I rechecked my board before fitting in the new components, found out that the output bias is only 10mA~ on both speaker outs. The R12 resistors were measured at 4mV, so I recalibrated them to 7mV and 14mV across both resistors. The output bias is still roughly 10mA. How is this value set? Is it parts component selection?
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I only build one DIY amplifier with limiters, it was a Bryston clone. It didn't sound as good as any of my other projects and I never did find out if the limiters were a factor in this. But I figure that the limiter is not foolproof, I remember reading about these things and discovering that there is very little safe ground between intrusive limiting and dead output devices. Why would I need a limiter ? - I don't let my kids wire up the speakers. The system is under my exclusive control. I'm not selling it for use in a college dorm. Hence, no limiters in any of my designs.
I do include speaker protection, which is a different thing from a limiter designed to protect the output devices - sure it may also help protect speakers indirectly by preventing a dead output device but I presume there are other amplifier failure modes that can threaten the speakers.
Minor update
Yesterday my parts arrived from Element14 so I opened the amp back up for overhauling. I checked the Vbias at R12 and it was only 4mV when its supposed to be 7mV. After adjusting I noticed the bass and extreme treble has returned, mids became less forward which I think because since the amp has higher bias voltage now it can drive the lows and highs as much as the mids. The output bias however is still 10~mA and it doesn't deviate when I adjust the trimmer.
I followed the parts list for the transistors, diodes, and caps. I didn't change any resistors, they're cheap and I assume the supplier can provide correct values.
The only things I left out for are caps C13-C16, transistors TR11-TR12, and transistors TR7a-TR8. I cannot find 2N5087 and 2SC2922 in Element14, and those C13-16 caps are not critical. Yesterday I went to the components store and got 2N5087 but they are China produced ones. I bought them because even though I already have them I can use the extra ones for HFE matching. I needed 4 so I bought 8 but it wasn't enough because I only got 1 matching pair.
In retrospect I should've done a lot of things different:
1. Buy at least 3-4x the amount of transistors needed to match HFE.
2. Double check amount written in parts list whether listed for one channel or both. Count based on the board part ID. Ex: 1N4148DO is written as 7 pcs but for both channels need double that.
3. Get multi turn trimmers. They're so sensitive.
4. Buy from Digikey in the first place because they got all INCLUDING 2SC2922.
I can confirm the SanKen 2922 provided by ZeroZone/Caowei are fakes because they have different font especially evident in number 9. The print quality does look similar to the original so it's easy to fool people. Although one of the defining characteristics for fakes is the head spreader is shiny, for mine only 3/4 are matte and the other 1 is shiny. Pay attention if you get matte back since they might be fakes too.
Here's a google drive link of the old and new components. Sorry my photos are dark. I'll brighten them up when I have the chance.
https://drive.google.com/open?id=0B3DG_Zx-jIG4d2s5X1dCN1ZERVk
Yesterday my parts arrived from Element14 so I opened the amp back up for overhauling. I checked the Vbias at R12 and it was only 4mV when its supposed to be 7mV. After adjusting I noticed the bass and extreme treble has returned, mids became less forward which I think because since the amp has higher bias voltage now it can drive the lows and highs as much as the mids. The output bias however is still 10~mA and it doesn't deviate when I adjust the trimmer.
I followed the parts list for the transistors, diodes, and caps. I didn't change any resistors, they're cheap and I assume the supplier can provide correct values.
The only things I left out for are caps C13-C16, transistors TR11-TR12, and transistors TR7a-TR8. I cannot find 2N5087 and 2SC2922 in Element14, and those C13-16 caps are not critical. Yesterday I went to the components store and got 2N5087 but they are China produced ones. I bought them because even though I already have them I can use the extra ones for HFE matching. I needed 4 so I bought 8 but it wasn't enough because I only got 1 matching pair.
In retrospect I should've done a lot of things different:
1. Buy at least 3-4x the amount of transistors needed to match HFE.
2. Double check amount written in parts list whether listed for one channel or both. Count based on the board part ID. Ex: 1N4148DO is written as 7 pcs but for both channels need double that.
3. Get multi turn trimmers. They're so sensitive.
4. Buy from Digikey in the first place because they got all INCLUDING 2SC2922.
I can confirm the SanKen 2922 provided by ZeroZone/Caowei are fakes because they have different font especially evident in number 9. The print quality does look similar to the original so it's easy to fool people. Although one of the defining characteristics for fakes is the head spreader is shiny, for mine only 3/4 are matte and the other 1 is shiny. Pay attention if you get matte back since they might be fakes too.
