Genial! 
I tried out to outwind a bit the trafo and disconnect those two couples of wires that where tied toghether and soldered at the end: and yes! Now I have dual secondaries.. both exiting with 12.8V (!!)
So now I'd need only to decide which two of the now 4 wires are to be connected toghether to form the center tap and I'd try it with one trafo alone.
The real incredible news is also this: I tried to carefully move a bit the windings and try to put them more "flat" and "parallel" I'd not know how to say, but this finally LET THE TOROID sound less noisy!!! Woa! Ok you can still hear the humm if you are close but really nothing compared to previousely!
The Lamp tester is still showing a dim light, but really dim (you can just see the filament is getting orange)... ?
well.. lot's of things to learn from toroids, really!
tent:wq
I tried out to outwind a bit the trafo and disconnect those two couples of wires that where tied toghether and soldered at the end: and yes! Now I have dual secondaries.. both exiting with 12.8V (!!)
So now I'd need only to decide which two of the now 4 wires are to be connected toghether to form the center tap and I'd try it with one trafo alone.
The real incredible news is also this: I tried to carefully move a bit the windings and try to put them more "flat" and "parallel" I'd not know how to say, but this finally LET THE TOROID sound less noisy!!! Woa! Ok you can still hear the humm if you are close but really nothing compared to previousely!
The Lamp tester is still showing a dim light, but really dim (you can just see the filament is getting orange)... ?
well.. lot's of things to learn from toroids, really!
tent:wq
I'm now trying to do a center tap configuration but when I connect two wires of different secondaries toghether I can measure still 12.8Vac between that just realized center tap and each of the remaining two wires, but I'm not able to measure 24Vac if testing only those reamining two free wires (I read 0Vac). Any ideas? I tried to connect both possilble wires togheter, excluding the other two that would short everything..
tent:wq
tent:wq
Connect each of the four secondary wires to separate terminals of an insulated terminal block.
Connect each of the mains (primary) wires to a separate insulated terminal block.
Connect a plug top to the mains terminal block.
Insert the transformer plug top into the outlet socket of your bulb tester.
Insert the plug top of the bulb tester into the mains outlet socket.
Switch on. The bulb should remain off. If it flashes or glows dimly there is something wrong with your transformer.
Test both transformers.
Do not use either until they pass this "bulb off" test.
Connect each of the mains (primary) wires to a separate insulated terminal block.
Connect a plug top to the mains terminal block.
Insert the transformer plug top into the outlet socket of your bulb tester.
Insert the plug top of the bulb tester into the mains outlet socket.
Switch on. The bulb should remain off. If it flashes or glows dimly there is something wrong with your transformer.
Test both transformers.
Do not use either until they pass this "bulb off" test.
AndrewT said:
Hi again,
and sorry for this neverending story..
I tried EXACTLY as you proposed above and BOTH trafos (220Vac-2x12.5Vac, 200VA) let the 60W bulb on the tester illuminate the tungsten filament very dimmly (but they certainly do).
So now I wanted to be 100% sure I was not doining anything wrong and decided to temporarily remove another toroidal transformer from another device and test it the EXACTLY same way on my light bulb tester (this third other test trafo is a 220Vac-2x25Vac, 120VA): the result is infact that the bulb is not illuminating in any way (not even dimly), only at the first power on it did very shortly but then no red filament any more.
Re tested back both the other trafos and again a very very dim filament gets enlightened.. is it possible they both are somehow broken/shortcircuited?
I decided to test them also with my instrument tester using the "beep" position to see if there are shorts between the primary wires (both) and the secondary ones (four), so like 8 test, but no beep (the beep only if touching the two primaries at the same time or any of the secondaries between them, so I suppose all regular. I also read the resistence of the primary winding (something c.a. 10ohm) and the secondaries (c.a. 1.5ohm) but this maybe makes no sense.
Well, I think that anyway now, even if they are not noisy any more, they have a clear destiny: tomorrow I'll se for some new ones..
Thanks for all the support, all was probably because of those two guilty trafos, sorry for the annoyances, and thanks again. :\
tent:wq
is it possible these are 110/120Vac transformers?
A transformer draws increasing idle current (when no load is connected) as the mains voltage is increased.
At some elevated voltage (~140% of rated voltage) the idle current increases rapidly and thus heats the transformer excessively. Eventually at some very elevated voltage the transformer will fail. During this elevated supply voltage the transformer is also quite mechanically noisy.
