MILA-1 decent build pictures

[Rybow]

Your build is absolutely amazing Kingston! Nice work!

 

[stitch-o]

Kingston, I just ran across this thread.
WOW! Really spectacular work!
You had some large cap jury-rigging to do as well I see.
Any which way - GREAT work. Total inspiration.

Cheers!

 

[skipwave]

Great work!

I think I sold you those crap-sounding RCA 12AV7s from my stash. I had a whole sleeve.  ;D

Weirdly enough, I have some RCA-JAN that are the best sounding I've tried in my One-Bottles, and I've tried various GE, Tung-Sol, National, and Philips. The plates are a bit longer in the JAN specimens than the standard RCAs.

I'll have to check those PIO caps, always used polyprops.

 

[MasonAtom]

Wonderful MILA build, both inside and out. I've just started to use mine on a more regular basis - sounds great on vocals and guitar cabs. I think I'll have to investigate your expanded feedback options.

Mason

 

[Kingston]

I think I sold you those crap-sounding RCA 12AV7s from my stash. I had a whole sleeve.

Oh yeah I remember those. My evil two-bottle preamp ate those years a go. I never solved exactly what it was. Someone here on the forum had a similar tube eating one-bottle pre, and it was something to do with AC heaters and bad PSU transformers. Took that thing apart and used the good parts for better projects, and no project after that has killed any tubes.

 

[MeToo2]

Looks nice. What exactly did you change in the design?

Some recap,

completely different PSU configurations, input configuration changes and additions, different input and output transformer loading (datasheets) obviously and output stage feedback range expanded.

I won't bother with PSU details. It was an experiment that works, but today I would do it different. The input module is pretty standard stuff too. Feedback range is easy: remove R18, and R19 could be configured as:

1. 50k (20dB NFB) (+5dB on input stage)
2. 50k (20dB NFB)
3. 100k (15dB NFB)
4. 200k (10dB NFB)
5. 470k (5dB NFB)
6. disconnect (no-feedback)

or a 1meg linear pot with about 50k in series with it.

those dB values are rough estimations.

more gain on no-feedback, not clean of course. It sounds best on around 200k-470k to me, depending on how loud the output stage is hit

NYD reports different gain values for the stages in his schematic. Mine measures a bit different, and hence the different values on the front panel (and above estimations).

didn't notice an impedance switch in daves design how did you implement that? (which Rs?)

Cinemag CMMI-10C datasheet. It's an additional tap on the transformer primary. Not that useful to be honest. Switch is DPDT relay.

Sorry to be dim, but could you just take a moment to clarify your modified wiring of the other half of the 2x6 (make before break) feedback switch:
I'm presuming you want to maximise gain in the 1st stage as soon as possible to avoid noise.

So is it?

1st stage fb
1) 22K
2) 0
3) 0
4) 0
5) 0
6) 0

2nd stage fb
1) 50K
2) 50K
3) 100K
4) 220k
5) 470K
6) open circuit

No worries with oscillations anywhere at max gain?
(I guess there are grid stoppers and local feedback resistors in place on each stage)

I also picked up some very similarly huge 6.8uF 250V PIO caps from Russia recently and I have an xsm10K/600 lying around: so this could be just the project for them.

 

[fazer]

Beautiful work Kingston.  I have the tubes and the input transformers, some of the passive parts.  Its on my list.  80db of gain for your ribbon mic lust.  Very Very nice.

 

[Kingston]

So is it?

1st stage fb
1) 22K
2) 0
3) 0
4) 0
5) 0
6) 0

2nd stage fb
1) 50K
2) 50K
3) 100K
4) 220k
5) 470K
6) open circuit

No worries with oscillations anywhere at max gain?

That was exactly how I wired them. No oscillations at any setting and overdrives easily on settings 5 and 6. When I originally built this it was the best sounding tube distortion I had ever heard but now I know better. It can be a bit on the grainy side. I have since heard and designed better plans. 12AV7 is not the best sounding tube out there. Great for linear stuff of course.

 

[Hank Dussen]

12AV7 is not the best sounding tube out there. Great for linear stuff of course.

What about a different tube? Maybe an 12AY7 will work?
I believe these have a more 'sweet' distortion.

 

[Kingston]

12AY7 has more than 4X the plate resistance of 12AV7. It will not work at all. It won't drive the output transformer and you will have a tremendous bass cut.

12AY7 is not that great sounding tube either. Quite close to 12AX7 in fact. That's why it's often recommended as a "drop in replacement" for 12AX7. But the difference in sound is negligible.

There isn't much point in trying to "improve" MILA-1. it is completely designed around 12AV7. Which means it takes advantage of the tube parameters by the book and any replacement tube will make things worse. There are very few similar tubes. It is rare to get this high mu (40!) with low plate resistance. MILA-1 was obviously meant to be linear, and the tube was never chosen for its sound.

For more colorful preamps, there are hundreds of other better plans.

 

[isophase]

wow its beautiful !

 

[zayance]

A little late, but that build looks great Kingston...

 

[dmp]

When I originally built this it was the best sounding tube distortion I had ever heard but now I know better.

