Counterpoint NP220s

Barry

Member Sponsor
Jan 8, 2012
222
12
18
Somewhere near Philadelphia, USA
#1
Not much going on here so I thought I'd spice things up with pictures of two NP220 Platinum Plus amps with every option possible and then some. These custom hybrid amps are beautiful sounding and take on the character of whatever tubes are in the front end voltage gain stage. In this case both use Mullard ECC35 CV569s. From rough count on the Aria website I think only about 60 of these NP series were ever made in any configuration ranging from Basic to Platinum and a lot ended up in Asia.

The first, black panel one (bottom pic), was originally an SA20 upgraded to Basic back in 1999 and successively upgraded over the years to Platinum by Counterpoint. It turned out to have a bad circuit board which was replaced along with more modifications and was one of the last jobs Dai Phan did for Mike in early 2012. It was the most extensively custom amp Aria ever produced. I never cared much for the Dynamicaps so I substituted CuTF coupling V-Caps instead and the PS has 16 10K uF Black Gates 'lytics - $4K worth.

Since I bi-amp Magnepan 3.6s, I bought a second amp (top pic) in late 2012 after Aria closed and had it upgraded by Music Technology as closely as possible to the other except I changed the pre-driver voicing resistors for just a bit warmer sound. The PS caps here are the legendary Siemens Sikorels.

One of the big surprises and improvements in the sound as you "scaled up" from the Basic model was a result of the increasing use of Texas Component TX 2575 resistors starting from 16 to over 60. These dramatically increase the transparency and let the true glory of the tube front end shine through.

I can't describe how wonderful these amps sound but they are truly special! The sound's the best of both worlds. They have all the best immediacy, spacial, tonal color, solidity, and textural characteristics of tube amps with good leading edge definition, tremendous bass impact, and huge power output of solid state.
 

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Likes: E9Guy

Barry

Member Sponsor
Jan 8, 2012
222
12
18
Somewhere near Philadelphia, USA
#2
Having handpicked every part in these amps in consultation with Michael Elliott, the designer, I thought I had reached the end of the road in sonic performance....

While I had tube rolled the pair of ECC35 input tubes in the front end voltage gain stage years ago, I never tried different tube rectifiers in the separate power supply that drives them until now. The substitution of an RFT EZ80 tube markedly improved the solidity and texture of recorded voices and instrumental images for much more in-room presence with a little more sound stage spaciousness too. These tubes were a favorite of many Counterpoint owners back in the company's heyday and are worth trying if you have any equipment that can use them. Oh and they're cheap too; less than $20.

Other interesting features of these amps are the use of thick wool felt damping material to prevent circuit board resonances, option of balanced or single-ended inputs, and a unique Plitron toroidal choke for filtering of the input stage.

The sum of these design and parts choices is a pair of beautifully, natural-sounding amplifiers that make listening to music an experience you really look forward to.
 
Likes: E9Guy
Apr 26, 2015
18
1
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#3
Glad to have found this post. I own several NP amps and I happen to have serviced quite a number over the years I finally got to try a pair of ECC34s in place of my trusty CBS5692 in my low gain NP220. I have modified the B+ to be about 280v and the ECC34s dropped in w plate voltage at 140 which couldn’t be better. I am sure the filament current from the Plitron is good enough so I let them run for a while. Initial impressions is that this is by far the best tube that ever graced the NP220. (Mine are 34s not 35s which I have never come across)
 
Apr 26, 2015
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#5
Ever tried Elna Silmic2 lytic caps for bypass on the daughter boards replacing the KZs?

Nice to hear from you! I think we have crossed paths before on these amps.
I heard they are better than Nichicon in every way. Only reliable source is Digikey. All the Ebay ones are fake.
Also I want to ask about the tubes B+ bypass caps. I see a light blue colored cap on each side
Are they some sort of orange drop small value like 1uF in blue color?
In my premium gold it's actually a small black gate lytic.
 
May 20, 2016
81
4
8
Torino - Italy
#6
Nice to see that Counterpoint NP-220 upgraded by Altavista are still considered competitive with high level class power amps.
Mine is a premium upgrade only with some further options (choke filter input, XLR connections etc.); with Sylvania VT-231 (6SNT WWII); unfortunatly the rectifier is a 6BW4 and I can't make tube rolling or substitutes.
I suppose that the only way to go to other rectifiers (EZ-80 or similar) is to take the amp in a laboratory to make modifications in two pins; furthermore mine unit does not have Plitron transformer and the power supply filter condenser are the original blue ones (Sprague?), maybe it's time to update them.
sometimes I'm also dreaming to change my Counterpoint with a modern brand (Dartzeel? Boulder?) but I'm reluctant...
my two cents
Marco
Turin-Italy
 
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Barry

Member Sponsor
Jan 8, 2012
222
12
18
Somewhere near Philadelphia, USA
#7
Mine is a premium upgrade only with some further options (choke filter input, XLR connections etc.); with Sylvania VT-231 (6SNT WWII); unfortunately the rectifier is a 6BW4 and I can't make tube rolling or substitutes.
I suppose that the only way to go to other rectifiers (EZ-80 or similar) is to take the amp in a laboratory to make modifications in two pins; furthermore mine unit does not have Plitron transformer and the power supply filter condenser are the original blue ones (Sprague?), maybe it's time to update them.
Hi Marco. Many people like the 6BW4 rectifiers. There's an old thread over at Audio Asylum "Tubes" on how to check do the conversion to allow use of other rectifiers and it should be inexpensive to have someone do it.

