John Bowers Active Control Unit preamp: Info sought - Page 2 - 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 26th June 2013, 10:07 PM   #11
diyAudio Member
 
Join Date: Jun 2013
Yes, I am sure there is an intermittent problem with the brick. There seems to be something loose inside it.
The 'best' measurements that I got were these:


0V 15V 15V wires:
----------------

200 ACV:

Yellow to LHS '15V' +15.2V
Yellow to RHS '15V' +15.2V

Without moving the brick, I then got these measurements for the 8-legged crawlies:

NE5534AN" and "S 8419" Opamps :
------------------------------

20 DCV range, for both opamps -

Pin 4: -14.1V <> -14.2V
Pin 8 +11.8V <> +11.9V (LHS seems slightly higher)


I did get some other measurements, but.......By 'best', I mean 'most representative of what the brick can do when the loose bits fall more or less into the positions into which they were inserted by their maker'. I have no evidence to support this assertion; perhaps the other (~9V) numbers were 'best', but this seems unlikely.

The terms REG1 and REG2 are printed on the PCB, near these 2 chips.

REG1 is closer to, and parallel to, the back panel:
7815
UC8420
KOREA

REG2 is closer to, and perpendicular to, the front panel:
7915
UC8419
KOREA
  Reply With Quote
Old 27th June 2013, 08:20 AM   #12
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
The 7815 and 7915 are standard voltage regulators and I would have expected the NE5534 etc to run on the full output of these which should be very very close to the stated 15 volts.

This is what I'm thinking...... the PSU is faulty, particularly as you say something is loose. Are the voltage readings really a good indication of what is going on... by that I mean that a definitive check would now involve the use of an oscilloscope to see if the DC voltages are "clean". Could the loose part in the PSU be a reservoir cap ? That could give all sorts of misleading info.

I think opening the PSU has to be the next step and to see what is going on in there.
__________________
-------------------------------------------------------
Installing and using LTspice. From beginner to advanced.
  Reply With Quote
Old 27th June 2013, 10:29 PM   #13
diyAudio Member
 
Join Date: Jun 2013
I have completed my desecration of a British audio sacred site by opening the brick. It seems the 3 retaining screws were covered by plugs of some sort of plastic formulated from Mr Bowers' hatred of me. Anyway, inside we seem to have a transformer and another component - could it be a fuse? I don't see anything else electronic inside, other than wires.

BELOW:
Looking at the bottom (the side closest to the power pins), it seems a plastic post or pin of some sort broke off (it was lying inside the case).
I don't know if this is an old injury, or was caused by my fiddling. I hope it's not an issue.
Click the image to open in full size.



BELOW:
Looking at the top, on the side that receives live AC from the wall (the primary side?) , it seems there is a component with some alphanumerics on the side "UM1" or "UM1" "100 degrees C" and "3A 250V" (it looks like it might be "3A 250V ~" - perhaps that little squiggle is an AC symbol) and "X100"
Click the image to open in full size.




BELOW:
This I assume is the secondary side, with the 2 wires Red, Blue and Yellow that connect to the pre.
Click the image to open in full size.

Do these pictures speak to you? Other than saying "I wish he'd get a better camera and learn how to use it"

I took a deep breath and plugged the open transformer into my power strip and measured it. The primary has 228V between the 2 wires (on 750ACV range). The secondary wires have a little over 15V (200 ACV range) which seems encouraging. The 15-0-15 PCB
points seem to be giving me 24V(Yellow to Blue) and 31V (Red to Blue). This seems a bit odd, have never seen this before....it's late and I am nervous about that open trafo, so I don't trust my measurements - will put away the grown-up toys for now.

I hope the pictures (such as they are) come through OK - they seem either too big or too small.
  Reply With Quote
Old 28th June 2013, 07:45 AM   #14
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
So it really is AC coming from the brick. There must be a diode bridge unsighted in all the other pictures of the main unit. That's one thing that has kept puzzling me. The other component is a thermal fuse to protect against overheating. Sounds like 100C and 3 amp rating

Its normal for secondary voltages from a small transformer to be a lot higher when unloaded.

Anyhow, we have to measure the exact voltages on all 6 legs of those regulators, the 78 and 7915. Measure from ground (negative meter lead on ground for all). Notice how the pinouts are different for the negative 7915.

