nytech ca252 woes

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Mmm, bought one of the above examples off ebay a few weeks ago, finally got round its various idiosyncrasies and got the thing running, something to do with bridging preamp and aux din sockets that where missing, sounded OK, 25 years taking its toll.... curiosity made me open the case, its a strange thing for sure!!!

After seeing the weird heatsinks and multiple cards, no ventilation whatsoever, I decided to modify it and bring it up to date with new caps and op trannies, then rehouse it all in an ally case, fine so far, then I thought i'd clean it up somewhat, fit decent sized heatsinks on the flipped amp boards and get rid of the tone control and tape inputs and pre amp outs, fit a stepped attentuator

this is where it all went slightly wrong!:D

I cant figure the tape /aux switch circuitry how it would work? firstly its on an output from the pre board, it has no connection to the phono stage, and seems to be linked to the tone control?

try getting a shematic !

:whazzat:

Might try connecting as originally intended one input RCA , to the mainboard phono input as the card was going to be removed anyway and bridge the tone pcb pins with a 100k resistor.

British hifi!

:D

Anyone got any info on this amp?
 
First of all:
The Nytech 252 is an absolute classic, a class for itself actually, and to modify it in the way you did or intend to is an insult! Please try to restore this device as it is, an idiosyncratic piece of british ingenuity and a part of british hifi history!

I do not remember any tone control and also my schematics do not show any. My schematics sheets (original drawn by Nytech Audio) do not show any, and I also remember that the CA-302 does not have any. Does your amp have a tuner also inbuildt?

Signals are routed from inputs (toggles) to the tape switch (another toggle).

Balance pot is before the line amp and the volume pot after (old type P1041-2)) and vol and bal following each other (new type P1041-3).

You can sensibly rework the amps by changing caps (amp output caps and others).


Before you change your amp to "a mess" please give it to me!

:devilr:
 
rocco gibralter said:
bought one of the above examples off ebay a few weeks ago
try getting a schematic !
British hifi!
Anyone got any info on this amp?

Nytech CA252 or Nytech CA 252
... and you did tell you DID SEARCH our forum, didn't you?
You must have when posting a new topic.
Was it the usual white lie we often do = not 100% true ;)

Now member forr has some guess about this amplifier SCHEMATIC
in this post
http://www.diyaudio.com/forums/showthread.php?postid=1551552#post1551552
Now, I have no idea, if forr is correct.
But you can have a look ;)

Lineup
 
Disabled Account
Joined 2008
Hangs head in shame :rolleyes: I know its british classic, I nearly bought one in 1982 but went for a.....NAD 3020, This was a sorry example that looked like it had been in an attic for decades so its not like i'm butchering a good one,

I know the one you mean its the ca252cta with active outputs built in tuner, this is just the amp version with power, aux/ disk and tape monitor buttons volume and balance which doubles as tape monitor

Anyway this is DIY Audio, tinkering, improving in out ever quest for the hifi nirvana!

I'll put it back..................:rolleyes:

I did look at previous threads and did a search on Nytech I swear!
 
when want to find something
here in diyaudio.com
we better do a 'site search' using www.google.com
I have found this is the most effective way to find here

I can not give you much hope to find anyone having schematic or service manua hare ion forum.
Anyway, my searching gave me this impression from pages I read:
This is one very good power amplifier .... Nytech CA 252

The actual search you enter at google, looks like this

Lineup ;)
Diy Amplifier projects & schematics (members only)

An externally hosted image should be here but it was not working when we last tested it.
 
lohk said:
'cause I do not have access to my website at the moment here are the schematics I have on a private site (open only for the next days)
http://klaus.hollinetz.at/nytech/NytechCA252.html
(scanned from original factory service copies)

enjoy

:) yes he will enjoy, lohk (Klaus aus Österreich)
he has waited several days now - for some helping angel :angel:
then comes along you - and not some angel
anyway, you have made his day now
and will go Straight to Heaven when you die
as some angel or not

Lineup

PS. I have saved copies of those images. For rocco.
In case he cant get them before you clean up your web files. DS.
:) http://lineupaudio.freehostia.com/forum/index.php :)
 
Thankyou very much Ihok :) now i can make some sense out of it! brilliant!!!

To be honest, The real reason i decided to mod the amp was....has anyone tried to get the tunnel shaped heatsinks back on the amp boards :bigeyes: its a nightmare, i heard the only way is to glue the nut and washer on to the trannies then the mica washers slip all over the place because of the thermal compound whilst you attempt to insert the two securing bolts!, not only this it serves as an oven to trap heat, prob the reason for the early reliability problems? definite room for improvement with more efficient heatsinks!!!

thanks again guys!



:)
 
Passive Mode

Hi All

How do you operate the CA252 is passive mode? It's been a very long time since I've listened to one of these amps and from what I can remember it was a noticeably warm sounding amplifier. Was there some sort of DIN connector required to be plugged into one of the DIN sockets? If so, does anyone know what needs to be connected to what?
Your help will be much appreciated.

Andy
 
Ah.....Ive modified mine But if I can remember you need to blank off the preamp din with a dummy connector ( short out the cons), Also the phono needs to be shorted, if using aux or tape..But dont take my word for the phono, A guy said this before I took out the phono boards..and the pre amp switching board and the switches.... and balance pot, and removing the tape loop, fitting rca jacks n decent speaker cons. A shootable offence!

ca252 is normal speaker wise, ie not active..unless you have..think the S version?

