Tom, you'd be surprised at how little my knowledge is on the subject matter of transformers.
I want to add input transformers to former reel to reel recorders' tube electronics (yes, those things...) to convert 'em into mic preamps and I am looking at contemporary catalogues from Cinemag and Sowter. I am also looking at old "mic to grid" transformers by UTC, Triad, Altec, Ampex, RCA, Rauland, Newcomb, Dukane, Bogen... You name it: they all have a secondary rated around 50.000 ohms and an input around 200 ohms. The former current manufacturers only have one model each with those figures (Cinemag has a good Altec 4722 replacement and Sowter has a replacement for the Ampex 351 in their vintage section) and when I personally inquired about which of their model could best suit my needs (providing schematics) they both indicated a 200 in/10.000 out ohms. Since I know nothing 'bout transformers, I keep wondering why the secondary figure has changed in years... Then again... sorry, maybe this is not the right place. Gabe. ________________________________ Da: Tom G <[email protected]> A: [email protected] Inviato: Ven 25 marzo 2011, 14:05:05 Oggetto: Re: NEOTEK: Adding Transformers Gabe, I would benefit from this too.; good idea. I know there are DIY forums that discuss transformers, but I wasn't impressed with the knowledge level. Tom --- On Fri, 3/25/11, Gabriele Ponticiello <[email protected]> wrote: >From: Gabriele Ponticiello <[email protected]> >Subject: Re: NEOTEK: Adding Transformers >To: [email protected] >Date: Friday, March 25, 2011, 3:42 AM > > >Speaking of transformers... > >Jim, Tom: is there a virtual place where we could discuss the specific subject >matter and I could ask questions without annoying Neotek aficionados? > >Thank you. > >Regards, Gabe > > > > > > ________________________________ Da: Tom G <[email protected]> >A: [email protected] >Inviato: Ven 25 marzo 2011, 04:23:39 >Oggetto: Re: NEOTEK: Adding Transformers > > >I should have enough spare parts (pots, caps, etc.) to start experimenting now >that I have my transformers. The series resonant circuit...I am quite familiar >with the resonant frequencies of guitar and bass pickups because I make them. >Usually during R&D of a new pickup design, one of the tests I do is to >document >the resonant frequency. > > >I will have to look up what capacitance's I'll be running into. My 2 track is >a >Sony APR-5003 and my AD/DA converters are SSL Alpha-Links. > >Thanks for all the info! This will be a very interesting and fun project to >build. > >Tom > > > > > > >--- On Thu, 3/24/11, Jim <[email protected]> wrote: > > >>From: Jim <[email protected]> >>Subject: Re: NEOTEK: Adding Transformers >>To: [email protected] >>Date: Thursday, March 24, 2011, 11:01 AM >> >> >> >> >>Greetings, >> >>Hi Matt, >> >>Great point.............I wasn't sure how much to write (or not). Please feel >>free to contribute anything else that comes to mind. >> >>Regards, Jim >> >> >>At 05:53 AM 3/24/2011, you wrote: >>> Hi >>> When simply adding a transformer on an output you need also to consider the >>>output capacitor, assuming the circuit uses them which many do. >>> This will cause a series resonant circuit with the transformer and it it >>>possible this resonance happens in the audio band, or nearby. High impedance >>>'line in' transformers of remote connected gear suffer less but it is quite >>>easy >>>to get a 3dB or more 'boost' at some frequency. Increasing the output >>>capacitor >>>WAY beyond usual values usually 'cures' this. Values in excess of 1000 uF >>>may be >>>necessary. >>> I had this discussion a while back with a guy using a 600 Ohm 1:1 >>> transformer >>>(Sowter but the principle is valid for any similar types) and with a 47uF >>>cap >>>(as used in the suggested circuit) it gave a 4dB boost at about 20Hz, hardly >>>an >>>accurate response. (I can't remember the exact values now but it is an >>>example). >>>Gratifyingly doubling the cap halved the boost frequency, as 'laws' predict. >>> Matt S >>> >>> On 23/03/2011 23:35, Jim wrote: >>>> >>>> Hi Tom, >>>> >>>> Sorry I didn't explain this..............I had posted about transformers >>>>previously and assumed you saw that. Please keep in mind that entire books >>>>have >>>>been written on these topics. Anway, to maintain its rated frequency >>>>response a >>>>transformer requires some specific secondary termination, usually an R, >>>>sometimes an RC. In many cases this is achieved by the input Z of the >>>>component >>>>that its feeding. Without going into too much detail and history, back in >>>>the >>>>"old days" equipment was designed to a standard 600 Ohm line (matching >>>>load); >>>>all inputs and outputs were "matched" so that anything could be connected >>>>to >>>>anything else and it would all work out just fine. >>>> >>>> Since we've pretty much abandoned that approach, we run into the >>>> situations >>>>of non-matching loads; which can adversely affect both frequency response >>>>and >>>>the optimum transfer of voltage/power/etc.. Now we tend to think in terms >>>>of >>>>bridging loads; which is to say that the optimal situation would be an >>>>output >>>>impedance of zero feeding an infinite input impedance. Of course in the >>>>real >>>>world that situation does not exist. In general, we'll figure the output Z >>>>is >>>>pretty low (a few Ohms) and the input Z is high (say at least 1K Ohms). If >>>>you >>>>have a scenario where the ratio is on the order of 1:1000 or greater, >>>>things can >>>>work out pretty well. The problem comes when the output Z is high and the >>>>input >>>>Z is low. The most common example of this is plugging a bass guitar (with >>>>passive pick ups) directly into a console. The relatively high output Z of >>>>the >>>>pick up is severely loaded down by the relatively low input Z of the >>>>console. >>>>That's why we usually would use some type of direct box that matched the >>>>correct >>>>loading for the pick up; for example plug the same bass into an old tube >>>>bass >>>>guitar amp. Its going to sound much better. Typical input Z will be over >>>>1MR, >>>>sometimes up over 5MR. >>>> >>>> Now lets look at your specific situation. The UTC is likely rated to >>>> drive >>>>into a 600R load (see if you can find the data sheet for it; there may be >>>>several ways to strap the input and output side for some other >>>>combinations; >>>>150R, 300R, etc.). The actual load will be determined by what the input Z >>>>of the >>>>device it is feeding. Say for example, it's feeding a solid state line >>>>level >>>>input device. That may have an input Z of between 1K and 10K; feeding a >>>>tube >>>>line level device may have an input Z of over 100K. So in either case a >>>>bridging >>>>load is in effect, but at pretty different ratios. Hook the transformer up >>>>"as >>>>is" or with the strapping set for 600:600. Then after you have >>>>measured/listened, etc. try installing a resistor in parallel with the >>>>transformer secondary; for example, try a 500R pot with just one end and >>>>the >>>>wiper connected. That puts the resistor in parallel with the input Z of the >>>>loading device, and will result in dropping the Z the output transformer >>>>sees. >>>>This will likely result in lower output level, but the interesting part is >>>>how >>>>it may affect the frequency response. So, this allows you to "tune" the >>>>circuit >>>>to perhaps achieve a beneficial effect. You don't have to limit yourself to >>>>the >>>>value I gave; try whatever you have; listen and let your ears be the judge. >>>> >>>> OK, hope that helps and that I didn't make too many errors. Just coming >>>> off the >>>>flu myself. Good luck! >>>> >>>> Regards, Jim >>>> >>>> >>>> At 01:22 PM 3/23/2011, you wrote: >>>>> Hi Jim, >>>>> >>>>> What do you mean exactly? Try using the different impedance taps on the >>>>> UTC's? >>>>>Sorry, but I think I might be on the verge of a nasty cold! >>>>> >>>>> Tom >>>>> >>>>> --- On Wed, 3/23/11, Jim >>>>> <mailto:[email protected]><[email protected]> >>>>>wrote: >>>>> >>>>> From: Jim <mailto:[email protected]><[email protected]> >>>>> Subject: Re: NEOTEK: Adding Transformers >>>>> To: <mailto:[email protected]>[email protected] >>>>> Date: Wednesday, March 23, 2011, 12:10 PM >>>>> >>>>> Hi Tom, >>>>> >>>>> After you get the project built up and do some testing, if you have time >>>>> mess around with the secondary terminations. I'd be very interested to find >>>>> out what happens. >>>>> >>>>> Regards, Jim >>>>> >>>>> >>>>> >>>>> >>>>> At 12:40 PM 3/23/2011, you wrote: >>>>> >I received a couple UTC A20's and should have my Edcor's in tomorrow. I >>>>> >should have the chassis made and wired by late weekend. I am very curious >>>>> >to hear the differences and see if they are very noticable. Regardless, it >>>>> >will be a fun project. >>>>> > >>>>> >Tom >>>>> > >>>>> >--- On Wed, 3/16/11, Brian Roth >>>>><<http://us.mc657.mail.yahoo.com/mc/[email protected]>[email protected]> >>>>> wrote: >>>>> > >>>>> >From: Brian Roth >>>>><<http://us.mc657.mail.yahoo.com/mc/[email protected]>[email protected]> >>>>> >>>>> >Subject: Re: NEOTEK: Adding Transformers >>>>> >To: >>>>><http://us.mc657.mail.yahoo.com/mc/[email protected]>[email protected] >>>>> >>>>> >Date: Wednesday, March 16, 2011, 10:11 PM >>>>> > >>>>> >On 3/16/2011 13:02, Ike Zimbel wrote: >>>>> > > >>>>> > > Hi Brian, >>>>> > > I'm pretty sure you