Can you insert a 10r0 resistor into the primary feed? Careful it will be live.
Use the light bulb as your limiter and measure the current through the 10r0 resistor and the voltage across the transformer. From this some transformer expert can probably identify if the transformer is faulty or overvoltage or OK.
A transformer draws increasing idle current (when no load is connected) as the mains voltage is increased.
At some elevated voltage (~140% of rated voltage) the idle current increases rapidly and thus heats the transformer excessively. Eventually at some very elevated voltage the transformer will fail. During this elevated supply voltage the transformer is also quite mechanically noisy.
Can you insert a 10r0 resistor into the primary feed? Careful it will be live.
Use the light bulb as your limiter and measure the current through the 10r0 resistor and the voltage across the transformer. From this some transformer expert can probably identify if the transformer is faulty or overvoltage or OK.
Hi, I finally solved the trafo issue by buying two new ones: those are completely SILENT and DO NOT let the bulb tester glow in any way, so very good I'd say..
The two old trafos are 220V rated, only one primary made of two wires, but if there is no error it's so. Did not get if the suggested resistor would be to inserted in series or in parallel to the primaries to do that test, Andrew.
Kr,
tent:wq
The two old trafos are 220V rated, only one primary made of two wires, but if there is no error it's so. Did not get if the suggested resistor would be to inserted in series or in parallel to the primaries to do that test, Andrew.
Kr,
tent:wq
/oh, well, I see: you're totally right!!
So, a couple of updates on my current situation:
But now I'm working with the new trafos (no bulb light if I use them alone).
Later I connected also the PSU: is it normal that so it is very very very dimly lit? (with my 60W lamp you can notice it only during the night by turning off all the other lights..
Then the next step was to connect also the lm1875 amp and no big difference in the lamp (and I also measured the diff voltage on the outputs and now I get a more beautiful 14mVdc..).
When I finally put there an 4ohm loudspeaker the lamp gets a little bit lighter but still so little it is difficult to notice. Is this supposed to be still good?
Anyway now that all was running more silently I begun to notice also some small humm and hiss from the speakers, I'm still without case and particular earth grounding.. so I tried some different setups but no particular improvement was reached.
I must now also confess that the volume levels of those small LM1875 chips is really ridiculous..
So I then also begun to do an LM3886, but starting from the PSU (the carlosfm felipe based one) again as buyed from chipamp.com (see there the PCBs if needed).
Now I did a quick test using that PSU on my current LM1875 system and I noticed two more curious things:
1) there is absolutely NO noise on the loudspeakers now! (shoking dead silent!)
2) now the bulb test is completely not glowing when also only the PSU is connected, but glowing a little bit more (still very few, almost unnoticeable) when I connect also the LM1875 amp.. is it somehow an issue or allright?
So, next step is assembling also the LM3886 amp.. see you soon.
tent:wq
PS: small schematic to sum up my current findings with the lamp tester ->
Thoroid = NO LIGHT AT ALL
LM1875 psu = ALMOST NOT NOTICEABLE ORANGE FILAMENT
LM1875 psu+amp = THE SAME AS ABOVE
LM1875 psu+amp+speakers = ORANGE FILAMENT A BIT MORE NOTICEABLE
(diff. 14mVdc)
LM3886 psu = NO LIGHT AT ALL
LM3886 psu+LM1875 amp = ALMOST NOT NOTICEABLE ORANGE FILAMENT
LM3886 psu+LM1875 amp +speakers = THE SAME AS ABOVE
(diff. 107mVdc)
So, a couple of updates on my current situation:
But now I'm working with the new trafos (no bulb light if I use them alone).
Later I connected also the PSU: is it normal that so it is very very very dimly lit? (with my 60W lamp you can notice it only during the night by turning off all the other lights..
Then the next step was to connect also the lm1875 amp and no big difference in the lamp (and I also measured the diff voltage on the outputs and now I get a more beautiful 14mVdc..).
When I finally put there an 4ohm loudspeaker the lamp gets a little bit lighter but still so little it is difficult to notice. Is this supposed to be still good?
Anyway now that all was running more silently I begun to notice also some small humm and hiss from the speakers, I'm still without case and particular earth grounding.. so I tried some different setups but no particular improvement was reached.
I must now also confess that the volume levels of those small LM1875 chips is really ridiculous..
So I then also begun to do an LM3886, but starting from the PSU (the carlosfm felipe based one) again as buyed from chipamp.com (see there the PCBs if needed).
