Jason Zhang
New Member
I found adjusting the idling current is quite difficult. It took long time to settle after adjustment. Maybe this is due to bad Q333/Q334?
NAD 2200PE upgrading
- Thread starter streetwise
- Start date
Gil Bucher
New Member
My experience shows the quiescent current drift as typical, especially if you're cutting power to the amp before attaching meter leads to TP201/202. What I've observed is that upon power application the bias will start at around 5mV then drift upwards quickly for about 30-45 seconds then slow. The NAD 2200/2600/2700 amps use NPN-PNP transistors in a "Sziklai" pair: https://en.wikipedia.org/wiki/Complementary_feedback_pair The article suggests ~10mV as a reasonable bias level, but at what latency? I've been using a stopwatch as a standard and setting the POTs for 10mV after 2 minutes on an idle (and properly warmed up) amp. if I measure after that the bias will continue to creep up but remember when in use it likely won't because the current will be used to drive the speakers.
Jason Zhang
New Member
Thanks for your explanation guys. I don't have scope to check if it is distorting. I tried to play 1khz tone which sounds clean to me.
Gil Bucher
New Member
IMHO, with respect to audio subjectivity is huge. And so is your system, what you hear is VERY dependent on speakers, source material/devices, and interconnects. Depending on your experience level, I'd advise finding ways to hear what distortion sounds like at various volume levels and frequencies without risking your "good" equipment. These NAD amps are AMAZING when in a properly configured "system" but can also sound like crap (and destroy things) when not. Google can be your friend, but so can a good dealer/technician who is willing to take a moment to measure and hopefully confirm your observations.
in then end, if you like what you hear then success!!
Jason Zhang
New Member
I like the result that I got now. My speakers are on the more resolving side. They are Martin Logan electrostats. But I kinda have POCD. I'll do a full check tmw to see anything else are out of spec. BTW, could the lower voltage that I got for +/- 1.77v related to Q309~312? Although it will be weird if they've all gone bad the same time and to the same extent.
the voltage variation is usually either the zener diodes(ZD301-304) or the bias transistor- if it is working and you like it then I suggest leaving it well alone.
Idling current should be 7.5mv at TP201/202- leave the amp on for about 10 -15 minutes or so and measure then- I leave the leads attached and you will see the voltage stabilize- make sure you have replaced SVR301/302.
Idling current should be 7.5mv at TP201/202- leave the amp on for about 10 -15 minutes or so and measure then- I leave the leads attached and you will see the voltage stabilize- make sure you have replaced SVR301/302.
Jason Zhang
New Member
I’ve checked all the voltages today. Everything else are normal. The 1.77v part has creeped up a bit to 1.69v. Thanks for your help. The unit itself sounds very detailed and very clean now. So I think it’s ok.
Gil Bucher
New Member
I'm guessing your Logans are from the ElectroMotion line? Not that it'd wrong to drive something from the Masterpiece series with a ~$250 amp, a 2200 can certainly deal with low impedance loads. Either way, I've always dreamed of owning something electrostatic but the closest I've gotten is a pair of HiFiMan HE400 planar magnetice headphones!
Jason Zhang
New Member
Mines are ML Vistas. It does have a bigger panel than the current ESL lines. But this amp is more than powerful enough to drive these speakers I feel. At about 1A, the volume is pretty much the loudest that I can bear. Before this I’m using Marantz sr6010 to drive these speakers, which ended up with not enough bass. This amp definitely has improved the low end a lot. I’ve also over killed it when I did the recap of this amp. I pretty much replaced all the ceramics with polystyrene, which I swear that I can hear the difference in terms of details. And later I changed the coupling capacitors to solen fast caps. This further improved the details and added a tiny bit of warmness to the sound. So overall, this project ended up well I think.I'm guessing your Logans are from the ElectroMotion line? Not that it'd wrong to drive something from the Masterpiece series with a ~$250 amp, a 2200 can certainly deal with low impedance loads. Either way, I've always dreamed of owning something electrostatic but the closest I've gotten is a pair of HiFiMan HE400 planar magnetice headphones!
Jason Zhang
New Member
Today I found something even more interesting. Somehow whether I put on the top cover or not has an effect on the idling current. With the cover on. TP201/202 slowly increased to about 12mv. When I took it off. It dropped back to 7.5mv slowly.
