circuits on breadboards, with no changes or substitutions.

Cheers
  Reply With Quote
Old 12th March 2012, 11:23 AM   #4
diyAudio Member
 
Join Date: Sep 2004
Location: hobart tasmania
Hi magnetman
No worries glad to help, if using the PNP version you might want to try the BC556 transistor and NPN a BC547 , they are readily available.

The pin out is with the flat part facing toward you and from the left Collector, base Emitter

I have a few oscilloscopes here, and can show you how the audio wave form changes
so give me a day or so to connect this up. i am flat out building LDR preamps at the moment, but this would be nice to do for you.

Cheers / Chris
  Reply With Quote
Old 12th March 2012, 11:41 AM   #5
diyAudio Member
 
Join Date: Jun 2011
Location: Hobart Australia
Hi Chris, that would be excellent I have also some germanium transistors that could be interesting.

Cheers
  Reply With Quote
Old 15th March 2012, 08:27 AM   #6
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Quote:
Originally Posted by magnetman View Post
The amp I would like to protect from damage.

Is this a real concern? If so how can I protect the amp?
AC couple the input to the amp using a bipolar cap (or use two identical small electros back to back). Probably looking in the 4.7 to 10 uf range at most.

Use a low value (say 1K) resistor in series with the cap.

Add a couple of low voltage zeners (around 2.7 to 5.6 volt depending on amp sensitivity) in inverse parallel across the amp input to clamp any excess voltage swings of either polarity that might appear.

That should protect from practically anything you can apply to the amp input running on the supplies you mention.
__________________
-------------------------------------------------------
A simulation free zone. Design it, build it, test it.
  Reply With Quote
Old 15th March 2012, 08:40 AM   #7
diyAudio Member
 
Join Date: Jun 2011
Location: Hobart Australia
hey excellent, that is exactly what i was looking for! just so i am clear when you say across the input you mean signal to ground?
  Reply With Quote
Old 15th March 2012, 12:24 PM   #8
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Like this,
Attached Images
File Type: jpg Untitled.jpg (14.0 KB, 34 views)
__________________
-------------------------------------------------------
A simulation free zone. Design it, build it, test it.
  Reply With Quote
Old 15th March 2012, 12:33 PM   #9
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
the protection diodes can also be applied from +IN pin to -IN pin.

Diodes are not ideal in this location. They leak current.
Some jFETs wired as diodes perform better as protection diodes. I can't recall which models. I think Jung mentions suitable types.
__________________
regards Andrew T.
  Reply With Quote
Old 15th March 2012, 07:45 PM   #10
diyAudio Member
 
Join Date: Jun 2011
Location: Hobart Australia
Ahh, Right! That makes sense! I am going to make this into a little enclosure with a 1/4" socket each end for all my testing.
Thanks very much!
  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
why is my amp protecting? mbugua Class D 2 19th January 2007 12:58 PM
Protecting electronic circuit lobo Everything Else 1 27th January 2004 02:03 PM


New To Site? Need Help?

All times are GMT. The time now is 03:33 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