Spencerleehorton

Re: Alternative / non-"boutique" transformers
« Reply #20 on: September 02, 2016, 06:33:28 PM »
I've got some great transformers for U47's, work a treat in my Api-312 pre amps as well, only got 6 left.
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!


ln76d

Re: Alternative / non-"boutique" transformers
« Reply #21 on: September 02, 2016, 06:41:20 PM »
For example, the JFET + PNP combo that's normal in mics like the sE 2200A - that one has a 4:1 ratio transformer.
I was just wondering what's the worst thing that could happen if that got replaced with something like a Neutrik NTE10/3 (apart from the level reduction).

Try, neutrik are so cheap that it's worth to try :)
Your output impedance will be around 30-40ohm so it's not bad for condenser.
Some condenser microphones have option for 200ohm and 50ohm outputs, changing connection of transformer windings, so it works :)

Khron

Re: Alternative / non-"boutique" transformers
« Reply #22 on: September 02, 2016, 06:59:26 PM »
Good to know, then. I've just been fine-tuning the "mechanical design" for a set of PCB's for some upcoming mic mods.

Nice thing is, the width between the PCB mounting holes is the same, for the sE 2200A and the chinese BM800's :)
"Audio" PCB goes on one side of the body rails, DC-DC converter goes on the back, switch PCB gets end-soldered to the "audio" board.

I was thinking of being able to use the switch & DC-DC converter with both audio circuits (JFET+PNP+trafo, and a modified Schoeps, like the stock BM800 circuit). There might just be enough space left in the bottom of a BM800 body, if you choose to shoehorn a transformer in there :D

Either way, just earlier today i placed an order from Mouser, i needed a bunch of components from them, and before the checkout, i searched for NTE10/3, and added 4pcs to the order. And now we wait... :P

Actually, getting the PCB's made in China's gonna take a while longer... ;D

For example, the JFET + PNP combo that's normal in mics like the sE 2200A - that one has a 4:1 ratio transformer.
I was just wondering what's the worst thing that could happen if that got replaced with something like a Neutrik NTE10/3 (apart from the level reduction).

Try, neutrik are so cheap that it's worth to try :)
Your output impedance will be around 30-40ohm so it's not bad for condenser.
Some condenser microphones have option for 200ohm and 50ohm outputs, changing connection of transformer windings, so it works :)
Khron's Cave - Electronics - Audio - Teardowns - Mods - Repairs - Projects - Music - Rants - Shenanigans

Gus

Re: Alternative / non-"boutique" transformers
« Reply #23 on: September 03, 2016, 09:59:32 AM »
When i first started working with microphones I spend over $1500 buying different transformers. They can sound very different even after adjusting the circuits.
I would build transformerless if you want to save money on a microphone output transformer.

mhelin

Re: Alternative / non-"boutique" transformers
« Reply #24 on: October 05, 2018, 08:42:49 AM »
How about using small power transformers (EI30 core usually, so size about same as BV8 but only single bobbin)? The 1-2VA 240V 8or 230V)/2x12V would make a 10(9.6):1 transformer and with 2x18V secondary you would get 6.66(6.39) : 1 one  with a CT for the phantom feed. Here a 2 x 15V (7.67:1) 2.3VA for an example: https://uk.rs-online.com/web/p/pcb-transformers/1213830/

There is also the Velleman LT44 (https://www.velleman.eu/products/view/?country=nl&lang=en&id=11604) which is quite small one (20x16x16mm in size) which is bigger than NTE 10/3 (14 x 11 x 12 mm),
Mikko

gyraf

Re: Alternative / non-"boutique" transformers
« Reply #25 on: October 05, 2018, 09:03:56 AM »
in power transformers you have pri and sec would on mechanically separate coils for isolation and safety - but this results in very poor coupling and high leakage inductance, making most of them unusable for audio.

Also, low-power cores requires so many windings on pri that you drown in wire resistance. And capacitance.

An exception is for power output applications - e.g. plate-to-headphone or even plate-to-speaker - here you can be lucky at times.

