Jim, Thank you for the information. I would love to learn more about your findings! Coils in general are interesting to me when related to audio. I make guitar and bass pickups and it is amazing at the difference in sound one can achieve with fairly minor tweaking. Tom
--- On Fri, 3/18/11, Jim <[email protected]> wrote: From: Jim <[email protected]> Subject: Re: NEOTEK: Adding Transformers To: [email protected] Date: Friday, March 18, 2011, 11:35 AM Hi Tom and group, I've had the chance to do some analysis of transformers over the years. Let me preface this by stating I am in NO way an expert on them! So, to the real experts out there, please don't beat me up too bad; these are generalizations only. This will be a very short treatment, devoid of actual measurements (for now). Audio transformers are a subject that I have a great interest in and have done some work in measurement in an attempt to quantify the effect they have. If the intention of installing transformers is for isolation, breaking up ground loops, ease of interface, etc. then you want to find a high quality unit that meets the band width specification AT the rated AC voltage that will be applied to it. Keep an eye out for how the ratings are stated. For example, a band width of 20Hz-20KHz at 100mV would not necessarily correlate to the same at 2V! The frequency extension at both ends is limited by core magnetizations/saturation and the distortion products generated by the increased applied voltage. The other way to look at that is that the band width narrows as the input voltage is increased beyond the rating of the device. Now the interesting way to look at that is backwards...............say you want to use the transformers for a coloration effect. You can then take advantage of the band width at lower specified input voltage by driving the transformer beyond that. This is what results in a "transformer sound". Meaning, either the band width becomes limited and/or the distortion products become audible. So, in this case you may not want to use a very high quality unit, but either something kind of funky or voltage under rated or band limited. When most (competently designed) transformers are used within the ratings, we weren't able to measure much of anything in regard to band limiting or distortion products. However if you push the input level to where the core saturates, some interesting and audible artifacts were noticed. Some years ago a client came to use with the idea of building a dedicated "transformer box", to be inserted anywhere in a line level signal path with the intent of adding some unique coloration. The specific units he wanted to use were a pair Western Electric 111C "repeat coils". These were line level 600:600R (or could be strapped for a couple different ratios). So we were tasked with the design of a circuit to bring maintain input : output at unity gain and package the whole thing up in a useable fashion. http://www.analogbros.com/pictures/coil%20box/ At the time we were working with a colleague who was investigating a very interesting amplifier topology as published by Dr N Thaggard. The initial design was as a low level phono stage, which could be easily adapted for say a mic level. We manipulated this for line level. In short, the active circuit measured essentially flat within the intended band width, exceeding it by a quite a bit on the high frequency end. Anyway, to cut to the chase. To be honest, when the project was complete, I really couldn't hear any significant difference between input and output when the levels were carefully calibrated. However...........................there is a kind of built in "adjustment" that transformers have to allow you to skew the response...........the secondary termination. There is likely a manufactures suggested termination; depending on where in a given circuit and type of transformer, this could be a simple R or an RC combination. Manipulation of this can indeed result in audible differences. We ended up installing a variable R termination on the device to allow for interjectional mis-adjustment of the termination. Given the time, there is plenty more I could write and if I can locate the data from the experiments I'll be happy to post it. Got to run now, work to do. Regards, Jim At 12:34 PM 3/14/2011, you wrote: > Hello, > > I have been thinking about adding some output transformers to my Series One. > I am thinking about building a rack chassis with two (for now) transformers > and having them available via patchbay... so obviously they are not > technically in the Neotek. I could then patch them in on a direct output or > on the master outs before hitting tape or my convertors. > > Should be easy enough, but my question is if anyone has some suggestions as > to what transformer is a good match sonically with a Series One. I am > considering this only for more options in terms of adding some different > sonic charactor and color. The design would be just a passive circuit. > > Tom ------ View the list online at: http://www.mail-archive.com/[email protected] You can unsubscribe at anytime by sending an email to mailto:[email protected] with "unsubscribe neotek" in the message body. If you have any difficulties, or questions --please send an email to mailto:[email protected]. The Neotek list is lovingly hosted by Catapult Web. Remember that any message or reply sent to the list will be automatically forwarded to all subscribers. Vive Le Neotek! Thanks.
