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. >