Jakob E.
« Last Edit: October 05, 2018, 09:07:09 AM by gyraf »
..note to self: don't let Harman run your company..

analogguru

Re: Alternative / non-"boutique" transformers
« Reply #26 on: October 05, 2018, 04:21:51 PM »
So when I need a fast and cheap solution I take a 600 Ohm 1:1 transformer cannibalized from an old computer-modem.  EI25-core, DC-resistance 35 Ohm, inductivity 4H : 35 Ohm/4H, ....

If I need a 1:10 transformer I cannibalize the next DI-box bought for € 9,90:
https://www.thomann.de/at/millenium_die_dibox_passiv.htm
EI25-core, 270 Ohm/750mH  : 1,1 kOhm/>20H

If I need a center-tapped I take on of these for € 14,50:
https://www.ltt-versand.de/Ton/Audio-Tools-und-Zubehoer/DI-Boxen/OMNITRONIC-LH-053-DI-Box-passiv::39430.html?language=de&utm_source=google&utm_medium=shopping&gclid=EAIaIQobChMIqaCVq4rw3QIVEVQYCh37eQCpEAYYASABEgKgQ_D_BwE
EI-25-core, 32 Ohm/200mH (CT) : 680 Ohm/14H

Did you now that my old Sowter mic-transformers (approx. 9045) which I used in the late 70's to make passive DI-boxes have an EI25-core too ? 2x 57 Ohm/2x 1,9H : 1,15 kOhm/>20H
Ok, ok, they are in a Mu-metal-can filled with wax.....

And yes, those transformers DI-Boxes are not Haufe BV107, but usually they arrive within 3 days, (not months or years):
https://groupdiy.com/index.php?topic=68862.40
.

« Last Edit: October 05, 2018, 04:49:19 PM by analogguru »

mhelin

Re: Alternative / non-"boutique" transformers
« Reply #27 on: October 30, 2018, 04:42:55 AM »
How about using two (cheap) transformers in the same output circuit, primaries in series, secondaries either in series or parallel (different ratio and output impedance)? Can you possible gain any mutual inductance by placing the transformers next to each other as close as possible (without actually taking the coils and bobbins  and using some UI laminations to make the single transformer the proper way)?
Mikko

ln76d

Re: Alternative / non-"boutique" transformers
« Reply #28 on: October 30, 2018, 08:17:02 AM »
How about using two (cheap) transformers in the same output circuit, primaries in series, secondaries either in series or parallel (different ratio and output impedance)? Can you possible gain any mutual inductance by placing the transformers next to each other as close as possible (without actually taking the coils and bobbins  and using some UI laminations to make the single transformer the proper way)?

I think that with two transformers, especially cheap, you can have phase issues. Didn't tried, only first thought ;)
I did parallel and series wiring in single transformer (for multiple different transformers) in microphone circuits with really good results.

gyraf

Re: Alternative / non-"boutique" transformers
« Reply #29 on: October 30, 2018, 09:45:24 AM »
..and no, you don't get any coupling by mounting them close..
..note to self: don't let Harman run your company..


mhelin

Re: Alternative / non-"boutique" transformers New
« Reply #30 on: October 30, 2018, 04:37:23 PM »
..and no, you don't get any coupling by mounting them close..
Yeah, an answer I kind of expected. I guess even if the two transformers - as an example model I use "Eagle" LT44 / P631M transformer from Ebay / Velleman / www.electronelec.co.uk which uses small EI-19 core just a little bit larger than that of NTE10/3's and costs less than 2 pounds or 3 euros - had the cores/laminations welded together I think the magnetic flow wouldn't flow  such way like in UI or C or other similar core transformer that it would give any mutual inductance.  You could cut the middle sector of E-laminations and put two coils on the same core but the sectors left have only half of the width (about 3mm or so vs. 5mm) so it doesn't work well either.  It's difficult to find such small UI laminations, or any other.
« Last Edit: October 30, 2018, 04:51:23 PM by mhelin »
Mikko