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Pete Millett's Menace

post #1 of 110
Thread Starter 
I'm going to create a thread for this amp since it is my intention at the end of the build to publish the schematic and any relevant details so that anyone who's crazy enough can build this amp. As of right now the amp is in working condition and headed to Florida for the party that will be CanJam. First, a little backstory...

A Brief History of The Meance

So really this started years ago, but if I tell the story that way it won't make a bit of sense to anyone other than myself. And I did say brief history and I swear I'll try to keep it that way.

This really got going in late December of this past year when I got a message from a friend (who shall remain nameless) that they had an abandoned project that I might be interested in picking up. The basic gist of the project was that they had taken the Van Waarde project along with the Wheatfield HA-2 design and started to improve upon the general concept. Most notably this involved paralleling the output tubes and increasing the output coupling capacitance to the point where driving low-impedance headphones would be possible. The original HA-2 was technically able to do this but not all that well in my opinion. So me being the unabashed Pete Millett fan that I am and a former HA-2 owner jumped all over it. Quick note - both the Van Waarde and the HA-2 schematic are out there if you know where to look, the Waarde is at Headwize (linked above) and owners of the HA-2 know where to find its schematic. I believe that Headroom still owns the HA-2 design and as such I won't be publishing that schematic, only my revised version. Now the revised design that started this mess had been taken to the proof of concept level but in such a way that things like the power supply still needed figuring. So while I won't be using much of what was done as a part of that project I do owe my friend a huge debt of gratitude in terms of motivation and inspiration, without that initial push I'm sure that this would have never happened.

Now I'm no designer, I never have been and I never will be since there just aren't enough hours in the day and honestly I'm completely comfortable leaving that up to other folks. I love building this stuff but typically my interest dies off quickly after that point. To a degree that had to change for this project since there was still much work to be done. So I started doing some basic math along with consulting with a few folks about the power supply. It was initially my hope to simply re-use the existing HA-2 tube-rectified design and tweak it as needed. This was quickly abandoned after seeing that the existing PS design was pretty much tapped in terms of current capacity. It was at this point that I decided to call in the big guns and see if I couldn't enlist the help of the guy who was really responsible for all this. I've communicated off and on with Pete Millett for the past few years, mostly as a result of my dealings with the Low Voltage Hybrid project as well as dealing with the issues that my original HA-2 had. Like I said, I'm a hug Pete fan the guy gives tirelessly to this hobby and I can't wait to shake his hand next week, I'm getting side-tracked, back to the story. But Pete's a busy guy and I didn't really expect to have him launch into it the way that he did but it'd be safe to say that this project may well have died without his help. He continues to be a integral part of the design process and I can't say thanks enough so, thanks Pete! I started talking power supply design with Pete and we quickly came up with a couple of concepts and I elected to go with what seemed to be the simplest from a parts perspective (fewer transformers and bits that I was used to working with). I also elected to have the amplification side of the equation be essentially a tweaked HA-2 that will run parallel output tubes, larger output coupling capacitors and modified heater supplies. This should help some of the issues that the original HA-2 suffered from which were some PS hum and output impedance that wasn't really all that suited for driving Grados.

So I sketched up schematics and sent them to Pete and what followed was some back and forth that culminated with some rather large parts orders in late March but I didn't get around to actually starting the build until April 10th. Nothing like leaving myself plenty of time to get it ready for CanJam.

I think I'll stop here and leave the details to later on in the process but hopefully that paints at least a little bit of a picture as to where this came from and where it's headed. As I said in the beginning it's my full intention to publish the schematics that Pete and I came up with when I get back from CanJam. The versions that I have uploaded right now have a few minor errors in them and I'd rather not steer someone in the wrong direction.

Here area a few pictures from during construction, all told I think I've got about 14 days/nights of on and off work into the amp. Maybe 40hrs or so, it's pretty hard to tell really as I'm sure if someone had large chunks of time rather than a hour here and there it could be done more quickly.





















Finally, here are two shots from testing the amp last night.





I'm going to hold off on internal wiring shots until I can update pictures since there are substantial changes from what i had before. I've posted one on this site already but since this is intended to be the source for good information about the amp I don't want to cause confusion.

I also can't offer much in the way of listening impression since I've spent a grand total of 2hrs listening to the amp, only one of which was after the final modifications. What I have heard so far offers great promise and the root of the design is sound so I have little doubt that the amp will perform up to my expectations, which are quite high.


So that's it, the introduction of The Menace. Once again I have to say a huge thanks to Pete Millett who's advice and help throughout this project was simply invaluable.
post #2 of 110
Thread Starter 
WARNING: The following schematics depicts a project that involves working with high voltages. Use of this schematic is permitted with the understanding that if you're not careful, this thing can kill you. Not only are you working with line voltages but the HV (B+) supply has a lot more current capacity than your typical tube project and should be treated with a great deal of respect. Getting hit by ~300V is no fun, assuming you live to tell the tale. That said with proper respect and care there's nothing exceptionally complex about this amp or power supply.