Here's a google drive link of the old and new components. Sorry my photos are dark. I'll brighten them up when I have the chance.
https://drive.google.com/open?id=0B3DG_Zx-jIG4d2s5X1dCN1ZERVk
Bias setting is by adjusting the 1k trimpot, marked VR2 on algar_emi's schematic. The 5-7 mV is measured and adjusted with the meter probes clipped safely across either R12 or R13 or preferably both in series, for a 10-14mV reading as shown in red. Be careful not to confuse R14 with these resistors, as they are all the same 0R22 value and type but you won't get much sense from trying to measure bias where there should not be any, like at the output, unless you had speakers connected - did you?
You should not need to change any parts to get a wide enough range of adjustment with the trimpots. Those supplied in the kit may even be upright, 15 turn types which are nice quality but slow and confusing to adjust also difficult to fit to the PCB but these only slip (you can feel clicks as you rotate the screw) at the ends of their range.
For anyone interested in the "lowdown" on Naim NAP and earlier Nait bias levels, don't take just my word for it, take a look at this easy to follow article: Naim, NAPs, Naits, distortion and bias-current settings
BTW, fakes are usually lighter than genuine MT200 parts. Mine from Caowei were fine but then, the kit was considerably more expensive too.
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No I didn't have speakers connected when I was measuring the bias at the output. The probes were connected in series with the speaker outs like measuring DC V offset. So does that mean I should get 0mA instead of 10-11mA?
And I found out that I have been measuring the bias current wrong. I thought you probe the 30mA value from the speaker outs like DC offset, and I kept calling it output bias when its actually the total current draw of the amp measured in series with the + power. Martin Clark and you plus a lot of of other people had made it very clear that the important measurement is the R12 or R12+R13.
How much was your Caowei kit? And are you positive the 2SC2922 you have are genuine?
Re : NAP200
I also received NAP200 from ZeroZone/Caowei through eBay.
However, what I ordered is "LOVE" version. that is, no filter cap and no 2922.
The reason why I choose "LOVE" version is, they are supplying 10000uF 50V cap from Nichicon GU series.
I believe the original NAP200 is using 40V 10000uF capacitor. Using 50V will significantly affect the sound field. I would rather using other brand of 40V capacitor.
Are you getting Nichicon GU 10000uf 50V ? Or something else ?
I also received NAP200 from ZeroZone/Caowei through eBay.
However, what I ordered is "LOVE" version. that is, no filter cap and no 2922.
The reason why I choose "LOVE" version is, they are supplying 10000uF 50V cap from Nichicon GU series.
I believe the original NAP200 is using 40V 10000uF capacitor. Using 50V will significantly affect the sound field. I would rather using other brand of 40V capacitor.
Are you getting Nichicon GU 10000uf 50V ? Or something else ?
2sc2922
Digikey is selling US$ 7 each plus shipping.
Paying $16 for 4 is expecting magic !
Matching HFE requires speficing the temperature, VDD ect.
Do you know his matching condition down to the percentage ?
Digikey is selling US$ 7 each plus shipping.
Paying $16 for 4 is expecting magic !
Matching HFE requires speficing the temperature, VDD ect.
Do you know his matching condition down to the percentage ?
In the 20 years or so that I spent repairing various audio amplifiers, I never encountered one where the bias being wrong changed the sound that drastically.
Sure, if it was set too low, then distortion would result, but not loss of bass...
Are you sure you don't have a fault?
The voltage rating of the capacitor is *highly* unlikely to make any difference to the sound quality.
The important ratings are the actual value in uF and the ripple current ratings, along with ESR.
But a 40V cap sounding better than a 50V cap....?
I received a Nichicon LS 10,000uF 50V, for now I am going to let it stay first. I looked through Farnell and RS and those caps are quite cheap so I think they supplied original caps. They look and feel genuine. But if I were to change them out, I'll probably choose something from Kemet like genuine NAP200 uses or follow the upgrade path with a Kendeil.
I gotta admit, $16 for 4 pcs 2922 is pretty farfetched, I'll probably get from Digikey or ProfusionUK. Reason being I am cheaping out because my currency is about 1/5th of USD. Including shipping, $49 equals to about MYR210.
My transformer was bought somewhere in eBay, I'm not logged in right now because I'm on a different PC, but when I receive it the packaging has ZeroZone labels on it. I think they have several eBay stores to cater for different countries and currencies. It's 300VA with 4x 28-0 secondary windings. Its possible to buy NAP200 replacement transformers with 2x 28-0-28 secondaries like the original but the prices are quite high.
No I don't know his HFE matching, I was referring to the packaging picture with the Y designation for production batch and the 2922 are also Y. The packaging picture and transistor pictures match.
Cap Voltage
From electrical stand point of view, yes, 50V has more margin and better reliability.
