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lundahl par-pp output transformers your thoughts?

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Posted on January 21, 2017 at 10:08:08
used-hifi
Audiophile

Posts: 1100
Location: Surprise AZ
Joined: March 18, 2003
It has been brought to my attention that my large PP output transformers are not good enough(not enough inductance) for parallel feed SE use

so I am looking for alternatives to use and I looked at the lundahl PP outputs that can be ordered for parallel feed use with no gap, what seems weird from what i have seen and others have told that PP outputs DONT have a gap! ok so then why would i need a so called correct output for parallel feed then? both are the exact same thing?!

anyways the lundahl parallel feed specifications are like 5 cycles to 70kc -3db points this is excellent


now with all this in mind what would be the correct lundahl transformer load for par gm70?

I would like to be able to experiment with loading and the lundahl transformers this is possible. In my idea I would like 6-9-11k for the primary or close

What are my options?
are there other good transformer company options?

Thanks for your help


Lawrence

 

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RE: lundahl par-pp output transformers your thoughts?, posted on January 21, 2017 at 10:42:12
Tre'
Industry Professional

Posts: 17263
Location: So. Cal.
Joined: February 9, 2002
I would think any PP transformer would have plenty of inductance.

It's single ended gapped transformers (and plate chokes) that often don't have enough inductance to make good bass.

BTW A PP transformer doesn't have a "on purpose" gap but there's always some space between the "E's" and the "I's" that make up the core.

With a SE transformer there is paper (used as a spacer) to purposely create a gap between the E's and the I's.

Tre'


Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: lundahl par-pp output transformers your thoughts?, posted on January 21, 2017 at 10:43:44
drsx
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Posts: 369
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Push pull OPTs have a small gap to allow for current imbalance. On EI cores, it also allows for the winding imbalance that is inherent to the way they are made.

The gapless ones are for places where you can guarantee no current, or at least no imbalance - such as parafeed. The small gap will actually linearize them a bit, and will make them usable for other applications. So if these are for experimentation I would get the standard version.

The LL1620's are probably what you want. At 300H of primary inductance, they will be fine for parafeed duty.

 

RE: lundahl par-pp output transformers your thoughts?, posted on January 21, 2017 at 11:30:50
used-hifi
Audiophile

Posts: 1100
Location: Surprise AZ
Joined: March 18, 2003
This is why I am going around and round here not figuring out what exactly I need to play down there with some power 20cycle range


ll1620's are bandwidth limited on the top end.

I am more looking into ll1679-pp much better bandwith and if you order without gap the lowest freq drops an octave!

your thoughts ???

 

RE: lundahl par-pp output transformers your thoughts?, posted on January 21, 2017 at 14:34:31
Scholl
Distributor or Rep

Posts: 1354
Joined: March 8, 2001
Lundahl uses a transformer geometry where windings are separated from each other on different sides of the core. That may work well for push pull but not single ended because the spacing causes a phase loop-d-loop in the 10-20Khz range. For SE an EI core is a better configuration since the windings are on top of each other and the phase issues are above the audible range.

Yes, this statement will cause a controversy.


 

RE: lundahl par-pp output transformers your thoughts?, posted on January 21, 2017 at 14:52:38
used-hifi
Audiophile

Posts: 1100
Location: Surprise AZ
Joined: March 18, 2003
interesting information can you please explain it more clearly?


BTW my gm70 is not series SE but parallel SE



Lawrence

 

RE: lundahl par-pp output transformers your thoughts?, posted on January 21, 2017 at 15:02:18
hennfarm
Audiophile

Posts: 535
Location: Oregon
Joined: October 8, 2008
To achieve many henries of inductance requires lots of turns of wire which increases interwinding capacitance which tends to hinder top end bandwidth.JH

 

RE: lundahl par-pp output transformers your thoughts?, posted on January 22, 2017 at 03:49:48
Scholl
Distributor or Rep

Posts: 1354
Joined: March 8, 2001
The dual coil single C-core style separates the windings so one set is on one side of the core and a second set is on the other. At a certain frequency that physical separation will matter. I used the L6660S and found that point to be 10Khz. It wasn't terrible and the frequency response amplitude was fine. Just a phase loop-d-loop. Using it as a push pull device maybe fine but that wasn't the need at the time.

Maybe look for transformers designed for para-feed or try an EI transfer. Old outputs from 6BQ5 or 6V6 amps can do surprisingly well.

YMMV

 

toroids, posted on January 22, 2017 at 05:10:22
RayP
Audiophile

Posts: 726
Location: Maryland
Joined: June 30, 2005
Another way is to use toroids that are normally used as power transformers. They are quite cheap from Antek.

Once you work out your load, use the following equation to determine the one you require. For example, if you wire the 115 volt primaries in series and the 9 volt secondaries in parallel you would get 5224 ohms for an 8 ohm load.

