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B4 Buffer PCB (and parts) new GB #3?

Thanks. From the references voltages above where does the problem seem to lie? The amp is currently functioning but with some 'interference' noise. I guess I may have damaged the regs with the former high VA power supply? Do I simply bridge the regulators to locate the problem? The voltage into LM317 is 4.7 and 3.2 on the output side. Likewise -3.8 into LM337 and -2.3 on the output side. Here are some pics (not that they show much) -
<http://www.flickr.com/photos/8074966@N08/9648716456/>
<http://www.flickr.com/photos/8074966@N08/9648701422/>
 
locky said:
The voltage into LM317 is 4.7 and 3.2 on the output side. Likewise -3.8 into LM337 and -2.3 on the output side.
Click to expand...
Those numbers are completely off (too low). If you have a +/-16v supply, the gyrators should drop around 1v. That would give around 15v in to the regs which would then need to be set for 12v, i.e., a 3v drop out.

The regs aren't even seeing close to the expected voltage in. So either your power supply does not deliver 16 under load or the gyrators are out of whack. Both of which could be true and it still doesn't eliminate a problem with the on board regs too. Given that the LM3x7s are dropping barley 1.5v, the interference you are hearing could be the regs oscillating.

So first thing, try bypassing the on board regs and see if that eliminates the problem. You can do this by feeding the appropriate supply rail to the output side of the LM3x7 regs.

If that works, then extract the gyrator transistors and bridge C-E on each then feed the rails to the main board inputs. Now measure the voltage around the on board regs - adjust to get a minimum drop of at least 3v.
  • If this works it suggest that the fault is in the gyrators and the onboard regs are OK.
  • If not then the regs are shot for sure and the gyrators may be too.
And FYI the links don't work.
 
Thanks. I bypassed Q7 and Q8, connecting the appropriate power rails to the output side of the 4 x respective regulators. Powered up and C112 went up in smoke... Could there have been a problem with this cap? I also took some readings before doing this and discovered that when the power is turned on there is initially over 9v at the emitter side of the gryators which quickly drops to the voltages stated above. Any thoughts? I'll try replacing C12 and C112 and see what happens...
 
Just fried C109 on powering up and in the process I've just discovered where I think the problem may lie - the tantalum caps have a polarity marking which I hadn't noticed before! Will try replacing the caps with correct polarity and see if this helps...
 
Replaced the caps and then soldered the regs back in place and I think I may have cracked it. The amp is now working and I have the follwing values -
LM317/R10 = 13.75vdc
LM317/R110 = -13.75vdc
LM337/R12 = -13.5vdc
LM337/R112 = -13.5vdc
Q1/2/3/D1 = 2.6vdc
Q101/102/103/D101 = 3.09vdc
Q4/5/6/D3 = -3.4vdc
Q104/105/106/D103 = -3.02vdc
R1/2/6 = -0.4
R101/102/106 = 0.04vdc
C5/C1 = -0.01
C105/C101= 0.01

Does this all look reasonable?
 
In fact someone might be able to help me here...

I've got Puffin's old B4 board which he only managed to get working on one channel. I removed every component, tested them & then refitted them... Every thing tested fine apart from Q7/Q8 which were reversed resulting in an O/C BC556. I fitted new BC546 & BC556 in Q7/Q8.

Anyway I've just lashed up a power supply using a 2x12vac transformer which gives 20vdc +/0/- output at the rectifier caps. Upon switching on there's no pops, bangs, flashes or magic smoke... All LED's light up & I've set all the regulator outputs to 17vdc no problem but attaching a source reveals the output is just a buzzing noise on both channels that doesn't vary with the potentiometer position :(

Any idea's where to look ? I was going to replace all of the TO-92 devices but thought I may as well ask if anyone else has encountered something similar.
 
I've taken a load of readings if that helps give an idea whats going on with this board... To start with I did PD's 4 suggested readings from the reference area [http://www.pinkfishmedia.net/forum/showthread.php?t=107753]

1.) 5.4v & 5.4v
2.) 11.4v & 10.7v
3.) 16.0v & 16.0v
4.) 16.0v & 16.0v

I have also taken measurements from each transistor...