Now I did a quick test using that PSU on my current LM1875 system and I noticed two more curious things:
1) there is absolutely NO noise on the loudspeakers now! (shoking dead silent!)
2) now the bulb test is completely not glowing when also only the PSU is connected, but glowing a little bit more (still very few, almost unnoticeable) when I connect also the LM1875 amp.. is it somehow an issue or allright?
So, next step is assembling also the LM3886 amp.. see you soon.
tent:wq
PS: small schematic to sum up my current findings with the lamp tester ->
Thoroid = NO LIGHT AT ALL
LM1875 psu = ALMOST NOT NOTICEABLE ORANGE FILAMENT
LM1875 psu+amp = THE SAME AS ABOVE
LM1875 psu+amp+speakers = ORANGE FILAMENT A BIT MORE NOTICEABLE
(diff. 14mVdc)
LM3886 psu = NO LIGHT AT ALL
LM3886 psu+LM1875 amp = ALMOST NOT NOTICEABLE ORANGE FILAMENT
LM3886 psu+LM1875 amp +speakers = THE SAME AS ABOVE
(diff. 107mVdc)
Hi,
and now I finished up also the two LM3886 based amps. Even better now! This amp really rocks! It rules!
Powerfull and clear, and most important really without hum and hisses!!
So updated situation:
Thoroids (two NEW 2x12V, 80VA) = NO LIGHT AT ALL
LM1875 psu = ALMOST NOT NOTICEABLE ORANGE FILAMENT
LM1875 psu+amp = ALMOST NOT NOTICEABLE ORANGE FILAMENT
LM1875 psu+amp+speakers = ORANGE FILAMENT A BIT MORE NOTICEABLE
(offset 14mVdc) so should I worry about the filament?
LM3886 psu = NO LIGHT AT ALL
LM3886 psu+LM1875 amp = ALMOST NOT NOTICEABLE ORANGE FILAMENT
LM3886 psu+LM1875 amp +speakers = ALMOST NOT NOTICEABLE ORANGE FILAMENT
(offset 107mVdc) maybe related to the fact that GN+ and GN- go to the same point on the amp?
Other thoroids (two other NEW 2x24V, 85VA) = NO LIGHT AT ALL
LM3886 psu+amp = NO LIGHT AT ALL
LM3886 psu+amp+speakers = NO LIGHT AT ALL
(offset 4mVdc !!) this sound great!
tent:wq
and now I finished up also the two LM3886 based amps. Even better now! This amp really rocks! It rules!
Powerfull and clear, and most important really without hum and hisses!!
So updated situation:
Thoroids (two NEW 2x12V, 80VA) = NO LIGHT AT ALL
LM1875 psu = ALMOST NOT NOTICEABLE ORANGE FILAMENT
LM1875 psu+amp = ALMOST NOT NOTICEABLE ORANGE FILAMENT
LM1875 psu+amp+speakers = ORANGE FILAMENT A BIT MORE NOTICEABLE
(offset 14mVdc) so should I worry about the filament?
LM3886 psu = NO LIGHT AT ALL
LM3886 psu+LM1875 amp = ALMOST NOT NOTICEABLE ORANGE FILAMENT
LM3886 psu+LM1875 amp +speakers = ALMOST NOT NOTICEABLE ORANGE FILAMENT
(offset 107mVdc) maybe related to the fact that GN+ and GN- go to the same point on the amp?
Other thoroids (two other NEW 2x24V, 85VA) = NO LIGHT AT ALL
LM3886 psu+amp = NO LIGHT AT ALL
LM3886 psu+amp+speakers = NO LIGHT AT ALL
(offset 4mVdc !!) this sound great!
tent:wq
Redshift187 said:Excellent work tent. Now you should connect the new toroids to the LM1875 PSU, check for light, then also the LM1875 amp and check for light. Then you'll know if it was entirely the transformers fault
Hi redshift,
well I did it! I have now two sets of new toroids, 12V and 24V but my question is exactly that now I'm not seing any light coming from the lamp if I connect only the trafos (do they seem ok now) but do see some very very dim one with the LM1875 psu and even more with the loudspeakers, is that normal? I also did some mixed test with PSU from LM3886 and amp LM1875 and also there a small orange filament can be observed, but now on a full LM3886 version. Could I still have something maybe in the amp of LM1875? or the speakers? or is this perfeclty normal dissipation somehow?
