Counterpoint NP220s

Apr 26, 2015
18
1
3
#21
STOP RIGHT THERE he likely DOESNT know what he's doing. I have HAD IT with those who claim to know how to service Counterpoint.
There is a combination of BIAS and DCO and predriver balance which requires 3 multimeters probing 3 things to adjust. He likely over-compensated the DCO pot causing your bias to run hot. You might end up frying your pre-drivers.
Buy 3 cheap multimeters and 3 pairs of cheap clip probes and check the darn thing yourself. Otherwise you will end up sending it to CA for me to repair!!!
Most people see the bias and DCO pots but fail to see the BAL pot (see 1st pic)
1.) hook 1 multimeter across speaker terminal, DCV. Goal is 0
2.) hook 2nd meter across bias test points (IMG_6227) on output driver card, DCV, goal is 50mV AFTER warm up for 10 min
3.) hook 3rd meter across TP1 and TP2 in first pic, goal is 650mV, this should be the same as TP3 and TP4 on motherboard next to TP1 andTP2, if not adjust BAL pot. Depending on your voicing resistors it may be anywhere from 580-750 but the goal is for the 2 phases 1/2 vs 3/4 to be balanced.

Adjust DCO to 0, you will see bias change
adjust bias accordingly. You may need to go back to DCO to tweak once you change bias.
Play safe and go for a LOW bias for starters, say fiddle with DCO and if you see bias shoot up back the hell off.

DO NOT over adjust, if you need to turn over 180 degress something is NOT right. Or you are reading something wrong.
It's a delicate balancing act.
 
Last edited:
May 20, 2016
82
4
8
Torino - Italy
#23
I quite assure you that the technician worked carefully on my amp, he's reputated ("L'Audiotecnico" here in Torino).
http://www.audiotecnico.it/riparazioni.htm
I gave him the full instructions and service manual obtained by Mike Elliott for all NP-220 versions and the technician had already a long experience of Counterpoint's electronics.
He used three or four multimeters and he knows very well that any little change in one trimmer will interact with all lecture of values in all stages.
He finally told me that DCO has already some fluctuations, he consider it almost normal, mo more than 100mv; after warming the bias DCV value was around of 40 mv.
I don't know the lecture of multimeter of balance circuit .

In these days amp runs a little bit colder than in the first days; neverthless it's already more hot than in the 13 years of use in my home (Mike made the premium upgrade to me in 2006; it has the optional Plitron choke). Nothing excessive, I measured no more than 50 degrees Celsius in the heat sinks; the rest of the amp is almost cold.
I left the amp ON continously for four days without music; after that I started listening and after 25 hours listening it's opening with pleasure in the mids, now it has reached almost 30 hours listening and I'm satisfied with the sound; as Mike stated in his papers the adding of Plitron transformer and new Capacitors Nichicon Superthrough gave a better bass, more powerful and generally more dynamic overall and finally also a better detail retrieval.
I suppose that a little bit better sounds will arrive after 50-100 hours listening.
My further test will be to try a different tube than my beloved Sylvania VT-231 and maybe to try an EZ80 (the best provided by Mike) in place of 6BW4 I use now.
The technician examined the circuit and told me that it seems that pin 3 and 9 are connected in my amp so probably I can use both.

In any case maybe I'll follow your kindly and detailed alert and I'll take the amp in the next month to the technician for another check if values are correct.
My best best thanks and regards
Marco
 
Last edited:

Barry

Member Sponsor
Jan 8, 2012
222
12
18
Somewhere near Philadelphia, USA
#24
Johnsonlwu thanks for the biasing/DC offset instructions!!! May have to check mine. too bad you don't live closer.... I'd have you do some other fine tuning.

Analyzer, try the RFT EZ80s. They're terrific, readily available, and are cheap on Ebay and elsewhere.
 
Last edited:

E9Guy

New Member
Jun 28, 2019
5
0
1
43
#25
Hello folks,

So glad to find a current board on counterpoint amps.