You might still be able to custom order the big toroid transformer (power rating 897 VA) and wiring diagram from Plitron in Canada by e-mailing their customer service. It was their part # 7085-X0-02, Date Code F:60. I paid $500 back in 2013. It weights 11.5 Kg, so not sure what it would cost to ship to Italy. It'd take about 3-4 months to make.

Not sure how these amps stack up against the latest and greatest. I considered buying ARC Reference 150 amps, but wasn't sure I liked them better. The price difference was significant in favor of the NP220.

Have fun.
 
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Barry

Member Sponsor
Jan 8, 2012
222
12
18
Somewhere near Philadelphia, USA
#8
I heard they are better than Nichicon in every way. Only reliable source is Digikey. All the Ebay ones are fake.
Also I want to ask about the tubes B+ bypass caps. I see a light blue colored cap on each side
Are they some sort of orange drop small value like 1uF in blue color?
In my premium gold it's actually a small black gate lytic.
Originally, I had all Black Gates bypasses on the daughter boards until the main circuit board developed a short and took one of them out. I use the Silmic 2s in my crossover network and as output caps in my CD player and like them but Mike wanted to use the KZs when he repaired the amp. As to the B+ caps, Alta Vista originally used Axon 1uF PP 250V caps here. Later they went to the blue ones (Says MF 250Vs on the cap, but you may be right).

At this point, I'm not doing any more upgrades to the amps. I've got the schematics, but some of the work is technically beyond me since servicing and changes require taking the whole amp apart and the only tech who can do it has avery long turnaround time. Too bad for me you're in SF Bay area.
 
Apr 26, 2015
18
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#9
If you don’t want to pull the motherboard to rewire for other rectifiers you can always change chokes to your liking. Similar “sag” effect. Ask the guitar people. I recommend you try Hammond 158L 158M for starters if you don’t have the mega $$$ plitron choke. They change the B+’a wee bit so it alters the operating point of the 6sn7 too. But what you will hear is “fast” vs “syrupy”.
 

johnsonlwu

New Member
Apr 26, 2015
18
1
3
#11
There are some rectifier tube conversion piggyback sockets for sale

Hi Marco. Many people like the 6BW4 rectifiers. There's an old thread over at Audio Asylum "Tubes" on how to check do the conversion to allow use of other rectifiers and it should be inexpensive to have someone do it.

You might still be able to custom order the big toroid transformer (power rating 897 VA) and wiring diagram from Plitron in Canada by e-mailing their customer service. It was their part # 7085-X0-02, Date Code F:60. I paid $500 back in 2013. It weights 11.5 Kg, so not sure what it would cost to ship to Italy. It'd take about 3-4 months to make.

Not sure how these amps stack up against the latest and greatest. I considered buying ARC Reference 150 amps, but wasn't sure I liked them better. The price difference was significant in favor of the NP220.

Have fun.
On Ebay, can be interesting. I used it to try out ECC99 and 6FQ7 on my NP220. Never tried it on the EZ81/6CA4 socket. I dont think they have one yet though.

https://www.ebay.com/sch/i.html?_fr...verter.TRS0&_nkw=6ca4+tube+converter&_sacat=0
 
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Apr 26, 2015
18
1
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#12
Barry

I am curious if you have tried to match the B+ going into the tubes on both units.
In my unit the unregulated B+ is 255V, regulated to 240V at the top of the plate resistors.
My schematics from Mike says target 315 (see pic). I have serviced a few units, none of them had Plitron chokes and all the B+ measured between 255-265 before regulation.
Are yours this way too?


Bplus.jpg
 

Barry

Member Sponsor
Jan 8, 2012
222
12
18
Somewhere near Philadelphia, USA
#13
I am curious if you have tried to match the B+ going into the tubes on both units.
In my unit the unregulated B+ is 255V, regulated to 240V at the top of the plate resistors.
My schematics from Mike says target 315 (see pic). I have serviced a few units, none of them had Plitron chokes and all the B+ measured between 255-265 before regulation.
Are yours this way too?
I have never measured the tube PS B+ voltages. I suspect your measured values for the tube B+ regulated, and unregulated, are more accurate than the schematics (Mine are the same as yours dated August 28, 2001 and show the "315V target" and "+350V" at the top of the plate resistors).

What might be helpful info is that when I asked Mike about the tube plate voltage back in 2009, he stated in an e-mail, " 250VDC is the maximum that the supply can put on the plate if the tube was cold, but once the tube is warm the normal operating plate voltage is about half that. Of course as you know, according to the schematic, the plate resistors are 250K for 6SL7's I'm using, versus 33.2K for the 6SN7's.

Hope this is helpful. If I can get around to measuring this I will let you know.
 