WARNING2: There may still be errors in the schematic (please see note below) and please feel free to tell me if you see any. Pete was kind enough to digitize my hand-drawn version and we've caught one mistake already. So please, just post or shoot me a PM, nobody's perfect and you won't hurt my feelings one bit.

Schematic (updated 5/20)

Amp
Important Correction - in the original schematic C3 is NOT CORRECT! It should be the same cap used at the C4 position (10uF/400V). You will probably have a very bad day if you use a 50V cap at this position. I've updated the image file but the old one may stay in your browser's cache for a while. If you're still seeing a 220uF cap at C3 you're seeing the old file.


PS


I'll be putting together some other thoughts and comments on the build at some point in the near future (hopefully) but there are a couple items of note to start:

Rectifier tubes: this PS can run on any of the following - 5AR4s, 5R4s, or 5U4s. Depending on the tube that you get you may exceed the peak current capacity of the tubes and see some arcing at startup. I haven't had this issue with any of the tubes but for both the 5AR4 and 5R4 we are at or near the peak. The issue with the 5U4 is that they stress the 5V winding of the BFT more than they should be. Pete and I spoke with the trafo manufacturer who essentially said that if we weren't exceeding the total VA for the trafo we should be fine. This was one of the reasons that we selected this transformer, it's absurdly overbuilt and I like that. I've run the amp for more than 5hrs straight with 5U4s in there and the trafo gets barely warm to the touch. My preference right now is to run 5AR4s since they offer a nice slow warm up of the B+ which is easier on the tubes in the amplifier section.

B+: we're running the HV section of the transformer pretty hard as well, but again, the man'f was consulted and the advice was similar to the filament section. Also, B+ will vary depending on the rectifier tube choice that you make, I haven't taken measurements with all 3 but I do know that I get an acceptably high B+ regardless of choice.

General Comment: clearly there are lots of alternate configurations that can be chosen depending on what your end goal is. What is presented here is simply one example of a working configuration that has, to my ears anyway, produced great results.

more later....
post #3 of 110
Thread Starter 
reserved for updates2
post #4 of 110
Having followed the HA family tree (Millett Hybrid, HA-1 and HA-2 (my long-time love)) this is uber interesting. Just wonder if it will sound better than the HA-2 on Senns as well?

And, I will throw the B word out - will this drive me back to SE?

Looks like a P2P even I could love.
post #5 of 110
We call it the van Waarde amp, but Dr. van Waarde attributes the original design to Rudy van Stratum.

OTOH, I guess for the purposes of this thread, we can keep calling it a van Waarde.

It looks like you're paralleling both sides of a 6080 per channel. I have seen small speaker amps like that.

So, this seems like big overkill. Am i not understanding the amp?
post #6 of 110
Amazing work, Nate!!
post #7 of 110
Thread Starter 
Quote:
Originally Posted by ericj View Post
We call it the van Waarde amp, but Dr. van Waarde attributes the original design to Rudy van Stratum.

OTOH, I guess for the purposes of this thread, we can keep calling it a van Waarde.
Well, regardless of what we call it I think it's important to give credit where credit is due so your information is appreciated. But really, this all probably goes back a lot further than that so I hope no offense will be taken by those who paved the way.

Quote:
It looks like you're paralleling both sides of a 6080 per channel. I have seen small speaker amps like that.
That is correct, the output tubes are run in parallel.

Quote:
So, this seems like big overkill. Am i not understanding the amp?
Overkill might be a strong word in the same sense that the beta22 is overkill.

The basic premise here was to take the Wheatfield HA-2 model and do some things to improve upon it that simply couldn't be done in the commercial realm. For example, the power supply weighs nearly 50lbs by itself. No commercial man'f is ever going to want to deal with that! So were all of the changes strictly required, of course not, but where would be the fun in stopping there. The parallel tubes and increased output coupling capacitance on the other hand allow the amp to be much better suited to driving low impedance headphones like my HF-1s. So to me those were required. Also, I wanted to retain as much of the original amps characteristics so I made choices based on that requirement that are clearly unnecessary for anyone but me.

I'm not trying to claim that what is presented here is either the most efficient or cost effective way of achieving a given goal. Just an approach that I chose based on my ideas and priorities. If only one of these gets built (mine) that's fine by me, maybe someone else will look at and find inspiration to do something different. The idea is just to share.
post #8 of 110
Thread Starter 
Quote:
Originally Posted by tomb View Post
Amazing work, Nate!!
Thanks Tom, as you well know these tend to be a labor of love.
post #9 of 110
Thanks Nate, for bringing such a promising design to the table. And thanks Pete for continuing to improve designs for the DIY community! ;-)
post #10 of 110
Quote:
Originally Posted by ericj View Post
So, this seems like big overkill. Am i not understanding the amp?
Hey, if you don't like overkill, go for a (practical and perfectly "adequate") opamp-in-a-box!



