First DIY job: Dual Tube Recording Preamp

[gibong]

An SM7 sounds like an RE-20?

There you go then! We have a few of each and I do reach for the SM7's first....the RE-20's are used almost exclusively for male VO work for that Frasier Crane syrupy baritone goodness. (Sorry for cluttering your thread neoific!)


Back to tube preamps:
You should have a look at this:
The MILA: http://musiciansgig.com/mila/
http://www.prodigy-pro.com/forum/viewtopic.php?t=24919




.

 

[neoific]

I'm compiling a parts list for the Dual Pultec MB1 design, but I cannot seem to find a Triad R-4A. I sent an email to Jensen asking if they could custom build a generic, any of you guys have any ideas beside eBay (no results)?

Btw, I'm working on my http://www.digilux.net/audio/index.php?title=Tube_Mic_Preamp wiki for this.

 

[gibong]

Have a look here:
http://www.hammondmfg.com/300series.htm

 

[neoific]

As I put on the wiki, I read about that 369JX, but I'm slightly skeptical. Is it a simple drop in replacement?

Btw, updated my Phantom Power Schematic

 

[gibong]

I hadn't looked at your wiki till just now. Nice job.

Have a look at this MB-1 clone:

It uses the 271X which only has the 115V primary (instead of the multi-voltage universal primary) and it is 280-0-280 (I think). The 369JX should work fine.

You must visit this place: http://www.prodigy-pro.com/forum/viewtopic.php?t=16013

Specifically:
http://www.prodigy-pro.com/forum/viewtopic.php?t=8400&highlight=mb1

This is one built by the Rafael Texiera, the inspiration for the one you referenced at your Wiki.

 

[neoific]

Thank you. I figured a
wiki would be better flow for readers, as well as make it easier for them to critique things or add other projects.

Looks like I found a source for all of my pultec knobs from your link! http://www.nrgrecording.de/html/pultec_knobs.html

Aha, so the same guy who hosts the original scanned design made one himself!

Great, I'll have something else to reference to now.

It uses the 271X which only has the 115V primary (instead of the multi-voltage universal primary) and it is 280-0-280 (I think).

Okay, it is using a different transformer, but I don't know what a multi-voltage universal primary is; does that mean the Triad R-4A works with any input voltage? I also don't know what the 280-0-280 represents. Time to whip out good 'ol wikipedia.

Edit:
I feel silly taking this job on and not understanding what this stuff means.
Time to buy
Tab Electronics Guide to Understanding Electricity and Electronics
and
Art of Electronics

 

[grhughes]

280-0-280 refers to the secondary ....

280-0-280 is a way of saying 280 volts on each side of center tap of the secondary winding. O refers to the center tap. Universal-international refers to the primary.ie. two, 115v primary windings that can be wired in series for 230v in England or in parallel for 115v in the USA. Most of the newer transformers have the iniversal-international feature whereas the older Triad units have on ly one 115 v winding on the primary. Ray Hughes

 

[grhughes]

Like this one....

International-universal primary:
http://cgi.ebay.com/Vintage-Freed-T...ryZ67815QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

 

[gibong]

Edit:
I feel silly taking this job on and not understanding what this stuff means.
Time to buy
Tab Electronics Guide to Understanding Electricity and Electronics
and
Art of Electronics

AOE is the bible.

Google for the PDF of the Radiotron Designer's Handbook. Morgan Jones's 'Valve Amplifiers' is also a good one.

You are pretty brave to start off with a tube amp as your first project. Way to go!

Without getting in the way of your learning process - let me recommend you have look at Cinemag and Edcor products for your transformer needs.

 

[gibong]

One more resource:
http://www.audioxpress.com/resource/audioclass/index.htm

 

[grhughes]

This place sells Belden 8450 by the foot

You can buy as much or as little as you need. You can use this between the inputs and transformers and from transformers to the outputs. You can also use it for filament leads. Good twisted pair shielded cable with SOLID conductors and a drain ground wire.
http://www.weisd.com/store2/BEL8450 010U1000B.html

 

[neoific]

Thanks, I've used Jameco on all of my cables that I've made so far (I make all of my own cables, though I cannot find a supplier for the higher-end switchcraft plugs).

I've hit a snag in terms of funding, hopefully I'll be able to convince the
'rents that investing in this is investing in my education

Edit: Yay, sounds like I've found someone to buy the transformers

 

[JPS]

Which transformer type no. of EDCOR is suitable as input transformer for PULTAC MB1 preamp in place of UTC A-11 ?

thanks

 

[neoific]

Which transformer type no. of EDCOR is suitable as input transformer for PULTAC MB1 preamp in place of UTC A-11 ?

thanks

"The UTC A-11 is a line to grid audio matching transformer with a 50 KOhm secondary and primary connections of 50, 200 and 500 ohms."

UTC A-11 information that I've gathered:
low-z to 1 or 2 grids
50, 200, 500 primary z
50k ct secondary z
mag shield yes
20-20k resp
52 pci-dcr
+3 max lev

Hopefully this will help someone else find the suitable equivalent, I don't know much about it though so I wouldn't know where to start. Sorry that I can't help you entirely JPS!

 

[gibong]

CMQEE-3440A from Cinemag should work for the input tx (and as a matter of fact, it was used in this MB-1 build: davoux's MB-1 .

CMMI-10 series should work too and has been used on at least one other MB-1 clone that I know of.

Cinemag's site

Nothing from Edcor will be suitable for the mic input (they don't have electrostatic or magnetic shielding) . Their 10K:600K output tx's will work for the output. They can custom wind a 15K:600K output tx for you too so it more closely mathces the original tx.

 

[neoific]

CMQEE-3440A from Cinemag should work for the input tx (and as a matter of fact, it was used in this MB-1 build: davoux's MB-1 .

CMMI-10 series should work too and has been used on at least one other MB-1 clone that I know of.

Cinemag's site

Nothing from Edcor will be suitable for the mic input (they don't have electrostatic or magnetic shielding) . Their 10K:600K output tx's will work for the output. They can custom wind a 15K:600K output tx for you too so it more closely mathces the original tx.

I just ordered my 15k:600k Edcors.

So you're saying that a CMQEE-3440A should be able to replace the UTC A-11?
Would it be better to buy that new over buying the UTC used?

 

[gibong]

Yes you can use ithe Cinemags to replace the A-11. I don't necessarily think it is "better" than the UTC. Use it if you can't find an A-11. If you are after the sound of the real MB-1, then you have to buy the original tx's because they contribute so much to the sound.

 

[neoific]

CMQEE-3440A from Cinemag should work for the input tx (and as a matter of fact, it was used in this MB-1 build: davoux's MB-1 .

CMMI-10 series should work too and has been used on at least one other MB-1 clone that I know of.

Cinemag's site

Nothing from Edcor will be suitable for the mic input (they don't have electrostatic or magnetic shielding) . Their 10K:600K output tx's will work for the output. They can custom wind a 15K:600K output tx for you too so it more closely mathces the original tx.

Correction, shouldn't this be 15k:600? Not 600k?

 

[gibong]

Oops. Yes of course. 15K:600.

 

[neoific]

Just wanted to clarify, would have sucked if I had ordered the wrong parts.