Apr 26, 2015
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#14
Thanks... figure as much

Very helpful info thx! Now I know it's probably a typo in the manuals.
Indeed it is 250 when tube is cold and once it draws it goes down to about 130.
I tweaked the LC stage on mine a bit to get 280/140 by using 2 smaller inductors with 50uF oil cans and it improved the sound by a wee bit all around.
Never was I able to get to 315 at any test point.
Spice simulation of this diff-amp config does show that the 6SN7 works better with a higher B+.

I have never measured the tube PS B+ voltages. I suspect your measured values for the tube B+ regulated, and unregulated, are more accurate than the schematics (Mine are the same as yours dated August 28, 2001 and show the "315V target" and "+350V" at the top of the plate resistors).

What might be helpful info is that when I asked Mike about the tube plate voltage back in 2009, he stated in an e-mail, " 250VDC is the maximum that the supply can put on the plate if the tube was cold, but once the tube is warm the normal operating plate voltage is about half that. Of course as you know, according to the schematic, the plate resistors are 250K for 6SL7's I'm using, versus 33.2K for the 6SN7's.

Hope this is helpful. If I can get around to measuring this I will let you know.
 
May 20, 2016
81
4
8
Torino - Italy
#15
My question is particularly to johnsonlwu and Barry that knows very well these units.
In the perspective of replacing the four great electrolitic capacitor placed close to the large transformer of my unit .. do you know the exact value to find? (it's not visible without pulling them out of the amp).
Furthermore... which brand is preferable? Mike Elliott suggested and used the Nichicon KZ Muse, maybe also Elna Sylmic or Mundorf are good choices, but without knowing exact value I can't start any research.
My unit works fine, neverthless the manufacturing date is probably 1993 approx. so... 25 years old... this is enough I suspect.
please let me know if possible, thanks very much
Marco
 
Apr 26, 2015
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#16
output stage PS caps for NP220

Mike suggested KZs for the low voltage predriver stages.
For output stage use Nichicon KG Super Through (not gold tune) 22000uF 100V which are almost impossible to find.
ALL Gold Tunes and Superthroughs on Ebay are fakes.
Buy only from Mouser, Digikey, Michael Percy, or Partsconnexion.
You can also try Elna Silmic as long as they are > 10,000uF and > 100V as the rails are a good 72V per pole.
I have also had very good results with TDK Epcos but its on an NP100.
 
May 20, 2016
81
4
8
Torino - Italy
#17
Mike suggested KZs for the low voltage predriver stages.
For output stage use Nichicon KG Super Through (not gold tune) 22000uF 100V which are almost impossible to find.
ALL Gold Tunes and Superthroughs on Ebay are fakes.
Buy only from Mouser, Digikey, Michael Percy, or Partsconnexion.
You can also try Elna Silmic as long as they are > 10,000uF and > 100V as the rails are a good 72V per pole.
I have also had very good results with TDK Epcos but its on an NP100.
Thank you very much for the quick reply!
as I stated previously my NP-220 (premium level rebuild late 2006) still works fine, neverthless I'm looking in advance in the eventuality of potential upgrade or replacement.
my best
Marco
 
May 20, 2016
81
4
8
Torino - Italy
#18
Dear all
as I expected my NP220 is starting to have some strange faults; it sounds always nice but when I shut-out in off mode I hear a strange ffffffff and some little noise coming from the woofer speakers during at least one minute...
I suppose that it's due to the old electrolytic capacitors that are reaching the end of their life; capacitors of mine amp dates from 1993 (the premium upgrade was made in 2006).
So... first of all I decided to order a Plitron custom transformer and I'm looking for some Electrolytic replacement.
After a long research I found two options for each channel: Nichicon KG Super through 80V / 22000x2 or the Cornell-Dublier 75V / 25000x2 (these are exact value than actual mounted on mine). I'm hesitating since Nichicon are reputated superior neverthless I'll end for reducing the microfarad value for each channel of more than 10% and I suspect that it's a little bit too much.
Someone has some suggestions to tell me? thanks in advance!!!
my best
Marco
 
Apr 26, 2015
18
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#19
Hi Marco, it's the ripple current tolerance and ESR that counts.
Anything over 20000uF per phase will give you plenty oomph.
I like the Nichicons (they are used in my Premium Golds), and I have used EPCOS/TDK with good results on NP100 upgrades.
The woofers should never rumble when in standy mode (or ever). Are the speaker terminals measuring a DC offset also?
 
May 20, 2016
81
4
8
Torino - Italy
#20
Thank you for your advice!
I finally bought Nichicons super through (22000 microf / 80 V) and placed also the new Plitron custom transformer and one new pair of Cardas' speakers terminals.
My NP220 Premium has now received the service here in Torino by one skilled technician ("L' audiotecnico" he has a website) who knows some Elliott's amplifiers. He told me that remains some DC offset (positive-negative) no more than 100 mv at the terminals.
Coming back to my home I checked the unit for half an hour and noted that now the amplifiers is quite hotter than before; strange.
About sound I'll wait a few days in order to reach at least 40-50 hours working; later I'll report my impressions.
cheers
Marco
 

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