Build Thread:MS76
- Thread starter Gustav
- Start date
Help Support GroupDIY Audio Forum:
When I did the last round of kits, I counted up the PCBs, and set the limit in the shop software, but when it came time to ship them, I couldnt find the corresponding amount in my stock.
I then had to order some extras, and ask people to wait, but...I found I had just misplaced a stack, when I was clearing out the space some weeks ago.
These are the same boards, just from a misplaced/lost stack.
Gustav
LinusGrane
Active member
Got my new 6.8uF tantulums today. And the unit works! ✌✌✌ calibrated using the TEAC meter, so i have to fix or replace the meters.
Thanks for the help
Thanks for the help
Got my new 6.8uF tantulums today. And the unit works! ✌✌✌ calibrated using the TEAC meter, so i have to fix or replace the meters.
Thanks for the help
Happy to hear it!
As mentioned, you can get by with a rectifier using the meters in the unit as is, unless you want more critical metering.
Gustav
Hello,
Powered up my unit today. No smoke, nothing blew up. All output voltages from the PSU are correct. However, something smelled burnt. It took some time for me to notice that the 100R resistor going to the emitter of the BC560 was burnt, and that's on both channels...
I cannot find out what's wrong. I'm using the BC557A in stead of the BC560 (found out that it's fine for replacing the BC560 which seems to be obsolete. Is that true?)
Can anyone help?
Powered up my unit today. No smoke, nothing blew up. All output voltages from the PSU are correct. However, something smelled burnt. It took some time for me to notice that the 100R resistor going to the emitter of the BC560 was burnt, and that's on both channels...
I cannot find out what's wrong. I'm using the BC557A in stead of the BC560 (found out that it's fine for replacing the BC560 which seems to be obsolete. Is that true?)
Can anyone help?
scott2000
Well-known member
Sometimes there's a chance transistor pinouts can be different between manuafacturers. Not saying that's the situation here but maybe worth a look if you haven't already.
Thank you for the help! Checked the transistors, and it was actually the BD140s that were placed the wrong way around... There are no markings on those, so it's quite hard to figure out the orientation.
Now, it's all powered up, almost everything seems okay, but when measuring the voltage at the resistor right next to the BD139 (where it's marked on the PCB to be around 12,7 volts), I get around 21 volts... And that's on both channels. I simply cannot seem to figure out why. Any ideas?
"almost everything seems to be ok" can be a little vague in terms of trouble shooting. Are you saying, you are able to calibrate and operate the unit, just that that specific voltage is off, or?
Did you just rotate the Bd140, or did you replace it? I would guess the voltage is higher, because you are not drawing any current on a fried transistor, hence, the resistor is not dropping the voltage correspondingly.
Hope that makes sense!?
Gustav
Sorry, I get that it's a little vague. The thing is, every other voltage is fine, but this particular one is just off. I can operate and calibrate the unit, but it doesn't sound right at all, although I can complete the calibration without any problems. Sound passes through, but it quickly starts distorting, and in M/S mode, it's very unbalanced. When I dial in both channels, the level is fine in the right speaker, but the left speaker is much more silent (and I can see it on the dBFs meter in my DAW as well, that the right channel is louder).
I rotated both the BD140s. Is it possible to measure them in some way to determine whether they're fried or not?
The measurement that you conclude is off is the closest thing to what you are asking, unless you have a scope, in which case, you can scope out the output of it. Waveform will probably be wonky, because you do not have proper drive on the positive side.
I would just replace - you are not dropping the voltage over the resistor, which means, you have the wrong resistor, or you do not have the current draw expected on the BD140. I highly suspect its the latter.
Its very common for these to fry if you reverse them. I would replace both, just for good measure.
Gustav.
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Noted! Thank you very much for the reply - I'll try throwing in some new BD140s.
Tried putting in the new BD140s today. Still getting the weird voltage around 21V before the 1k2 resistor where it's supposed to be 12.7V. I can see in the schematics that the 1k2 resistor is placed after one of the BC560s. As mentioned before, I'm using the BC557A in stead of the BC560 (obsolete/hard to get). Does it have something to do with that??
I have never tried the BC557, nor have I researched it as a replacement, or checked the pin-out for compatibility.
Its probably an easier question for yourself to answer, since you chose the replacement/know the reasoning!?
I was under the impression that one channel was working, by what you wrote earlier, and if its a bad replacement, it would come across on both channels.
If it is indeed a problem on both channels, the mentioned transistor could be the culprit.
This is the part used in the build.
https://www.reichelt.de/dk/en/transistor-pnp-to-92-30-v-0-1-a-0-5-w-bc-560b-p5027.html?&nbc=1
Gustav
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I tried using the BC557s because as far as I could see, they'd make a fine replacement. However, that might not be the case. They do have the same pinouts, the same specs etc.
You see, the thing is: when the unit is in M/S, and I play something through it with the in and out turned up on the M channel only, I do as expected get the same level on both L and R channel on meter in my DAW (it is mono as it should be). However, when I start dialling in the S channel, it's not at all balanced. I have much more volume in the right speaker than in the left speaker - that's not only something that is very obvious when hearing it, I can see on the meter in my DAW as well that the right channel is ahead by more than 10-12 dBFs. That's what I think is really weird.
Transistor could be the culprit as you're mentioning.
I would leave out MS for basic trouble shooting, and get the two channels to work as separate mono channels before doing anything else.
MS can do unexpected an finicky things, and if you check the schematic, youll see, it adds another variable, which is not integrated into the mono channels themselves.
Its still not clear to me if your channels work in split mode, by what you wrote, and if they do, the problem is definitely isolated to the "MS-wrap". (possibly using a 1246 or 1243 instead of a 1240?), or maybe because you are only injecting signal into one side, or maybe....
In any case - worry about the split channels working independently, before even looking at operations in MS mode.
Gustav
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You're right, sorry...
I tried using the channels independently. What I see now is, when sending the exact same signal to both channels with the same settings in split mode, channel 1 does compress as expected. But channel 2 doesn't do anything. The meter reacts on the input/output setting, but the needle is resting at 0 in G.R-mode while I can hear that it doesn't do any compression at all.
The good news is, you can compare the bad channel to the good one for trouble shooting/voltages etc.
Find the discrepancy = find the problem, and try swapping ICs! (one at a time).
You only mention the meter and lack of compression. Are you hearing signal through channel 2, and you can change the gain with the pots?
If so, its definitely the SC youre looking at.
Gustav
I am hearing signal through channel 2, and I can change gain with the in/out pots.
I'll try to do troubleshooting by comparing voltages, swapping ICs etc. And I'll be focusing on the SC.
LinusGrane
Active member
The unit still works great, but i still haven't got the meters working. I have build a bridge rectifier out of schottky diodes like this:
But whiteout the resistor.
In GR mode the meter shows to less (-5) but if i switch to "All buttons in" it peaks, but i guess i maybe have to re-calibrate whit the new meter?
Yes, the 0 trimmer adjusts bias for the zero point on the meter in GR mode.
In all buttons mode, it will alwyas peak. It is also nick named "slam", because this all buttons feature slams the meter to max.
Gustav
