Bob Cordell Interview: Error Correction

[mikeks]

Has anyone got a copy of the Tandberg schematic?

 

[TOINO]

Relevant Part of TPA-3006. The only I have...
The image size imposed by this forum is a great communication obstacle and a real pain.
The time I lose trying to compress is very discouraging…

 

[TOINO]

The missing information:

Wire marked 0V is the output line.
Q230//Q231 are the drivers of two pairs of S-follower 2SK175/2SJ55 with 680ohm gate resistor(2SK) and 390ohm gate(2SJ).
Looks like a kind of Hawksford EC ...

 

[TOINO]

 

[mikeks]

Hi Toino,

Check your mail.

 

[mikeks]

Looks like a kind of Hawksford EC ...

A poor form of HEC.

By the way, Coimbra is a very beautiful city!

 

[TOINO]

 

[Fanuc]

A poor form of HEC.

By the way, Coimbra is a very beautiful city!

Would you say this is worse than Bob's implementation ?

 

[mikeks]

Yes.

 

[TOINO]

Locks like they take of components, one by one from Bob circuit, at the point it stops to work.
Than they have putted the last one again in their place.

 

[Fanuc]

Yes.

Thanks for the tip.

I think I will try get the Meyer Sound MS1000 schematics instead then. Bob mentions this amp up north somewhere.

Maybe later tandberg amplifiers had better EC system. Am waiting for a new workbench to be fitted and will start knocking some circuits up.

Kevin

 

[jacco vermeulen]

Relevant Part of TPA-3006.

As good as identical to that of the Tandberg 3009A Power Amp

 

[lumanauw]

Hi, Jacco,

How does this Tandberg 3006 sounds?

 

[jacco vermeulen]

Good one,

remarkably well for a low bias mosfet amp in those years, i did not understand why untill i read Mr Cordell's paper. The high priced TPA-3016A out-tricked a P-300V in the late 80s, imho.
A big Hitachi TO3 Mosfet amp like a Perreaux PMF series did not give me the shivers either, but the Hot Kiwi output stage operated at a high class A level, up to 25-30W (fttomh)
(naturally my preference was for the equally expensive Threshold SA/3, me don't need no 200 watts)

 

[mikeks]

I think I will try get the Meyer Sound MS1000 schematics instead then.

Here:

http://www.diyaudio.com/forums/showthread.php?postid=1108768#post1108768

 

[forr]

Mikeks,
---Has anyone got a copy of the Tandberg schematic?---

In case of need : there was a short article published in Electronics World where a Cherry's scheme, one of the first John Curl's amplifier and a Tandberg Error Correction scheme were shown. I can provide a copy.

 

[mikeks]

Hi Forr,

You have mail.

 

[Bob Cordell]

Relevant Part of TPA-3006. The only I have...
The image size imposed by this forum is a great communication obstacle and a real pain.
The time I lose trying to compress is very discouraging…

This is probably a decent implementation of HEC, but I think it would perform better if the VAS was buffered from the HEC circuit. Also notice that the collector of the EF that follows the HEC summing node (Q224/Q225) is not bootstrapped to signal, but returned to the power supply, so it must be a HV transistor and its ccb will create some nonlinearity. Nice that they regulate the rails to the input and driver circuits, and nice that they cascode the VAS.

Cheers,
Bob

 

[TOINO]

Just a small curiosity:
Believing in this information here http://www.nrhf.no/t-TPA-3006A.html the amplifier is from 1984 which is the publication year of Mr. Cordell paper on AES http://www.cordellaudio.com/poweramp/mosfet.shtml

 

[mikeks]

This is probably a decent implementation of HEC....

On the contrary, because it relies on resistively loading down the transimpedance stage for correct operation, this is a sub-optimal implementation.