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RE: Parafeed PP transformer?

141.151.17.78

In Reply to: RE: Parafeed PP transformer? posted by twystd on May 20, 2009 at 13:43:16

Hi Roe:

Thanks for the post. As usual I am tardy in my email replies. So let's see if this answers your questions.

I did write a post on the benefits of parafeed pp--- please see the hot link below.

The RH-PF is a single ended parafeed trans--- you could potentially use any of the appropiate PP tranneys that we build. The first one that quickly comes to mind is our Peerless S-240-A. It is a twenty watter with a 5K primary winding. We also have some limited coil stock of our AS-250 twenty watter (based on original Acrosound design principles).

But none of the units that we currently have in stock--- twenty watters with a 5K primary--- are going to have a "split" center tap---- meaning two leads out. We could potentially build a pair like this for you the next time we run a group of a particular 20 watt design.

I believe you had also asked (in your email) about a special IT and if we might be able to build one for you. At this time I would beg off as we are just way to bizzy and I am still trying to catch up on existing orders.

Our main sheet of stock\catalog designs can be found at

http://www.magnequest.us

hope this helps.

MSL

Builder of MagneQuest™ & Peerless™ transformers since 1989

pp parafeed benefits (Open in New Window)

Follow Ups:

RE: Parafeed PP transformer? - twystd 10:55:31 05/21/09 (14)
After re-reading your post, I see that you were talking about using an existing PP transformer, not winding a special version with thinner gage wire. I'm not familiar with the AS250, can you tell me something about it?

I saw an article in you Tech Corner, IIRC, about transformers with high inductance, and the more desirable load lines they create. What kind of inductance are we talking about with these transformers? I assume that the inductance goes up, with either pin stripe or nickel cores, is this correct?

twystd
- inductances and loadlines..... - mqracing 12:50:00 05/21/09 (5)
  Hi Roe:
  
  I have written extensively on this subject--- the import of primary impedance and it's effects on loadlines and, hence, the behaviour of
  the amplifier. If you do a search across the different audioasylum forums with my name and inductance--- you'll have plenty of material to read and absorb.
  
  The article written by Voltsec (published on our magnequest.com site) is quite comprehensive--- and uses the 845 tube and circuit application as a the working example. What is shown is that the tube generated distortion itself goes down dramatically as the primary inductance increases. This is because the tube is seeing and working into a larger EFFECTIVE load impedance.
  
  In essence what it required is that to have a stable (relatively non-reactive load for your tube to work into) you must have enough primary inductance to adequately support your nominal reflected primary impedance.
  
  Years ago (and perhaps yet to some extent today) folks would take the nominal or advertised pri impedance of a transformer as it's effective impedance. Which can lead to a lot of mischief--- and misleading specsmanship.
  
  How much inductance--- there is no hard and fast rule--- unless we were living in the Platonic world of forms--- in which case, of course, we would have transformers with infinite inductance and no resistances of any kind--- and no core losses of any kind----
  
  but, here on earth--- we must juggle how much L we can aim at or achieve against a host of other design factors and etc. As a very rough rule of thumb--- the most excellent designs extant (that I know of) are ones that can produce approx 100 henries of L per thousand ohms of reflected pri impedance while keeping the leakage L at or below 1 millihenry per thousand ohms of the nominal reflected pri impedance.
  
  The above level of performance is near rave.... the Peerless 20-20 Plus series will generally meet this spec... and there are perhaps a few other tranneys made worldwide to this high level of specification. But these units are tough to design and quite intricate to wind. They will have a ton of interleaving--- the insulation materials must be carefully chosen--- the lead positions, starts, and stops of the windings must be laid out near perfectly--- it is really the state of the art that goes into these guys.
  
  Is this level absolutely required to enjoy music? Nope. It's an IDEAL. Quite, quite nice if you can acheive it design wise--- and even better if the customer can afford to buy and use it.
  
  And, again--- my "rule of thumb" simplifies the shit out of the design process---- and how you must really optimize for a very wide range of factors in design--- stuff in addition to the amount of L that the primary has--- but the primary L is none-the-less one of the most critical design parameters.
  
  hope this helped---
  
  MSL
  
  Builder of MagneQuest™ & Peerless™ transformers since 1989
  - RE: inductances and loadlines..... - twystd 13:14:15 05/21/09 (4)
    Michael- Thanks for taking the time to explain this, and I realize there are trade offs and no one spec makes or breaks a transformer. The intricacies of all of this is obviously over my head. Let me just ask you to advise me on this.
    
