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K&K Audio / Lundahl Transformers

New LL1592 - suggested uses?

172.143.218.62

I've used the LL1540 in parafeed as a line output transformer following the RAKK DAC and Raleigh line stage (discussions below) and it seems to do the job as long as the voltage through it is kept down to around 2v. The LL1592 is billed as a superior replacement, with mumetal laminations.

This sounds good. Has anyone tried this new transformer out? Any views on how it would work in parafeed following a differential pair? Andy

Follow Ups:

RE: New LL1592 - suggested uses? - Dave Davenport 09:53:33 10/05/07 (2)
Hi Andy,

You really need some step-down for your output transformer to get a low output impedance. The LL1592 has a 1+1 : 1+1 ratio so the best step-down with it would be 2:1. I would recommend an LL1674 which would provide either a 4:1 or a 8:1 step-down.

I think that the 5676 has an rp of about 9K Ohms. If so, that is pretty high for this application. Since the two sides are in series, that would be 18K across the primary of the transformer and with a 2:1 step-down you would have an output impedance of 4500 Ohms. With an 8:1 step-down you would have an output impedance of about 280 Ohms.

Dave
- RE: New LL1592 - suggested uses? - andy evans 15:00:26 10/05/07 (1)
  > > You really need some step-down for your output transformer to get a low output impedance. The LL1592 has a 1+1 : 1+1 ratio so the best step-down with it would be 2:1. I would recommend an LL1674 which would provide either a 4:1 or a 8:1 step-down.> >
  
  Hi Dave. Good point. In my particular case, I'd be looking to use the line stage into another valve stage, so input impedence would be high. The input is also balanced, plus cables are designed to be short. So this wouldn't be a priority as it would in the general case - as you point out - where it might need to feed a ss amp or whatever. I also don't want to lose gain if it means another valve stage. Seems like with the RAKK into 70 ohms i/v resistors and 5676 (mu = 15) I get about line level with 1:1. With the 6N6 you can probably afford a stepdown, but I don't envisage using any valve with mu over 15 (DHTs).
  
  > > I think that the 5676 has an rp of about 9K Ohms. If so, that is pretty high for this application. Since the two sides are in series, that would be 18K across the primary of the transformer> >
  
  That's right. So my first priority is to find various usable output transformers that will cope with this. I can't find any data on input impedence on the Lundahl site for the LL1592 - just says it replaces the LL1540. The static resistance is lower - 270 instead of 800 but could be wire thickness (?) since it's physically bigger. I like the idea of mumetal, so if this actually does substitute for the LL1540 I'd be interested in trying it. Do you or Kevin have any more information on it?
  
  I'm also happy to look at other 1:1 transformers for the reasons above, particularly in parafeed judging from the good sound I'm getting. Andy
  - RE: New LL1592 - suggested uses? - Dave Davenport 16:02:27 10/05/07 (0)
    Hi Andy,
    
    I have not used that transformer and do not have any information on it other than that which is publicly available. You will have to rely on Kevin's expertese and experience.
    
    Dave

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