Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Equipment & Tools From test equipment to hand tools

Oscillator coil with common wires?
Oscillator coil with common wires?
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 13th July 2019, 12:47 PM   #31
PhantomBox is offline PhantomBox  Venezuela
diyAudio Member
 
Join Date: Jan 2008
I guess 1N4148 will have to do then, for now...
The 22nF caps are polyester layer (salvaged from a really old Midas audio console), but the critical caps 1.5nF and 680pF are ceramic discs.
  Reply With Quote
Old 13th July 2019, 05:40 PM   #32
Elvee is offline Elvee  Belgium
diyAudio Member
 
Elvee's Avatar
 
Join Date: Sep 2006
Here is the final, tested version:

Oscillator coil with common wires?-editedesr5-png

I have tested 1N4148's, and the circuit can be adjusted to accomodate them.
The only small inconvenient is that the left of the scale is more compressed, meaning resistances greater than 5~10 ohm become difficult to read, but that is not really problematic, because such a value already means that the cap has dried up.

I have tested ordinary ceramic caps: the 680p tolerates any type, and for the 1.5nF, only one posed problem: its losses were too high, meaning a reduced oscillator amplitude.
So, it is not too critical, but if you can find multilayers, it is preferable.
The 22nF is absolutely not critical.

To calibrate the meter you can use a new, good quality, large Ecap (1000µ or 2200µ) as a short-circuit reference, with known series resistors added.

First, you should leave the test terminals open, set R9 to its minimum resistance, and progressively increase the value until the meter deviation is reduced almost to zero.
Stop just before the actual zero.
Then, connect the reference cap directly (no series resistance) and adjust R1 for exactly the full scale deviation of the meter.

When that is done, your meter is ready to go, but if you want to have an idea of the scale, or write indications on the dial, you can connect various resistors in series with the reference and observe the deviation.

With 10 x1 ohm resistors connected in parallel, then in series, you can cover the whole 0.1 to 10 ohm range.

I think the original project has details on this procedure.

Note that the calibration/scale will be different if you change the diodes.

The circuit is designed for a 50µA meter having a total series resistance of 20K.
Other values would require modifications.
Attached Images
File Type: png EditedESR5.PNG (48.2 KB, 30 views)
__________________
. .Circlophone your life !!!! . . ♫♪ My little cheap Circlophoneİ ♫♪
Electrify your daily life!!! ....⚡⚡ ELEKTRIA ⚡⚡
  Reply With Quote
Old 14th July 2019, 03:21 AM   #33
PhantomBox is offline PhantomBox  Venezuela
diyAudio Member
 
Join Date: Jan 2008
I'm not really sure how much µA my meter has. I took it from an old professional audio console, it says on the front: 0VU = 1.228V = 7500Ω. @ 1000~. I really don't know if you can derive the Ampere value from this information.
And don't worry, I'm not sooo much in a hurry.
  Reply With Quote
Old 14th July 2019, 03:34 AM   #34
ubergeeknz is online now ubergeeknz  New Zealand
diyAudio Member
 
Join Date: Aug 2018
Quote:
Originally Posted by PhantomBox View Post
I'm not really sure how much µA my meter has. I took it from an old professional audio console, it says on the front: 0VU = 1.228V = 7500Ω. @ 1000~. I really don't know if you can derive the Ampere value from this information.

And don't worry, I'm not sooo much in a hurry.
Check the back. If nothing there you might have to derive it through measurement.

The Care and Feeding of Analog Meters | Nuts & Volts Magazine
  Reply With Quote
Old 14th July 2019, 04:31 AM   #35
PRR is offline PRR  United States
diyAudio Member
 
PRR's Avatar
 
Join Date: Jun 2003
Location: Maine USA
Quote:
Originally Posted by PhantomBox View Post
I'm not really sure how much µA my meter has....
200uA. We know this from the voltage, the (non-standard) resistance, the fact it is rated at 0VU while the scale goes to +3VU. Also it looks like they didn't use the last 10% of the range.

BUT this is probably an AC meter with internal rectifier. While the better plans above use a DC meter plus a rectifier, I'm not 100% sure it can be an exact swap. Maybe the ESR-meter gurus have insight.

