Slow Blow pre?

[Bluzzi]

michal,

I can do a PCB design but I think this design is best suited for P2P no? Thing about doing tubes on PCB is if you get just 1 trace that causes hum then you have to re-design. With P2P you just move the wire around (I have that experience when building my first LA2A. The second one was 100% because I learned from the 1st.)

But maybe the Power Supply could be done PCB. I'd be willing to do it.

I'd like to do a 12sn7 version only because descriptions of the sound seem to be what I'd prefer. Isn't the 6sn7 a 6v heater?

Should I put your PS schematic up on the FTP site as well?

Jim

well, I don't see any difference in your PSU schematics. I didn't look careful though. Here's a simpler PSU I found that I believe will do just fine.

i also think it's worth waiting for sismofyt's verified schematics. I'm interested in 6sn7 version cause I like this tubes.

one more thing: are we doing this PTP or someone designs PCB?

 

[michal_k]

I didn't design it, just found it somewhere on a forum so I guess it's ok to publish it. I think it's good idea to keep all files in one place.

I also prefere ptp - much more fun 
cheers,
Michal

 

[Bluzzi]

The other option is Turret board as in LA2A.

Michal, if you look  at both PS schematics (psu1.gif and psu2.gif) on psu2.gif there are 2 120R resistors going to the negative and positive rails on the heater supply. There is also 270K and 56K 2W resistors with a 220uf on the B+ circuit. What are those for?

Also why isn't the heater supply grounded or is it supposed to float like that?

Jim

 

[Bluzzi]

Here's a simpler PSU I found that I believe will do just fine.

michal, other than a few values and a choke this is same as PSU.jpg that I just put up on the FTP site. I downloaded yours but I couldn't get it to open (i get file error). So now there are 3 versions on the FTP plus the one you show. See what I mean?

Jim

 

[michal_k]

all these parts are for lifting heater supply. that's why 12.6V section isn't connected to ground. It is used when you're afraid of reaching max cathode-heater voltage which might be a case when srpp stage is concerned...

... I guess  ;D

 

[sismofyt]

forget about all these schematics, it's getting too messy. you people are thinking too much  ???

i will upload the definitive versions, including the original, the asymptot and the dual SE during this weekend

sorry for being (1 to 10, take your pick) years too late ..

kiss kiss,

ole

 

[michal_k]

oh come on, that's not gonna be fun then!  

waiting for schematics,
thanks a lot!

 

[ioaudio]

hi ole, how are you doing lately - back to diy?
-max

 

[DaxLiniere]

Hey Ole,
Hope you're well.

In case you didn't see page 9 - Congrats on your little one, mate. All the very best!

 

[michal_k]

Hello everybody,

I've just got a preeliminary price for choke which is ~20eu, don't know anything about quantity discounts yet.
Power Transformer was 30eu(audio version) and that makes the whole set 70eu, pretty much for a power supply. Anybody looking for a cheaper alternative?

PS. I can write to a jj-electronics and ask for a caps cause we're gonna need a lot of these and once again, discount is possible. I live about 200km and one border from their factory  

Now, we should know how many of us would be into building that pre, time for a feeler?

 

[pyjaman]

Hi,
Michal_k, I could be interested in the PSU iron set, but it made me think about one problem: I'll go for 6,3v heaters, and I think some others would want it too. So couldn't we think about a compromise, for example two 7v heaters, connected serial for 12,6v, and paralleled (with the sacrifice of more expensive use of low drop regs) for 6,3V? (We could also use 2*9v but with the sacrifice of much more dissipation for 12,6...).

regards,

Laurent.

 

[penquista]

hi,

i'm using the psu design that michal_k posted. 3x 1000uf + 3 x 1uf pio caps
the caps can be found quite cheap at ebay. i paid not more then 10 euro for 4 of 1000uf/400V
one difference to the posted schematic is that my heater psu is not regulated. i'm using big smoothing caps and dropping resistors.
the power tranny i use was about 35 euro and is big enough to power 4 channels.
the choke i use is hammond 193J and is available at www.tube-town.net
my psu is an external 2U and i use a 8 pole speakon to connect psu with preamps.

for the 6n6p srrp i use 1k2 resistors

 

[michal_k]

Hi,
Michal_k, I could be interested in the PSU iron set, but it made me think about one problem: I'll go for 6,3v heaters, and I think some others would want it too. So couldn't we think about a compromise, for example two 7v heaters, connected serial for 12,6v, and paralleled (with the sacrifice of more expensive use of low drop regs) for 6,3V? (We could also use 2*9v but with the sacrifice of much more dissipation for 12,6...).

regards,

Laurent.

