Author Topic: My new amp  (Read 22841 times)

Offline springcreek

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Re: My new amp
« Reply #60 on: January 15, 2014, 10:51:16 PM »
Thanks Zen

Didn't know there was that much feedback. Explains a lot.

Will see what adding the AB's will do. Craig C and Steven have both managed to get some real magic out of the Leak. Suspect if I don't stray too far from what they did I should be in the ballpark.

Would love to build a copy of Stevens 50 amp one day or maybe a push pull 45.

Cheers, Andy

Offline springcreek

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Re: My new amp
« Reply #61 on: January 16, 2014, 08:31:28 AM »
Zen

The guy I bought the Leak off in the UK deals in Leaks and Quads. He converts the Stereo 20 to triode as says he loves what it does. What do you think of doing this?

Cheers, Andy

Offline vitavoxdude

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Re: My new amp
« Reply #62 on: January 16, 2014, 10:13:15 AM »
 ;D If you are happy with what Craig and Steve  have achieved with a leak stereo 20 then replicate exactly what they done, simple!
V ;)
We all like different things so lets all agree to disagree and if any common ground is found then worship it.  Mine is the KD hence being present on this forum.

Offline zenelectro

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Re: My new amp
« Reply #63 on: January 16, 2014, 01:12:56 PM »
Zen

The guy I bought the Leak off in the UK deals in Leaks and Quads. He converts the Stereo 20 to triode as says he loves what it does. What do you think of doing this?

Cheers, Andy

Hi Andy,

The existing circuit is designed and optimized for Pentode operation (which has more gain).
It works with feedback wrapped around the whole thing to get low OP impedance / lower distortion.   

With Triode operation the power is around 1/2 of Pentode so you need to double up on OP tubes to get same power.
However, Triode operation is more linear, has lower distortion and OP impedance than Pentode.
As such the amp can run without any feedback - which nearly always sounds better - for a given parts quality.

The Leak cct design is pretty standard approach for the day, simple and worked very well being fairly tolerant of layout parts drift / quality.
To make major change the existing amp is not really recommended. I can certainly do it but OP power will 1/2 and it's a significant design change.   

However if the quest is the best sounding low (or high) power PP amp - then I think a better foundation to start with is definitely the triode / NFB approach.


cheers

Z

Offline springcreek

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Re: My new amp
« Reply #64 on: January 17, 2014, 08:12:38 AM »
Thanks for the advice guys. I will stick to the original circuit and make changes according to what Steven and Craig have done. Have orderd some Shinkoh's for critical spots and will order the rest of the Allen Bradleys soon.

Appreciate the input everyone has provided in this thread...will report back soon  ;D

Cheers

Offline zenelectro

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Re: My new amp
« Reply #65 on: January 17, 2014, 10:37:18 AM »
Thanks for the advice guys. I will stick to the original circuit and make changes according to what Steven and Craig have done. Have orderd some Shinkoh's for critical spots and will order the rest of the Allen Bradleys soon.

Appreciate the input everyone has provided in this thread...will report back soon  ;D

Cheers

No worries.

WRT 'critical' components - ref circuit diag below. IME these parts being part of the feedback loop itself always make a big difference to sound.

Anything you change 'inside' the feedback loop, the amp will try to null that change to a degree or make the change less.
The components circled will have a direct and profound influence.

As an example, I repaired / modded a 200W Marshall Major amp last year. The tone controls were inside the FB loop... very strange ??
The first thing I thought on listening to it, 'why don't the tone controls work properly'? Being inside the loop the amp is nullify their very operation.

Disconnected FB loop - much better sound (no esoteric parts required), tone controls work as they should. Owner V happy. :)
 
Z


Offline Jehuty

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Re: My new amp
« Reply #66 on: January 18, 2014, 12:32:48 AM »
Zen, I would like to try remove the local feedback cap (C9) completely. Would this be a problem?