Also: a working pro VU meter is worth much more than the type of $2 meter this project really deserves. (Sadly hard to find a $2 these days.)
  Reply With Quote
Old 14th July 2019, 01:00 PM   #36
Elvee is offline Elvee  Belgium
diyAudio Member
 
Elvee's Avatar
 
Join Date: Sep 2006
Quote:
Originally Posted by PhantomBox View Post
I'm not really sure how much µA my meter has. I took it from an old professional audio console, it says on the front: 0VU = 1.228V = 7500Ω. @ 1000~. I really don't know if you can derive the Ampere value from this information.
And don't worry, I'm not sooo much in a hurry.
As PRR said, it is probably a 200µA AC, which is not suitable: I just tested a 200µA movement, but the circuit is incapable of supplying such a current, and it cannot be increased in a simple way, because of implications and constraints on other parts.
In addition, the internal rectifier could be selenium or similar, which is not suitable for 100kHz operation.

Depending on the internal construction, the actual, naked galvanometer might be more sensitive (because of scaling, half-wave rectification or similar cause).

If it is possible to dismantle it without risking damages (be super-careful!), you could see what is inside, and test the actual DC sensitivity.

Up to 100µA is manageable: I just did the test with a meter having 1K internal resistance and 6.8K series added.
It practically requires schottky or Ge diodes though: with ordinary 1N4148, the calibration remains possible, but the left of the scale becomes so compressed that it is not usable for more than 5 ohm.
Small Ge diodes are very common: all transistor radios used to have at least one.

There is an example of such a diode at the center of this picture:
Attached Images
File Type: jpg ESR1.jpg (471.0 KB, 23 views)
__________________
. .Circlophone your life !!!! . . ♫♪ My little cheap Circlophoneİ ♫♪
Electrify your daily life!!! ....⚡⚡ ELEKTRIA ⚡⚡
  Reply With Quote
Old 14th July 2019, 02:09 PM   #37
PhantomBox is offline PhantomBox  Venezuela
diyAudio Member
 
Join Date: Jan 2008
The old Midas console had 3 of the original VU-meters and 4 of smalles ones that at some point were installed to preplace the original ones.
On the attached pictures you can see that the replacing ones have a rectifier of 4 1N4148 diodes installed on the back, which can easily be removed.
Attached Images
File Type: jpg MIDAS VU's front-min.jpg (396.5 KB, 20 views)
File Type: jpg MIDAS VU's back-min.jpg (399.0 KB, 22 views)
  Reply With Quote
Old 14th July 2019, 02:11 PM   #38
PhantomBox is offline PhantomBox  Venezuela
diyAudio Member
 
Join Date: Jan 2008
You will not be able to observe it, but the scales on both meters are the same.
  Reply With Quote
Old 14th July 2019, 02:29 PM   #39
Elvee is offline Elvee  Belgium
diyAudio Member
 
Elvee's Avatar
 
Join Date: Sep 2006
You can check the sensitivity of the small one using a fresh 9V battery and a 180K resistor (in series).
You do not even need to remove the diodes.
If it results in a full scale deflection, it is a 50µA.
If it's half => 100µA
1/4 => 200µA

You can try the same manipulation on the larger one: depending on the internal circuit, you could have a deflection -or not-.
Try both polarity: if it has a halfwave rectifier, only one will work
__________________
. .Circlophone your life !!!! . . ♫♪ My little cheap Circlophoneİ ♫♪
Electrify your daily life!!! ....⚡⚡ ELEKTRIA ⚡⚡
  Reply With Quote
Old 15th July 2019, 03:12 AM   #40
PhantomBox is offline PhantomBox  Venezuela
diyAudio Member
 
Join Date: Jan 2008
The meters are all 200µA. I will check tomorrow to see if I have another one, hopefully 50µA...
  Reply With Quote

Reply


Oscillator coil with common wires?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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Attaching flexible leads to aluminum voice coil wires cyclecamper Multi-Way 1 8th September 2014 06:17 AM
Commercial Pre-Pre Amps for Moving Coil Cartridges (MC Head Amps) in Common Base tiefbassuebertr Analogue Source 8 11th December 2012 08:54 AM
Is a Fuzz Face a common-emitter or common-collector circuit? ninopelo29 Instruments and Amps 6 9th December 2011 01:38 AM
glue for voice coil wires malcontent Multi-Way 5 6th March 2007 01:12 AM
Conductors (I.C.'s, RCAs, internal wires, speaker wires) bigphil Parts 1 25th November 2005 06:47 PM


New To Site? Need Help?

All times are GMT. The time now is 09:52 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Copyright ©1999-2019 diyAudio
Wiki