Leak Stereo 20

I have moved to the 8R taps, bass a little flabby(er) on 16. It took a visitor for me to listen critically enough to care. Also moved the speakers about 2 inches.

Ground loops were certainly an issue, now resolved thankfully (without doing anything foolish).

As for valves, Mullards still probably my preference but the EI ECC83 works well as do the 6P14P ERs in place of the EL84s and I can happily live with them as a cheaper alternative.

 

I'll have to reread this all. My Leak is being collected on Sunday (exciting). I've already ordered in some valves ready, including an EI and Mulllard ECC83.

 

Is it sensible to use an ECC82 as the input valve to reduce gain instead of the usual ECC83? I was advised to try this today but wondered if anyone knows definitively?

 

@Tony L

OK thanks Tony. Actually, I just found a thread from 2012 where @Robert and @Arkless Electronics were advising you on this same question.

I was just curious after Deco Audio suggested trying it earlier today. I’ve been asking them about doing some mods to my Croft 25 (with cathode follower mod) which I’ve been using with my Leak. They’re going to add a ground lift switch to the Croft so I can put the earth wire back in the Leak mains lead, and will also rewire the mute switch to be a mono switch.

Perhaps surprisingly, the high-sensitivity Leak 20 and high-sensitivity Klipsch Cornwalls don’t produce too much background noise but I was wondering how to make it even better.

 

There was a long thread on Audiokarma that came up with this ECC82/12AU7 schematic:


And Lilienthal Engineering came up with a suggestion too:
http://lilienthalengineering.com/wp-content/uploads/LEAK-ST-20-modification-1.png

hmmm - the image has disappeared! I could try again if anyone is interested.

 

Changing the '83 to a '82 will only reduce the open loop gain.
However the closed loop gain is mostly defined by the negative feedback so you'll be hard pushed to notice any difference.
The feedback will be less so the distortion will go up.
That Lilienthal circuit is very silly as with lower gain you'll end up with poor bass as the NFB will struggle to keep anything there.
The way to reduce gain is to increase the NFB, but if done alone will cause the amp to become unstable, so you have to reduce the open loop gain also.

 

Those mods look like a recipe for low frequency instability too.

 

What about soldering a higher value resistor across the input to bring down the sensitivity to around 500mV? Would this alter the impedance figure?

 

I’m still waiting to hear back from Deco about mine. Did they give you any indication about waiting times?

regards

Kevin

 

I've started reading through this all. I am realising how high gain it is and it reads as if it will be zero to superhero loud!

Mine arrives on Sun and will be paired with a NVA P50SA MKII passive pre. Should I be plugging in some attenuators before I fire it up the first time? My speakers, whilst I think will be a great match, and pretty efficient at 90db and easy load, are also not cheap and I don't want to damage them (perhaps an unfounded concern).

 

@Amormusic

Don’t worry about, it’s not no big deal. Relax man.

 

ok, so the Audiokarma circuit I messed up loading last time is this:

No idea if it makes any sense - I can’t find the thread anymore, but there was lots of scoping and stuff going on IIRC. Interesting to see what you fellows make of it.

 

Definitely you don't need or want attenuators with a passive.

 

Can someone please explain the ST20s characteristics - output impedance, hopefully high - damping factor, hopefully low - feedback, hopefully zero.

The next grand plan will involve TT (I have ideas there) and speakers. I really like what widebanders do and do like the Zu Druids but I’m looking at the Cube Audio Nenuphar Mini that would apparently prefer the above amp characteristics. (Sadly I just can’t accommodate wide speakers).

TIA

 

Thanks Tony, absolutely, the amp’s a keeper, narrow-ish baffle, room filling-ish speakers to go with it is what I’m looking at. Happy with the Druids for now.

 

Tony, don’t want to derail this into a speaker thread, I’ll drop you a PM at some future point if that’s okay.