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Pete Millett's Menace - Page 4

post #46 of 110
ISC ;-)
post #47 of 110
Quote:
Originally Posted by grawk View Post
Aniston's Revenge?
Not sure how obscure that reference is to many here, but I just about spit my drink out!
post #48 of 110
It can't be THAT obscure, can it?
post #49 of 110
hi dsavitsk

i was looking at the less-pressivo thread over at headwize, and that amp looks sweet. I like original design too, but too much money

i was curious with the balanced schematic why you put the cap between the halves of the transformer with no ground connection rather than at both ends with the centers grounded. it is still parafeed, and no current flows in the primary, but why drop the safety feature of having the transformer grounded?
post #50 of 110
Quote:
Originally Posted by nikongod View Post
i was curious with the balanced schematic why you put the cap between the halves of the transformer with no ground connection rather than at both ends with the centers grounded. it is still parafeed, and no current flows in the primary, but why drop the safety feature of having the transformer grounded?

So, two issues. The first is what it means to be balanced, and the second is the parafeed part. For my own personal safety, I don't believe in using balanced phones that have no connection to ground, especially with high voltage amplifiers. OPTs are inherently going to give out a balanced signal, but I always ground one side of the secondary. So, when I say balanced, I really mean that the amp is balanced throughout, but not on the output necessarily. If you really want to do balanced phones, I'd connect another wire to ground the body of the phones.

For the parafeed part, any high voltage amp (for dynamic phones) is going to have something between you and the high voltage. With OTL and most single ended parafeed, it is a capacitor -- parafeed (though not the original Espressivo) having a transformer too. With single feed designs, the primary of the transformer sits at a high voltage with the secondary grounded. With the balanced design, like the single feed design, the transformer acts as the block.

Your suggestion essentially puts a secondary safety measure in place. The down side is that, as drawn, the signal path includes 2 tubes, 1 transformer, and one cap. Your suggestion would add a second cap plus the biasing mechanism which would need to be bypassed with a cap (or LED) which would impact in the sound quality. But, being aware of these issues and knowing what stands behind you and oblivion, is important. I happen to trust transformers more than caps to block voltage.
post #51 of 110
Question for Nate. Where did you get those nifty tranny mounting isolators?
post #52 of 110
Thread Starter 
Those are from McMaster Carr - I'll grab part numbers and post them later since you're not the first to ask.

If you want to look in the mean time I believe that they are listed under vibration isolating grommets or something like that.
post #53 of 110
Thread Starter 
The Blue ones are part no:9311K139. Based on that you should be able to find the range that they carry, which is how I found the black ones.
post #54 of 110
Wow, look what I miss when I leave for a few days. Sounds like a great project Nate... can't see the pics right now unforunately, but I'm gonna try to get to a internet cafe or something to have a look. Can't wait to hear this at CanJam!
post #55 of 110
Well, I'm at home now and stealing internet from someone in my building. WOW! That is what I call a power supply! You never cease to amaze Nate... I can't wait to hear this beast.
post #56 of 110
Quote:
Originally Posted by philodox View Post
when I leave for a few days.
A few days!? We had the national guard working with the Canadian authorities trying to locate your body. Good to see your OK!
post #57 of 110
OK, long time, no update - any impressions, specifically from CanJam? How is she to live with, Nate?

Still looking for the BOM, and build details... pretty please?
post #58 of 110
This post brought a big smile on my face...

Back in 2002 I took Pete's design and started doing rounds and rounds of PSU design testing and tube/components permutations and started harrasing everyone around, including Pete (who kindly explained the design and suggested things to try)

The fact is my final setup is still over a woodboard, never cased it up as I thought it was overkill and wanted to test other amp designs, as everyone told me WCF were a very constrained design in terms of improvement.

In short the beefiest and more expensive section of the amp was the PSU, its design had the most impact on final sound. I end up with tube rectified (5C3S) to a double LCLC stage with plenty capacitance (900uF). Used a seperate transformer for 6.3VAC heating. B+ was around 210VDC.

I tried tons of input and output tubes, including paralleling sections, the final tube chosen for input was a 6H30P-DR, and the output a 5998.

With that coupled to my K401 (120Ohm, 89dB sensitivity) sound was incredibly organic, plentiful of controlled bass and overly lush while having very good distortion figures and characteristics. I'm not a classic music listener but know how real instruments sound like, and strings and piano sound was incredible. I did some sims aided by Alex Cavalli but ended up using pots and fiding sweet bias spots by ear.

For inputs I tried Ecc88, 6SN7 both short and tall bottle, 6N1P and 6H30P-DR. Sound with the 6H30P-DR was clearly the best, sounding like an octal tube in terms of distortion characteristics but like a noval in terms of "definition" when biased in its sweet spot. 6N1P was second best but more analytical.

For output I tried 3 different 6AS7 NOS tubes, a RCA 6080, svetlana NOS 6C13C, and TungSol 5998. Also 6H30P-DR. Tried paralleled sections, etc...

A single 5998 came out as a winner probably due to its lower Zo as advised by Pete, followed by the 6C13S.

The key there was to run it hot enough (original Waarde amp didn't sound quite right to me) and the kind of Rk resistors used.

Of course the output caps were key, I tried tons of kinds and combinations and in the end I found the Solens to be the most neutral, there are non electrolityc caps today much better than the Solens...

In the end I discovered I needed a better source also but that got put on hold until recently I buillt a USB based DDDAC and tube DIY "sparked" back on me . I may give it another shot!

Can't wait to see the final Menace design published!
post #59 of 110
Quote:
Originally Posted by pabbi1 View Post
OK, long time, no update - any impressions, specifically from CanJam? How is she to live with, Nate?

Still looking for the BOM, and build details... pretty please?
Sorry to be a PITA, but x2 or x3 or x(n).
post #60 of 110
Thread Starter 
Quote:
Originally Posted by pabbi1 View Post
OK, long time, no update - any impressions, specifically from CanJam? How is she to live with, Nate?
Sorry, I've been busy trying to play catch-up after CanJam. I have a final version of the schematic that Pete did based on my hand-sketched ones, I need to do a final review of that and then I'll post it. Impressions from CanJam were all really positive and are scattered throughout the thread in the Meet Forum. For most of the meet it was running with a Sylvania Bad Boy on the input and Cetron 5998s on the output, this was a very nice combo and seemed to drive both Grados and Senns equally well. Since getting the amp home I've been running a CBS 5692 on the input and Tung Sol 421A's on the output and I've been loving every minute of that experience. I've added some additional heat sinking to the top panel of the amp and I think that has it running pretty reasonable surface temperatures. It's a little hard to measure with it in my rack so I may need to pull it again and run it in the open to make sure that further heat sinks aren't required. At CanJam it was running a pretty consistent 150F directly over the resistors and that dissipated pretty quickly as you moved away from that location.

Quote:
Still looking for the BOM, and build details... pretty please?
It's going to be a bit before I get anything like that uploaded but I think you'll be able to see from the schematic that putting together a BOM is not all that difficult. Parts count really is pretty low and Pete included the grounding configuration that I used in the schematic. I do still have just a bit of ground hum to try and trouble shoot at some point but it is in audible for almost the full first half of the volume pot. With my source if you're running the volume half way up you are well into the mid 90's of db's, which is a LOT louder than I listen. Still, I'd like to get it even quieter if I can but that experimentation may have to wait a while. Also, I need to take some updated pictures of the internal wiring to post along with the schematic, that will help explain a lot of what I did I think.

Ok, I'll try and get motivated right now to at least review the schematic and also take the updated pictures. With a little luck I'll post up at least the pictures tonight.
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