I usualy use a 40 to 60W type light bulb to discharge the capacitors while I work on an amplifier.
Unfortunately, when a capacitor performs not far from nominal specs, there is no way to have the evidence that it is a fake one, unless it blows or swell when used within its own specs.
I have your same tester, different cabinet but same circuitry.
Before testing the capacitors, they should have been working with a voltage equal to half the working voltage for at least one day.
Before shorting the capacitors, they must be discharged, if charged, with a power resistor, lets say 100-390Ohms.
You should use a pair of Tweezers shorting the capacitor while connected to the tester; disconnect the tweezers and push the tester button at once.
I'm posting some readings of 3 capacitors.
Tweezers shorting the capacitor while connected to the tester: 0.17 Ohms, value that includes the small cables of the tester; actually only the value of the cables, because the tweezers have a unmeasurable resistance.
Nippon Chemicon 1 of 8, perhaps fake, 10mF 80V used at 74V: 10.05uf 0.9% 0.19Ohms 63g weight.
CDM 6.8mF brand new, never used, never connected to any voltage: 6771mF 0.9% 0.19Ohms 61g weight.
Kendeil 4.7mF 63V, old hard worker for long time at 55V: 4281uF 1.2% 0.22Ohms 37g weight.
You should subtract the tweezer reading from the ESR.
The Nippon Chemicon was the only survivor that didn't swell over 8 capacitors in the board, then it is a suspect fake. But performs as the best of all. The expected weight should be 73g but this is a personal idea of mine.
9200uF are "legally" acceptable because this value is within the 20% tolerance, even if, usually, the reading is greater than nominal capacitance.
I think you cannot return the board because there is not any good evidence that the capacitors are fake unless somebody, reading here, had some better ideas than mine about evidences.
0.21Ohm-0.17Ohms (my tweezers-cables)=0.04Ohms, excellent ESR, if my measuring method is correct.
What I know about ESR and Vloss:
The ESR is like a resistance put in serie to the speaker, so the lower the better; with paralleled capacitors you should have no problem on the sound. The Vloss should be a value that measures the ratio between the charging voltage and the voltage still stored by the capacitor after a certain amout of time, after the charge was disconnected. Then a low value of Vloss means high dynamic capability.
Should someone have better information, please share.
59Vdc is a too low voltage to see if 80V capacitors swell. You should use at least 75V for a week at least.
All my machines run at 230V, even the WHA-216 because I brought them or their transformers from Italy to USA. I use an auto-transformer to raise the voltage up to 230V. As a fuse, I use a 2A one on the WHS-216, it serves the paralleled primaries of 2x625VA toroidal transformers with a 300W halogen bulb, as a damper shorted after 4-5 secs, and 24x6.8mF capacitors. I didn't test at maximum volume, I am afraid to burn the Acoustat's transformers. I just blew a woofer of another pair of speakers, instead of the fuse, and do not want to replicate.
I have your same tester, different cabinet but same circuitry.
Before testing the capacitors, they should have been working with a voltage equal to half the working voltage for at least one day.
Before shorting the capacitors, they must be discharged, if charged, with a power resistor, lets say 100-390Ohms.
You should use a pair of Tweezers shorting the capacitor while connected to the tester; disconnect the tweezers and push the tester button at once.
I'm posting some readings of 3 capacitors.
Tweezers shorting the capacitor while connected to the tester: 0.17 Ohms, value that includes the small cables of the tester; actually only the value of the cables, because the tweezers have a unmeasurable resistance.
Nippon Chemicon 1 of 8, perhaps fake, 10mF 80V used at 74V: 10.05uf 0.9% 0.19Ohms 63g weight.
CDM 6.8mF brand new, never used, never connected to any voltage: 6771mF 0.9% 0.19Ohms 61g weight.
Kendeil 4.7mF 63V, old hard worker for long time at 55V: 4281uF 1.2% 0.22Ohms 37g weight.
You should subtract the tweezer reading from the ESR.
The Nippon Chemicon was the only survivor that didn't swell over 8 capacitors in the board, then it is a suspect fake. But performs as the best of all. The expected weight should be 73g but this is a personal idea of mine.
9200uF are "legally" acceptable because this value is within the 20% tolerance, even if, usually, the reading is greater than nominal capacitance.
I think you cannot return the board because there is not any good evidence that the capacitors are fake unless somebody, reading here, had some better ideas than mine about evidences.
0.21Ohm-0.17Ohms (my tweezers-cables)=0.04Ohms, excellent ESR, if my measuring method is correct.
What I know about ESR and Vloss:
The ESR is like a resistance put in serie to the speaker, so the lower the better; with paralleled capacitors you should have no problem on the sound. The Vloss should be a value that measures the ratio between the charging voltage and the voltage still stored by the capacitor after a certain amout of time, after the charge was disconnected. Then a low value of Vloss means high dynamic capability.
Should someone have better information, please share.
59Vdc is a too low voltage to see if 80V capacitors swell. You should use at least 75V for a week at least.
All my machines run at 230V, even the WHA-216 because I brought them or their transformers from Italy to USA. I use an auto-transformer to raise the voltage up to 230V. As a fuse, I use a 2A one on the WHS-216, it serves the paralleled primaries of 2x625VA toroidal transformers with a 300W halogen bulb, as a damper shorted after 4-5 secs, and 24x6.8mF capacitors. I didn't test at maximum volume, I am afraid to burn the Acoustat's transformers. I just blew a woofer of another pair of speakers, instead of the fuse, and do not want to replicate.
