U47 Style Clone EF80/800 with New style Transformer

[Murdock]

I Would buy one!
I've send you an email.

 

[Spencerleehorton]

Here is some specs!

B5887 is a 6.5:1 ratio audio transformer designed to interface between valve microphones and pre-amps.

As a microphone output transformer the high impedance side connects to the valve output (nominally 10kΩ output impedance), and the low impedance side provides the microphone output, intended for a pre-amplifier input impedance of 1.5kΩ to 3kΩ.

As a pre-amp input transformer the low impedance side is configured as the input, and the high impedance side provides the stepped-up signal connected to the amplifier circuitry.

In neither of these applications does the transformer operate in a classic impedance matching configuration, and thus descriptions of such devices as being ‘200 ohm’ transformers or such like are practically meaningless. Individual winding resistances have negligible effect on overall performance other than introducing a fixed signal loss. The loss introduced by B5887 is typically less than 2dB compared to an ideal lossless transformer.

B5887 is designed to provide extremely flat frequency response 20Hz to 20kHz in the above applications, with very low levels of harmonic and intermodulation distortion at typical signal levels. Its magnetic core material and low parasitics ensure excellent audio transfer. Harmonic distortion levels are given for worst case situations (single tone, lowest frequency, highest operating level). In most practical situations, signal distortion will be inaudible, typically below 0.01% THD. Caution: do not pass DC current through either winding as this may permanently impair signal performance.

B5887 is available packaged as a through-hole part (order code B5887.00) and with flying leads (order code B5887.01). Other packaging (flange mount, screened etc) available on request.

Note: all measurements at low impedance side (4-6) unless otherwise shown.

 

[Spencerleehorton]

If anyone else wants to test there only a few more available from the first batch, so get in touch fast!

 

[Matt Nolan]

B5887 is a 6.5:1 ratio audio transformer designed to interface between valve microphones and pre-amps.

As a microphone output transformer the high impedance side connects to the valve output (nominally 10kΩ output impedance), and the low impedance side provides the microphone output, intended for a pre-amplifier input impedance of 1.5kΩ to 3kΩ.

As a pre-amp input transformer the low impedance side is configured as the input, and the high impedance side provides the stepped-up signal connected to the amplifier circuitry.

In neither of these applications does the transformer operate in a classic impedance matching configuration, and thus descriptions of such devices as being ‘200 ohm’ transformers or such like are practically meaningless.

Not meaningless, actually true. In your mic output scenario, the low impedance side *is* around 200 ohms. The 10k source impedance on the primary is divided down by the turns ratio squared to look like 237 ohms on the secondary. This is good, as you want a "bridging" connection into your pre-amp. Impedance ratios between 5 and 10 are good for this. You have about 6.3 for a 1.5k input impedance pre-amp, more for a higher input impedance pre-amp.

Matched impedance connections in the audio world are only really useful for loudspeakers and very long transmission systems like telephone networks. Mic to pre-amp and other equipment outputs to other equipment inputs are almost always "bridging" impedance connections.

 

[TLRT]

Email sent!

 

[Spencerleehorton]

Here is the proper spec sheet.

 

[Spencerleehorton]

Page 2

 

[Murdock]

Hey Spence,

would be really nice to have some more comparison tests with other transformers. 

 

[Spencerleehorton]

That's exactly what I have suggested!
But need people to test them, to get as many point of views as possible.

 

[Spencerleehorton]

Here is what the designer has said:

The issue is that the 200 ohms is not a parameter of the transformer itself, so it cannot be in the transformer specification. If I sent the transformer to a test lab and asked them to characterize it they would never come back with a parameter that said anything like 200 ohm impedance. If I look at transformer specifications for suppliers of similar transformers they state ‘Impedance 200 ohm’. In any case, I can tell you that those transformer present nothing like 200ohm except at low frequencies because of their leakage inductance, which is 40mH in the AMI T67. That leakage inductance on its own contributes over 5000 ohms of impedance at 20kHz, so stating that the impedance is 200 ohm (which they do) is at the very least misleading.

Regards

Spence.

 

[Matt Nolan]

It presents a nominal 200 ohm output impedance when used in the 10k ohm valve mic output configuration. Specs like this are usually measured at 1kHz spot frequency.

 

[Spencerleehorton]

updated Spec sheet.

 

[Spencerleehorton]

Hi All,

I have the first little batch of test transformers now, sorry about the wait, but i will send out tomorrow to the people who have  already given me their details.
If anyone else is interested i have about 6 left for testing.

regards

Spence.

 

[Spencerleehorton]

Another pic from iphone.

 

[Spencerleehorton]

make that only 4 left now.

 

[Spencerleehorton]

I have asked the designer to talk about what differences he make in the design compared to the other designs available, so hopefully once he has sent that to me you can read and hopefully comment on that.

regards

Spence.

 

[Spencerleehorton]

Have got 8 left now as I was going to use 4 of these in my API-312 preamps but I will get some more made for this purpose.
Anyone else need some for testing?

Regards

Spence.

 

[Murdock]

Hey Spence, sorry, but have you received my payment?

 

[Spencerleehorton]

Hi Murdock,

Yes I will send tracking details in a little bit.

Regards

Spence.

 

[Spencerleehorton]

sent tracking finally!!!