What have you built in the year since? I'm trying to decide on a second tube preamp project and am leaning towards something with 6sn7 tubes, but would like to hear what you have done and why you liked it, since I am on the same path as you were a year ago. I built a one-bottle, and really like it so far. I am looking for preamps to capture acoustic instruments with a rich, full, warm sound... (I think you saw the sound samples I posted) - right now I really like the ez1290 I built, in addition to the one-bottle.  
When I think of tube distortion, I think of guitar amps, and that is not something I would think to have on a  mic'd acoustic guitar, or vocals, or fiddle, etc... What type of recording are you using tube distortion for? Does tube distortion in a preamp create a big, harmonic, warm sound?

p.s. I am watching your design-in-the-works http://www.groupdiy.com/index.php?topic=41509.0

 

[canidoit]

Great workmanship, looks slick! Dig the design and clean build.

 

[audiophreak]

Hi,
  Kinda in the middle of a quad of NYDave one-bottles, trying to figure out a regulated B+.  I am still a Newbee, but am learning. I understand that the one-bottle is a " Heavy Feed back design "  and was wondering if your variable NFB  could  be impimented in the one-bottle design?

 Thanks for all the wonderful information posted, if its not possible or impracticle, I may try your design next  

BTW  Gorgeous Build  !!

 

[kambo]

you dont need regulated B+, but well filtered.

 

[Kingston]

I understand that the one-bottle is a " Heavy Feed back design "  and was wondering if your variable NFB  could  be impimented in the one-bottle design?

It's there already. NYD one bottle gain control works exactly by varying global feedback. When its set to the loudest position you get least feedback. I suppose you could extend the range by replacing the feedback pot with 470k. But you will need input padding of some kind because things will clip. And I mean way more than the usual 20dB in front of the input transformer.

What have you built in the year since? I'm trying to decide on a second tube preamp project and am leaning towards something with 6sn7 tubes, but would like to hear what you have done and why you liked it, since I am on the same path as you were a year ago. I built a one-bottle, and really like it so far. I am looking for preamps to capture acoustic instruments with a rich, full, warm sound... (I think you saw the sound samples I posted) - right now I really like the ez1290 I built, in addition to the one-bottle.  
When I think of tube distortion, I think of guitar amps, and that is not something I would think to have on a  mic'd acoustic guitar, or vocals, or fiddle, etc... What type of recording are you using tube distortion for? Does tube distortion in a preamp create a big, harmonic, warm sound?

I've experimented with 6SN7 (actually a russian alternative) in several circuits, similar to one bottle and LA2A line amp. This is a great tube when over driven, much nicer than 12AV7. Then I've experimented with SRPP's. It's a good sounding mildly "tubey" circuit if you find the right tube. I built found a superb line amp and experimented with a feedback EQ design also. Most of these finally condensed in into that "overkill" project. I'll be writing an extensive report on these later on.

The types of distortion I really like with tubes is a kind of wide "invisible" distortion. the closest I've ever had was an EQ into this 6n6p line amp. Boost bass a bit when it goes in to shape the distortion and instruments an vocals really start to sing. I wouldn't do that for acoustic guitar, but for just about everything else it's magic. For highly transient acoustic instruments I would use MILA-1 at the most linear setting. Don't want those sharp attacks distorted in any way.

These things are a bit hard to describe.

 

[audiophreak]

I understand that the one-bottle is a " Heavy Feed back design "  and was wondering if your variable NFB  could  be impimented in the one-bottle design?

It's there already. NYD one bottle gain control works exactly by varying global feedback. When its set to the loudest position you get least feedback. I suppose you could extend the range by replacing the feedback pot with 470k. But you will need input padding of some kind because things will clip. And I mean way more than the usual 20dB in front of the input transformer.

  I seam to remember someone ( probably you ) stating that the gain/volume control on the one-bottle was not really a gain/volume but a feedback control  -  sorry for my Newbiness  ;D

I've experimented with 6SN7 (actually a russian alternative) in several circuits, similar to one bottle and LA2A line amp. This is a great tube when over driven, much nicer than 12AV7. Then I've experimented with SRPP's. It's a good sounding mildly "tubey" circuit if you find the right tube. I built found a superb line amp and experimented with a feedback EQ design also. Most of these finally condensed in into that "overkill" project. I'll be writing an extensive report on these later on.

The types of distortion I really like with tubes is a kind of wide "invisible" distortion. the closest I've ever had was an EQ into this 6n6p line amp. Boost bass a bit when it goes in to shape the distortion and instruments an vocals really start to sing. I wouldn't do that for acoustic guitar, but for just about everything else it's magic. For highly transient acoustic instruments I would use MILA-1 at the most linear setting. Don't want those sharp attacks distorted in any way.

These things are a bit hard to describe.

  can't wait to read / hear what you report !!

  Thanks 

 

[ilfungo]

GREAT GREAT WORK Kingston!!!
sorry
where can I find the layout of MILA-1?
and part list?
I'm not good with the schematics ...
thank

 

[chrispsound]

Kingston, do you have a front panel express file for this build, or does anyone for that matter?  Thanks, ChrisP