Thanks,
William
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Offline stevenvalve

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Re: My new amp
« Reply #67 on: January 18, 2014, 01:33:14 AM »
William take out the 22K from the R2R and R2L positions, leave it out, but leave the 1M to ground and make it a shinkoh 2 watt tantalum.

Offline zenelectro

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Re: My new amp
« Reply #68 on: January 18, 2014, 01:35:41 AM »
Zen, I would like to try remove the local feedback cap (C9) completely. Would this be a problem?

Thanks,
William

Yep - could be. The amp may well oscillate if the cap is removed, or if not it may be less stable.

Unless you can check it with a CRO, I recommend leaving it there, just use a good qual film cap.
Wima FKP are not bad. If there are any Ceramic disc caps in the amp, I recommend replacing them. 

cheers

Z   

Offline zenelectro

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Re: My new amp
« Reply #69 on: January 18, 2014, 01:41:23 AM »
William take out the 22K from the R2R and R2L positions, leave it out, but leave the 1M to ground and make it a shinkoh 2 watt tantalum.

Yep, that's worth doing - it's also outside the FB loop.

Grid resistors used on fast tubes like 437A 417A etc to stop oscillation and RF issues. With 12AX7 not generally necessary.

Z

Offline Jehuty

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Re: My new amp
« Reply #70 on: January 18, 2014, 01:50:06 AM »
Great advice gents. Thanks heaps  :)
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Offline stevenvalve

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Re: My new amp
« Reply #71 on: January 24, 2014, 01:48:34 AM »
Having fun, Because the leak Stereo 20 found its way back home. The buyer sold it back to me (Crazy). I put it on straight away and was amazed at how good it sounded. So I decided to start working on it. The duelunds where removed when I sold it. I will decided later if they go back in, at the moment it uses 4 old NOS Mullard mustard caps, they are very good sounding. As you can see no posts on the back, Eichmann's are coming, I must say, the leak sounds incredible.
« Last Edit: January 24, 2014, 01:54:12 AM by stevenvalve »

Offline Jehuty

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Re: My new amp
« Reply #72 on: January 24, 2014, 02:36:22 AM »
We need to figure out how to extract more body and weight from the Leak. But I guess if the Leal is run with reel to reel setup we will have more body and weight.

Steve, forget the binding posts, just solder the speaker cable directly!  ;D
Not all that matters can be measured, not all that can be measured matters.

Offline springcreek

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Re: My new amp
« Reply #73 on: January 24, 2014, 08:22:57 AM »
Yes more body is what the Leak needs.

I have Eichmans on mine  ;D

Keen to get some Cu WBT's on the input.

Offline Jehuty

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Re: My new amp
« Reply #74 on: January 24, 2014, 12:53:27 PM »
I got this Cardas CCBP-s unplated pure copper as my binding posts: http://www.partsconnexion.com/product7444.html

I chose it over Eichmann because I think the Eichmann is a bit flimsy. I broke a couple already  >:(

I hope the Cardas sounds as good as the Eichmann.

Andy, the Cu WBT next gen is the one to get US$ 88: http://www.partsconnexion.com/product9725.html

There's another Cu WBT on sale US$ 39.95, could be pretty good and save you some bucks: http://www.partsconnexion.com/wbt0274cu.html

 ;D
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Offline springcreek

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Re: My new amp
« Reply #75 on: January 24, 2014, 01:39:10 PM »
Cool thanks William, nice looking posts.

I need three sets of next gens. One set for the Leak and two for my volume control....ouch!

Offline Jehuty

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Re: My new amp
« Reply #76 on: January 24, 2014, 02:11:27 PM »
Hi William

I like the Leak a lot. Still have Sovteks in it at the moment which are pretty awful. They are really limiting the magic. Also there has been a lot of changes to my system around the same time. I have new speaker cabinets (Shindo style cabinets that Damian made), new speaker wires (Auditorium 23 also from Damian), new turntable (Micro-seiki), new tonearm (Fidelity Research), new cartridge (Garrott P77i), and new phono stage (Graham Slee Reflex M).

