New custom monoblock tube amps....

[hometheaterdoc]

As many of you locals know, I've been on a quest for a new tube amplifier line to compliment all the solid state and hybrid stuff I've been carrying.  Something that will work well with my lineup of loudspeakers (Harbeth, Usher, and now PSB... although I mostly got PSB for the surround sound packages).  But also something that was affordable.   I've been through a number of options and nothing has wowed me yet.  

So I decided to go in a different direction.  I contracted out a custom tube amplifier. The initial design was finalized this evening and now parts are being ordered.  There's going to be some seriously cool new circuit features in this amp.  I'm very excited to get this put together and have a listen.  I have very high hopes for it.

Until the prototypes are built and we get to listen, I'll just whet your whistle with a couple design elements:

Push-Pull for ~80 watts per channel into 8 ohms
3 tubes total - one driver, two outputs - all of them being driven very conservatively for extremely long tube life
zero negative feedback
fully balanced circuit
seriously cool, truly genius auto bias - I've never heard of anyone else doing this
completely regulated power supply
amorphous core output trannies (easily the most expensive part of the whole amp)
extremely simple circuit allowing use of top shelf parts without making the overall cost of the amp too outrageous

There are some other goodies.  Like I said, I'm very excited to hear this amp.  It's at least a month or more away before all the parts get here and the prototypes get assembled.  But I was too excited to keep quiet that long.  Here's hoping it sounds half as good as I hope....  If it's total garbage, I have no one to blame but myself as I made most of the final decisions on this after hearing different options and possibilities.  I'm now turning it over to the genius that knows exponentially more about these things than me to make me look good  

If these turn out as well as I hope and are as easy to put together as I hope they are, this might become a commercial product so said genius can make a few bucks for the really cool things he designed into this amp. 

[stereofool]

Sounds very interesting  !

[hometheaterdoc]

One concern I had was the input twin triode tube can be a bit pricey to find the best NOS variants... but the genius assures me that because of the way the tube is being used in the circuit, matched sections and matched pairs aren't really necessary.  Ebay dumpster diving here I come!

Here's hoping I finally get wowed by something in this arena....

[Bob in St. Louis]

Does the designer have a name, or are we sticking with genius for the time being? 
Sounds neat Doc.
Anxious to see pics and hear prices.

Bob

[hometheaterdoc]

Bob,

The gentleman's name is Sol.  He attends a lot of our local get togethers.  He did some modification work on a Buffalo DAC kit using the ESS Sabre32 chip I have here and did some minor work on the Oppo 83SE player I have here as well.  He's been working on a number of integrated amplifier projects using transistors over the last couple years.  His I60 has really come a long way.  I shudder to think how many iterations he's worked through to come up with what appears to be very close to his final design.  But it's been great getting to hear the various stages of development and how it's come together.  I think his final product is going to be a heck of a value when he releases it. 

Despite his recent solid state work, he originally worked for a number of years in tubes.  He's been very helpful to local members fixing equipment issues.  I think this amp design is right in his wheelhouse and we'll work together on it to come up with a very good sounding piece.  It's not going to be super cheap.  The output transformers alone are quite pricey.  But I'm consciously trying to balance cost versus performance and so is Sol.  That's why he's simplified the circuit as much as possible and helped me make some of the choices we have.  By choosing the input tube we did, it dramatically simplified the regulated power supply.  If everything works out, that should reduce overall cost a fair bit. 

I think it will be a very nice unit when completed.  As for aesthetics, I have a few ideas there as well to make it cool looking without requiring CNC work or outrageously expensive casework....  We'll work on the sound first, though

[Bob in St. Louis]

Ok, good deal Shane, thanks for the info.

Bob

[hometheaterdoc]

building has commenced on the initial prototypes of these...  almost all the parts are here....  looking forward to getting these built up enough to have a listen...

[Bigfish8]

building has commenced on the initial prototypes of these...  almost all the parts are here....  looking forward to getting these built up enough to have a listen...

Shane,

I am just wondering if you are thinking of a product name for your new amps?

Ken

[hometheaterdoc]

not yet, Ken... I figure it will come to me after listening or seeing them built up... it will likely depend on how they look and what I do with CNC metalwork...

[hometheaterdoc]

Progress is slow, but coming along... as with all prototyping, once you start building out a circuit you find some things you weren't anticipating and end up trying something else.  The circuit is still in place... but slight adjustments have been made.  Sol is throwing the kitchen sink at each part of the circuit he builds up.  Hopefully we'll have a working monoblock soon.  We're laying things out now for how it will all layout on the chassis.  It will be essentially breadboard with a piece of plate until we finalize the prototypes.  No sense spending $400 on a CNC'ed chassis until we're sure.

I'm getting antsy to get this up and running....

[hometheaterdoc]

Progress is still happening.  Sol has a regular day job that eats up most of his time.  But as time has allowed, he's finally starting to get closer to a working unit.

The B+ supply has been completely redone after the first few prototypes didn't work as perfectly as intended.  I want supreme reliability with lots of protections for any conceivable issue, even if it means slight degradation in sound.  Sol feels the same way.  So he went back to the drawing board and found an even better solution that looks pretty bulletproof so far.  The new B+ was fired up on Monday for testing and it's looking like this will be a go.  So far, it appears that was the last hurdle to get over before getting a working unit.... 

I'm getting very, very antsy to hear an initial prototype in action.... soon.... soon........

[richidoo]

I was at Sol's house today, got to feast my eyes on all the circuits, transformers and tubes. We laid them out on a piece of wood to mark the hole locations. I'll put it into Front Panel Express' CAD program to order the top plate. After that arrives, build a wood box for it.

The audio circuit is extremely simple, but the tubes and power supply are very stout, and some design choices naturally cancel out distortion while allowing minimal (or is it no?) feedback with low Z-out.

Getting close now....

[StereoNut]

Shane,

I am just wondering if you are thinking of a product name for your new amps?

Ken

How about

H(ome)T(heater)D(oc)-1000's or if they're based on a particulate tube (Like KT-88's)...



maybe, H(ome)T(heater)D(oc)-88's ???

 SN
 

[tmazz]

Getting close now....

You guys sound like expectant fathers with Sol being the "Audio Obstetrician".  

Do we all get cigars when the amp is launched? 

[richidoo]

I am making the boxes for these prototypes.  The last few days I have been working hard on them. First Sol and I laid out the parts on a wood template and marked the positions. Then I transferred the positions into CAD, printed full size, center punched onto aluminum, and 8 hours of drilling and cutting, deburring and filing later:


We saved a lot of money destroying the plates ourselves (diy) compared to Front Panel Express would have been $300+. Only a couple minor screw ups. Glad that is behind me.

Tomorrow I'll make the boxes and get it to Sol for final assembly. We are on schedule to play them at the 10/9 g2g.