Stagefright13

Mila Dual Tube Preamp Help Thread
« Reply #20 on: November 27, 2007, 08:08:39 PM »
Your right Dave now that I look at it. It may have been the 100 uf or 100 pf that wasn't available. But I probably have that here already also.

I still need to order the tubes cases and turret boards. The cases is what I need the most help with.
Amateur experimenter


Stagefright13

Mila Dual Tube Preamp Help Thread
« Reply #21 on: November 28, 2007, 03:12:08 PM »
Oh I do have 1 question. Where did you get the Beyer input transformer? I have everything on the way except that and cases. I think I'll decide on cases after I see how big everything will build up to. Does Edcor make something I can use? Cause I can add to that order as it won't ship 'till next Tuesday.

Thanks
Amateur experimenter

MasonAtom

Mila Dual Tube Preamp Help Thread
« Reply #22 on: November 29, 2007, 10:24:01 PM »
I went with a Cinemag transformer because I couldn't find a Beyer at a reasonable price.

I'm not certain, but I think that some people have said that the Edcor transformer is not good on the input (shielding issue or something like that).

Mason

Stagefright13

Mila Dual Tube Preamp Help Thread
« Reply #23 on: November 29, 2007, 10:42:57 PM »
Thanks Mason. Wich Cinemag would be suitable if I may ask?
Amateur experimenter

louder

Mila Dual Tube Preamp Help Thread
« Reply #24 on: November 30, 2007, 06:26:35 AM »
Hi John
i got the beyer trannys from kuby.
regards
pedro

louder

Mila Dual Tube Preamp Help Thread
« Reply #25 on: November 30, 2007, 06:30:49 AM »
i have a question that makes me blush:
how to connect the input sw?.
that`s why i have been delaying this project.
sorry.
best regards
pedro

dissonantstring

Mila Dual Tube Preamp Help Thread
« Reply #26 on: November 30, 2007, 12:25:35 PM »
hi pedro,
are you speaking of the input pad switch or the Hi-Z input switching jack?
if you're speaking of the Hi-Z jack, use a N.C. 1/4" TS jack and wire accordingly.  
regards,
grant

louder

Mila Dual Tube Preamp Help Thread
« Reply #27 on: November 30, 2007, 05:25:03 PM »
Hi Grant
thanks for the reply,but stupid me,i was refering to the range sw.
best regards
pedro

Stagefright13

Mila Dual Tube Preamp Help Thread
« Reply #28 on: November 30, 2007, 07:19:56 PM »
Did ya look at the layout in post 1? It has a drawing of the switch wiring. It is here:

http://musiciansgig.com/mila/MILA2_updated.pdf

One thing on that drawing tho. You want to remove the jumper that is shorting the DI jack switch.

Woohoo a bunch of parts came today :)

Could I use a Cinemag CMMI10 as input if I change R4 to 178k and Jumper C1? Is this transformer the same as the Jensen 115?  Thanks.
Amateur experimenter

dissonantstring

Mila Dual Tube Preamp Help Thread
« Reply #29 on: November 30, 2007, 08:32:24 PM »
thanks stagefright13.  forgot about that layout.

hi pedro,
since this is point to point wiring, better to just look at the schem but you can reference the layout to help you understand the range SW wiring better.   i haven't built mine yet, but it doesn't seem to difficult.  

2 pole / 3 position SW.  one pole "A" (or whichever) goes to one side of R20 and from the R20/C2 junction go to positions 2 & 3.  leave position 1 unterminated.  for pole "B" (the other pole not used yet) wire to the R11/18 junction. from the other side of R19 (opposite from the C7 side)
wire to both positions 1 & 2 and leave 3 unterminated.

can't say this helps because i'm just interpreting the schem, but i hope it does.  good luck pedro.
kind regards,
grant


MasonAtom

Mila Dual Tube Preamp Help Thread
« Reply #30 on: November 30, 2007, 10:58:46 PM »
Thanks for the clarification Grant. That's how I drew it up in the layout I did, so it's nice to know that I'm on the right track (being that I'm a newbie). I've built three guitar amps, but this is my first time dealing with rotarty switches, input transformers, and the like...

Also, I had a question regarding the power supply. I'm doing mine a little different than Dave's schematic and I'd like to test it out before I wire it up to the preamp board to make sure my voltages are right. As long as I have the mains/fuse wired in and the power supply circuit complete and grounded, I can fire it up without having to worry about complications, correct?

Mason

NewYorkDave

Mila Dual Tube Preamp Help Thread
« Reply #31 on: December 01, 2007, 03:55:48 PM »
Quote from: "kubi"

The Zobel network flattens the frequency response and suppresses the highs that the Beyers naturally over emphasize. Leaving out the Zobel network gave more "air" and highs, but a sometimes too harsh sound on certain sources. To make the pre more versatile a switch in series with the network to switch it in and out seems to be a good idea.


Indeed, this is a good idea. Paul Stamler and I were talking about this at AES. Switching out the Zobel might give more satisfactory results with some mics--e.g., certain ribbons. This can be done with a simple SPST switch. I intend to add this to my own prototype someday.

