Favorite designs?

[modman]

Anyone here have favorite topologies for power amp designs? I have a few myself after 50 years of building/designing this stuff. First up is the Bipolar Bear. I love a great linear bipolar device based power amp with minimal gain staging and feedback. Older Nelson Pass designs come to mind.

The bipolar is a bear because he has two inputs and no exit. No wonder he's a bear.

Futterman push-pull tube designs are also quite nice to listen through.  Dangerous to speakers though.

The only Class D designs I've used that are marginally acceptable are made by Bruno Putzy marketed as Hypex.  I've used those in MI bas amp designs, a great choice for those.  Still, not good enough for critical control room monitoring.

Another bone to pick are the mosfet outout devices. I don't like any of them. They generate ugly harmonics only massive feedback correction can somewhat reduce. They are all the rage now days with Hafler and even Adcom now using them. They have a hard midrange and dampen the micro transients and replace them with 'aural excitement' AKA distortion. They cause listening fatigue.

So what say you?

[audiobill]

Hafler? Adcom?

Ancient history, many have gone back to bipolars, in an effort to sound like tubes, the real deal.

[leonski]

I'll see your Nelson Pass and raise you a John Curl.

Pass makes an interesting line in his 'First Watt' effort. Not for all tastes OR speakers. Some are fairly high output impedance and pair best with either a full range single driver or one of the old-school 'Big Box' speakers of higher than average sensitivity.

Funny you should drag Adcom into this. Pass is the designer of record for the Adcom 555, sort of a well regarded vintage piece to this day. Threshold was also a Pass effort, at least the 'Stasis' stuff and generated several patents as a result.

I wouldn't put too much stock into 'all' of any type of device being of a certain characteristic. MOSFETs are easy to make, robust, and I suspect have several characteristics making them desired for output sections of amplifiers.

Bob Carver went thru an IGBT output phase, using them in his Sunfire amps.

Pass has had some good luck with VFET and I think commisssioned a 'run' thru a fab so he could have some to play with and sell. That ain't cheap and I must wonder where he got the Mask Set used in the fab. If Pass commissioned an all-new design or
run of masks (used in the photo steps of manufacture) that would REALLY run up the bill. All other steps are 'whole wafer' and fairly flexible.

Anything done well will trump a poor version of a 'better' topology. Bruno is a BIG fan of laying on LOTS of feedback.

[klinemj]

Personally, I'd say that the names Pass, Carver, and Putzy deserve a place in the amp Hall of Fame. And, Lonnie V certainly is in there for me - for what he's been able to do with low cost/high performance gear.

Mark

[leonski]

Putzeys. That's the last name.
Great guy, too. And while it doesn't come out in any of his interviews, he's a big fan of Spicy Hot food. In SoCal for a show, he'll try to get some local 'hot stuff'.

Attachments:

[audiosyndrome]

Jan 7, 2018 17:31:29 GMT -5 leonski said:

I'll see your Nelson Pass and raise you a John Curl.

Pass makes an interesting line in his 'First Watt' effort. Not for all tastes OR speakers. Some are fairly high output impedance and pair best with either a full range single driver or one of the old-school 'Big Box' speakers of higher than average sensitivity.

Funny you should drag Adcom into this. Pass is the designer of record for the Adcom 555, sort of a well regarded vintage piece to this day. Threshold was also a Pass effort, at least the 'Stasis' stuff and generated several patents as a result.

I wouldn't put too much stock into 'all' of any type of device being of a certain characteristic. MOSFETs are easy to make, robust, and I suspect have several characteristics making them desired for output sections of amplifiers.

Bob Carver went thru an IGBT output phase, using them in his Sunfire amps.

Pass has had some good luck with VFET and I think commisssioned a 'run' thru a fab so he could have some to play with and sell. That ain't cheap and I must wonder where he got the Mask Set used in the fab. If Pass commissioned an all-new design or
run of masks (used in the photo steps of manufacture) that would REALLY run up the bill. All other steps are 'whole wafer' and fairly flexible.

Anything done well will trump a poor version of a 'better' topology. Bruno is a BIG fan of laying on LOTS of feedback.

If I remember correctly, Nelson bought up Sony's full stock of the VFETs some time ago. Heard the Sony VFET amp (designed by Nelson) at the NY show several years ago. Sounded excellent.

Russ

[405x5]

“Tracking Downconverter”
(Carver’s Sunfire)
I bought the 400 plus watt 5 channel version in 2001, after a perfect 13 year run with the magnetic field amps.

And I can’t kill this one either.
After 11 years, I did some homework, to make sure I had someplace to go if I needed service.....That was over 6 years ago and it has never needed it. Nothing but dead quiet until the music starts.
I got with Bill Flannery who worked for Bob Carver and services those amps.
Bill let me know about any signs that it would be time to do something.....so far, there are none.....17 years this month.

Bill



It matches perfectly to the XMC-1 which triggers the auto sensor of the amplifier, so of course, I don’t use the preamp trigger.

[leonski]

Bob went thru a bunch of revisions of his POWER SUPPLY ideas. The early Carver amps had such a PS and worked well. But I think it clipped the Voltage from the wall, not current. My m400t would flicker the lights of the house in time to the music.
Poor amp eventually went south. It had even been repaired once, at power company expense, after a brown out took it out.