I am getting a great result so far, but need to do some tuning as while the bass is very good I'd like it better still. Only minor really, but I'm hoping I can get it sorted. The results are a long way ahead of where I was before!  ;D

I will be replacing the front baffle (see pic) with a veneered one when funds allow.

Let me know how you go with the new speaker cabinets.

Cheers, Andy

Ps. To give some idea of scale the TV is 50 inches.
 
Pps. The Rainbow Diffusor is for sale at $500 a pop  :P

I finally got a chance to have a good listen to Andy's new system a couple of days ago.

As you can see in the attached pic, Andy's using a Shindo style cabinet where the back panel is half open. Beautiful cabinet! Thumbs up! To Damian, I'd like to order some cabinets and hifi racks please  ;D

During listening session, Andy covered his 55 inch LED TV with a blanket, wise move there as I usually find the reflection from the glass panel can be a bit distracting. What I like the most about his system is that how his system can convey music in the most musical way, gone are the edginess and brittleness of the modern hifi sound. People will say it's coloured but when the media and the so called expert hifi reviewers in general tell us that lean and analytical sounding is fcukin' ACCURATE  >:(  then I will choose coloured anytime anywhere.

I notice his system has all the fundamental attributes to be a great one such as sheer musicality, very engaging and organic, would love to have more harmonic richness, it's there but more would be better. No digital harshness I could detect anywhere. Some things that he needs to address are slight dryness and thinness. His system needs more body and weight. I believe he's got a few tricks up on his sleeves already with the help of our friend Duc in Melbourne  ;)

There's also a bit of smear in sound when he was playing bass heavy track. I could hear the vibration of the cabinets causing the smear and the sound became less focus. He's already got a pair of vintage Goodmans Sherwood cabinets to address this issue. I just hope the new cabinets will not thin out his system more. This is a very hard thing to get balance.

Andy, you've done very well there with your Goodmans Axiom 300 (great driver by the way!) and the Leak Stereo 20. Not far away from a great sounding system that we always crave. I personally can't wait to listen to your system again with the new upgrades on the way. I wish you all the best in your journey! Thanks so much for a nice listening session, man I stayed there for 3 hours and it simply felt like 10 minutes at most, I guess that what usually happens when an engaging and musical system is presented, just like when I first listened to stevenvalve's system in the mountains.

Cheers,
William
Not all that matters can be measured, not all that can be measured matters.

Offline Jehuty

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Re: My new amp
« Reply #77 on: January 24, 2014, 02:13:31 PM »
Cool thanks William, nice looking posts.

I need three sets of next gens. One set for the Leak and two for my volume control....ouch!

Yeah, a lot of money but it's worth it. Just buy a pair every month like what I've been doing and you can end up like me having a stash of it  ;D
Not all that matters can be measured, not all that can be measured matters.

Offline springcreek

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Re: My new amp
« Reply #78 on: January 24, 2014, 03:16:41 PM »
Great write up William, as always it was a pleasure to have you here. I think you captured the system perfectly.

The lack of body is a real issue for me as is the tonal dryness that the Graham Slee phono adds or at least accentuates. Hopefully the changes on the way will address these issues. I am always looking for ways to add more body to the system.

One thing the system does very well is highlight the differences between recordings. I love the trait and don't want to lose it, even if the end result can be somewhat confronting or not what you expect.

As a few of you know Heldulfa and I are planning another GTG later this year. I am on a mission to have the system really singing by then.

Hopefully you guys can make it!

I will post more soon when we set a date, nominally it will be either the last two weeks of April or the first week's of May.

Thanks again for an enjoyable listening session and write up William.

Cheers, Andy

Offline Jehuty

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Re: My new amp
« Reply #79 on: January 24, 2014, 03:25:34 PM »
One thing the system does very well is highlight the differences between recordings.

That is so true. I should add that initially I thought the system didn't have enough high frequency extension and not open enough but then when you started to play better records the system certainly showed the high frequency extension which was missing in the lesser quality records and it was actually very open sounding too.
Not all that matters can be measured, not all that can be measured matters.