vintage AD9 output very quiet - diyAudio
Go Back   Home > Forums > Live Sound > Instruments and Amps

Instruments and Amps Everything that makes music, Especially including instrument amps.

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 15th February 2009, 02:19 AM   #1
thegnu is offline thegnu  United States
diyAudio Member
 
Join Date: Jan 2009
Default vintage AD9 output very quiet

So I got these two non-working Ibanez AD9s, and I'm trying to get them fixed. There are a couple issues, and I'm focusing on one of them right now. The schematic is here:
http://www.dirk-hendrik.com/Ibanez_ad9_analog_delay.pdf

1. DIODE
In B7/B8, there's a diode, D4. it was cracked on one of the AD9s, and the other pedal was grounding out my DC Brick, so I put the "good" diode in the pedal that didn't short the power supply, and lo and behold, the power supply shorted on that one. And now the other one turns on. So I'm functioning without that diode there, and that's weird. What does this diode do? Is this just a bad diode?

2. SIGNAL
I bridged a broken trace, and now it outputs signal, but it's very very attenuated on the Main Out. Dry Out works fine. So I looped signal on my DD5, and grounded the sleeve of a cable to the chassis of the AD9, and started touching signal path to test out where the signal goes bad.

3. RESISTOR AND OP-AMP
So I'm tracing back through the circuit with the tip of my guitar cable. Signal is good @ the place the output signal is soldered to the board. On the schematic in A1-3, the signal attenuates once over R65, and again at pin 6 of the JRC4558D. Is this normal behavior? The resistor will lower the signal, right? But the opamp?

Since my signal is fine from the Dry Output jack, the input and dry signal stage is fine. Since both the dry and wet signal coming out the Main Output jack are weak, then my problem has to be after wet/dry rejoin (in A1-3,B2-4 area), right?
  Reply With Quote
Old 15th February 2009, 08:37 AM   #2
es44 is offline es44  Denmark
diyAudio Member
 
es44's Avatar
 
Join Date: Apr 2005
Location: Fredericia, DK
I am not experienced enough to read the complete schematic, but at least i know, that D4 is sitting there to protect from reverse polarity of the PSU.
Ideally, it should blow the fuse in the PSU connected, but if that fuse is a lot more than 1A, maybe even slow blow, then the diode protects the fuse by commiting suicide

Best regards
Ebbe
  Reply With Quote
Old 15th February 2009, 12:53 PM   #3
diyAudio Member
 
Join Date: Jul 2005
Location: North Derbyshire
As es44 says, D4 is a reverse protection diode, it's blown because the power had been connected the wrong way round.

This could have damaged other components, you need to work through the circuit, either injecting, or tracing, a signal to find out where it's getting lost.
__________________
Nigel Goodwin
  Reply With Quote
Old 15th February 2009, 02:54 PM   #4
thegnu is offline thegnu  United States
diyAudio Member
 
Join Date: Jan 2009
OK, cool. I figured the diode was either a reverse polarity thing, or a voltage bleed in case you hooked up too high a voltage. I've got the right polarity, but it IS pretty troublesome that it works WITHOUT the diode.

I think I mis-identified the pin on the opamp, but if I'm on the input side of the opamp, and the signal coming out the output is quieter, then it's either not getting the right voltage or bias, or the opamp is bad, right? Because the opamp is suppose to amplify stuff, right?

[EDIT: just found the 4558 pinout, and I was right... (EDIT: that pin 6 is input) http://gaussmarkov.net/wordpress/par...1-description/ -- 3/5 down the page, the second diagram]

I've been learning quite a lot about electronics with my current ventures, lately, but I'm still like a child in the woods.
  Reply With Quote
Old 15th February 2009, 05:38 PM   #5
diyAudio Member
 
Join Date: Jul 2005
Location: North Derbyshire
Quote:
Originally posted by thegnu
OK, cool. I figured the diode was either a reverse polarity thing, or a voltage bleed in case you hooked up too high a voltage. I've got the right polarity, but it IS pretty troublesome that it works WITHOUT the diode.



Not at all, that's a nice bonus

Quote:

I think I mis-identified the pin on the opamp, but if I'm on the input side of the opamp, and the signal coming out the output is quieter, then it's either not getting the right voltage or bias, or the opamp is bad, right? Because the opamp is suppose to amplify stuff, right?
If it's an inverting mode opamp, then the input pin will have essentially nothing on it, because it's a virtual earth point, so you can't signal trace (or inject) on the non-inverting input.
__________________
Nigel Goodwin
  Reply With Quote
Old 15th February 2009, 06:14 PM   #6
thegnu is offline thegnu  United States
diyAudio Member
 
Join Date: Jan 2009
Quote:
Originally posted by Nigel Goodwin
If it's an inverting mode opamp, then the input pin will have essentially nothing on it, because it's a virtual earth point, so you can't signal trace (or inject) on the non-inverting input. [/B]
So does that mean that the signal is supposed to be coming in on pin 5 (the positive input)? So I would inject the signal there? Or did I misunderstand?

I appreciate you sharing your knowledge.
  Reply With Quote
Old 15th February 2009, 10:25 PM   #7
diyAudio Member
 
Join Date: Jul 2005
Location: North Derbyshire
Quote:
Originally posted by thegnu


So does that mean that the signal is supposed to be coming in on pin 5 (the positive input)? So I would inject the signal there? Or did I misunderstand?

No, you misunderstood, the input is at pin 6 (the non-inverting input), BUT you can't see it, or inject it, at that point - because it's a virtual earth mixer - you could inject it via a suitable resistor though.

You need to check at the input resistors feeding it, R44 and R47.
__________________
Nigel Goodwin
  Reply With Quote
Old 15th February 2009, 10:48 PM   #8
thegnu is offline thegnu  United States
diyAudio Member
 
Join Date: Jan 2009
Quote:
Originally posted by Nigel Goodwin



No, you misunderstood, the input is at pin 6 (the non-inverting input), BUT you can't see it, or inject it, at that point - because it's a virtual earth mixer - you could inject it via a suitable resistor though.

You need to check at the input resistors feeding it, R44 and R47.
Someday I will understand. For now, I will follow your instructions.

Thanks.
  Reply With Quote
Old 15th February 2009, 10:48 PM   #9
thegnu is offline thegnu  United States
diyAudio Member
 
Join Date: Jan 2009
[deleted duplicate post]
  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
Looking For Output Transistors For Vintage Car Radio 65blkbkgt Car Audio 14 29th May 2010 02:58 PM
How quiet is dead quiet? pchw Tubes / Valves 36 22nd November 2007 05:36 AM
Hammond Vintage two 6v6 output transformer FranStar Swap Meet 0 17th November 2006 11:11 PM
How quiet will it be? MMicke Chip Amps 8 12th July 2003 09:26 PM
Too quiet! grataku Everything Else 14 14th February 2003 05:39 PM


New To Site? Need Help?

All times are GMT. The time now is 05:37 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