NYDaves MILA or Dynaco pas based mic pre

a while back i got 2 utc 0-10 ouncers and a tube mic pre schematic to use them with.(based on the dynaco pas2 preamp.) see here
now i'm thinking i would rather build nydaves MILA preamp instead. mostly because of daves rep on the board and some things i've read(somewhere?) about 12ax7 vs 12av and au7 preamps.
i was hoping i could use the 0-10s in the MILA. I've heard some good things about them. if i am correct the 0-10s are 30K:500. should i bother persuing this idea or are these transformers unusable in the MILA. what could i expect if i used them with this circuit? am i right in thinking i'll end up with a significant decrease in gain? or would the decrease be small enough to be acceptable?
i also have a TRIAD R-29A power transformer i'd like to use for the psu. it has a 6.3V secondary and a center tapped 230V secondary ,40MA. DC would this be enough amperage to supply two channels?

> based on the dynaco pas2 preamp.

It's got tubes, but I don't really see any relation to the PAS2.

For another thing, the PAS2 made sense in a good-value way. Why does this play sport a 10uFd cap to drive a 250K pot to the world outside???? Three triodes to get gain of 20 and Zout as high as 60K??? We could do that with two triodes back in 1920.

Do we need 0.06Hz response?

Do we want up to 60K output impedance? If the extreme subsonic response is balanced with an equal supersonic response, 6MHz, then at -6dB pot setting we can drive up to 0.1pFd of cable, or a cable 0.03" long.

I hate stacked volt-amps. I often compute them wrong. This appears to have gain around 20 (R3+R4)/(R5+RkV1b). With 0-10 gain near 8, that's gain of 160 from the mike. That's not enuff fow low-output mikes, yet gives trouble for high-output situations. I believe it would work better withOUT V1a sapping voltage, but assuming output swing 20% of 300V we can swing 60V peak or 40Vrms out, 250mV max input.

> some things i've read (somewhere?) about 12ax7 vs 12av and au7 preamps.

You know that bunch of monkeys banging on typewriters trying to recreate Shakespeare? That is the modern audio-yak world: every possible combination of words will appear "somewhere".

> i would rather build nydaves MILA preamp instead. mostly because of daves rep on the board

Dave is a very experienced audio and amp tech, school of hard knocks in amp servicing and large facility support. His design skills are unsophisticated, his copy-cat skill is first rate and he copies from the best of the past. This leaves him 100 times more credible than 99% of the cruft you read "somewhere".

It's not as complicated as some monkeys make it. Transformer. Tube. Gain pot? Tube. Got enuff yet? Maybe another tube.

OK. i'll abandon the "pas2" mic pre.(the designer told me it was based on the pas2) i had my doubts about the mic pre because i had asked questions about the psu for this pre i got from the designers web site and the forum members pointed out that it was a poor design. does any one know a "quality" tube pre that will allow me to use the components i already have? think i'll check the metas and web. i just got 12 used 12au7s and one 12v7. hopefully out of the bunch there will be some good ones. any suggestions are appriciated.

Dave is a very experienced audio and amp tech, school of hard knocks in amp servicing and large facility support. His design skills are unsophisticated, his copy-cat skill is first rate and he copies from the best of the past.

Click to expand...

I wouldn't call Dave unsophisticated as a designer; he has a preference for straightforward solutions rather than complex ones, yes, but often that's the key to good results. When examined his designs reflect a lot of thought and subtlety.

Peace,
Paul

Is that schematic in the first post an edited one from the first issue of glass audio?

Looking again at the schematic...the 10uF coupling cap to the output pot is actually not a bad thing, because when the pot's wide open the cap will be feeding the next device's load, which is likely to be 10k. The 250k pot, however, is bad news.

Also...whoever drew up specified the type of 12AX7 as being a 5751. Contrary to what a lot of folks seem to think, a 5751 is quite different from a 12AX7; if it resembles any other tube in performance, it would be the 6SL7...but they're still somewhat different. The curves of the 5751 and 12AX7 are way different.