Q1 C=14.v,B=5.4v,E=5.5v ~ Q101 C=6.2v,B=5.5v,E=6.2v

Q2 C=15.2v,B=15.1v,E=14.6v ~ Q102 C=15.9v,B=7.0v,E=14.6v

Q3 C=14.6v,B=7.2v,E=11.5v ~ Q103 C=13.9v,B=0.1v,E=7.2v

Q4 C=6.2v,B=5.4v,E=6.2v ~ Q104 C=13.9v,B=5.5v,E=0.1v

Q5 C=6.2v,B=0.5v,E=11.5v ~ Q105 C=13.9v.1v,B=7.1v,E=10.7v

Q6 C=15.9v,B=7.8v,E=6.1v ~ Q106 C=15.9v,B=0.00v,E=13.8v


Sorry if that appears confusing but its hard to format on here... Does that show anything glaringly obvious ?
 
on PDs 1,2,3,4 there should be no voltage at 1,2?, Check that the transistors BC 550 & BC 560 are in the correct positions Eg. Q1 & Q4 could be mixed up.
Check the diode D1/ 101 are the correct way round or not shorted
Ah just noticed you are using BC546/556, the B-C-E on these transistors are not pin compatible with the BC550/560 so check that they are the correct way round, this would cause your problem

BC550 C=3, B=2, E=1
BC546 C=1, B=2, E=3

Have you put the wire link in between the signal and the 0v

Are you using an input Cap


Alan
 
337alant said:
on PDs 1,2,3,4 there should be no voltage at 1,2?, Check that the transistors BC 550 & BC 560 are in the correct positions Eg. Q1 & Q4 could be mixed up.
Check the diode D1/ 101 are the correct way round or not shorted
Ah just noticed you are using BC546/556, the B-C-E on these transistors are not pin compatible with the BC550/560 so check that they are the correct way round, this would cause your problem

BC550 C=3, B=2, E=1
BC546 C=1, B=2, E=3

Have you put the wire link in between the signal and the 0v

Are you using an input Cap

Alan
Click to expand...

Yeah I found the presence of voltage on the input/output confusing ! Everything is installed as per the silkscreen, BC546/556 are only used in Q7/Q8 as per the silkscreen everywhere else its BC550/560.

I've checked the diodes & they are installed the right way 'round & arent shorted.

Its all very :confused:

 
Okay, I [think] I've discovered the problem.... I removed every BC550/560 & double checked them, every single one tested perfect.

I then removed the ccd's which I had only previously tested with the diode test function of my meter but earlier I read how to test them with a 9v battery so tried that... Here's the results:

J501:

11mA
7.4mA
9mA
3.7mA

J505:

0.8mA
0.8mA
0.7mA
0.7mA

I guess those J501's are causing all the trouble !
 
For a cheap source of 1N5287s take a look at the link in my post #253 on this thread. Also endorsed by Neil (post #262.)
 
Yes they seem to be rather problematic ! I had managed to source some more J501's but I don't trust them anymore... I'll see if Grazie has made his order yet.
 
After a couple of weeks of burnign in the caps the B4 is really singing now and is a great little preamp. I have a question re-earthing however. I am getting crackles when touching the potentiometer and also when touching the input caps. Could this be a problem with the earthing? I have the board itself, along with the PSU, earthed to the casing at a star point and the ground from the outputs connected to the ground at the RCA plugs for the line out. The ground from the line in RCAs is connected directly to the board at the allocated points. The 240v supply is earthed at a seperate point to the casing. Does this all seem OK? Any thoughts on the crackles?
 
Got a picture ? I would suggest you need to keep the signal ground & chassis earth separate.

Power inlet earth should go to the chassis only, both in/out phono grounds & the power supply's 0v point all go to signal ground in the middle of the B4 board.
 
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