Problem putting together my preamp (simple) - please help :) - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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
Thread Tools Search this Thread
Old 31st March 2003, 07:28 PM   #1
elizard is offline elizard  Canada
diyAudio Member
Join Date: Mar 2003
Location: Winnipeg, MB
Send a message via MSN to elizard
Default Problem putting together my preamp (simple) - please help :)

Hey guys
Well, I managed to put together a good part of my preamp. It comes with 2 PCB's, one just for left channel input, the other (bigger) for right channel input, and everything else.

I managed to finish the left one, and do about half of the right one so far. And I decided to test the diodes, make sure I didn't fry anything.
All of the diodes on the main PCB test ok (~ 0.5v one way, nothing the other), but the diodes on the left channel pcb (6 of them) all test 0.125v both ways (when i reverse the multimeter probes). So I thought I fried the diodes, so I desoldered one leg of one of the diodes (the other leg was still soldered to the pcb) and I tested it again, and this time it tested ok (0.5v one way, nothing the other). So I know the diodes are ok.

I tried looking on the board for anywhere where I might have messed up a soldering and accidentally caused a short, but I can't find anything. Can anyone suggest anything else that might be causing this?
The preamp schematics and the manual can be found at
The PCB contains several transistors, reed relays, capacitors, resistors and rca connectors. Could it be that one or more of these are not working properly so that they're causing a short? Or is it most likely just a short while soldering?

PLEASE PLEASE help with this .. I greatly appreciate it
I'm a newb at all this, so my knowledge is very limited.

Thank You in advance!
  Reply With Quote
Old 31st March 2003, 07:57 PM   #2
Netlist is offline Netlist  Belgium
diyAudio Moderator Emeritus
Netlist's Avatar
Join Date: Jan 2003
Hi, elizard

I didn't have an in-dept look at the schema, but I guess you mean the diode in parallel with the relays?
When everything is well, you should measure about 0.125V over the diodes.
So I think there could be something wrong if you measure 0.5V.
The diodes are in parallel with the relay coil.
This coil will always measure low DC resistance, so if you parallel them with a diode (like it should be, the drawing is correct)
you measure that same low resistance. If you don't, something is wrong.
Measure the resistance of the coils when not in the circuit.

"Diodes are most often used across the coil to provide a path for current when the current path to the relay is interrupted (i.e. switched off, coil no longer energized). This allows the coil field to collapse without the voltage spike that would otherwise be generated. The diode protects switch or relay contacts and other circuits that may be sensitive to voltage spikes."

Quote from

Does your left channel work?

  Reply With Quote
Old 31st March 2003, 08:24 PM   #3
elizard is offline elizard  Canada
diyAudio Member
Join Date: Mar 2003
Location: Winnipeg, MB
Send a message via MSN to elizard
hmm, that's weird ..

this is the mutlimeter that i have (the instructions on how to check diodes):

For checking the diodes on the main pcb, i get the readings that conform to:
.5-0.6 OL silicon good

the readings on the left channel pcb are:
very small very small germanium/silicon shorted

(note: in my manual it says 'very small, approx. 0.1v or less)

also as i said, when i remove the diode from the circuit, it measures 0.5v when i hook up the + to anode, - to cathode, and OL when i reverse the probes .. which is what its supposed to be according to the multiimeter manual
  Reply With Quote
Old 31st March 2003, 08:29 PM   #4
elizard is offline elizard  Canada
diyAudio Member
Join Date: Mar 2003
Location: Winnipeg, MB
Send a message via MSN to elizard
wait a minute .. i think i just realized something ..

don't i need to actually remove the diode from the circuit itself before measuring in order to determine if its ok or not?

that would make sense .. since the left channel PCB is completed (i.e. all the components are soldered), but the right PCB isn't completed .. so on the right pcb it would be as though i removed one lead of the diode from the board, right?

or does that actually not make any sort of sense whatsoever?
  Reply With Quote
Old 31st March 2003, 08:35 PM   #5
tiroth is offline tiroth  United States
diyAudio Member
Join Date: Dec 2001
Location: Pittsburgh, PA, USA
You'd really have to try hard to kill a diode from soldering.

Like Netlist said, you are measuring the parallel resistance of the coil, in which case your meter will not return a proper result. Just check orientation and for obvious shorts, and don't worry about checking the diodes in circuit. They are only there for back-EMF protection at any rate.
  Reply With Quote


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
Putting the Simple SE back together - blown PT - Flashing Rectifier cjkpkg Tubelab 13 15th October 2008 01:27 PM
The Hum problem: THAT simple. maxlorenz Parts 0 17th April 2008 12:07 AM
Problem with really simple circuit! Garbz Solid State 14 8th March 2006 03:18 PM
Odd problem with simple PS Zodiac Power Supplies 8 11th June 2005 07:53 PM
I think/hope this will be a simple problem for you lot! Fraser Solid State 3 6th March 2004 09:13 AM

New To Site? Need Help?

All times are GMT. The time now is 02:12 AM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2