Peace,
Paul

i'm not sure what the origins of this schematic were. i purchased it along with the 2 utc transformers. i dont know enough to judge a circuit design so i posted it for opinions. i'm glad i did. now i'm hoping someone could suggest a simple circuit that i could use the 0-10 ouncers in.

> the 10uF coupling cap to the output pot is actually not a bad thing, because when the pot's wide open the cap will be feeding the next device's load, which is likely to be 10k. The 250k pot, however, is bad news.

It's just hodge-podge design. Thoughtless. 250K pot can just about drive a nearby grid, or a few feet of cable to a lo-fi guitar amp. 10uFd will drive 10K to 2Hz, but can the CF drive large voltages into 10K? If that were a primary goal, the 100K cathode resistor ought to be smaller. As it is, the 12AU7 is underutilized. But we don't actually want giant voltage in most 10K inputs. But the fixed-gain amplifier gives it to us anyway. So we have to turn the pot down. As soon as it is down 4% of 250K, the 10uFd cap sees 20K and gives us 1Hz response. Meanwhile the added 10K is clobbering 20KHz in long cables.

The 100uFd decoupling cap is pretty generous too. The CF only has ~~20dB PSRR. With 10K+100uFd the first stage gets 46+dB PS cleaning, which is rather overkill when the CF will leak 20dB. (And it is certainly not for motorboating stability.)

Did I say I hate tube most totem-poles? Another objection to this one is that it reduces tube "sound" by canceling some or most 2nd harmonic curvature. Well, fine, but if that's the goal we could put in a BiFET chip, get an easy gain-trim and honest lo-Z output. Why use tubes and then more tubes for less tube sound?

And tube sound is very level-critical. A whispered ribbon will pass through dead-clean. A condensor percussion will be very distressed. Singers can be adjusted with placement and vocal-effort to put them on the edge of "flavor", but singers have enough problems without also being adjustable-level sources.


> but often that's the key to good results.

I agree. Sorry if that was not clear. The Great Gatsby:

"Sophisticated - God, I'm sophisticated." Chapter 1, Daisy.

"It's a triumph. What thoroughness! What realism! Knew when to stop, too" Chapter 3.

"Can't repeat the past?…Why of course you can!" Chapter 6, Gatsby.

"So we beat on, boats against the current, borne back ceaselessly into the past." Chapter 9, Nick

> a "quality" tube pre that will allow me to use the components i already have?

What is "quality"?

What are you going to USE it for? I just had to bail-out a neophyte who bought quality mikes, quality portable recorder, and quality headphones... which just won't play well together. The mikes are high output and overload the recorder inputs in acapella work. The hi-Z headphones expect high voltage and just wisper from the porta recorder's low voltage outputs. "

What parts you got? Some grid-input transformers and some common tubes? The trannies are suitable for most any tubewerk. The tubes are fine on the face of them.

What you need is some idea what input and output you need.

Are you recording whispers or banged percussion. Ribbon or large condenser? Going to porta-recorder or driving a long line? It is "possible" to build a preamp to do "anything"; but narrowing your goals to what you really need can save a lot of time and effort.

Before this thread devolves any further.... :green: . I built a MILA and I wouldn't trade it for ANY preamp..I own a bunch, have heard a ton. That said I used Cinemag iron for my input, solen caps throughout and an edcor 4:1 on the output... I am unfamiliar with your utc's....My MILA has the sweetest top end I have heard.

