MILA-1

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NewYorkDave

Well-known member
Joined
Jun 4, 2004
Messages
4,378
Location
New York (Hudson Valley)
Meet MILA-1. The name is an acronym for "Mic/Instrument-Line Amplifier."

MILA1Front.jpg


I built this a while back but between illness and work, I haven't had a chance to run bench tests and upload pics until now.

The design arose out of the experiments described at length in the "Small Line Amp" thread. With the cleaner layout of this prototype (compared to the breadboard) I was able to use 12AV7 successfully in both positions instead of having to resort to the more expensive and heater power-hungry 12BH7 for the output tube. The maximum output level is only marginally lower with the 12AV7.

Bench test results and many more pics can be seen in this album:
MILA-1

I'll see about recording some sound clips... when I get my voice back, that is.
 
Fine work, as always! :thumb:

So is that chicken-head on the "range" switch?

How's that Beyer input tranny sound with this circuit?
 
I don't know. I haven't listened to it yet. When it comes to audio gear other than, say, guitar amps, it's gotta meet a certain minimum standard of quality in bench tests before I even bother with listening tests. So anyway, now that I'm satisfied that I haven't built a fuzzbox, I'll get 'round to listening to it.

By the way, for the handful of people who care about the measurements, I should note that a 200-ohm signal source impedance was used in all cases. I forgot to specify it on the images.
 
Well, this one doesn't seem to be generating too much interest here. But I can understand that we're all getting burned out after seeing 1000 preamp designs every month. Anyway, for anyone who happens to be interested, I just uploaded a PDF with schematics of the MILA-1 to the photo album.
 
Oh, I'm more than interested. I'm just still busy with the One-Bottle. Or rather, I'm busy with the job search that will eventually make me the money to buy the remaining parts I need to finish it.
 
Dave, where did you get those boxes? They seem rather handy and durable! Another project in the queue... :twisted:

-Jay
 
I wish I could offer some counterpoint .. :sad: . Never "just another" anything to me, all of it inspires learning in observing the differences between. Thank you for opting to use a slightly uncommon tube, the fact that this design works allows me to contrast it with other designs and see how the tube data fits.

:guinness:

Frank
 
[quote author="NewYorkDave"]Well, this one doesn't seem to be generating too much interest here. But I can understand that we're all getting burned out after seeing 1000 preamp designs every month. Anyway, for anyone who happens to be interested, I just uploaded a PDF with schematics of the MILA-1 to the photo album.[/quote]
That's not it, a lack of interest. Just too many other things going on.

Nice compilation of files - if not for the design itself already it'd be a nice 'template' to RMAA-characterize other stuff.

12AV7, hmm, that doesn't translate to ECCxx too well :cry: :wink: :thumb:

Regards,

Peter
 
[quote author="NewYorkDave"]Well, this one doesn't seem to be generating too much interest here. But I can understand that we're all getting burned out after seeing 1000 preamp designs every month. Anyway, for anyone who happens to be interested, I just uploaded a PDF with schematics of the MILA-1 to the photo album.[/quote]

Hey Dave,

please don't be discouraged - this stuff is amazing for learners like me, I just downloaded the PDF and will spend many hours trying to get my head around the circuit.

My wife pointed out that I hadn't been to bed before 4am in the last 7days - groupdiy has a lot to answer for.....

Thanks for your efforts Dave, and all the others ho make this a great place to learn,

cheers,
Ruairi
 
Thanks for the comments, guys.

In other news: man, it's always something! I proofed the PDF several times before I uploaded it just before leaving work for the weekend. But on the way home, it suddenly dawned on me that I goofed up the EIN figure in the specs. Just call it "Friday afternoon math." :wink:

Anyway, since I won't be able to fix the PDF until I return to work on Monday--but I didn't want to pull it offline altogether--I've changed the file name to call attention to the error. Please check back on Monday after, say, 5PM New York time and the corrected version should be there. Just download again and overwrite the old one.

Jay, the cases were cheap, plain aluminum "jiffy boxes." I sanded 'em, cleaned 'em, shot a couple of coats of primer and then a few coats of grey hammertone. I did this over the course of a few days, allowing each coat to dry.
 
dave, thanks for sharing - in fact i think your projects are the best documented around. everything in your circuits seems predictable and you describe perfectly whats going on!
like clintrubber said 12av7 are not so common in europe, so it might be harder for "us" to try that circuit...
think :thumb:
 
Damn, Dave, you've done it again. That's a really nice design and a solid build as well. You're in the process of converting me back to feedback pairs, ya know?

Also very smart, the way you switch the gain of the input stage.

One question: have you looked for subsonic peaks on the first plate of the feedback pair? That's a possible danger point.

Peace,
Paul
 
Now, Paul, why would you say that? Just because of that li'l subsonic bump in the response plot? :wink:

You raise a good point. I didn't encounter any problems during the bench tests, but I should hit the amp with some sub-20Hz action and check the stability. I believe, but haven't confirmed yet, that the peak is caused by the output coupling cap resonating with the output transformer primary. And being a series-resonant circuit, that means the impedance would be low at the resonant frequency, and in turn the voltage level at that frequency seen at the plate should be reduced, which means less feedback to V1B cathode. But at the same time, the low impedance at resonance means more current through the primary, therefore a higher induced voltage across the secondary--and the bump in the response as seen at the output jack.

But that's only my conjecture. I'll check it out.
 
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