Update the Sonab 4000

Hi Guys,

Here's the improvements I'm thinking of:
Replace Output transistors, electro & tantalum caps,
Remove protection circuitry,
ac bypass bias chain with a cap, 47uF?

Some Q's: Is the diode on the - input of the LTP necessary?
Are all the HF roll-off caps necessary? or is this symptomatic of dodgy layout? (C704 at 2200pf seems high?)

Any other suggestions, or should I forget it and use the case/ps/heatsinks for something more modern?

Thanks,
Pete McK
 

Attachments

  • sonabsm.jpg
    sonabsm.jpg
    92 KB · Views: 483
Pete,
I have an R4000-3. I was never reallly happy with the sound of it.
The preamp sounded a bit dull and the poweramp sounded, I don't know....brittle. And no, the combination did not complement
one another.
All I did to it was to upgrade the caps in the PS and put some local
decoupling on each poweramp. And changed the wiring from the
PS to the power sections.
I don't think youd benefit much from modifications.
Just keep it for the really cool design, that's what I did.

/ Mattias
 
Hi Mattias,

The preamp in mine is stuffed, but I'm not going to use it anyway;
I wired inputs straight into the main amps, and they work fine, and have more than enough power for me (enough to fill the back yard & annoy the neighbours :). They do have a bit of an edgy sound though.
I'm only going to use them for driving woofers (< 250Hz), so I think they'll be OK as is.
Cheers,
Pete McK
 

myglaren

Member
2007-12-15 6:29 pm
Hi,
I'm just looking at purchasing a Sonab 4000, more out of curiosity and nostalgia than any expectation of audiophile bliss.

I lived in Sweden when these things came out and always lusted after them but never had the cash. One has jus come up on eBay and I'm tempted. I have a Sonab 75s turntable that I bought in 1971 and it would be nice to pair them up.

There were as I recall 2 amps offered, the first was built by Cambridge Audio in the UK and the second, better one (that looked like it belonged in a tank) was made by Yamaha, as was the turntable I own.
 
Sonab kit

Hello there!
Just discovered and signed up on this site! Interestingly I also have a sonab 75s turntable, I understand its a Yamaha tweaked to European specs with a different (Swedish?) tonearm. Got it off ebay couple of years back. Its a great sounding machine! Am thinking of getting new cartridge for it. Any idea of one which will work well with it? Am no techie, just love the design and sound of those 60s and 70s turntables.
Am interested in the P4000 amp that you posted on, looks a bit like an old audiolab, have no idea what it sounds like though or how much its worth, does anyone out there know? Ive seen one advertised recently and the guy asked me to make an offer, am tempted if it aint too much.:xeye:
 
You sure it's a 75S? I found only a 85S.

Anyway, looking at the 85S , you can use any cartridge with it, the arm is probably medium mass, so any MM (moving magnet) cartridge will work nicely. If you want to stay on a tight budget, try the Audio-Technica AT 95 E.

Have fun, Hannes