Cheers,
Ray

PRR "quality" was in quotes as i know it can be very subjective. but i think others with circuit designing skills would agree with you that the circuit design above is not a "quality" design. could we define quality in a circuit as: using the components in a circuit and their interaction with each other efficiently and to maximize audio quality for the application they willl be used for.
so that brings us to your question about the intended application. i have a G7 tube,SP c1, a soon to be MXL2001 Royer Mod (santa bought me a transformer for this today) an sm57,Beta 58 and an SM58. going into an M-audio 192 audiophile.
most recordings are of rock, blues,reggae and folk.
i would love to build a tube pre amp for micing guitar and bass cabinets. if the pre sounded great on vocals that would be a bonus. i dont mind some "color"

Looking at it as a schematic, the MILA does most of what good vintage tube preamp designs do, and has every feature one might miss in an actual vintage preamp. Flexibility, gain, and headroom are exactly what you want in a general purpose pre.

Quality of transformers and remaining parts is a giant variable, and there are a ton of color options.

The UTC O-10's are an incongruent option for the MILA circuit. The decrease in gain will be for practical purposes negligable with the UTC O-10 as both input and output. The problem is it won't handle the drive level of the MILA circuit as an output, and I'd put $ on it having wacky response if used as a SE input. Though it would work. They are better off sold IMO, unless you want a circuit with minimal headroom, be it the MILA or some other design. You could build a fairly elegant pure PP circuit with them as a design experiment, but you won't easily get a flexible starter project going that route.

Your power supply parts should do the job.

I understand "Quality" as "Optimum".

emrr wrote: The problem is it won't handle the drive level of the MILA circuit as an output, and I'd put $ on it having wacky response if used as a SE input.
I'm not sure if i understand? are you thinking i was considering using the 0-10 as an output transformer? "won't handle the drive level of the MILA circuit as an output"
i was thinking of making 2 channels.
this will be only my second diy. aside from 2 simple electric guitar circuits. so i'll go with a tried and true circuit. i dont know enough to start experimenting. (although im thinking i can put a 0-10 ouncer in the mila chassis with a switch to alternate between transformers)
emrr: could you tell me what an SE input is so i can read up on it?
thanks

UTC O-10: Push pull plates to line, primary 30K plate to plate, sec 50/250/600. Max level +8dbm. Output transformer.

SE = single ended
PP = push pull


O-10 response may not look good in SE connection, as compared to the PP it was intended for. As an output. Or an input.

http://www.groupdiy.com/index.php?topic=15918&highlight=

oh ok. i know the difference between the two from looking at guitar amps i'm just not to familiar with them and dont recall(although maybe i have) seeing a non push-pull circuit referred to as SE. thanks for the link. i understood some of it and im working on the rest

mm... I´ve used O10´s as input transformers and it works great for this. It was intended as an output transformer, but it has nickel laminations, and woks just as good as input transformers. Better in fact, because it has not enough iron drive for outputs, IMHO. I´ve used it in my first tube mic preamp, a pultec MB1 clone, but now I see it was an error, althought it sounds really good... For this, and other SE mic preamps, the more common O8´s will do the same job. I have some 10-15 pieces O10´s here, and after some experimentation, I´ve found where they really shine. Try it with a PushPull preamp circuit, like the langevin 5116B. It´s really great. RCA had also some PP mic preamps, and also Universal Audio, so just look for somePP preamp schematics around. Using a trafo like this in a SE preamp is a waste, as it has perfect balanced primaries (that we are going to use as secondaries in that case), and this goes really well for a tube mic preamp input, using a first-stage in PP. So, do not go for the MILA with these ones, you can find plenty of more common vintage and newer types for the MILA that will work great, like cinemags, lundahls, utc´s, and so many, even the low cost oep´s... But for the best with your O10´s, go for a pushpull circuit. Also, if I recall, (hint) Kevin from K&K had a really nice PP hybrid mic preamp going... You might wanna ask him. I think he sells PCBs for that, and it would really help you out, if it´s your first tube pre build. Anyway, PushPull is the way to go.

Hope it helps!

> UTC O-10: Push pull plates to line

Argh. I missed that. I recall using the O-10 for "everything", back when it was cheap. And especially when it was cheaper (I scored two for $0.50 each when the neighborhood electronics shop cleaned the back room).