I'm still having trouble with slight overheating on full vol...balancing the inputs to the output after fitting bigger caps....But it sounds fan-tas-tic!:D
 
Andy..Any chance you could take some pics of the internals if you have a digital camera, Just i didnt, and would like a look at the orig config, esp the 0v loop, Cant figure out how Nytech got away with the way they wired the safety earth to the switches then to the psu without causing stray current, Ive got the ESP loop breaker.

Its one screw at the front middle underneith the amp to open, then the whole thing flips like a stapler!

No worries if you cant BTW! :)

Cheers m8!!
 
I've figured out the DIN plug thingy. I've basically looped the output back into the input and it's working fine.

Don't hang your head in shame over the changes you are doing. A classic it may be but when you open it up :bigeyes: Transformer next to the inputs, wiring going backwards, forwards and sideways, separte circuits boards all over the place and a dodgy switch that's probably worn out. In fact, it's a classic in how not to do things from an engineering point of view.

For reliability get rid of as many swiches, circuit boards and connectors in the signal path (which you've done) and solder everthing directly to where it's meant to connect to. Not a shootable offence in my opinion!

Are the caps you've changed the power supply caps or the output coupling caps? Cooling is inadequate anyway and I suspect that the components on the amplifier board are gently roasting as the ouput transistors warm up.:whazzat:

Are both channels at the same temperature? Best way is to leave it standing without music playing through it for an hour and measure the temperature with a probe in exactly the same spot on each channel. Even a slight variation is an indication that the bias levels may be different between channels and a multimeter may be necessary to check voltages around the circuit. I don't have a schematic so I can't say where yet.

I've noticed the earthing arrangements and yes, you've guessed it!
:bawling:
I'm a bit rusty on my engineering skills but is I remember rightly, there is no particualr reason why signal ground should be connected to mains ground. Signal ground should be single point anywhere wheres convenient. Mind you to be fair I don't hear any mains hum at all through my speakers due to an earth loop.
Having slated everything is wrong with the way the amplifier was constructed it does sound good though and I'm very pleased to have aquired it after about 20 years since I last heard it.
Andy
PS I will take some photos for you at the weekend and post them up for you.
 
Hi Andy, Glad you got it sorted out!

There quite sensitive to changes the ca252's the unfortunate thing for me was perhaps I went a bit gung ho with the mods and didnt document anything!:rolleyes: the input caps have been changed from 3300 to 6800, outs from 2200 to again 68's with 220uf coupling caps and new filter, bypass what have ye! Problems started when I took out the balance circuit, initially I just wired two 47k resistors on the preamp inputs this worked, then I did something else..cant remember which made it unstable, with 10mv bias there's not alot of room to play with, I suspect mine wasnt the best unit to start with, having had some replacement components over the years, Cant find anything fundamentally wrong, and god knows ive been over it several times, replaced o/p trannies resistors pre tranny etc as a matter of course, its got bigger (open) heatsinks and now lives in a larger ally case, both main amp boards measure the same and are even temp wise, upping the input R's slightly should solve the problem?!?!?

I have an idea I might have left off some 0v return from the orig spaghetti poss to do with said balance circ hence the photo idea!

Oh the other thing, they wired the inputs to the safety earth too if I remember, these things should hum like crazy...but they dont???

doesnt make sense!

cheers andy!!:)
 
Mmmm....what symptons are you experiencing? What can you hear? Changing the power supply caps to 6800uF ok. It's those outs that might be a problem. Never liked the idea of decoupling capacitors on the output. The trouble is that the amplifier is driving a complex load i.e. resistive and inductive and those output caps makes things even more complicated. I take it that putting larger output caps in was to improve the low frequency response?
What's the purpose of the 220uF cap and filter? I hope you haven't made the amplifier unstable. Ok the amp might not be an oscillator but you never know at some frequencies!
Mind you, having said all that about the output caps, they are outside the feedback loop and so may not be the real issue here.
Ok, going back to basics. Changing the output trannies....you need to be careful here. These are most definately inside the feedback loop and I remember when I was replacing blown output trannies (when I used to fix audio equipment to earn my crust) I had to be careful about the stability of the amp.
I'm not too sure what you mean by the balance circuit. What does it look like? This is where I'm getting confused now because I'm not sure what all those additional circuit boards are for. Ok the only thing left now is the changes you have done at the input. What could possibly cause problems here? And you do say this is where the problems started! I wonder if this could be input sensitivity or it could be earthing. Hmmmm now you got me thinking! ;)
 
Mmmm, I bought mine untested, Hooked it up, it sounded muffled so thought Ah! o/p trannies, replaced them with bd911 &12's slightly higher V..then discovered the pre shorting!:xeye: But to be fair they fell to bits when I removed them with 2 burnt mica washers so were probably no good anyway.

Contacted Zolt at heed audio about the bigger caps, he said go to 10,000uf on the power supply and outputs..AND DONT CHANGE THE RECTIFIER DIODES! might try 4x 4700uf's on the power end, i'm sure its gone slightly lazy compared to when it had the orig smaller caps.

Its working ok now, running cool, still some 0v earthing issues, slight hum on startup that fades after a few seconds then quiet, Might try moving the signal earth around some more at some point.

The balance circuit or tape loop removal made the biggest sonic difference,

From the inputs it went to two toggle switches, then to a cheapo 100k slider balance pot, This all had to go, Now two shielded wires from gold rca's go to the preamp inputs with 2x 47k resitors to compensate.
 
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