But do you know the original, not clone, NAP200 with 28-0-28 AC, 39.59DC, Naim is using 40V cap.
This is also true for Musical Fidelity A1. After fully loaded (class A), the transformer is ~26V AC, 36VC and 35V capacitor is used.
50V capacitor is everywhere. And probably cheaper.
Do you know why manufactures are all choosing this suicidal path ? Make it prone to fail and cost more to manufacture ?
From electrical stand point of view, yes, 50V has more margin and better reliability.
But do you know the original, not clone, NAP200 with 28-0-28 AC, 39.59DC, Naim is using 40V cap.
This is also true for Musical Fidelity A1. After fully loaded (class A), the transformer is ~26V AC, 36VC and 35V capacitor is used.
50V capacitor is everywhere. And probably cheaper.
Do you know why manufactures are all choosing this suicidal path ? Make it prone to fail and cost more to manufacture ?
Honestly I don't know, I probably was only imagining things as well. Might I add that I'm a little tone deaf?
I didn't test with the same songs I was listening to before so it could have been the tracks I was playing. The change wasn't drastic but I do feel the bass is a lot better while the treble extends a bit higher.I don't think there's a fault, the board was bought as built and tested. Nothing performed out of the ordinary and my only complaint was it was bass light.
No way to test the supplied components anymore, I've already gutted and swapped the components. I haven't tested it yet, I am contemplating about where to get the 2922.
It'll be a week or so until the 2922 arrives after I get it, so I won't know until then.
Re : Transformer
Just like the counterfit 2sc2922, I am concerned that the transformer is also taking a short cut. But I did not see it. Can you strip a little of wire more, ignore the tinning, and see the real color of the conductor please ? See whether it is copper wire (bronze color) or aluminum wire (silver) ?
Since the wiring needs to carry heavy current, to save money, they will use cheaper wire. Probably not copper wire. However, it indeed, is able to carry several amps of current without issue.
That will affect the sound as well.
In Chinese NAP 200 forum, They all choose "Audio grade transformer" instead of industrial grade transformer. Simply wrapping black clothes similar like Naim, does not make it higher quality.
Just like the counterfit 2sc2922, I am concerned that the transformer is also taking a short cut. But I did not see it. Can you strip a little of wire more, ignore the tinning, and see the real color of the conductor please ? See whether it is copper wire (bronze color) or aluminum wire (silver) ?
Since the wiring needs to carry heavy current, to save money, they will use cheaper wire. Probably not copper wire. However, it indeed, is able to carry several amps of current without issue.
That will affect the sound as well.
In Chinese NAP 200 forum, They all choose "Audio grade transformer" instead of industrial grade transformer. Simply wrapping black clothes similar like Naim, does not make it higher quality.
I'll see whether I can check the wires later today. Transformers are quite expensive, mine I think costs almost the same as the assembled board.
Are you planning to swap out the other components later too?
Re : NAP200
I do not buy assembled board. They may used recycled component.
Occasionally, you can see on eBay that assembled board is cheaper than kits.
I may replace trim pot if it is very sensitive. I think the total current per channel is around 28-34 mA.
And I may not install protection circuitry. If I do, I will find out the correct capacitor to replace the Panasonic FC.
Cowe did a good job try to find original parts if feasible. (cost wise)
So for the tiny capacitor, I may keep it.
Within my knowledge base, I do not know whether it make difference. The silver MICA should definitely a keeper.
I also want to implement the pre-amp power supply.
Can you read Chinese ?
HIFIDIYÂÛ̳-ºÚÏ»×Ó¤ÎÓÕ»ó-È«Á¦´òÔì naim пîºó¼¶NAP200£¨³ÖÐø¸üÐÂÖУ© - Powered by Discuz!
I do not buy assembled board. They may used recycled component.
Occasionally, you can see on eBay that assembled board is cheaper than kits.
I may replace trim pot if it is very sensitive. I think the total current per channel is around 28-34 mA.
And I may not install protection circuitry. If I do, I will find out the correct capacitor to replace the Panasonic FC.
Cowe did a good job try to find original parts if feasible. (cost wise)
So for the tiny capacitor, I may keep it.
Within my knowledge base, I do not know whether it make difference. The silver MICA should definitely a keeper.
I also want to implement the pre-amp power supply.
Can you read Chinese ?
HIFIDIYÂÛ̳-ºÚÏ»×Ó¤ÎÓÕ»ó-È«Á¦´òÔì naim пîºó¼¶NAP200£¨³ÖÐø¸üÐÂÖУ© - Powered by Discuz!
Good that you now know how to set bias and what it means. That will help with future projects too.
