Slow Blow pre?

[ricothetroll]

hi, I thought you could pick it up on the 50V bias tap.

I might be wrong, but I thought maybe this could also help :

creating 48VDC from 12 or 18VAC :

http://www.sonelec-musique.com/images2/electronique_alim_phantom_ac_01a.gif
http://www.sonelec-musique.com/images2/electronique_alim_phantom_ac_01c.gif

from 24VAC :

http://www.sonelec-musique.com/images2/electronique_alim_phantom_ac_01d.gif

The page's URL with explanations in french :

http://www.sonelec-musique.com/electronique_realisations_alims_phantom.html

Maybe that can make the transformer's choice easier, only needing 320V and 12V.

That guy's website is a real goldmine for project ideas, and he's really nice, helped me a lot on some projects on a french forum (I think he's around here also sometimes) :

http://www.sonelec-musique.com/electronique.html

Pretty cool site ! Thanx, Chimimic.

 

[DaxLiniere]

My apologies, Chimimic, I didn't even see the 50v tap

 

[ricothetroll]

No problems !

But chimimic isn't me, it's the guy that did the website I was talking about

 

[DaxLiniere]

Oh, right. I guess it's epic-misinterpretation on my part :/

 

[kambo]

can anyone  provide a link for the PSU PCB (home etch) please  

 

[syn]

For now, it is P2P. No?

 

[kambo]

its P2P but i wouldnt mind the PSU on a PCB

still need to finish my Mu P2P  anyway

 

[yoons]

Hi every body!

I have started to build the classic version of the SlowBlow.
I would like to put 4 channels in a 3U or 4U case.
My problem is the 12V that must be able to drive the 4.
If I take the original schematic, is that simple as to change the Vreg for one that can supply 6A?
Or can I use another schematic as this one : http://www.sonelec-musique.com/images2/electronique_alim_simple_007c.gif?

 

[yoons]

You can see few pics of the beast here : http://fr.audiofanzine.com/construction-de-micros-amplis-pr/forums/t.142838,special-slow-blow-p2p-tube-preamp-en-cours,post.6054652.html

Next step is Jazzy's version!

Thanks Sysmofit for sharing this nice baby.

 

[Bluzzi]

I have to go out now so I only looked at the link briefly but it looks beautiful man!

Have you used it on any sessions yet? Would love to get your reaction to it.

Still looking at this as my next project (now that I finished the 1084 EQ project).

Jim

 

[yoons]

Thanks!

Yes I have used it in session for vocal (classic version but 12sn7 instead of 12au7). Really really nice!
It sounds very clean. On vocals and in the clean range (0VU) it's really close to the Green (here is my version : http://fr.audiofanzine.com/construction-de-micros-amplis-pr/forums/t.399528,realisation-d-un-green-8-canaux-v14-pas-a-pas,post.5753116.html ).
You could confound them as they sound similar!

I have not pushed my tests as the bypass caps have started to burn slowly due to bleeder (look at the 3rd pic).
I will fix it next.

If you want I can post samples. It's not a big projet ( home made) but you could hear it!

 

[kambo]

just finished my P2P slowblow

i have about 5 db loss at 20hz, 4db at 30hz etc
curve starting at around 110hz,
(tested with 20db pad)

anyone else has the same problem...

 

[Kingston]

What output tube, what output transformer and what output transformer coupling cap?

 

[kambo]

i did the moded version... not 12au7 vesion btw...
its now fine... i think it was a cold solder somewhere... i went through soldering points....
6.3V heaters...
5687
1uf, 10uf auri caps (yellow ones)
solen fast etc.. all caps are good quality...

what is the recommended output trx for this baby tho...
there is two, and i think one is typo... 1517 or 1577 ???
couldnt i just wire lundahl 5402, 1504 in someway, or a cinemag ?

 

[Kingston]

i did the moded version... not 12au7 vesion btw...

This is one of those rare projects where there are more versions than builders! You need to be very specific with details.

what is the recommended output trx for this baby tho...
there is two, and i think one is typo... 1517 or 1577 ???
couldnt i just wire lundahl 5402, 1504 in someway, or a cinemag ?

I doubt there is one recommended output transformer, but if you look at G9 and G-pultec projects, they both have the exact same output stage as slowblow. Same options apply.

But where LL5402 actually doesn't work well in G9 (with 12au7), it will work great in that same configuration with 5687 or ECC88 (g-pultec). 5687 packs such great punch (ie. low output impedance in SRPP configuration) that you can use a lower stepdown like LL5402 . You could also use the even more flexible LL7902, but it's probably unnecessary for this project. Don't need that much headroom here.

LL1577 is a mic input transformer so yeah there's a typo somewhere, but again, I have no clue which of the 50+ documents you are talking about.

 

[KrIVIUM2323]

1517 is the one for output (1:1) but curiously Sysmofit don't recommend using it, as he prefer the sound of the unbalanced out.

 

[kambo]

this is the one i made... i used 5687 for the first stage too.
http://i128.photobucket.com/albums/p174/mtvermie/SlowBlowSchema.jpg

LL5402 cuts of below 120hz... excellent HPF  ;D

http://www.hicksorganservice.net/misc/stuff.html

if you look at this page, he is using 1577 for the output... you can see it on his pictures too... huge trx on left corner...

 

[Kingston]

LL5402 cuts of below 120hz... excellent HPF

No it doesn't, running 2:1. And definitely not on 5687 unless there is a mistake in your build somewhere.

By the way, the slowblow SRPP output stage running to a 1:1 output transformer is a bad idea because output impedance will be too high. It won't have enough drive for the very common 600-ohm inputs and that's when you certainly will go bye-bye-bass.

You will of course lose 6dB of gain with 2:1 output but then, that's life with the SRPP since it's a bit sucky design component to use in the first place. It was the fashion about a decade back, but most designers know better now.

 

[kambo]

oooops, my bad... this 5687 tube has such confusing pin_out...
i mixed grid-cathode pins on second stage... i was still getting really nice sound tho...
anyway, corrected that stupid mistake, and 5402 on output works now... bass is back
thanks for the help...
cheers

 

[Kingston]

this 5687 tube has such confusing pin_out.

Yes it does. I don't understand why all noval dual triode tube's don't use the same pinout.

But then, I don't understand why they vary it for transistors either. I mean come on, it's only three pins, is it really that hard to always have the same order.