advertisement


The unlikely star-candidate - Linn LK-100

Sziklai stages have one great merit - thermal stability; the temperature of the main transistors hardly matters, and it is easy to tie the drivers to the VBE circuit.

The use of 2 VBE of bias means the output stage will be mildly underbiased; replacing one of the 220R resitors with a trimmer would let you adjust it to correct operation. At least there is a correct bias point, unlike the Naim circuit which wants different bias settings for the two sides.

The main drawback is that they can be unstable going into clipping. This is less of problem in this design; the regulated front end voltage (30V) is so much less than the output rail, that it will not clip the output transistors in normal operation. There is a fix for this instability - you add base stopper resistors on the output transistors.
 
martin clark said:
Heavily compensated was really my point; C203/R207 straps things down at 270Khz, presumably because the miller cap isn't enough on its own - or a larger miller cap causes some other problem. It just looks like a patch for something else.
Click to expand...
Two pole compensation allows greater feedback at higher frequencies?

The drivers are three surface mount transistors using PCB area for heatsinking, the bias generator is an example of the same transistor mounted adjacent. This quite possible tracks better than the common arrangement of dissimilar transistors for bias/driver output. No adjustments is good.

This circuit is clearly a direct (albeit somewhat simplified) descendant of the first LK2/LK280 amps. From memory you could make it 'Selfish' with an emitter follower in front of the Vas, a capacitor across the bias generator and a mess with the output compensation. I guess he'd not have bothered with the front end regulation either. Compared to a Naim it's a paragon.

I think it needs proper measuring before proper criticism. I have one which I thought was only worth £100 or so, so I'm quite pleased... But I'm prepared to abuse it in the search for data.

Paul
 
Paul R said:
Two pole compensation allows greater feedback at higher frequencies?

The drivers are three surface mount transistors using PCB area for heatsinking, the bias generator is an example of the same transistor mounted adjacent. This quite possible tracks better than the common arrangement of dissimilar transistors for bias/driver output. No adjustments is good.

This circuit is clearly a direct (albeit somewhat simplified) descendant of the first LK2/LK280 amps. From memory you could make it 'Selfish' with an emitter follower in front of the Vas, a capacitor across the bias generator and a mess with the output compensation. I guess he'd not have bothered with the front end regulation either. Compared to a Naim it's a paragon.

I think it needs proper measuring before proper criticism. I have one which I thought was only worth £100 or so, so I'm quite pleased... But I'm prepared to abuse it in the search for data.

Paul
Click to expand...

Sounds like a good plan to me, it certainly deserves a better welcome than it did receive here ;)
Yair
 
PigletsDad said:
Sziklai stages have one great merit - thermal stability; the temperature of the main transistors hardly matters, and it is easy to tie the drivers to the VBE circuit.
Click to expand...


For the Sziklai circuit to be thermally stable, the 12 ohm emitter degeneration resistors would have to go and then there could only be one driver transistor as you cannot current share properly with no emitter resistors. My guess is that they under biased it into class B as it was not thermally stable, the collector load resistance of 0.47 Ohms points to this as its normally less than that at around 0.22Ohms.
 
I gave it to a friend for a listen, he wont give it back, so It's on hold :D
 
No short circuit/overload protection on this schematic, so either there's another board or this one is dangerous to your speakers.
 
THX for the inspiration. :D

Sadly there are very few doing mods to scottish amps. Linniacs fear modding,
many DIYer don't like Linn gear. Several sites covering Naim mods show the
way though.

This has beeen one of the starting points to think about decreasing value of
C1 and increase C2/C20 - measurements of the der LK260 on the Vintage-
Radio-Forum:

Left Channel:

Frequency response, -3 dB points: < 10 Hz and 37 kHz
Frequency response, -1 dB points: 18 Hz and 17.8 kHz
Frequency response, -0.5 dB points: 25.0 Hz and 12.0 kHz
Distortion: 0.012%
100 Hz spikes visible on output with no signal

Right Channel:

Frequency response, -3 dB points: < 10 Hz and 38 kHz
Frequency response, -1 dB points: 17.5 Hz and 19.0 kHz
Frequency response, -0.5 dB points: 24.0 Hz and 13.0 kHz
Distortion: 0.04%
100 Hz spikes visible on output with no signal
Click to expand...

... and on Stereophile of the LK280, slightly better:

At a 1V output level, the '280 was ostensibly flat throughout most of the audio band, though
there was a slight droop at the edges, the response being 0.75dB down at 21Hz and 20kHz.
Click to expand...

Measurements will be probably better after mod. ;)


16217689ht.jpg


16217585wa.jpg


16217587qt.jpg


16217780ee.jpg


Linn LK2 Service Manual free download,schematics,datasheets,eeprom bins,pcb,repair info for test equipment and electronics

LK260:

Linn LK2 power amplifier - UK Vintage Radio Repair and Restoration Discussion Forum

http://www.diyaudio.com/forums/solid-state/106226-tweaking-classic-linn-lk1-lk2-lk280.html



I'd strongly recommend to do these mods to any owner of a LK2/60:

- do the Reliability Mods (R33 und R49 > 2 W, C6 & C19, see below)
- heatsinks for Q10, Q11 und Q14 (the still get hot)
- evtl. heatsinks for LM317/337
- add the two 100 µF, the LK2/75 comes with
- renew several lytics, e.g. Pana FC, Silmic or Nichicon Muse
- consider to renew the big lytics, go for 10.000 µF
- if you remove the transformers and put them in an external case, you'd gain spce for additional capacitance
- swap C5, C6 & C19 for Micas
- decrease C1 to 2.2 nF, C2/20 > 330 µF + MKP (e.g. 150 nF)

Hope I didn't miss anything.



Does it sound better?

It does. :D

The modded LK260 plays more authoritively, quicker and more dynamicly. The
former "british Sounding" has gone. If you like the old british day, don't do it.
If you like music and realism - do it !!
Probably there are more modifcations you could do, but there's already more
air and a deeper basement. I can listen to Marcus Millers Bass lines better.

I have to say I already have put the transformers into an external case
(similar to "Spark").
Hard to understand why Linn chose C1 that big and C2/20 so small. I cannot
understand also why there are no heatsinks for Q10/11/14. Even with small
copper HS they still get 55° - 60° C hot. No wonder they melt the styrenes.
R49 also still gets hot. This one is prone to burn as it's just two 1/4 W types
from factory.

As stated the later Klout and LK100 etc. have similar circuits. The Klout is a
LK280 in a more beautiful chassis and DC servo, the LK100 has a simple PSU
and lacks dual mono design. Likely LK240 monos are similar. The later LK85/140
are not though.
 
As the only easily accessible power amp in the house I retrieved my old LK100 from the loft and connected it to a very recently acquired pair of Quad ELS57. I remembered this thread and looked it up to see what maximum voltage one could expect from an LK100.

It appears to be an ideal match and in practice seems to work really rather well.

The plan is to take the Quads to the Hifi Wigwam show at Scalford Hall in March. It would be completely rational to use a Linn amp.

Paul
 
Dit you ever finsh your star Candidate? , I also dit buy a LK100 whit a Fisher Trafo.

I wil place new mundorf MLytic caps.
Maybe some ideas i found out here to look futher in to that. Thats wy i like to now how went for you.

I also know it's a long time a go , but i'm curius.
 
Lars, definitely do C201 (input low-pass filter, 2.2 nF).
Any value between 330 pF and 1 nF will audibly improve upper treble response.
I used Wima FKP3 on my LK2s.
 
ticktock2 said:
Lars, definitely do C201 (input low-pass filter, 2.2 nF).
Any value between 330 pF and 1 nF will audibly improve upper treble response.
I used Wima FKP3 on my LK2s.
Click to expand...

C201 / I wanne try to replace it whit as Wima 470pF.

I hope i't not to high? I hope response will get better.

And replace it with 2x 10.000 Mundorf MLytic Caps.

C212 / C213 - With small 100UF condensators by same size and Value. (The better Pannesonic condensators)

C204 - C205 The will be untouchd. I'm not gonne change them for other size i think.



Thats the plan so far.
 
470 pF will certainly be fine. You'll notice the difference especially on cymbals.
The huge Mlytics probably improve bass impact.
For the smaller lytics I'd recommend Panasonic FR - even better than FC and FM.
 
ticktock2 said:
470 pF will certainly be fine. You'll notice the difference especially on cymbals.
The huge Mlytics probably improve bass impact.
For the smaller lytics I'd recommend Panasonic FR - even better than FC and FM.
Click to expand...

I have also MLytics in miy Majik-I (LK case version) from 1997.
2x 15.000UF that improved the bass impact en especialy Majik could use extra.

Back to my LK100...

I expect to MLytics also improve the bass impact als treblle. Same size i expect to bult in 2x 10.000uF

And that are panansonic series i got ,
FC and FM series if got from the internet today.
 
You must log in or register to reply here.


advertisement


Back
Top