published those specs on the Ampex list...check the >>>>> > > archive! >>>>> > > All the best, >>>>> > > Ike >>>>> > >>>>> > >>>>> >Dear Ike, >>>>> > >>>>> >I forgot I had posted some measurements on the Ampex list! I found the >>>>> >following from the Jan, 2005 archives, which I believe were measurements >>>>> >of the "smaller" series of Edcors: >>>>> > >>>>> ><<http://www.edcorusa.com/products/143-wsm600-600.aspx>http://www.edcor >>>>> >us >>>>>a.com/products/143-wsm600-600.aspx><http://www.edcorusa.com/products/143-wsm600-600.aspx>http://www.edcorusa.com/products/143-wsm600-600.aspx >>>>> >>>>> > >>>>> >Here is what I wrote 6 (!) years ago: >>>>> > >>>>> >The replacement Edcors (600:600 impedance versions) arrived today, and the >>>>> >DCR was MUCH more reasonable. Approx. 54.1 Ohms primary, 54.5 >>>>> >secondary. Level drop from open loading on secondary to 600 Ohms was just >>>>> >a bit under 1.5 dB, much what I would expect. >>>>> > >>>>> >For testing, I breadboarded a "zero Ohm source" driver with a 5534 opamp >>>>> >running as an inverter: 10K input and feedback R's, 22 pF compensation cap >>>>> >(between pins 5 and 8) and 22 pF in parallel >>>>> >with the feedback R to tame any overshoot and ringing from the opamp >>>>> >itself. -3 dB response with the opamp circuit calcs to around 723 kHz. I >>>>> >powered the 5534 with +/- 20 VDC from my bench >>>>> >supply, which allowed just over approx + 24 dBu/m at clipping. >>>>> > >>>>> >1 and 10 kHz squarewave response through the iron looked very good, loaded >>>>> >or unloaded, with just a tiny bit of overshoot and ringing. Frequency >>>>> >response was beyond anything I could measure with my >>>>> >Amber (bandlimited at around 500 kHz or so) which came up with -1 dB at >>>>> >approx 6 Hz and 300 kHz. Bypassing the Amber and just watching the scope, >>>>> >usuable response was extended, and limited by the >>>>> >rolloff of the opamp driver on the top end. With a 50 Hz square wave, >>>>> >there was very little tilt which indicates LF response well below 20 Hz. >>>>> > >>>>> >Next I measured THD, and at some of the lower levels I was fighting noise >>>>> >picked up from the breadboarding! Here are various "spot measurements". >>>>> > >>>>> >1 kHz, 0 dBm = 0.0085% +10 dBm = 0.005% +20 dBm = 0.0025% (noise was >>>>> >an obvious factor!) >>>>> > >>>>> >100 Hz, 0 dBm = 0.03% +10 dBm = 0.015% + 20 dBm = 0.05% ** >>>>> > >>>>> >50 Hz, 0 dBm = 0.055% +10 dBm = 0.035% +20 dBm = 0.18% ** >>>>> > >>>>> >20 Hz, 0 dBm = 0.07% +10 dBm = 0.085% + 20 dBm = 0.7% >>>>> > >>>>> >Spot checks at LF and + 20 dBm: 40 Hz = 0.3% 30 Hz = 0.45% >>>>> > >>>>> >(Actual 20 Hz numbers may be a bit lower since my 20+ year old Amber was >>>>> >having a hard time nulling at 20 Hz). >>>>> > >>>>> >** Notice the THD dip at the "middle" levels at those frequencies. I >>>>> >also think I detected a THD rise at levels below 0 dBm but was fighting >>>>> >noise issues. >>>>> > >>>>> >I have a bunch of other numbers, but you get the drift. Looking at >Jensen >>>>> >choices, this Edcor is just a bit "rattier" than a JT-11-EMCF which sells >>>>> >for $66.85. These Edcors are a bargain!! >>>>> > >>>>> >Bri >>>>> > >>>>> > >>>>> > >>>>> >------ >>>>> > >>>>> >View the list online at: >>>>> ><<http://www.mail-archive.com/[email protected]>http://www.mail-arc >>>>> >hi >>>>><mailto:ve.com/[email protected]>ve.com/[email protected]>http://www.mail-archive.com/[email protected] >>>>> >>>>> > >>>>> >You can unsubscribe at anytime by sending an email to >>>>> ><mailto:[email protected]>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]>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. >>>>> > >>>>> >>>>> >>>>> ------ >>>>> >>>>> View the list online at: >>>>><http://www.mail-archive.com/[email protected]>http://www.mail-archive.com/[email protected] >>>>> >>>>> >>>>> You can unsubscribe at anytime by sending an email to >>>>><mailto:[email protected]>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]>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. >>>> >>>> >>>> ------ >>>> >>>> View the list online at: >>>><http://www.mail-archive.com/[email protected]>http://www.mail-archive.com/[email protected] >>>> >>>> >>>> You can unsubscribe at anytime by sending an email to >>>><mailto:[email protected]>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]>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. >>>> >>>> >>>> >>>> >>>> No virus found in this incoming message. >>>> Checked by AVG - <http://www.avg.com>www.avg.com >>>> Version: 9.0.894 / Virus Database: 271.1.1/3524 - Release Date: 03/23/11 >>>>07:34:00 >>>> >> >> >>------ >> >>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. >> > >