Carver was always one for the Terrific Circuit Name. Tracking downconverter? Asymmetrical Charge Coupled Detector? Sonic Hologram? T-mod?

I may still have the cooling system I built for the m400t around here somewhere. It was a shroud which fit the amps back. And a suckthru fan. It was very effective and I could play the amp VERY loudly for hours without warming it up.

[geebo]

Jan 8, 2018 12:03:08 GMT -5 audiosyndrome said:

Jan 7, 2018 17:31:29 GMT -5 leonski said:

I'll see your Nelson Pass and raise you a John Curl.

Pass makes an interesting line in his 'First Watt' effort. Not for all tastes OR speakers. Some are fairly high output impedance and pair best with either a full range single driver or one of the old-school 'Big Box' speakers of higher than average sensitivity.

Funny you should drag Adcom into this. Pass is the designer of record for the Adcom 555, sort of a well regarded vintage piece to this day. Threshold was also a Pass effort, at least the 'Stasis' stuff and generated several patents as a result.

I wouldn't put too much stock into 'all' of any type of device being of a certain characteristic. MOSFETs are easy to make, robust, and I suspect have several characteristics making them desired for output sections of amplifiers.

Bob Carver went thru an IGBT output phase, using them in his Sunfire amps.

Pass has had some good luck with VFET and I think commisssioned a 'run' thru a fab so he could have some to play with and sell. That ain't cheap and I must wonder where he got the Mask Set used in the fab. If Pass commissioned an all-new design or
run of masks (used in the photo steps of manufacture) that would REALLY run up the bill. All other steps are 'whole wafer' and fairly flexible.

Anything done well will trump a poor version of a 'better' topology. Bruno is a BIG fan of laying on LOTS of feedback.

If I remember correctly, Nelson bought up Sony's full stock of the VFETs some time ago. Heard the Sony VFET amp (designed by Nelson) at the NY show several years ago. Sounded excellent.

Russ

I still have a VFET Sony integrated amp. The TA-5650.

[405x5]

Jan 8, 2018 14:14:04 GMT -5 leonski said:

Bob went thru a bunch of revisions of his POWER SUPPLY ideas. The early Carver amps had such a PS and worked well. But I think it clipped the Voltage from the wall, not current. My m400t would flicker the lights of the house in time to the music.
Poor amp eventually went south. It had even been repaired once, at power company expense, after a brown out took it out.

Carver was always one for the Terrific Circuit Name. Tracking downconverter? Asymmetrical Charge Coupled Detector? Sonic Hologram? T-mod?

I may still have the cooling system I built for the m400t around here somewhere. It was a shroud which fit the amps back. And a suckthru fan. It was very effective and I could play the amp VERY loudly for hours without warming it up.

I like the current PS (no pun intended) because it’s on 24/7 on standby unless you pull the plug.
When it calls for power, it’s more civilized especially when things get really loud.
I experienced a similar light show with the early Carvers and mine were the 1.ot’s.....A bridged pair.......admittedly ridiculous. That was before I understood about relegateing much of that juice to a subwoofer.

Bill

[leonski]

Never had any luck with bridging. Nobody I know has, either. Oh! It works, but can hinder SQ. Maybe with 16ohm speakers? 8 ohms speakers which MAY have a dip to 4ohms will appear to the amp as 1/2 that and Potentially harm the sound.

As for relieving stress on amps with subs? Sure. I'd allocate NO LESS than 20% of my power to frequncies below maybe 60hz or 70hz. That can easily be done setting your crossover to maybe 50hz to 55hz and using the common sub 24db / octave slope.
Generally considered the 50:50 power point, 350hz is used for 'normal' music, not weird stuff or test tones!

I use a PAIR of Parasound A23, with the intent of eventually going to a ACTIVE line level crossover and performing some internal speaker mods.

[modman]

An overpowered Class AB bipolar power amp also has the advantage of staying in Class A for more of it's dynamic range. I've used Bruno's Class D Hypex designs in commercial MI bass guitar amp designs and also in the Rhodes Mk7 electric pianos, a great choice for that. Still, I had to replace the NE5532 input opamp buffers with a more linear opamp for best performance. I still would never use that stuff for a studio control room monitor amp.

I have the benefit of good audio lab here with Audio Precision analyzers, etc. I'm able to find errors during the design stages. Some of those older Pass long tailed pair front ends and secondary gain stage designs have yet to be bested if separated and tested alone for linearity. The AES has had a couple of great articles in the journal exploring those stages and their properties.

Then it's about the parts. I'm a bit partial to Vishay VAR naked bulk foil and Mills wirewound resistors in my amps here but that stuff is too expensive for the masses.

Threshold was very popular in LA studio control rooms back in the 1980's along with Perrough. Adcom 555's and 545's are very common in control rooms as well. A GFA 545 driving old Yammy NS-10's is still a popular combo.

[DYohn]

I prefer designs based on the theories of Lee De Forest.

[leonski]

I've known the name, DeForest for years. But never knew he lived until the 1960s.

And was possibly even worse at business than Nikola Tesla.