Gil Bucher
New Member
That's normal, output transistors (and probably most passive electronic components) have an optimum operating temperature. I linked this article on bias adjustment earlier in the thread: https://www.tnt-audio.com/clinica/bias_e.html The manufacturer's recommended spec is made for a number or reasons and is always likely to be conservative. As long as the unit isn't WAY out of spec it'll be fine.
The use of bias current in a class B amp is to "prime" the transistors by keeping them partially on in order to reduce the crossover distortion that results from the fully off to on transition. Class A amp transistors are on by default which is why those amps use more current and run hot even when idle. Bias in a class B amp is a compromise between minimizing crossover and dissipating excess current. I can't find it at the moment but there was an article posted on Motorola's website that mentioned the optimum bias current for a Sziklai pair amp using Toshiba 2SC3281/2SA1302 transistors (like the 2200) is around 10mv. I've adjusted both of my 2200s and my 2600 to be around there with no ill effects so far.
Last edited:
Spenser
Mostly Discrete
Hey how'd it go? I had a question on this. This is a nice tip! Looks like they still have 30 in-stock. Did you mean C413/414? I might not have done anything with these and C411/412. The big ones. Did you?
C411/412 10,000uF 120V
C413/414 10,000uF 80V
Maybe digging my 2200PE out; checking my work; and putting it on-deck in my rotation ... will help cure a confounded itch i've got right now to get a MOSFET power amplifier. I've only ever just had the 2200PE obtained at the end of 2018. Modified end of 2019. Have the 1155 pre.
Gil Bucher
New Member
I've installed the Kemets at C411/412 on a pair of 2200s so far and they seem to work quite well, good enough that I have one more pair to use in my 2600 too. Pwauk12's posts earlier in the thread nicely cover the application. The high voltage rails on the 2200/2600 run around 90v so a cap with a 100v rating (and higher surge spec) is compatible. Dimensionally they're smaller than the OE Nichicons so I've been using a thin layer of black RTV sealant on the bottoms to hold them to the PCB a little better as the snap pins take much less solder than the OE blade style terminals.
For C413/414 I used the United Chemicons pwauk12 suggests and they work well too with the same caveats about size/snap pin termination. For my 2600 I'm going to use Nichicon LKS caps on the low voltage rail: https://www.mouser.com/ProductDetail/647-LKS1K103MESC My thought is since NAD upped the "low" voltage from 65v to 72V in the 2600 it'd be smart to use something "better." And the LKS series is specified as an audio grade component.
Not sure how a BJT amp like a 2200 will cure your itch but as long as you're pleased that's all that matters!
You could replace the OE BJT OP amps on the input board with a FET device like the OPA2134!
Spenser
Mostly Discrete
Aha! -- I missed that before, and do see it now. I got it. Thank you! So now I've a draft plan to go with the United Chemi-Cons on the high and the KS series on the low. Have used the KS before. I'm so glad you said something on rolling the input IC. Have been saying 'nah' until this. I've the socket in there (with LM4562 installed). Why not have some fun. Thanks again!
Last edited:
Gil Bucher
New Member
Keep in mind that the 100v United Chemicons have a pair of dummy terminals so you'd have to drill holes in the PCB to accommodate that. According to their spec sheet that series is available without the extra terminals but I didn't find a convenient vendor that sold them.
Yeah, I did the same thing...installed DIP sockets. I bought LME49720NAs for both 2200s and a pair of OPA2134 ICs to try as well but haven't gotten around to swapping those in yet.
Spenser
Mostly Discrete
I saw that and was thinking about it today. My original thought was planning on drilling the PCB or snipping the dummy leads depending on what I saw. What I was thinking and having second thoughts about though, today, was -- I could not really tell the Chemicon's specs from the datasheet. I was wondering if perhaps additionally the Kemet might offer superior properties. Someone was telling me today if I was hankering to update the filter caps in my Yamaha A-1020 integrated he would recommend with going with one of the Kemets.
I suspect the difference between the Kemet and United Chemicon is marginal, though I have not done an A-B measurement test- for which ideally one would need an Audio Precision or better. I use the dummy leads on the UC to make sure the caps are rigidly attached to the PCB.