I'm new here and need some beginners advise. First up, I was given what I thought was an SA-20. Much to my surprise and delight, it's actually an NP220 "1999 upgrade" done by Alta Vista.
Unfortunately it's first run after letting it warm up yealded granny audio and hardly any volume gain.

I would really appreciate feedback on which 6SN7's to use (or otherwise) as well do I need to order a new rectifier ? (6CA4/EZ81).

My hope is drop in new tubes and off we go as opposed to finding someone who thinks they know what they're doing.

Thanks for any feedback.

Orion
 

E9Guy

New Member
Jun 28, 2019
5
0
1
43
#27
Don't forget to check the fuses. There are 4 PS rail fuses on the main board, 1 each on the 4 ouput boards on the sides of the amp and there's also 1 line fuse behind the front panel.
Thanks Barry.
All the fuses are visibly intact. Would tired tubes cause what I described?

Thanks again
 
May 20, 2016
82
4
8
Torino - Italy
#29
I tried many tubes in my NP220 (2006 version). I finally ended with Sylvania VT-231 WWII version.
They are not the best of the best, Tungsol of the same era have slightly better extension at extremes, Ken-Rad VT-231 have more bass and so on... but the Sylvania in my opinion are very well balanced overall. Excellent detail; nice sound presentation, good focus; not harsh in the mid-highs... so I'm sure that they are a respectable choice.
About rectifiers my favourite are EZ80 or EZ81 German made RFT; they are also cheap on ebay.
I strongly recommend a technical check to your unit; you have surely read this thread so it will be better to verify set-up values of bias, channel balance and DCoffset in a laboratory
 
Likes: E9Guy

E9Guy

New Member
Jun 28, 2019
5
0
1
43
#30
I tried many tubes in my NP220 (2006 version). I finally ended with Sylvania VT-231 WWII version.
They are not the best of the best, Tungsol of the same era have slightly better extension at extremes, Ken-Rad VT-231 have more bass and so on... but the Sylvania in my opinion are very well balanced overall. Excellent detail; nice sound presentation, good focus; not harsh in the mid-highs... so I'm sure that they are a respectable choice.
About rectifiers my favourite are EZ80 or EZ81 German made RFT; they are also cheap on ebay.
I strongly recommend a technical check to your unit; you have surely read this thread so it will be better to verify set-up values of bias, channel balance and DCoffset in a laboratory
Thanks for your reply. Yes, I do plan on having it checked out and bringing a fresh set of matched tubes to go with. And probably print out this thread for service reference as it's the most informative I've come upon in all my searching. Sorry folks, didn't mean hijack the thread.
 
May 20, 2016
82
4
8
Torino - Italy
#33
just a little update. since I find that my NP220 after the upgrade of a new Plitron custom transformer and new Nichicon superthrough condenser was running too hot (50 degrees celsius measured on heatsinks) I take the amp back to the technician, he decided for a more conservative low bias overall (among 38 mv), also DCO and balance predriver values are correct; now the amp running cooler.
Neverthless I find that now the sound is not so dynamic and prompt as before. It's a subtle difference, neverthless audible; I listenend to many discs and I feel that when the amp had a bias value higher (it was around 45 mv that is also far from the goal of 50 mv) it was better performing.
I'm asking if there's a relation in SS amps concerning sound performance and bias calibration...:rolleyes:
 

About us

  • What’s Best Forum is THE forum for high end audio, product reviews, advice and sharing experiences on the best of everything else. A place where audiophiles and audio companies discuss existing and new audio products, music servers, music streamers and computer audio, digital to audio convertors (DACS), turntables, phono stages, cartridges, reel to reel, speakers, headphones, tube amplifiers and solid state amplification. Founded in 2010 What's Best Forum invites intelligent and courteous people of all interests and backgrounds to describe and discuss the best of everything. From beginners to life-long hobbyists to industry professionals we enjoy learning about new things and meeting new people and participating in spirited debates.

Quick Navigation

User Menu

Steve Williams
Site Founder | Site Owner | Administrator
Ron Resnick
Site Co-Owner | Administrator
Julian (The Fixer)
Website Build | Marketing Managersing