[BUILD] GIX-51X tube preamp

[Toure14]

cool... i really want to get the most out of this pre so i was looking at the XL38 and XL78...thanks for clarification Rodney

 

[Brolik]

Hey guys, this might be a stupid question, but I noticed that the Gyraf G9 design calls for a LL1528 input transformer, while this 51X version calls for a LL1538. Just wondering what the deal is there...

 

[gemini86]

I changed it. The 1528 had split windings that aren't needed for this application and by switching to the 1538, we could use other lundahls with the same pin out, so we have more options.

Just a heads up:
I may be a little hard to get ahold of for a bit. My wife and I just had our first child on Monday and I've taken on a second job to make ends meet. I'll still be around but my free time is super limited.

 

[shabtek]

Congrats!

it was nice knowing you buddy.

 

[bruce0]

Congratulations Rodney!

And don't worry... kids love to have a 1:00AM feeding while you are posting to GroupDIY! 

 

[gemini86]

haha! Yeah it's already been a rough few days. I'm working graveyard shift a few night a week (weekends mostly) at a coffee stand, which has actually been really fun so far. My day job is starting to really wear on me, and it's getting to the point where I don't know how much longer I'll be there. Once I'm more stable financially, I might make a plunge and quit my day job so I can focus on my family and my next career move.

I'll for sure be around, since it doesn't take much time to respond to posts, but my current projects are on hold for now. I have a couple more 51x projects coming, and you know me, they won't be simple or straight forward to build. So, prototyping will take a long time with so much on my plate.

So, back to the 1538 VS 1528:

The 1528 has dual secondaries, which could be wired for 1:5 or 1:2.5 step up. We don't want or need 1:2.5 for this application, so there's no need to have the option.

The 1538 and 1538XL have a different pinout, and only a single secondary winding. It can still be wired for 1:2.5 operation, but only by wiring the primaries in series instead of parallel. This is still not needed, but here's where the bonus comes in; the 1538 has the same pinout as the 1576, 1577 and 1578/1578xl which are 1:7, 1:14 and 1:10 respectively. So, now you really have some options to play with the build. Sometime soon I'll be pulling out my oep iron and putting in a 1:10 input, into a 12ax7 for V1, reducing the overall feedback to increase gain and then hand winding a 4:1 output. I predict this will take the preamp from a very mild, clean warm sound to a dark, brash, grungy sound when really smacked hard.

So, that's just some insight into why I chose the input transformer options that I did.

 

[Brolik]

Awesome, thanks. Congratulations on the new family member!

 

[mulletchuck]

is the BOM finalized yet?

 

[gemini86]

Chuck,

The BOM is current and accurate. The mouser carts that people are posting are, however, not verified yet. (I don't think)

 

[Toure14]

Bey Rodney quick question. How much would a faceplate cost in all black with white lettering? pretty much a color reverse of what u have now?

 

[gemini86]

Well, the cost per unit would be the same, but I think the tooling fee would be around 80 bucks, then another 30 or so for air shipping. You really only get a good deal in large quantities. I'd suggest using Schaeffer or contact Dan with collective cases in the white market.

 

[kvothe]

Hey Toure, I had the same idea for my number 5&6 

I am ordering some faceplates from Frank at NRG in Germany. If you want in I could order more and send some your way.
fpd file: http://uploaded.net/file/1htg2hj2
I will also order some SSL9k 500 frontplates with culteousness1´s design as seen here: http://www.groupdiy.com/index.php?topic=42552.160

Prices will be about 20-25€ excluding taxes and shipping.

regards, Kvothe

 

[Toure14]

Hey Toure, I had the same idea for my number 5&6 

I am ordering some faceplates from Frank at NRG in Germany. If you want in I could order more and send some your way.
fpd file: http://uploaded.net/file/1htg2hj2
I will also order some SSL9k 500 frontplates with culteousness1´s design as seen here: http://www.groupdiy.com/index.php?topic=42552.160

Prices will be about 20-25€ excluding taxes and shipping.

regards, Kvothe

Funny You should say lol. I'm currently e-mailing Frank back and forth Now. I am also about to purchase SSL 9K5 and 4K5 face plates. I posted a pic of the Black Faceplate for my 9K5

 

[Toure14]

Here is a pic of the other face plate frank is doing for me

 

[Toure14]

I cant get your FPD file to open up but I assume if its Rodney's original design but just black with white lettering I may be interested. Where do you live Kvothe?

 

[kvothe]

Great timing! You need the latest front panel designer software to view it. I live in Germany, but if you are already in contact with Frank just order some.
Frank is a great guy

 

[Toure14]

Yeah I just got it to open thanks. I am going to send Frank your all black FPD file so he can add 1 to my order for the GI 51X. thanks Kvothe

 

[kvothe]

You are welcome Toure!

 

[Benny]

Hey guys,

I just tested my preamp and everything seems good so far. No smoke, tubes light and heat up as they should and the unit is passing signal. But I have to crank up gain and output all the way to get a 'usable' signal level. I just built the unit following the latest BOM and the actual schematic. First thing I'm gonna do is measure the HV. Can I just check the voltage at the output of the HV board or is there a better point?
After the first powerup I also realized that I had put the additional 100n cap on the HV board across the lower two resistors (R503+R504 see attached pic) instead of the outer two resistors R503+R502).
I corrected it now but still have the weird behaviour. Is it possible that this damaged something, leading to that lack in gain I have?

Cheers
Benjamin

 

[Benny]

I checked the HV on the output of the HV board and it's 242V when I power the unit up and then decreases to about 233V after half a minute. The voltage should be around 245V I guess.
Should I change the resistors on the voltage-divider to get closer to the 245 Volts?