Frohe Weihnachtszeit, mein Freund!

dissonantstring

Mila Dual Tube Preamp Help Thread
« Reply #32 on: December 02, 2007, 12:27:27 PM »
Quote from: "MasonAtom"
As long as I have the mains/fuse wired in and the power supply circuit complete and grounded, I can fire it up without having to worry about complications, correct?


i'm no expert mason, but it should be o.k.  but if you are testing it in the configuration you mentioned, all you'll get is the AC readings off the xfrmr (unless that is what you are worried about).  is it a new power xfrmr?  if it is, i would just wire up the whole PSU (only 6 resistors, two caps and a bridge rectifier more than what you have now) then test it with a power indicator lamp on the 6.3V heater rail.  oh, and remember to use a slow blow fuse.

kubi,
that's a great idea about a switching zobel on the input!   maybe i'll try a 3 position toggle "air - no zobel"/"normal - with zobel"/"grit - altered zobel".

cheers,
grant

usekgb

Mila Dual Tube Preamp Help Thread
« Reply #33 on: December 03, 2007, 05:48:21 PM »
Quote from: "kubi"
I should mention, I build it with a 1:15 transformer at the input as I didn't have the one Dave used at hand. But it worked perfectly after recalculating the Zobel network.


I have a bunch of Beyer TR/BV 370 215 006 transformers sitting here.  Is the transformer you used similar to these?

Thanks,
Zach
Zach Griffen Audio
EvilTone

usekgb

Mila Dual Tube Preamp Help Thread
« Reply #34 on: December 03, 2007, 06:29:02 PM »
Great!  I have a pile of these things, and I've been wondering what to do with them.  What values did you use for your Zobel network, if you don't mind me asking?

Cheers,
Zach
Zach Griffen Audio
EvilTone

MasonAtom

Mila Dual Tube Preamp Help Thread
« Reply #35 on: December 04, 2007, 09:51:22 AM »
Quick question on grounding scheme:

I've built 3 guitar amps (the extent of my DIY experience) and in each of these I've installed a chassis ground at the Hi-Z input and at the mains power input.

On the NYDave schematic, it looks like there are multiple locations of chassis grounds. Are all of these separate, or can I tie some of them together (i.e. Lo-Z input and mic input transformer ground to the same chassis ground)? I was under the impression that if you have too many locations for chassis grounds you run the risk of ground loops, but I'm new to this whole DIY and electronics thing, so I'm probably wrong.

Any assistance would be greatly appreciated.

Thanks!
Mason

NewYorkDave

Mila Dual Tube Preamp Help Thread
« Reply #36 on: December 04, 2007, 10:06:38 AM »
Circuit ground and chassis ground are connected together at one point only, at the power supply. I thought I made this apparent in the schematic, but maybe not...

There are multiple shield ground points shown: the input and output XLRs, the electrostatic shield on the input transformer, etc. Just connect these to the chassis right at the mounting point. Actually, connecting the input xfmr electrostatic shield to circuit ground instead of directly to the chassis may, in theory, yield some noise improvement, although I didn't do that in the protoype.

MasonAtom

Mila Dual Tube Preamp Help Thread
« Reply #37 on: December 04, 2007, 10:25:14 AM »
Quote from: "NewYorkDave"
Circuit ground and chassis ground are connected together at one point only, at the power supply. I thought I made this apparent in the schematic, but maybe not...

There are multiple shield ground points shown: the input and output XLRs, the electrostatic shield on the input transformer, etc. Just connect these to the chassis right at the mounting point. Actually, connecting the input xfmr electrostatic shield to circuit ground instead of directly to the chassis may, in theory, yield some noise improvement, although I didn't do that in the protoype.


Excellent. Thanks for the assistance Dave. I should have the wiring done tonight, but I'm still waiting on the tubes... Can't wait to hear how this baby sounds.

Oh, and my power supply section is different from yours, so I haven't really looked over your supply schematic in awhile, which explains why I didn't catch the single ground point.

Mason

PS - I also built your re-amping box and it is a great and handy tool for my home studio. I've been a lurker on this forum over the past several month and I gotta say that I think it's amazing how genuine and forthright you are with your help with problem solving and posting designs. I'm a big fan.

Stagefright13

Mila Dual Tube Preamp Help Thread
« Reply #38 on: December 04, 2007, 07:41:55 PM »
Look what I found:

http://www.trcelectronics.com/Meanwell/ps-05-48.shtml

Looks like a good thing for the phantom power cheap... Think?

OOPS wholesale only but Mouser has them for 15 bucks part number search PS-05-48.
Amateur experimenter

usekgb

Mila Dual Tube Preamp Help Thread
« Reply #39 on: December 04, 2007, 07:46:30 PM »
Looks cool.  Plenty of current.  It would be tough to build one that cheap.  I wonder how clean the power is?

Cheers,
Zach
Zach Griffen Audio
EvilTone


 

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