K&K Audio / Lundahl Transformers

Welcome! Need support, you got it. Or share youe ideas and experiences.

Return to K&K Audio / Lundahl Transformers

Message Sort: Post Order or Asylum Reverse Threaded

Amity Amplifier

99.50.127.127
Posted on December 29, 2011 at 23:52:50
chrismercurio
Audiophile

Posts: 155
Joined: August 4, 2008
 I am writing to ask about the "sound" of the Amity. Can anyone that has built or heard one describe the subjective qualities?

Thank you in advance for any replies. Someone in the TubeDIY asylum suggested I ask here.

Chris

 

Hide full thread outline!
    ...
RE: Amity Amplifier, posted on December 30, 2011 at 05:23:02
Jim Womble
Audiophile

Posts: 202
Location: Tennessee
Joined: December 15, 2004
 My amitys use 2a3 outputs. In the past I have used 300b, but since I don't need the extra power, and could never get them quiet enough, I converted them to 2a3. With 2a3, ac heating, noise is less than 200uv. They use all lundahl iron, including amorphous output transformers. They make right at 7 watts before onset of visible distortion, and using my scope and signal generator are flat from about 10-15 hz out to past 20kz at full power. To describe the sound of amitys would be difficult. The driver tube is critical, I use ecc99, and had to go through several to get examples with good section to section match (measure them in the amp), but once you get a well matched set, the amps are very neutral in their presentation, and I would venture that you will hear much more of the preamp (must have one with good drive, the 2a3 version needs better than 3 volts to get to full power) than the amps themselves. The power supply may be a bit over the top. I use a lundahl mains tranny with two -250v secondaries paralleled to give almost 850ma capacity, damper diodes in hybrid bridge feeding cap input filter to give about 320 vdc on main b+ feeding 2a3 outputs, separate rectifier feeding choke input filter/shunt regulated supply for the driver tube. These amps are expensive to built, but very nice.

 

RE: Amity Amplifier, posted on December 30, 2011 at 22:22:43
fiacono@optusnet.com.au
Audiophile

Posts: 31
Location: Melbourne, Australia
Joined: May 21, 2003
 Hi Chris
Built the Amity with varies driver tubes using Emission Labs 2A3 mesh plates output tubes. IMO I much prefer Kevin’s 3 stage power amps. Using KT120 triode strapped outputs and 6H30pi as input and drivers would cost less than the Amity.
No preamp required if connected directly to a CD player. Use CCS on all tubes - you won’t be disappointed.
regards
Frank

 

RE: Amity Amplifier, posted on December 31, 2011 at 09:43:54
KurtP
Audiophile

Posts: 245
Joined: January 25, 2007
 Tread carefully; this design has a high reward, but only if done correctly. Test equipment is your friend- some aspects of performance require measurement of phase angles and gain.

I built the 3 stage Karna design, and am very happy with it. Went through a number of iterations, including having to replace some poor performing IT's. From a highly respected vendor, but the measured performance was just pathetic (and yes, ears confirmed the poor performance, but measurement was needed to identify the culprit). The key to success with this particular design is an IT that retains good phase balance input-to-output over the full frequency range. Without that you end up with distortion that is recombined in each stage and becomes complex. The LL1692A in 2:1.75 step-down was my saviour in this arena. A specific winding configuration was required to get the phase balance to track just right. Your scope should be set to xy mode, not yt mode to perform this measurement.

I also experimented with CCS under the cathodes versus RC as Lynn designed; I did not notice any difference in performance, so you can decide if you want to pursue CCS or toss in a flavored capacitor in the amp. Nice to get rid of capacitors, but then again you have to squeeze in a negative supply for the bottom of the CCS.

Choice of 2 or 3 stage largely depends on what speakers you are driving. My suggestion is unless you have a high output voltage preamp or high eff. speakers, go with the 3 stage. You will be happy with the few extra watts and potentially simpler drive requirement with a wider range of systems.

Insist on shielded or split bobbin power transformers throughout, and keep the PS in a separate enclosure. PITA but gives lower noise pickup especially with the input transformer. I did use a custom shielded xfmr for the filaments, which was located in the amp proper and tucked away in the corner. Runs at 108V primary to keep stray flux down, and lower voltages to the DHT's. I wish Edcor offered shields on their xfmrs, because the power supply iron was nearly $1000 for this amp. Went Electraprint. Too expensive for what you get IMO- Jack builds a nice product but you rarely get the specification to closely match performance.

If I were to do this all over, I would go 3 stage design but only use an IT for the final stage. DC couple the first to second stage, but I haven't yet found a topology that satisfies me. Input transformer should be both electrostatic and mu metal shielded. 1:1+1 maximum for step up, step down is even better. 6SN7, 6N6P, 12A4, 6N8S for the first stage. Triode strapped 46 or even 6W6 works nicely for the driver. 45 IMO is a waste of money, as your distortion will come from both input stage and (in my amp, 300B plates distort with clean grid signal). Why bother with a 'perfect' driver when the 300B output stage is distorting. LL1692A in 2:1.75 for the IT.

Output transformer is another issue, but IMO is less finicky than the IT. Because the secondary is low impedance, I think you will get decent performance out of a number of different OPT's. Not to say you can't get better performance out of an amorphous Lundahl, but that IT will make or break your amp.

AC heating throughout is fine if you pay attention to layout and use shielded xfmrs. I get less than 1mV of mainly 120Hz hum. CCS driven gas tube regulators in the input and driver stage is a great feature that I recommend; cascaded DN2540 or 10M45S is sufficient and compact.

 

Amity and Karna are very good but not great......., posted on January 3, 2012 at 02:18:04
pushpulltriode
Audiophile

Posts: 805
Joined: September 20, 2000
 Hi!
I have built Lynn Olson designed amplifiers since Y2K, Amity and then Karna, and Lynn Olson has revised the design and settle in 2004 for the Amity and the Karna in 2006. I've tried both. I prefer Karna over the Amity due to sensitivity issue with preamp matching. Yes those are pretty expensive to build, and sounds like a "pretty good" SE amplifier, it sounds very fast and transparent but sorry it lacks of the immediacy of the SE amplifier. The only loudspeaker I love to put the Karna on is Quad ESL 57, SE amp "no way" has the control like the PP does on this legendary ESL speaker.

Yes I agree with other builder, interstage transformer is very critical to both Lynn Olson designed amps. Lundahl has no AM core when I started the project in Millennium. But I end up something else with nickel core 1+1:1+1 afterwards.

In Fall 1998, I started a project that is EC8020 as driver 1:1 intersage transformer coupled to the KR300BXLS, and parallel feed the output section in 1999 with custom Double C core plate choke. It takes me many years to refine the amplifier. The output power almost the same as the Karna, which is between 16-18W. But much much much more powerful!! This amplifier completed in 2002, and my friend helped me to assembly and done the measurement. Couple weeks ago before X'mas, one of the fellow drop by my place has listened to this amplifier still amazing by its performance. One of the guy want to build it and ask for operating point but I'm really forget.

I've done a comparison many times between Karna and my reference 300BXLS amp. The SE amp hands down the Karna in terms of immediacy and low level resolution. However, the Karna might be very good on extremely efficient loudspeakers since push pull is more quiet than the SE amplifier by "theory", but I hate to speculate. Hey think about it, Lynn Olson built those amp for his Avangarde as far as my memory serve me properly,

What is the efficiency of your loudspeaker? If this is around 90db range, I highly recommended you built the 300BXLS, and that the end of it!!

I've done refinement to this amplifier over last decade, mainly components upgrade in the power supply such as lower DCR double C core filter choke, more efficient and lower noise power transformer, oil filled poly cap instead of lytic. At the beginning, I have double 274B (those are very cheap from Valve Art at that time) in the power supply for each monoblock. I have done tube rolling from Full Music and EML, and those sounds fantastic and crystalline. But sorry, I switched to Schottky fast recovery diode for better sounding, better drive, better rhythmic and better layer of depth!

I should give the TV-damper a try since my reference preamp also has TV-damping but regret I didn't. Maybe I'm getting older and very easy to satisfy.

And it's worth every penny and effort for last 13 years!! I should say thank you to my best friend Rich for mentioning the approach of this SE amplifier to me in 1998!!

Have Fun and have a happy new year!!
PPT

 

RE: Amity Amplifier - Driver ?, posted on July 17, 2017 at 09:58:58
chrismercurio
Audiophile

Posts: 155
Joined: August 4, 2008
 Hi,

I know this is an old thread, but since I started it and I have a related question, I though it best to ask here.

For the dual triode drivers in the Amity, 7119/5687/etc... did people:
- use 2x tubes for the PP pair and leave one triode disconnected?
- use 2x tubes for the PP pair with each half in series?
- use 2x tubes for the PP pair with each half in parallel?
- use 1x tubes for the PP pair?

Thank you very much! I really appreciate it.

Kindest regards,

Chris Mercurio

 

RE: Amity Amplifier - Driver ?, posted on July 17, 2017 at 12:56:08
KevinC
Manufacturer

Posts: 2984
Location: NC
Joined: April 19, 2001
 This people used 2 tubes per channel using only one of the triodes in each. Much easier to select matched triodes that way.

Kevin Carter
K&K Audio
www.kandkaudio.com

 

RE: Amity Amplifier - Driver ?, posted on July 17, 2017 at 14:39:03
chrismercurio
Audiophile

Posts: 155
Joined: August 4, 2008
 Thank you very much Kevin! I really appreciate it.

I searched quite a bit before I asked. How do you think an EL84 (triode strapped) would work in this circuit?

Kindest regards,

Chris

 

RE: Amity Amplifier - Driver ?, posted on July 17, 2017 at 14:52:30
KevinC
Manufacturer

Posts: 2984
Location: NC
Joined: April 19, 2001
 If you mean as an output tube, it will work fine, but you will need moderately sensitive speakers (>94dB) speakers to get good dynamics.

As an input tube, it will also work, but the resulting overall gain will be lowish. Many EL84s are microphonic, though.

Kevin Carter
K&K Audio
www.kandkaudio.com

 

RE: Amity Amplifier - Driver ?, posted on July 17, 2017 at 14:57:24
chrismercurio
Audiophile

Posts: 155
Joined: August 4, 2008
 Hi,

In this case I mean as the input/driver.

Something like:

1:1+1 - EL84 PP - 1+1:1+1 - 300B PP - OPT

I know the gain will still be low, but with an active low impedance preamp I think it may be okay.

Kindest regards,

Chris

 

RE: Amity Amplifier - Driver ?, posted on July 17, 2017 at 16:55:56
KevinC
Manufacturer

Posts: 2984
Location: NC
Joined: April 19, 2001
 Sounds like you've decided!

Kevin Carter
K&K Audio
www.kandkaudio.com

 

Page processed in 0.030 seconds.

[ Top Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2024, Audio Asylum, all rights reserved ]
[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]