My kit of parts was as per the link in post #1752 that I also gave you earlier. When Zerozone later released their kits, they were only about $80 US including postage, compared to $100 for Caowei's. The Caowei basic kit included standard type Nichicon GQ caps. On my comparison, the audio grade KG was no better. Incidentally, you must use ≥50V rated caps if the supply rails are nominally 40V - otherwise 40V rated caps would be damaged by continuous over-voltage where mains supplies will typically exceed the nominal transformer primary ratings, regardless of whatever peak voltage ratings apply to any particular components or transformer regulation.
Don't forget that transformers are not constant voltage devices, their regulation spec. allows that secondary winding voltage will only fall to the rated voltage at maximum rated power with the nominal supply voltage. Mostly though, we listen at very low power and the rails will then be some 7% high with a low cost 300VA Toroid. Certainly, Naim engineers would not knowingly have fitted 40V rated caps to a 40V rail for basic safety and liability reasons.
Then I build and listen... If in doubt, I may swap out and compare by test and measurement with a curve tracer, though that's just what I do because I have collected the gear over many years of audio DIY. Occasional DIYs will find it hard to test them properly without high current power transistor test instruments and jigs + learning how to use them reliably
There are also plenty of threads here already showing other fake faults. If you are concerned to know the details, do a little searching for yourself. Note that there is also a parts forum here, for just such discussion. Parts - diyAudio
I can't read chinese but I do visit that site often. I use Google Translate and it is accurate enough that I understand what they're talking about. The thread also showed what happens when there's thermal runway so we need to focus on the chassis to be sealed to prevent air from moving.
I don't trust those Mica capacitors so I've swapped them out according to the PDF by Algar. You can populate the pre-power supply too, but I'd advise to build a HICAP clone instead because that pre psu is a very rudimentary design.
Good that you now know how to set bias and what it means. That will help with future projects too.
My kit of parts was as per the link in post #1752 that I also gave you earlier. When Zerozone later released their kits, they were only about $80 US including postage, compared to $100 for Caowei's. The Caowei basic kit included standard type Nichicon GQ caps. On my comparison, the audio grade KG was no better. Incidentally, you must use ≥50V rated caps if the supply rails are nominally 40V - otherwise 40V rated caps would be damaged by continuous over-voltage where mains supplies will typically exceed the nominal transformer primary ratings, regardless of whatever peak voltage ratings apply to any particular components or transformer regulation.
Don't forget that transformers are not constant voltage devices, their regulation spec. allows that secondary winding voltage will only fall to the rated voltage at maximum rated power with the nominal supply voltage. Mostly though, we listen at very low power and the rails will then be some 7% high with a low cost 300VA Toroid. Certainly, Naim engineers would not knowingly have fitted 40V rated caps to a 40V rail for basic safety and liability reasons.
Then I build and listen... If in doubt, I may swap out and compare by test and measurement with a curve tracer, though that's just what I do because I have collected the gear over many years of audio DIY. Occasional DIYs will find it hard to test them properly without high current power transistor test instruments and jigs + learning how to use them reliably
There are also plenty of threads here already showing other fake faults. If you are concerned to know the details, do a little searching for yourself. Note that there is also a parts forum here, for just such discussion. Parts - diyAudio
Thank you very much for the parts forum link, I do visit there every now and then. Photobucket seems to change their linking policy so photos hosted there don't show up anymore. So frustrating.
The Caowei board I have has badly made traces. There are a few solder that had ripped the tracing off the board. One trace came off when I used my solder sucker when I was desoldering the components. The pics from the board you bought look like they contain genuine 2922s. From the picture at least the font looks correct.
Also I've just found out that Digikey provides free shipping for orders above $50 to my country. The shipping cost was the reason I shied away from it and now I'm kicking myself in the head for it. I could've ordered the 2922 from there along with everything else. Weak currency is bad.
Re : HICAP clone
Oh, HICAP clone is exactly the same circuitry with the exception of TO-3 packaged LM317 plus high power transformer.
It is easy to clone the appearance.
However, to achieve the same performance, the transformer, as well as the wiring and the socket, is the key.
Did you have chance to look at the wire used in the transformer ?
I am still curious about it.
Oh, HICAP clone is exactly the same circuitry with the exception of TO-3 packaged LM317 plus high power transformer.
It is easy to clone the appearance.
However, to achieve the same performance, the transformer, as well as the wiring and the socket, is the key.
Did you have chance to look at the wire used in the transformer ?
I am still curious about it.
Full rail voltage on the speakers terminal , very likely one of the power device is dead open. Make sure when ever you adjust or set up your amplifier you do not connect your $$$ speakers to that amp. Use something cheap even a raw driver would do the job for that.
Start measuring you power devices,