Feel free to drop in anytime, Dave. Bring the 507.
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The issue of hum can be pretty easy to fix, just unplug the powercord and reverse it. The psu is directly connected to the mains so this is important.
As Frank points out, the SRD-7 transformers were designed for the SR-5 so they are woefully small for something like the Lambdas or the Omegas. I'm also not a fan of the high ratio as with modern amps we have plenty of power on hand.
What was the ratio of your Lundahl units? I forgot.
I noticed the Transformers in the Woo unit were pretty large.
The one I had at CJ? That was about 1:14 but the larger LL1627's I'm working on are about 1:17 for my unit and 1:23 for the other to make sure Victor's tube amp can drive them properly.
The transformers in the WEE are just slightly larger than the SRD-7 unit's, at least that goes for the prototype. The production units are all hidden away and I don't think anybody has opened them up yet. The transformers in the Illusion were also not that big and again, bog standard EI-cores.
I am looking to build a transformer interface for Stax phones, and am trying to find dome suitable trannies.
People tell me that the Hashimoto transformers are excellent sounding, and I wondered if the HW-40-10 Push Pull would be suitable.
The following sheet shows the recommended usage and connections. The 40-10 is the 3rd down in the chart:
I know people have used Lundahls with success, but I cannot source these for several months, as no one carries stock, and Lundahl are shut for European holidays.
I know very little about connecting transformers, so would appreciate any advice.
I don't read Japanese, but it looks like the transformer you're referring to is designed for speaker use and would not be an appropriate candidate for your intended application. Theoretically, a step-down transformer can be wired in reverse for a step-up. In actuality, because of the construction techniques used in building the transformer, this is rarely practical.
One possible way to increase your knowledge in this area would be to buy a cheap "normal" bias Stax SRD-7 transformer box, build your own bias supply, and experiment. Usually these can be had for about $75.00. on Ebay.
I have an SRD6 SB, but wanted to try something a bit better.
I know that people have used the Lundahl 1630 PP and 1627, and also Sowter transformers. I am just looking for alternatives.
I may be wise to just wait until I can get my hands on the Lundahls.
Just as a follow up to this, I have found some suitable transformers.
There was a guy here in Australia in the 80's, called Alan Moss who was making large quality electrostatic speakers - that looked a lot like Martin Logans.
Being 81, he has long since retired, but a friend mentioned that he has some left over NOS transformers for a SOTA speaker that never reached the market, and that I should talk to him about my requirements.
Anyway, they should be perfect for my requirements - High quality, C-core, bifilar, paper laminated, rated at 100W, with multitaps that will allow me to choose the input impedance and either 25 or 50 turns ratio. Price AU$100 each.
Here is a thread with a few pics of one of Alan's speakers from the 80's: http://www.diyaudio.com/forums/planars-exotics/148251-alan-moss-esls.html
Pic of the transformer: