U47 Style Clone EF80/800 with New style Transformer

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Spencerleehorton

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Joined
May 12, 2012
Messages
4,034
Location
Felixstowe, Suffolk, UK
Hi Guys,

Thought i'd do a new topic as i had started to put it in another one about the U47 FET!!

This is about a new transformer that i have had designed from the ground up to suit a U47 and other variants.
Im planning on having other versions U67, U87, M49, M269 and C12 to name a few which will be tuned to the circuits and valves to get best performance.
This was an idea of going back to basics and saying, what if we just started again rather than another clone of something that is already out there.
These transformers are very small but pack a powerful punch, very low distortion at very high db(600mV @ +120db)
My arrangements with U47 are using EF800 and at the moment some Chinese capsules, i've made my own pcbs and bodies which i will detail once i get more time after testing.

Spence.
 

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1st test complete and the A version sounds amazing!!! lovely bottom end and clean as a whistle right across the frequencies.
A little more output than what was in my U47 as well!  which means it must be better tuned for this U47 circuit.
Going to test the B version now.

Spence.
 
Here is a few links of some very basic tests.
pretty happy with the results to be honest, didn't believe that the size of the transformer would deliver a good low end but its all there!!

U47 with EF800 about 8 foot away at about waist hight, through Neve 1290, no EQ, all levels at unity and no gain on preamp or line in.

http://picosong.com/ZbsS

Same as above with Abbey Road TG12345 compression on.

http://picosong.com/ZbwR

i will do some basic comparisons with some other transformers as well.

be nice to have a bit of feedback from everyone.

regards

Spence.
 
I would be interested in trying one in a 47-style mic I'm building--what's the ratio? UI construction or something else?
 
Hi,

we are trying out a C version and once testing complete we will decide on which one suits this configuration the best.
the designer has said this:

I’m assuming the output impedance of the valve output stage is around 68kohm (100kohm resistor in parallel with the valve’s own output impedance, which from EF80 characteristics I have deduced is of the order of 185kohm) and that the input to the pre-amp is around 1.6kohm (which is of the order of what you indicated previously). Given these conditions the frequency response of the transformer stage (68kohm source, 1.6kohm load) is around 10Hz to 30kHz (almost completely flat from 20Hz to 15kHz). It is possible to obtain 600mV rms sinusoidal output from the transformer (i.e. input level into the pre-amp) over the full audible range 20Hz to 20kHz, which corresponds to maximum sound pressure, without any visible distortion on the oscilloscope. I suspect that with normal signals there will be little audible distortion.

in the final version there will be flying leads, funky colour, and a few other possible refinements.

regards

Spence.
 
Hi,

Would anyone else be interested in testing these transformers either in a U47 clone or similar?
Seem we have about 5 people interested already and I'm looking forward to what everyone has to say about them.
Should be a small batch of about 25-30 being made.

Regards

Spence.
 
I'am interested too in testing one out, just waiting for the groupbuy capsules to arrive and i already have a spare u47 psu.
what about the cost getting it to Holland.

Best Regards,
Iwan
 
Hi,

Thought I'd put a bit up explaining the ratio of this transformer as a few people did ask about it.

Although you said that these other types are 200 ohm, that cannot really be the output impedance of the microphone because the transformer appears in series with the output impedance of the valve stage suitably transformed down by the transformer ratio. The output impedance of the valve stage itself is very high (Class A stages, which is what that valve stage is, are modulated current sources, which theoretically have infinitely high impedance), and must be of the order of 68kohm if the valve characteristics are to be believed (which I think they can be), so when transformed down by the transformer the mic output impedance cannot really be less than 1.6kohm if a 6.5:1 transformer is used. I know that there is a ‘rule of thumb’ in the audio world that the mic output impedance should be at least 5 times lower than the input impedance of the preamp. I have to say I’m sceptical of that rule of thumb – I think it’s based on nominal impedance at low frequency, because when reactive impedance is included at high frequencies there is no way that the existing transformers on the market will meet that rule of thumb because of their leakage inductance. On the other hand, the reactive impedance of mine is much lower, so there should be no loss of top end even into preamp inputs as low as 600ohm – you should find that response goes on and on, to way above 20kHz,. Like I said, I’m designing this as an electronic engineer, looking at the circuit, and I’m not interested to copy old designs.


Hope this helps.

Regards

Spence.
 
I don't suppose you have any idea about some ballpark final price figures, do you?

... Or perhaps some design details? ;D
 
Hoping to confirm price this week as testing a Third version today.
I have asked the designer for some more details, I don't know how much he is going to give away but I have posted what he has said about and how he has looked at the design as regards valve and preamp.
As far as I'm aware these are the main components a transformer needs to comply with.
More info will follow.

Regards

Spence.
 
Hi,
Had another meeting today and have got a 3rd version to try out.
We talked a little about price and should be around the £50 mark, possibly a little higher with mumetal can.
Designer is going to put together a technical summary to hopefully answer any questions anyone has about it.
The three versions that have been made so far have three different core materials, so far out of two versions I can't hear any difference. Apprentley with higher input levels they should reach distortion at different points but I need him to explain this so as to clarify. So far I haven't heard any distortion at all.
Friday I will be testing them all and moving the mics much closer to see if there is any difference when recording drums.
Please feel free to put some questions together and I will get them answered.

Regards

Spence.
 
I have two more  from a final version which is meant to be the best balance of everything.
Will test them hopefully Friday, will then look at choosing on a version to then start sending out for you guys to test. Email me your details and what other transformers you can test against please.
If anyone want to put these through test equipment they will look very good.
Feedback will be crucial on moving forward with these, I have blown a capsule tying to get them to distort!! So even though they are small, they sure are solid!
Happy to hear everyone's suggestion.
Pricing should be around the £50 mark and you can eithe have mumetal can or not.

Regards

Spence.
 
Hi All,

well i have done some testing of 4 different types in the end. Version D has come out on top as having the best overall performance.
I have also put one into my API preamp and it sounds very good in there compared to the Sowter 4257 and 4220 i was using.
I have also A/B'd against SSL 9K preamp and Neve 1290 with Carnhills in and it comes out best in my opinion as it has a slightly better mid range, bottom end more open and top end is crystal clear.

Time to start sending some out for testing!!!

Who's up for doing some testing?

msg me or email me your details if you haven't already theres only going to be about 12 available for testing!!!!

regards

Spence.
 
Hi Spencer,
I'd be interested in a an M49 variant.
I'm going to be building a couple of  M49 esq mics when Andriejus has my bodies ready.
paul


 

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