MILA-1

[fallout]

I plan to try this circuit out using a 150:15k mic input transformer.. Would there be any obvious problems doing this? Besides the values of R4 and C1.. Thanks!

-Jay

 

[pstamler]

That's essentially what NY Dave is doing. The main question is what resistance your transformer wants for termination. Usually there'd be a 150k resistor and a Zobel network like Dave's, but it'll be different for different trannies.

Peace,
Paul

 

[chrissugar]

Hey Dave, just want to say thank you for this nice and well documented project. :grin:
:guinness: :guinness: :guinness:

chrissugar

 

[clintrubber]

[quote author="Sleeper"]I was just going to post in the new books uploaded or specifying noise thread about where to learn more about this raised cathode bias thing.
I'm sure one of those design texts will explain.
I could use a point in the right direction:?:[/quote]

Hi,

I'm not sure what you're looking for, but if it happens to be the raised heater then have a look at page 13 & 14 of this file for instance:

http://195.178.239.50/ax84/media/ax84_m35.pdf

Regards,

Peter

 

[ioaudio]

hey dave,

did you come around listening to your preamp yet?
regarding the beyer input transformer termination: how did you determine c1 & r4?
by the way i realised that your mila uses the same input/output transformer pair (beyer & edcor) like my pre#7 with the only difference that my output is 2,4k:600.

-max

 

[NewYorkDave]

I've been too busy to even take the preamp off the shelf since I finished with the measurements. But I'm hoping to find enough free time this weekend to cut a sound sample or two. Stay tuned.

 

[NewYorkDave]

Well, the conditions are far from ideal, but I wanted to post some sort of sound sample this weekend, so here we go... It's an MP3 of male voice, comparing the MILA-1 against a popular solid-state console preamp. To avoid listener bias, I won't identify the make and model of the "competitor" preamp nor will I identify which preamp is which--at least not right now. They're just called "preamp #1" and "preamp #2."

The level and sources of noise in the room were high and variable (computer cooling fan noise, a heavy rainstorm outside, air conditioners turning on and off, etc.) so it's not a valid noise level comparison. This is especially true since I absent-mindedly ran the MILA at the highest setting of the Range switch with the Gain control turned down about halfway. If I'd paused to think about it more carefully, I'd have realized that a lower setting of the Range switch and a higher setting of the Gain control would have yielded better S/N. But time was limited and I was in a bit of a hurry.

The mic (an original no-logo ShinyBox ribbon), the physical position of the mic and the speaker's distance from it (1') were the same in both tests. Levels were matched as closely as possible. Both preamps were running at about 50dB of gain.

493kB MP3

 

[chrissugar]

preamp #2 = MILA
preamp #1 = other

chrissugar

 

[ioaudio]

thank you for posting!
i think you should start thinking about using dc heaters, at least for high gain applications - there´s some audible hum in preamp #2. maybe there´s a chance to fix it without switching to ac, but i´ve no clue.
soundwise your preamp sound much more direct, lots of bass (regarding the beyerdynamics) though it seems to be recorded a little closer.

 

[NewYorkDave]

See my comments above about the difficulty of comparing the noise levels because of all the uncontrolled and sporadic sources of noise in the room. This was meant purely as a "what does it sound like?" test. A more rigorous test would have to take place in a quieter environment than that of my apartment. But yes, a tube preamp with AC heaters is generally going to have a greater 50 or 60Hz hum component than a transistor preamp, for obvious reasons.

Also, see my comment about the speaker's distance from the mic--it was the same in both cases, ensured by the use of a 1' ruler between the tip of the speaker's nose and the microphone grille :wink:

Two responses in two days... :? Maybe I should only post SPICE simulations from now on; they seem to generate more interest around here, and it's certainly less work than drilling and soldering. :razz:

 

[skipwave]

I was struck by the subtlety of the difference. I was expecting extreme contrast, but it wasn't there. Both sound very solid, with different character. The voice was very bass-y, but that is common when speaking at lower volume and the ribbon mic is darker sounding. I was a little disappointed that it wasn't a serenade.... :razz:

I didn't notice the hum so much, maybe I'm really loosing my hearing sensitivity, or this soundcard on my work PC is really crap. I'll have to listen on my monitors later.

Anyway, a very strong showing, Dave! :thumb:

 

[NewYorkDave]

I'm planning to cut a sample of electric guitar with an SM57 next. I suspect the difference will be less subtle in that case, but we'll see (I mean, hear)...

Condenser samples will have to wait till I can obtain or build a good external phantom supply.

(I'm glad my shameless, attention-grabbing bump garnered at least one more reponse! :wink.

 

[louder]

alo dave
i heard with heaphones,and they sound very close,except #2 has more bass,and more hollow(?).seems you spoke closer to the mic.
best regards
pedro

 

[Guest]

I have followed the thread with great interest, unfortunately, my hearing is very bad so I can not offer any comment on what your samples sound like. This is just to let you know that there continues to be interest, even if folks like me post less than we should.

 

[Consul]

Dave, it's because your posts are so thorough that it leaves nothing left to discuss.

When someone posts a simulation, it's really easy to fire back with all sorts of ideas and critiques, because it's only a simulation, and prone to error.

But when you post about this thing you actually built, the theory behind how it works, and "oh, by the way, here's what it actually sounds like," well, there's really nothing more that needs to be said, other than, "Cool! Time for me to build one now! Thanks, Dave!"

Oh, and thanks, Dave!

 

[NewYorkDave]

Funny... I heard a fairly pronounced difference in the original WAV file; but listening to the MP3 now, it definitely didn't translate.

 

[AnalogPackrat]

Dave,

Thanks for posting--I somehow missed your original update with the audio. I agree that the difference is subtle, but it is there. I noticed that you used a 128kbps rate on the MP3. If you can host the WAV that would be great, but if not, can you try converting to MP3 with VBR (variable bit rate) or at least a higher bit rate, say 320kbps? That may make what you heard in the WAV more apparent. Of course we're all looking forward to some NYDave guitar samples next...let 'er rip!

A P

 

[matta]

I was expecting you to break out into 'Ring of Fire' with that sexy voice

But seriously though, Thanks Dave, it sounded great, I listened through headphones and could hear the difference quite clearly, even with the MP3, the 2nd sample sounding deeper and a bit warmer than the first.

Great little pre amp, hopefully I'll get to build it one day. Looking forward to hearing the guitar.

Cheers

Matt

 

[tk@halmi]

I have been happy with the AV7 & BH7 line amp combo you published some time ago with the XSM2.4k/600 on the output.
I am not sure why I would use this one isntead. The BH7 is just a few bucks more and plentiful.
This project is very nicely documented though. Thanks!

 

[skipwave]

[quote author="NewYorkDave"]Funny... I heard a fairly pronounced difference in the original WAV file; but listening to the MP3 now, it definitely didn't translate.[/quote]

Aye, there's the rub! I've been appalled by how unfair MP3 compression is to translating the important details of a comparison. Somehow the information that is removed, which we are not supposed to notice so much, is exactly what reveals the performance of recording gear.