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Balanced L'espressivo - Page 2

post #16 of 29
8/28/09 at 2:32am
Quote:
Originally Posted by luvdunhill View Post
Doug, are you sure you don't need a true RC filter after the input transformer?
well, you can do this by ear, or by scope ...

Anyway, the Lundahls don't need the RC filter.

Quote:
Originally Posted by luvdunhill View Post
I'd probably use a proper 10K volume control in this case myself, as the fewer things in the signal path, the better, right
They both have the same resistors in the signal path. But, with the single pot the sides stay in balance. With the "proper" pot, they don't.

Quote:
Originally Posted by luvdunhill View Post
nope, it's there. I'd go with the Cinemag's personally.
As a budget option, agreed. Though, the edcors are actually pretty good. They lack the 30db shield, but sound quality is reasonable, especially for the budget build.
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post #17 of 29
8/28/09 at 9:49am
Sorry, I should have been clearer. In my experience the RC is needed with the Edcor transformers specified in the schematic, and I wasn't sure if your experience mirrored this or not.

On the pot, yup you're right. I just assumed it was connected differently and didn't actually look at it (wiper connected to the input tube, and other legs across the input tranformer output). The important thing is that the input impedance remain constant and as close to 10K as possible.
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post #18 of 29
8/28/09 at 2:49pm
Quote:
Originally Posted by luvdunhill View Post
Sorry, I should have been clearer. In my experience the RC is needed with the Edcor transformers specified in the schematic
What do you mean by "needed"? My edcor experience is limited to clip leading them in on breadboards.

Quote:
Originally Posted by luvdunhill View Post
On the pot, yup you're right. ... The important thing is that the input impedance remain constant and as close to 10K as possible.
That is one of the issues with this pot arrangement -- the Zin changes. But, it goes from high to higher, the minimum being 2x the input resistors. And, I just don't see this is an issue. If the thing driving the pot's sound changes with different Zin's then the driving stage has issues.
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post #19 of 29
8/28/09 at 3:58pm
Quote:
Originally Posted by dsavitsk View Post
What do you mean by "needed"? My edcor experience is limited to clip leading them in on breadboards.

That is one of the issues with this pot arrangement -- the Zin changes. But, it goes from high to higher, the minimum being 2x the input resistors. And, I just don't see this is an issue. If the thing driving the pot's sound changes with different Zin's then the driving stage has issues.
I found that I need to add a few puff to tune the square wave response of the Edcor. To my ears, this sounded better than just sticking it in uncompensated.

I haven't had good luck with using input transformers in the case where the input impedance of the pot wasn't constant and nearly identical to the output impedance of the input transformer. They didn't sound right to me. Looking at the data sheet as well of many input transformers (well, the few that actually have a comprehensive set of measurements, like the Cinemag), there might be some corroboration for what I'm hearing

edit: I'm assuming the PCW10K/10K is a PCB mount version? Also, there is a 1/4W version called the PC10K/10K. Interesting..
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post #20 of 29
8/28/09 at 5:33pm
Thread Starter 
So how should the output transformers be wired?
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post #21 of 29
8/28/09 at 7:04pm
Quote:
Originally Posted by FallenAngel View Post
So how should the output transformers be wired?
Which OPTs in which topology?
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post #22 of 29
8/28/09 at 7:08pm
Quote:
Originally Posted by luvdunhill View Post
I found that I need to add a few puff to tune the square wave response of the Edcor. To my ears, this sounded better than just sticking it in uncompensated.

I haven't had good luck with using input transformers in the case where the input impedance of the pot wasn't constant and nearly identical to the output impedance of the input transformer. They didn't sound right to me. Looking at the data sheet as well of many input transformers (well, the few that actually have a comprehensive set of measurements, like the Cinemag), there might be some corroboration for what I'm hearing
Fair enough. The (amorphous) Lundahls seem to not have this as an issue which is frankly enough reason for me to use them. Well, that plus I think they sound a lot better than anything else

What is your sense on TVCs and AVCs that have changing impedance and ring in all sorts of uncontrollable ways -- I think, at least with the ones I've used, the positives far outweigh the negatives.
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post #23 of 29
8/28/09 at 9:38pm
Quote:
Originally Posted by dsavitsk View Post
Fair enough. The (amorphous) Lundahls seem to not have this as an issue which is frankly enough reason for me to use them. Well, that plus I think they sound a lot better than anything else
Which Lundahls do you like to use Doug? I'm looking for a set for a project I'm working on.
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post #24 of 29
8/28/09 at 10:44pm
My experience is with the LL1674's. They are 1+1:4+4 so they can be used 1:2, 1:4, 1:8, or any of those in reverse. Nice general purpose transformers for line level stuff.

I actually also quite like the LL1930's for line level output -- slightly less detail, but a little warmer and more forgiving. Also a lot less expensive.
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post #25 of 29
8/29/09 at 1:02am
Quote:
Originally Posted by dsavitsk View Post
My experience is with the LL1674's. They are 1+1:4+4 so they can be used 1:2, 1:4, 1:8, or any of those in reverse. Nice general purpose transformers for line level stuff.
That's a lot of cash though at ~$250. Basically, from a price stand point there is Lundahl > Jensen > Sowter > Cinemag if we consider each vendors TOTL offering.

Jensen added a threaded bushing option in case anyone is interested.

Nate, if you'd like to borrow a few from me to try out down the road, you're more than welcome.
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post #26 of 29
9/1/09 at 4:56pm
Doug:

Seems the LL1690 the only amorphous core that can be wired 1:1? Any idea how it would compare to the LL1674 and LL1930??
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post #27 of 29
9/1/09 at 6:22pm
Quote:
Originally Posted by luvdunhill View Post
Doug:

Seems the LL1690 the only amorphous core that can be wired 1:1? Any idea how it would compare to the LL1674 and LL1930??
The 1676 is 1+1 : 2+2, so if you put the primaries in series and the secondaries in parallel, it is also 1:1. These are all on the same core, and Kevin at K&K says they behave virtually the same, the only difference being what ratio you need. I've not used them, so I can't comment on differences.
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post #28 of 29
9/1/09 at 9:48pm
Quote:
Originally Posted by luvdunhill View Post
Nate, if you'd like to borrow a few from me to try out down the road, you're more than welcome.
Thanks for the offer but I'm a sucker for symmetry and ordered the Sowters yesterday.
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post #29 of 29
9/2/09 at 10:47am
Quote:
Originally Posted by n_maher View Post
Thanks for the offer but I'm a sucker for symmetry and ordered the Sowters yesterday.
cool! I finally decided that my 3575 with "OCC" wire upgrade will go into my new four channel monster amp, along with the largest 5K four-deck, open frame stepper this side of the Mississippi, sporting a custom attenuation curve

Brian says it's stable (i.e. square wave response) with a 5K impedance on each side of the center tap (so 10K across the secondary), but I still plan to do some tests with a square wave generator to see for myself.
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