    I think you've seen the circuit I'm trying to build, It's something I want to try, but if it doesn't work out, I'll try a more conventional design. Whatever I end up with will be a PP class A amp, running either 2A3-40s or 300BXL tubes. The dual center taps are required.
    
    If you were building a beast like this which would be your choice, in the $400.00 (possibly a little more) a transformer range. I could go slightly more, but would have a tough time affording the price of the Peerless 20-20 plus.
    
    twystd
    - RE: inductances and loadlines..... - Caucasian Blackplate 13:17:09 05/23/09 (3)
      What aspect of the circuit demands a split primary?
      - RE: inductances and loadlines..... - twystd 15:43:31 05/23/09 (2)
        
        In Reply to: RE: inductances and loadlines..... posted by Caucasian Blackplate on May 23, 2009 at 13:17:09
        
        I was thinking of a parafeed PP with CCSs on the plates. The center taps have caps that return to the cathodes.
        
        twystd
        
        RE: inductances and loadlines..... - braubeat 08:01:00 05/24/09 (1)
        
        In Reply to: RE: inductances and loadlines..... posted by twystd on May 23, 2009 at 15:43:31
        
        You know there is no particular reason to put caps to the cathode in a shunt feed PP. If you had a center taped primary you could put a cap between the two sections to insure no unbalanced DC in the windings. But it would probably sound even better to balance the current some other way and eliminate the caps all together. Then you do not need a center tap at all.
        Google Marcel and Clovis by Phil Sieg. He has built an amp along these lines.
        Michael
        
        RE: inductances and loadlines..... - twystd 13:16:10 05/24/09 (0)
        
        In Reply to: RE: inductances and loadlines..... posted by braubeat on May 24, 2009 at 08:01:00
        
        Yes Marcel and Clovis is a really interesting design. The design I'm thinking of uses the garter circuit to balance the tubes. I can't have a shared cathode resistor for the garter circuit to work, so it's a PP stage rather than a differential stage.
        
        PP amps usually require a cathode bypass cap for full power. By putting the cap returning to the cathodes, I don't think I'd need a cathode bypass cap, plus they block any DC on the transformer. The thought is to have a really balanced PP stage, with minimal capacitors, and taking advantage of no DC, unbalanced or not, on the transformer.
        
        No telling what it will sound like, it's just an experiment I want to explore. I haven't seen a schematic like it before, and neither have my local DIY friends, so thought it might be interesting. If it shows promise, I will release the schematic to the DIY community. If it sucks oh well, I'll just drop back and punt to something more proven.
        
        twystd
- AS250 info - mqracing 12:31:41 05/21/09 (7)
  This is a 20 watt push pull transformer which is designed in accord with the principles of the original Acrosound transformer patents. It is a 5K CT primary (i.e., 5000 ohms end to end) and has 16, 8 and 4 ohm secondaries. It is available with nickel lams or nickel pinstriped laminations. I have several of these coils in stock--- we built them custom for an overseas OEM--- it is not a normal catalog item.
  
  MSL
  
  Builder of MagneQuest™ & Peerless™ transformers since 1989
  - RE: AS250 info - twystd 12:53:18 05/21/09 (6)
    Can you please tell me the H of primary inductance for the different options of the AS-250, as well as the S-240-A. I was thinking of going with a nickle core S-240-A, but would like more details. The AS-250, and the S-240-A are similar in rating and impedance, what are the differences. Sorry, don't want to be a PITA, but want to make sure I get the best transformer for my needs.
    
    twystd
    - RE: AS250 info - mqracing 13:10:48 05/21/09 (5)
      Hi Roe:
      
      Like I said in another post today--- primary L is important--- very important--- but not singularly important. There are 436 other factors\variables that you must also optimize to get a good to great output transformer.
      
      On many of our products we do not publish L numbers for many, many reasons.
      
      What your safe in assuming is that nickel will have greater L than a nickel pinstripe which will likewise have greater L than M4 which itself will have greater L than M6.
      