Besides, it can double as a beverage warmer.

I really think this thread needs to be titled "Nate Maher's Menace". Nate did all the work. I only helped because Nate promised to pick up my beer tab at CanJam. He doesn't know what he signed himself up for

Or maybe call it Maher's Menace...

...Maher's Millett Menace...

...Menacing Maher's Millett...

...Maher's Mega-Massive Menace...

Pete
post #11 of 110
Quote:
Originally Posted by ericj View Post
So, this seems like big overkill. Am i not understanding the amp?
Z out is defined by 1/Gm. Gm on the 6080 (7000 umho) is not that high which means Z out is high. Paralleling the sides halves it. Even with one, there is still plenty of current to drive low Z phones to be very loud, but even with a bunch of sides in parallel, damping factor is still not very good.

If you want to use a cathode follower to dive phones, (and I think there are better ways to drive low Z phones, but you probably already knew that that was my opinion) and you are willing to parallel sides, a 6922 or a 6H30 seems like the better choice. 6080's need a ton of heater current and a ton of plate current, and while they also thus have a ton of output power so they can afford to be really inefficient, a few parallel 6922 sides also has plenty of current and a lower Z out as well.

Here is a nice primer: http://www.tubecad.com/2005/June/blog0049.htm

You'll notice that a 6as7/6080 can output 1.63W into a 32 ohm load, while the single 6922 can only muster 25mW. But, you can double this for parallel sides, (3W v. 1/2 watt) and, more importantly, if you put 25mW through your Grados, you will lose your hearing. I measured mine, and at normal listening levels, I was at 3mW. 5mW hurt.

More important, in my experience, is that damping factor matters more for these low Z phones. Damping factor, which is the ability of the amplifier to control the speaker, is the ratio of speaker Z over Z out from the amplifier. I think with Grados you want at least 5 in an ideal situation. That means a Z out of about 6, which means 24 total 6as7's for 32 ohm phones. Obviously that's just silly, but it illustrates the point that this is an inelegant brute force method not really appropriate for low Z phones. The old truism that Grados need current and Senns need voltage is basically true. Ironically, while there is a history of 6080's in headphone amps, I don't think they are actually a very good choice for either.
post #12 of 110
Quote:
Originally Posted by pmillett View Post
<snip>

I really think this thread needs to be titled "Nate Maher's Menace". Nate did all the work. I only helped because Nate promised to pick up my beer tab at CanJam. He doesn't know what he signed himself up for

Or maybe call it Maher's Menace...

...Maher's Millett Menace...

...Menacing Maher's Millett...

...Maher's Mega-Massive Menace...

Pete
How about Maher's Menacing Bar Tab
post #13 of 110
Sweet looking amp. I can't wait to hear more details about it (won't be at canjam).

For some reason, I keep thinking AM/PM...NM/PM...PM/NM...Those damned am/pm commercials.

"AM/PM. Too much good stuff."
post #14 of 110
Aniston's Revenge?
post #15 of 110
Quote:
Originally Posted by dsavitsk View Post
If you want to use a cathode follower to dive phones, (and I think there are better ways to drive low Z phones, but you probably already knew that that was my opinion) and you are willing to parallel sides, a 6922 or a 6H30 seems like the better choice.
Or two sides of a 6N6P, for example.

Quote:
Originally Posted by dsavitsk View Post
More important, in my experience, is that damping factor matters more for these low Z phones. Damping factor, which is the ability of the amplifier to control the speaker, is the ratio of speaker Z over Z out from the amplifier. I think with Grados you want at least 5 in an ideal situation. That means a Z out of about 6, which means 24 total 6as7's for 32 ohm phones. Obviously that's just silly, but it illustrates the point that this is an inelegant brute force method not really appropriate for low Z phones. The old truism that Grados need current and Senns need voltage is basically true. Ironically, while there is a history of 6080's in headphone amps, I don't think they are actually a very good choice for either.
You have a point about the damping factor i suppose.

In my own use, I have no senns or grados. Well, I have senns, but px100 and hd25sp are portables and don't count.

i seem to have a lot of 600-ohm cans, which just need a lot of gain or as you say voltage, and orthos, which need unusually high gain for their relatively low impedance - 150 ohms at the most - and thus seem to need both more than average voltage and more than average current. A damped-flat Yamaha HP-1 at 150 ohms needs slightly more gain than a 600-ohm K240-M or DT990 for the same SPL.

And yeah, I'm building an amp with a 6080 too, but mostly just out of curiosity.
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