1pcs Luxury Power Amplifier Board AUDIO Imitation DarTZeel NHB 108 Power Amplifier Circuit Board|Amplifier| - AliExpress
Very satisfied with quality of PCB
Very satisfied with quality of PCB
Sorry for mistake, here are corrected readings.
Nippon Chemicon 1 of 8, perhaps fake, 10mF 80V used at 74V: 10050uf 0.9% 0.19Ohms 63g weight.
CDM 6.8mF brand new, never used, never connected to any voltage: 6771uF 0.9% 0.19Ohms 61g weight.
Kendeil 4.7mF 63V, old hard worker for long time at 55V: 4281uF 1.2% 0.22Ohms 37g weight.
Nippon Chemicon 1 of 8, perhaps fake, 10mF 80V used at 74V: 10050uf 0.9% 0.19Ohms 63g weight.
CDM 6.8mF brand new, never used, never connected to any voltage: 6771uF 0.9% 0.19Ohms 61g weight.
Kendeil 4.7mF 63V, old hard worker for long time at 55V: 4281uF 1.2% 0.22Ohms 37g weight.
Thanks for your reply.
I actually used a resistor to "short" the capacitor + it had never been "charged"
I actually used a resistor to "short" the capacitor + it had never been "charged"
Hello,
Have been reading all of your postings about the modifications ect of the Dartzeel NHB108.
Would purchasing a pair of these assembled from a manufacturer off ebay a good Idea or has anybody heard of such??
Have been reading all of your postings about the modifications ect of the Dartzeel NHB108.
Would purchasing a pair of these assembled from a manufacturer off ebay a good Idea or has anybody heard of such??
The best you can do is buying a bare pcb and build it up by yourself using good components. I cannot find a bare pcb on eBay anymore, I could find it on Aliexpress, probably I will buy it there, even if I don't like buying outside eBay. If you find a better source, please share.
Marigno, many Ali and eBay sellers are the same. They sell over many platforms. I purchase over both Ali and eBay.
I have never had a problem with an Ali purchase that their support will not solve, always got my money back after (relatively very few) disputes after having placed more than 200 over the years. Use "Ali Express Standard shipping" for much faster deliveries (than China Post). Many Ali sellers offer shipping from EU, US for faster deliveries and zero customs and VAT charges (just like many on eBay) Just avoid buying during big promotions, like Black Friday. Those orders may take very long to be delivered and I heard some sellers sell rejects at low(er) prices during Supersales. That is just an assumption, though. As always, check how long the sellers have run their shops on Ali and their ratings. You can always communicate with sellers before purchasing.
I have never had a problem with an Ali purchase that their support will not solve, always got my money back after (relatively very few) disputes after having placed more than 200 over the years. Use "Ali Express Standard shipping" for much faster deliveries (than China Post). Many Ali sellers offer shipping from EU, US for faster deliveries and zero customs and VAT charges (just like many on eBay) Just avoid buying during big promotions, like Black Friday. Those orders may take very long to be delivered and I heard some sellers sell rejects at low(er) prices during Supersales. That is just an assumption, though. As always, check how long the sellers have run their shops on Ali and their ratings. You can always communicate with sellers before purchasing.
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Even more mods
I need another couple of pcb to use better quality components, to try to improve the main circuitry and to get rid of the mid-point servo board. Here are some more mods to be experimented, the schema and the values are a starting point. I think I'll buy pcbs on Aliexpress.
Any comments will be appreciated.
I need another couple of pcb to use better quality components, to try to improve the main circuitry and to get rid of the mid-point servo board. Here are some more mods to be experimented, the schema and the values are a starting point. I think I'll buy pcbs on Aliexpress.
Any comments will be appreciated.
Attachments
I received yesterday the Output transistors MJL 1302A and MJL3281A (10 pairs), MJE 15032G and MJE 15033G (12 pairs), 2N5401 and 2N5551 (50 pieces each).I'm waiting for my transistor tester to arrive so I can pair them as well as possible.Now I want to order resistors, so I'm interested in which manufacturer the resistors are in the original (lower power and higher power).?
If you think the servo sound bad could it be the bad supply for it? Thinking maybe better with a discrete supply!
Erlend Sæterdal, I can't hear any difference with/without servo. But I never used the original circuitry, I modified it as soon as I got it. However, as soon I can get a couple of bare pcbs, I will try to eliminate the servo by applying the mod in the schema. Even if I think it will not work correctly because the CC feedback should be higher in voltage. But it is so simple that it is worth a try.
I found it at my supplier Vishay SMA/MBB0207 0,6W, Vishay PR02 2W and
Vishay AC05 5W.
I will try to make an amplifier without a servo circuit first, and if necessary I will make it later.
Can you post a schematic of a modified servo circuit and explain what part of the change they are in and why it is so much better
He has added an RC filter at the output. Despite this i bet the opamp type is still clearly audible.
....and replaced the opamp, I believe? The modified schematic specifies OPA2277 and it is marked in brown color (as in Substitusions)
Attachments
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