      Of greater import (at least in our designs--- which will have adequate L unless otherwise stated) is that the choice of lamination types is best made from a subjective point of view--- not a solely technical bench derived measurement--- and here it is personal experience and preference that will come into play. We have some customers who love nickel--- others who prefer M4 and yet others who swear by nickel pinstripe.
      
      Each sounds a bit different--- each has it's own colours--- their own strengths sonically--- and unless your willing to marry the girl I pick out for you (smiles here) then you need also to explore and learn of your own sonic preferences in terms of core materials and etc.
      
      Mike
      
      Builder of MagneQuest™ & Peerless™ transformers since 1989
      - RE: AS250 info - twystd 20:57:08 05/21/09 (4)
        
        In Reply to: RE: AS250 info posted by mqracing on May 21, 2009 at 13:10:48
        
        Being a poor boy, I don't have the funds to "date" the beauties, so will probably have to rely on your pick. I like my transformers like my women, fast, warm, and lots of bandwidth!;-)
        
        twystd
        
        RE: AS250 info - Paul Joppa 22:09:39 05/21/09 (3)
        
        In Reply to: RE: AS250 info posted by twystd on May 21, 2009 at 20:57:08
        
        Even "bandwidth" is an imprecise term, I'm afraid.
        
        Here we are talking of bass response since this is about core materials. Technically, nickel will (for example) have more inductance at smaller signals, hence deeper and lower-distortion bass. But will overload with too much deep bass. So for small signals it has more apparent bandwidth but when pushed it can seem like less bandwidth. And pushing it starts to happen at less than 1/4 of the rated power - another reason Mike is notoriously conservative about ratings.
        
        All this is simplified to steady-state sine wave signals. Music of course in neither steady state nor sine wave, so there is no reliable way to interpret the science in subjective terms. It depends too much on your taste and your music, and how much power you demand from the amp - again your taste but also your speakers and your room. And of course your mood - none of us has only one single personality or taste!
        
        RE: AS250 info - twystd 23:46:15 05/21/09 (2)
        
        In Reply to: RE: AS250 info posted by Paul Joppa on May 21, 2009 at 22:09:39
        
        Thanks Paul, that was very helpful. I do like very dynamic music, at pretty high volume. For example, I like Peter Gabriel's "Up" at pretty high volume with my Straight 8s. Other artists I like are Patricia Barber, Jennifer Warren, Keb Mo, too many to mention, tastes all over the place. I find my single ended 8 watt amp a little lacking, so was looking to take it up a step, to a 15-20 watt PP. Sounds like pin stripe might be the way to go, a little of both worlds.
        
        twystd
        
        RE: AS250 info - DLK1 06:41:45 06/24/09 (1)
        
        In Reply to: RE: AS250 info posted by twystd on May 21, 2009 at 23:46:15
        
        My experiences with the AS-250...
        
        I got a pair of the AS-250 units (M4 I guess, no nickel was offered at the time) when Mike first offered them (mid '90s?). I combined them with a pair of the MQ/Peerless Altec 17173 centertapped driver chokes and made a Brook 22A clone. (WE396 input amp/phase splitter, 5687 driver, Sovtek SP 2A3, no NFB). This made one great-sounding amp. While my speakers are quite efficient, this amp sounds more powerful than the 80W solid-state amp I was using previously. Even with zero feedback the bass is well-controlled.
        
        If this is a relatively-simple coil wind job (compared to a 20-20 series unit), it might make a good budget offering. It sounds good to my ears, anyway.
        
        -Dan
        
        RE: AS250 info - mqracing 21:11:46 06/25/09 (0)
        
        In Reply to: RE: AS250 info posted by DLK1 on June 24, 2009 at 06:41:45
        
        neat. I was just stacking a few pairs of these today from a newer run of AS-250's. These are really nice designs.
        
        A topology such as you describe is so easy and straightforward... that with good tubes, good iron, good layout, etc... it would just plain have to sound quite good.
        
        And funny you mention about the nickel.... I actually stacked one pair with all nickel lams. Did one other pair with M4 lams... and a third pair with M6 laminations.
        
        I'll probably be putting these up for sale very shoortly---- look for an announcement over the next few days or so.
        
        Mike
        
        Builder of MagneQuest™ & Peerless™ transformers since 1989

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