DIY Ribbon transformer Part II - The McGyver Way

[clintrubber]

[quote author="tony dB"]After replacement of the stock transformer with the Edcor RMX-1 it's safe to say that this became a very useful mike immediatly.
The stock version sounds hi passed and rather thin, compared to the Edcor pimped one. The difference is huge. No golden ears needed to hear the upgrade :twisted:[/quote]
Oops, I'd say my RB500 is 'thick' and not too much top-end (not surprising for a ribbon). So while replacing the stock-TX for an Edcor sounds promising, I wonder if I'll get even more thickness. :roll:

Bye,

Peter

 

[tony dB]

I'll try to get some recordings done with a factory and pimped one on the same spot. Studios are occupied so it will not be for today.

 

[clintrubber]

[quote author="tony dB"]I'll try to get some recordings done with a factory and pimped one on the same spot. Studios are occupied so it will not be for today.[/quote]
Nice !
Are you accepting votes for the source ? :wink:

(elec. guitar !)

 

[tony dB]

I will only post A and B samples at equal levels. Need a gtrplayer now :twisted:

 

[clintrubber]

[quote author="tony dB"]I will only post A and B samples at equal levels.[/quote]
I understand, any comparison would already be nice to hear. :thumb:

Need a gtrplayer now :twisted

Hey what's that, you're not a gtr-plyr yourself ?

 

[tony dB]

of course I play(ed) gtr :twisted:

In the previous millenium during the 80's ... :green:

 

[Rossi]

For the record: the old and new RB500 sound very different. The difference between the old tranny and and the Edcor is less striking than the difference between the Edcor and the tranny in the new RB500.

Sorry I can't be more precise, and I can't post my soundfiles, either. I have to keep that stuff to myself until my article is published.

 

[tony dB]

[quote author="Rossi"]It is a dual bobbin UI tranny, right?

[/quote]

I see 2 (white plastic) bobbins side by side, windings covered with yellow tape.

 

[tony dB]

Rossi, do you prefer I hold back soundfiles til you had the chance?
I don't want to sabotage your article

[quote author="Rossi"]For the record: the old and new RB500 sound very different. The difference between the old tranny and and the Edcor is less striking than the difference between the Edcor and the tranny in the new RB500. [/quote]

Wow, and the difference is already big in what I heard (old RB500 compared to new pimped RB500) :shock:

 

[Rossi]

Tony, I don't want to keep you from posting files (as long as you don't post mine :wink: ). These guys wanna know.

Yes, that's how the old tranny looks like. But that would mean you're comparing the old Edcorified RB500 to the new version RB500, no?

That's a difference my mom or your sister would hear, I'm not sure they would hear the difference between an Edcor modded RB500 and the old version RB500 with the stock tranny. There is a difference, of course, but maybe not an enormously striking one. The Edcor sounds cleaner, more pleasant, but the frequency response remains the same.

 

[mhelin]

How about the noise floor with tbone stock vs. edcor?

 

[Marik]

[quote author="mhelin"]How about the noise floor with tbone stock vs. edcor?[/quote]

What are the pri and sec DCRs for both?

 

[Rossi]

I'm not home, so I don't have the numbers handy, but the Edcor has somewhat higher DCR, on the secondary in particular. Maybe Tony can supply exact numbers.

Noise performance of the older version RB500 tranny is very good, actually. At least if you have a very low EIN preamp. The newer version is not quite as good, nor is the Edcor, at least in my initial tests. That said, my comparison wasn't quite fair, because the older RB500 I compared it to has thicker leads connecting the ribbon. Which, as has been said, does make a bit of a difference in noise. Also, I did not shorten the wires on the edcor tranny, as I'm still experimenting. Those additional inches of connecting wire on the primary may also contribute some noise.

The Edcor does sound better, though. There is a slight murky quality to the original tranny. The difference is not unlike ceramic caps vs. polyprop or polysterene in condenser mics. The difference in ribbon trannies may be a bit more obvious.

 

[tony dB]

I didn't shorten the leads neither, no noise issues at all.
The leads coming from the ribbon are thick indeed. The solderjoints are much better now, they appeared a little dodgy at first :?

Is the orientation of the tranny of any influence?
I just want to strap the Edcor to the little pcb where all wires come together, to prevent contact noises inside the lower body part. I tried to move it around a little while talking in the mic, but couldn't notice any differences.

 

[Huss]

No, my take is that DCR of the tranny windings should be as low as possible, i.e. lower than the ribbon's DCR if possible.

DCR means noise. The ribbon produces signal + noise, the connecting leads and the transformer winding DCR produce nothing but noise. The tranny amplifies both signal and the DCR related noise floor. Since the signal is so low, the noise floor matters a lot. The secondaries' DCR produces some noise as well.

On the other hand, you need some windings to get enough inductance (which you need for good LF response), so you can't just use one or two primary windings and 30-60 windings secondary. That's why a good core is important: you get enough inductance with a minimum of windings.

Don't confuse DCR with impedance. As far as the ribbon itself is concerned, DCR and impedance are about the same. But for the tranny, DCR and impedance are very different. The ribbon should see very low DCR but high impedance. The impedance on the ribbon tranny primary is the preamp impedance stepped down via the tranny ratio. It should be at least 10 times the ribbon impedance. If your preamp's input impedance is 2k and your tranny has a 1:30 ratio, the ribbon will see an impedance 2000 ohms / 30^2 = 2,22 ohms. That would already be slightly on the lowish side for a .3 ohms ribbon. In other words, it's the tranny's ratio that must be in some relation to the ribbon impedance.

Regarding your theory that "As far as the ribbon itself is concerned, DCR and impedance are about the same", I think not. The ribbon has a resonant frequency just like a loudspeaker does, so at that fundamental resonance there will be a large peak in impedance.