((115+115) * (115+115) / (9*9)) * 8 = 5224

I am not suggesting that 5224 is a suitable load for a GM70. It is just an example for the equation.

The transformers sound confused to begin with but eventually they break in and become quite listenable. You could get your amp working with the inexpensive transformers ($11 for 25 watt, $17 for 50 watt), try them out for a while as you adjust your amp and eventually move to more expensive iron when you make up your long term decision about operating point.

ray

 

RE: lundahl par-pp output transformers your thoughts?, posted on January 22, 2017 at 06:38:41
TomWh
Audiophile

Posts: 764
Location: Tucson Az
Joined: August 7, 2003
Call Kevin at K+K audio. (Lundahl dist) He is a member here and also has a forum. Kevin is a straight shooter. He knows all the numbers but also listens to results. He will get you in the ballpark.

Regardless of direction you go, I would go with the multiple outputs, so you can fine tune the load with speakers.

Enjoy the ride
Tom

 

RE: lundahl par-pp output transformers your thoughts?, posted on January 22, 2017 at 07:08:45
used-hifi
Audiophile

Posts: 1100
Location: Surprise AZ
Joined: March 18, 2003
Tom, I would agree thanks for your input!



Lawrence

 

RE: toroids, posted on January 22, 2017 at 07:34:27
used-hifi
Audiophile

Posts: 1100
Location: Surprise AZ
Joined: March 18, 2003
Hello Ray, like minds :)

I have several 100va 115v+115v dual 6v secondary antek transformers that I have experimented with and they sound remarkably good, but where they lack is low freq definition in the lower 20-35 cycle range, will they get better with use?. what I like about them is there VERY LOW DCR! they can be very dynamic

I have found other uses for them, including common mode choke duty for both my B+ and for my heater supply, the myths of toroids of not standing any DC current is BS in the newer designs, As a matter of fact they work better then any choke I have in the house.


experimentation is paramount as long as you take precautions as I have done


I have a cheap inductance meter and I do not think its measuring is correct because the torroid measures like 4h and my regular outputs measure like 20h

The torroid should measure very high for 100va core

your experiences??
Lawrence

 

RE: toroids, posted on January 22, 2017 at 08:10:51
RayP
Audiophile

Posts: 726
Location: Maryland
Joined: June 30, 2005
Could you provide a diagram of how you wire the toroid as a common mode choke in your B+. I presume this is your plate choke.

Could you also give an example of a newer design that can handle DC.

My experience of toroids as output transformers is very limited since I only used them in a 6V6 amp designed to cost less than $200.

ray

 

RE: toroids, posted on January 22, 2017 at 08:32:14
used-hifi
Audiophile

Posts: 1100
Location: Surprise AZ
Joined: March 18, 2003
good morning Ray, the same 115v + 115v dual 6v secondary torroid

just use the dual 6v secondary part one on the b+ rail and the other on the neg rail= common mode choke for cheap! just leave the primary leads alone I fuse the neg rail lead just in case the hi voltage wants to short to the neg rail lead. I have used this for a few weeks now with ZERO ISSUES and this is with 1300v dc! make for a quite amp esp with all this hi freq stuff on the power lines these days!

anyways the newer torroids are made differently (core material) that seems to not be bothered my dc, as a matter of fact they do not buzz at all


if you can do a quick experiment give it a go.


Lawrence

 

RE: toroids, posted on January 22, 2017 at 08:42:28
RayP
Audiophile

Posts: 726
Location: Maryland
Joined: June 30, 2005
That's an interesting idea.

By the way, do you have any more info on the type of core material in the newer toroids. Is Antek using this?

ray

 

RE: toroids, posted on January 22, 2017 at 08:44:33
used-hifi
Audiophile

Posts: 1100
Location: Surprise AZ
Joined: March 18, 2003
Ray sorry no I do not you could possibly ask them but then they may change it so you cannot use this LOL

I say dont look a gift horse in the mouth or um something like that


just try it


Lawrence

 

RE: toroids, posted on January 22, 2017 at 15:12:09
used-hifi
Audiophile

Posts: 1100
Location: Surprise AZ
Joined: March 18, 2003
Ray I am looking for some speaker Line matching transformers...the ones i want are 24watts and say 6v6HFL on them


if you or anyone might have a pair or more I would be very interested


Lawrence

 

RE: toroids, posted on January 22, 2017 at 16:27:33
RayP
Audiophile

Posts: 726
Location: Maryland
Joined: June 30, 2005
I don't have line transformers with that designation. Why do you want them?

ray

 

RE: toroids, posted on January 22, 2017 at 16:31:01
used-hifi
Audiophile

Posts: 1100
Location: Surprise AZ
Joined: March 18, 2003
I would like them because I have used them years ago


not that there good or anything :)


so if you happen to see a pair please let me know


Thanks

Lawrence

 

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