But to PAY for a "mike transformer" and get a cheezy output tranny.....

seavote, you are getting all different advice and I'm not sure you have enough experience to filter the BS. There comes a time to buy an education.

It's hardly cheap, but I think you should sell the O-10s and save up for Hamptone two channel tube micpre KIT. Instructions. Scott knows his stuff. He picks good parts. He supports his stuff. Two weeks' salary seems like a lot of loot, but when you use good iron and add up all the nickel/dime details, you won't build as nice a preamp for much less, maybe more when you buy wrong parts(*).

(* I had $450 in a Champish gitar amp, realized I'd bought the wrong PT, use the $69 PT as a nut-crusher and spent another $80 with shipping to get something else, which hardly fits....)

no,no,no, they make perfect mic input transformers, better than most things you buy today, specially for a PP circuit. UTC did it perfect balanced, low resistance windings, good nickel core, very high inductance, very nice frequency response... Look at the O8´s. UTC sold it as plates to line, and lots of professional gear manufactures, like ADM, UREI, etc... used O8´S for mic inputs, so you get the picture...

TRY the O10´s, do not sell it, I say. Be surprised about how t sounds. I wouldn´t trade mine for jenses and cinemags. These you can buy new anytime. Those old UTC O series have something about their sound. Just make sure you can get the O17 shields to go with your O10´s, or try a PSU out of the box, for lower hum.

PRR when reading threads here i 've learned to "take it from where it comes". determining who has the experience and "know how" (reading previous threads,profiles and visiting web sites helps)is easier than learning all the electronics point by point.(although its good to try) i looked back at the hamptone preamp last night,befor reading your thread to see how much it costs. $900 is to steep for me . i do have a Hamptone schematic for a tube pre that probably is, or became, the one offered on the web site. i'll take another look to see if i would like to try the build from the schematic.
Daves pre has more info available and a BOM for the project so it has that going for it.
Raffa i've spoken to kevin at k&k 2 times and he helped me without my even asking for help.i'll definitly take a look at the schematic at the web site and maybe pick up an output transformer from there if i chose that project.The UTCs came with the O17 sheilds
whichever i choose i'm sure it will be a great addition to my less than impressive preamp collection. a studio projects vtb1,which i like the sound of with no tube blend and a TFPro P3(the same as a Joe Meek VC3Qc).
thanks to all for the advice and suggestions.

Rafafredd, gotta ask if you've verified reasonably even response in single-ended mode with those by shooting an RTA. Not saying it's not good, but if you read my other thread and get results resembling mine you'll start to question what's best used where. The O-10 isn't a split winding unit, so it may be okay either way. It may sound great to the ear, which is fine, but it may shoot a scary RTA at the same time. I personally think the pro manufacturers you mention who used O series iron did it because they saved space, saved $, and got the job done within engineering specifications. NOT because they were the best of all possible choices for the job on merit alone. It makes sense to me that they would seem to really shine in push pull circuits, since that is what they were designed to do. I'm not kidding when I say I've seen -12 db notches in the 12kHz range with at least one example of PP iron used in SE mode. Along with big top resonances after that and drastic quick early roll-off. Put the same iron in a push-pull circuit and it starts to look like a nice texbook rolloff. Not saying every piece of iron responds this way, but you should really look at your response and not take it on faith and ears that it's doing what you think it is.

PP RCA preamp.......what would that be? I can only think of the circuit Jim posted:

http://www.groupdiy.com/index.php?topic=21224


RCA didn't do pure PP in preamps at all, other than that one, which almost no one's ever seen in person. I've only seen one tube amp resembling a preamp from RCA that is pure PP, and it's a plug-in line amp with a single PP 6V6 stage. They did a few 100W to 250W power amps that are PP, but even most of the power amps are single ended up to the output stage.