Do you need 6.3V heaters for a tube that doesn't take 12V? Thing is there's already 7812 regulator, the nearest to the 6.3V is 5V which is beyond typical 5% tolerance of the tube.
A reasonable solution could be current regulator. One could calculate value of regulator's resistor for own needs.

 

[penquista]

a pic of my slowblow psu
i will rearrange the heater psu for security reasons. it works pretty good without regulators. i first had

pics of the preamps wiring will follow later.

 

[toffifee]

At first, my apologies to some of the German forum members here who now have to see this for the second time. But there seems to be some new interest here for this preamp, so: doubleposting terror! (hi Kubi!)

Then, greets to Ole, and many thanks for this design - you never saw pics of my finished build, but at that time you somehow disappeared from DIY.

Now to the pics:

"Classic" slowblow, 12AU7 SRPP into 5687 SRPP:

Here you can see how I did the illumination for the gain pot dials. With the help of my CNC router I first did these elliptic cutouts into the front panel. Then I cut out the same ellipse from acrylic glass, and just inserted this into the frontpanel (I even did not have to glue them in, fitted just perfectly. CNC is very precise):

Inside pics:

The signal part: the sweet music enters the preamp and meets those high quality gold plated Siemens relays. Then it is the users decision to either send it to the Lundahl input transformer, which is clean and "HiFi", or to those funky old Telefunken thingies, which distort a bit and hype the highs in a crazy way. Perhaps they technically ring like hell, but I don´t care. Caps between the tube stages are Russian PIO, bypassed with some German film caps; output caps at the moment Solen, but I think I will change them back to those big Russian PIOs that I had there first. I run the output unbalanced, no transformer there.

The signal part is built onto a seperate sub chassis (alu and steel), so that it is shielded from mains transformer hum, and of course because at that time I thought it would look cool and absolutely overdone You can see the star ground point, all those grounds are connected very tightly to this point with ring eyelets. The tube sockets are made of cast iron, which is a good thing because they can stand the heat of the 5687s and transmit it to the chassis - the 5687 is such a hot tube! I think it wouldn´t be a good idea to use cheap plastic sockets and do this preamp on a PCB, would probably just melt away...

Now to the PSU: My PSU is G9-style for the heaters and the phantom power (thanks Jakob!), which means: two (too) big toroids back to back, and a tripler for the 48V.

The HV part is a bit different: at first RC filtering, then a separate LC for each channel (there is 6000yF in total, each cap has its own bleeder). I got those big chokes from the company "Jan Wüsten" in Germany, not very expensive.
I would strongly suggest to NOT build the PSU like I did ;D
At the time I built this preamp, I did not know that you can have a custom mains transformer made which is not very expensive; I don´t like the back-to-back configuration very much.
In my opinion this preamp should not be recommended for DIY newbies as one of their first projects, the PSU is big and dangerous. Be careful with what you are doing here. A friend who has also built this preamp told me of an american fellow who had his SlowBlow PSU burning. Imagine a short with 300 to 400 V and 6000yF

Enjoy!

 

[andrew_k]

toffifee, I'm so glad you've posted, I stumbled upon your fantastic build pics in the gallery prior to reading this thread. I have a few EM80 and am looking for a compact way to drive them. Would you please be willing to share your EM80 driver schematic?
Impressive work, inside and out!

 

[DaxLiniere]

Looks fantastic!!

 

[ioaudio]

woha, thats really 

dont even try to bring that unit through the airport - the name slowblow wont exactly help either 

-max

 

[skipwave]

Holy sh!t..... that's... impressive.  8)

 

[[silent:arts]]

I miss those pictures in the german forum - they are gone :
would have posted the links here otherwise.
since you have the most impressive slow blow ever build.
no double post terror with me ;D ;D ;D