Expected readings would be plus 15 volts and negative 15 volts respectively for the 7815 and 7915. The inputs voltage should be at least 19 volts or higher (all DC). The ground pin should be at zero volts but measure it to confirm.
Attached Images
File Type: jpg 7815.JPG (44.6 KB, 42 views)
File Type: jpg 7915.JPG (24.7 KB, 41 views)
__________________
-------------------------------------------------------
Installing and using LTspice. From beginner to advanced.
  Reply With Quote
Old 30th June 2013, 06:02 PM   #15
diyAudio Member
 
Join Date: Jun 2013
Hi

I am have been unable to get the 3 '0V 15V 15V' wires going into the PCB to give me 15 volts again. I am reluctant to toss the transformer around like I did with the black box, as it is now exposed. It seems that the transformer secondary happily gives 15VAC from the red and blue wires, measured against the yellow, but when I measure the 3 '0V 15V 15V' wires at the PCB, they are 3.5V - 3.7V AC. With those results, I am not sure it is worth trying to measure anything further?

I did notice this stain at the base of one of the 4 biggest capacitors - it's the one closest to the power switch.
Click the image to open in full size.
Could this be enough to cause all the problems? Or at least, is this something that will have to be fixed before it is worthwhile to continue testing?



Also, when you mentioned the words 'diode bridge', I thought of these things.
Click the image to open in full size.
There are 3 of these little black cylinders with the silver collar. They are labelled D1, D2 and D3 on the board.
There is also a hockey puck-shaped thing labelled BR1. They are all very close to the power switch , the 4 biggest caps, and the '0V 15V 15V' landing. I tried to indicate D1 D2 and D3 with red lines.

So...regarding the possible cap leak - Do 'we' need an operation?
I still don't see how to get the board out without an angle grinder.
  Reply With Quote
Old 30th June 2013, 06:20 PM   #16
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Your last picture does indeed show the "missing" diodes and bridge rectifier I mentioned earlier.

So it sounds like you have some breaks on the wires from the tranny... that's an easy fix... new wire. Or you could try shortening it, the breaks are probably where it is stressed at those cable grommets.

The cap may or may not be a problem. Hard to say just from the picture. Sometimes they have glue put on them on them to help with mechanical stability.

Fix the wire first, then we can see what is happening.
__________________
-------------------------------------------------------
Installing and using LTspice. From beginner to advanced.
  Reply With Quote
Old 27th October 2013, 10:36 AM   #17
diyAudio Member
 
Join Date: Dec 2011
Hi
I think I may have the same problem....and I suspect its the BR1 bridge rectifier.

I have 16VAC going in and +15.9VDC coming out of one terminal and only -7.4VDC coming out of the other!

Similarly I have 15.3VDC at pin 4 on the opamps and only 6.5VDC on pin 8

From the regulators I have +15.3VDC from 7915 and 6.00VDC from 7815.
All this seems to me to suggest the rectifier.
Also it seems the 12 VDC relay is not engaging an so shorting the output.... probably because it only has 7.53VDC going to it! The non-relay output (tape rec) outputs signal fine...but of course no volume control. Difficult when you are feeding active speakers!!

Is it worth a go replacing??
please let me know
  Reply With Quote
Old 27th October 2013, 10:51 AM   #18
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Plus 15 volts from a negative regulator suggests something really basic.

I wouldn't suspect the bridge at this stage, the voltages are correct... 16vac in and 23 out (15.9 + 7.4).

What seems in error is the 0 volt reference. Without seeing a circuit its all guesswork but with the unit in front of you it should be easy to see whats going on. Check if the bridge output goes to a single reservoir cap or whether its a dual split supply with zero volts taken from the junction of two caps. Or, does it use a virtual earth ?
__________________
-------------------------------------------------------
Installing and using LTspice. From beginner to advanced.
  Reply With Quote
Old 27th October 2013, 02:37 PM   #19
diyAudio Member
 
Join Date: Dec 2011
seems to be a split supply with one bridge output goes the capes with zero taken between the two caps

the other bridge supply goes to two diodes and a smaller cap to field the 7.4
  Reply With Quote
Old 27th October 2013, 03:17 PM   #20
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
The junction of the first two caps off the rectifier we assume is ground (check it). If so then the measured voltage should be equal on both caps. What happens after that point depends on the circuit but as a basic first step those two voltages across those first two caps have to be equal.
__________________
-------------------------------------------------------
Installing and using LTspice. From beginner to advanced.
  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
Active Tone Control and preamp. Need help urgent! CasperSort Analog Line Level 12 7th July 2012 12:24 AM
My active preamp/tone-control and TL074 kaushama Chip Amps 27 13th June 2011 02:54 PM
John Bowers Active 1 Netlist Solid State 4 11th August 2010 09:37 AM
john bowers active ones dazfj Swap Meet 2 5th June 2009 11:42 AM
John Bowers active 1 speaker prob iorr Solid State 3 30th June 2005 12:11 PM


New To Site? Need Help?

All times are GMT. The time now is 03:38 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