<!-- DIV {margin:0px;} -->
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
<!--#yiv2125300545 DIV {margin:0px;}-->
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/compose?to=BrianRoth-
[email protected]>[email protected]> wrote:
>>> >
>>> >From: Brian Roth <<http://us.mc657.mail.yahoo.com/mc/compose?
[email protected]>[email protected]>
>>> >Subject: Re: NEOTEK: Adding Transformers
>>> >To: <http://us.mc657.mail.yahoo.com/mc/compose?
[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.
No virus found in this incoming message. Checked by AVG -
www.avg.com Version: 9.0.894 / Virus Database: 271.1.1/3527 -
Release Date: 03/24/11 19:34:00
