[Roger A. Modjeski]

A while back someone asked me to discuss particular differences in some popular output circuits. If there is interest we can start with OTL  and High Voltage Direct Drive for Electrostats (two favorites of mine). If there is enough interest we can also consider SEPP, MU followers, single ended and push-pull. Some of these circuits also appear in the output stages. The particular application should be considered in every case.

Since switching amplifiers have been popular here, we can discuss those too. My goal is to give the participants a clear understanding about what is different in these circuits and where they are best employed.

[richidoo]

Sounds great. Maybe one of the most ambitious threads ever started? Destined to become a valuable reference for future generations of amp designers.
Rich

[sonicboom]

Excellent topic!

It would be nice if along with the discussion you could post basic hand drawn schematics, for comparison and education purposes between the different circuit topologies.  I am also very interested in OTL circuits and would like to be educated on the differences between say the Futterman, Cyclotron and MU follower designs, as I know these are used in some commercial products.

Your opinion as well as your objective analysis on the merits and/or limitations of each of these designs is off course expected and welcome!

[bill92050]

I'm very interested in this thread's topic.  Although the more basic the better, I'll gladly read anything I can.

[Imperial]

Sounds like a great treat Roger M!
I'll be a keen reader here for sure!

Imperial

[Roger A. Modjeski]

Thanks for the encouragement. Right now I am fixing the fuel pump driver module on my 99 Mustang. Any tips will be appreciated. I am going at it on a component level. It's really nicely made and the cover just pops off and there are 3 IC's, big torroid choke, diode and MOSFET.

As to schematics, 'll have to break out the scanner and see if it likes my HP laptop.

BTW, I am always on the lookout for a web/computer helper. Someone who can post to my website and other fun things with pictures, schematics, etc. You help me, I'll help you. I will make a new post for that.

Homework Assignment:  Have a look at Art Dudley's review of the Joule Electra (May 2007, page 33). See if you can spot the errors. It's worth reading, some of it is correct, some not. We can use it as a springboard to start our discussion. I am in the process of writing a letter to the editor.. so don't tell till it's published we will just let it be our little secret here at AC.

Let's hear from anyone who has had a Joule or other OTL using the 6C33 tube. I contend it is a very bad choice for OTL application. What's more, I'll even tell you why.

Roger

[kyyuan]

Roger,

Some very interesting discussions here.   

Any update on your letter to Stereophile?  And, do you have any thoughts on the NOS 6350 tubes that Joule uses in its Mu Follower and Gain Stages?  Thanks.

Ken

[Roger A. Modjeski]

The 6350 is not something I would use for audio.  They have an unusual pin out (9CZ)and there are no easy subs as there are for the normal pinout out (9A) that 12AX7, 12AU7, 6FQ7 all share. There are better tubes out there. I do provide 6350s so customers can get all their tubes from one source. If someone can find a link to a full data sheet I would be happy to comment further.

Often manufacturers choose a tube because it is available at very low cost. That's generally because no one else uses it. The 6350 and 6C33c output tube fit those categories. A 12BH7 or 7044 is better than a 6350 but have gotten rather expensive. Most anything is better than a 6C33c for an output tube. The full story on that tube is not pretty.

BTW, if you need some unusual tube type that is not on in our on line store: http://www.tubeaudiostore.com/ please call. I have virtually everything here including antique radio tubes, transmitting tubes, tubes for Beveridge and Acoustat direct drive amps and all OTLs, even a few of those 6C33s that could use a better home than my attic.