Thanks,
tent:wq
PS: the summary was:
Toroids (two NEW 2x12V, 80VA) = NO LIGHT AT ALL
LM1875 psu = ALMOST NOT NOTICEABLE ORANGE FILAMENT
LM1875 psu+amp = ALMOST NOT NOTICEABLE ORANGE FILAMENT
LM1875 psu+amp+speakers = ORANGE FILAMENT A BIT MORE NOTICEABLE
(offset 14mVdc) so should I worry about the filament?
LM3886 psu = NO LIGHT AT ALL
LM3886 psu+LM1875 amp = ALMOST NOT NOTICEABLE ORANGE FILAMENT
LM3886 psu+LM1875 amp +speakers = ALMOST NOT NOTICEABLE ORANGE FILAMENT
(offset 107mVdc) maybe related to the fact that GN+ and GN- go to the same point on the amp?
Other thoroids (two other NEW 2x24V, 85VA) = NO LIGHT AT ALL
LM3886 psu+amp = NO LIGHT AT ALL
LM3886 psu+amp+speakers = NO LIGHT AT ALL
(offset 4mVdc !!) this sound great!
Sorry, I didn't realize those results were only with the new transformers.
Are both PSUs chipamp.com PSUs, but one is for the LM1875 and the other is for the LM3886?
There would obviously be a little current at idle, how much it takes to make a 60W bulb glow very dimly I don't know. As AndrewT said, if DC offset on the output is low with a source connected and the volume not at minimum, it should be fine.
Are both PSUs chipamp.com PSUs, but one is for the LM1875 and the other is for the LM3886?
There would obviously be a little current at idle, how much it takes to make a 60W bulb glow very dimly I don't know. As AndrewT said, if DC offset on the output is low with a source connected and the volume not at minimum, it should be fine.
AndrewT said:
Redshift187 said:
Hi,
yes exactly, both PSU from chipamp.com each for the corresponding LM.
I measured with a muted source ad volume halfway the following:
. 13mVdc on the left channel of LM3886
. 32mVdc on the right channel of LM3886 (is something wrong with that channel?) and
. 112mVdc on both channels of the LM1875 (so is there here something wrong probably?)
The lamp turns dimly only on the LM1875 but somehow noticably only with connected speakers..
Kr,
tent:wq
In general the bulb tester is used for checking that the amplifier is properly wired up.tent said:
This should be completed and then the bulb tester should normally be removed.
Then connect your speakers to your thoroughly tested amplifier.
The output offset is checked with no load on the output.
If you connect an 8ohm speaker with R~6r0 then 112mV of offset will cause ~19mA to flow through the load. If the offset changes when your source is connected or when you alter the volume control then the offset current through the load will change.
This could account for the dim glow you are seeing in the bulb tester filament.
Look at the datasheet for these chipamps. You will find a large variation in quiescent current (no load connected). This too will account for differences in the filament temperature.
Neeraj, a lot depends on the speakers involved, particularly how efficient they are.
For instance, I can get a reasonable performance form 12v rails with some 12 inch full-range drivers, but I would use that type of supply for more demanding drivers.
So it would be very useful to know the exact drivers that your amp will be powering, and how they are connected up, ie passive crossovers etc.
For instance, I can get a reasonable performance form 12v rails with some 12 inch full-range drivers, but I would use that type of supply for more demanding drivers.
So it would be very useful to know the exact drivers that your amp will be powering, and how they are connected up, ie passive crossovers etc.
Thanks Nukk & Andrew T,
Speakers Are 8 ohm 3 way 100 W RMS Sealed Enclosure (DIY)
Woofer 100 WRMS
MID 90 W RMS
Dome Tweeter 60 W RMS
With 12db /Octave crossover network
As i have read somewhere that 47 labs used 170 VA /channel in Original Gainclone ( 8 Ohm,50 W Model).
Plz confirm A=(VA*PF)/V then 170 VA= 4.08Amp./Rail is it accurate?
Nuuk said:So it would be very useful to know the exact drivers that your amp will be powering, and how they are connected up, ie passive crossovers etc.
Speakers Are 8 ohm 3 way 100 W RMS Sealed Enclosure (DIY)
Woofer 100 WRMS
MID 90 W RMS
Dome Tweeter 60 W RMS
With 12db /Octave crossover network
AndrewT said:
As i have read somewhere that 47 labs used 170 VA /channel in Original Gainclone ( 8 Ohm,50 W Model).
Plz confirm A=(VA*PF)/V then 170 VA= 4.08Amp./Rail is it accurate?