Slow Blow pre?

[mickey76]

Great info! I think I made up my mind now... I'm building one this summer!
Thanks!

 

[Bluzzi]

Thanks for all your help here sismofyt. The spirit of DIY is with you.

I've got a few projects to finish but this is THE tube preamp I want to build.


jim

 

[FotisGR]

Hi, Sorry for non write to forum but i am really very busy and most of the time away from my city.
I wanna thank Sismofyt for those nice infos.

Have you still got these to sell, whats the secondary currents, can I pay by PAYPAL?

Yes i have them.
The 80VA =230/150mA, 12V/3A, 48V/100mA
The 150VA =250/300mA 12V/6A, 48V/100mA
I have paypal account so no problem for payment.

Also Fotis - did you continue with single channel version of G9 - psu looked similar to this from what I can remember!

Yes i finished but i didn't like so much. A guite dirty sound without dynamics... etc. You can read more of my test http://www.groupdiy.com/index.php?topic=10751&highlight=fotis

Cheers
fotis

 

[Bluzzi]

Can we use with 110v on the primary?

jim

 

[mikeyB]

Hello again Fotis, - can you give me dimensions of both transformers and chokes - I'm trying to keep things compact. How many channels will each of the transformers supply?

 

[sismofyt]

[quote author="Bluzzi"]Can we use with 110v on the primary?

jim[/quote]

i think fotis said it's no problem to wind one with dual 115VAC primaries. this will make it universal over the entire planet. connect the primaries in parallel in the us, series in the eu

 

[sismofyt]

eta, wrong info - sorry :roll:

 

[sismofyt]

[quote author="FotisGR"]Yes i have them.
The 80VA =230/150mA, 12V/3A, 48V/100mA
The 150VA =250/300mA 12V/6A, 48V/100mA
[/quote]

aren't both with _250VAC_ secondaries? there's no need to go down to 230VAC for the 80VA. just a typo? :wink:

 

[sismofyt]

note, that the currently proposed 12V heater Vreg will _NOT_ power more than two channels though. actually, i'm thinking about ditching that Vreg for a 13V zener + 2N3055 combo. that'll drive eight channels without any mods ... hmm .. cheaper too than getting a 3-6A Vreg

driving eight channles means you need to waste 35W though. and that is just the heater. total power consumption will be around 140W

and this is one of my more economic designs and ... wait, do i see black helicopters outside my window..?? oh, no, they're RED. argghhhhh, it's the green peace hit squad .. :green:

 

[sismofyt]

[quote author="mikeyB"]Sorry Fotis - forgot to ask for transformer and choke dimensions. I am interested in both the 80 and 150VA transformers.[/quote]

i don't have them, but standard unpotted toroids pretty much always have the same size, like these nuvotem talemas:

80VA = 93 x 38 mm / 0,9kg / M5 bolt

150VA = 105 x 42mm / 1,35kg / M6 bolt

allow a few millimeters for the topplate and rubber thingies ..

 

[mikeyB]

sismofyt - Thanks for the info :thumb:

 

[sismofyt]

ok, i did some calculations and updated my site regarding power consumption

80VA good for two channels only

150VA fine for four channels

 

[FotisGR]

Sorry to be late... but i will promise you for pics and dimensions tomorrow

Yesterday i did some tests with my second channel slowblow. I changed the 5687 anode follower with a 12sn7. 15k anode R 390Ohm cathode R and 370VDC. It likes me. Full sound (a litle fat) but very nice. The interested is that i have 12 pieces of 12sn7 RCA and every tube has difenent sound :shock:
So what can i say? I don't know ...
I played also with cathode's cap and there was a big sonic diference. The best for my ears was a quite big 470uf/25V Black gate in parallel with a 1uf Jensen PIO. More capacitance = more fatness and a rise to mid-bass frequencies like harmonic enhancer. I think the balance will be 100-220uf but at 470uf my TLM103 sounds like a good tube mic :grin: .
You know it's a matter of taste. :thumb:

Later
fotis

 

[sismofyt]

you got 370VDC with that transformer and a 100ohm resistor in the B+? that seems a little high. what is your voltage drop across that resistor? and on the first cap after the diodes? not that there's anything wrong with 370VDC. it's better actually. both the 12SN7 and the 5687 SRPP likes that better

with 320VDC which is what i'm aiming for, you need a little higher cathode resistor for the 12SN7, 500ohm instead. you're pushing a bit more than 12mA through it (asuming around 182V at the plate), i specced it out at 10mA. iyou're running a little more than two watts through. fine and within limits. i would like to run 15mA through it, but with a low 15kohm plate resistor, i'd need a 450V B+ which goes past the magic '400V' mark. above that components become very expensive. it's more important with the low plate resistor. 2,5-3x Rp is my majic spot for these tubes. at that point the tube really sings. 2C22 types further benefit from a 600V B+ (they can take 500V _at_ the plates)

if you raise the plate resistor significantly (and change the cathode resistor accordingly) you'll get less 2nd order harmonic distortion and a little more gain. sounds gets boring quick though

you could also try to lower the resistors in the 5687 SRPP. 820ohm works better

odd, jazzy liked the 12SN7 _with_ the cathode cap as well. i generally do not like it. the bass tends to get to phat and uncontrolled. but it's a nice sonic variation i guess. one could just throw in a switch :wink:

12 RCAs yummy. one could do serious gear with those suckers

 

[FotisGR]

you got 370VDC with that transformer and a 100ohm resistor in the B+? that seems a little high

Yes, the B+ is about 370-380VDC. My trafo's AC is 270V not 250. :grin:
I had calcuate the psu so to maximize the voltage but not to overvoltage
caps (400V limit).

Later
fotis

 

[sismofyt]

damn, that is dissapointing fotis .... i had hoped that you somehow had made a device that could turn 250VAC into 380VDC. that would solve the worlds energy problems :razz:

380VDC is real close to 400VDC, you must have quite a stable grid down there

but like i said the higher the voltage the better

 

[mikeyB]

Has anybody used the brand "LCR" axial polypropylene capacitors - any good?

 

[sismofyt]

are you thinking about the yellow ones from rs / farnell? if so, they're fine, but not as good as solen / scrs. about same price. i use them a lot for PSU bypass duties though as they come up to 1kV

if you got a bunch you can always start with these and swap later. good tubes + lcr caps is better than shit tubes + expensive hifi caps :wink:

 

[Jazzy_Pidjay]

HS to Sismofyt :

Hi my man !!!!!! happy to see you back !
check your mail, i suspect a Gmail fuc**d up !!
We have a lot of things to discuss !!
miss you !

 

[ubxf]

Is the Lundahl 1577 a good alternative to the 1538xl for this preamp
Thanks
francois