ImPasse Preamplifier

[nkostop]

Interesting, some questions:
1) You didn't use transformers on the input signal?
2) You didn't add a volume potentiometer?

In my design i try to incorporate a switch in order to choose between XLR and RCA output.

Also if I add a DC panel meter on the second tube, does it mean that slight change to the LEDs has to be done?

 

[luvdunhill]

My boards can be seen in Post #307.

 

[DIYspaceW]

I have an original pcb with dn2540 on it, I also have a nice pair of jensen input transformers if someone is interested let me know!

 

[nkostop]

luvdunhill your boards look amazing, is it possible to share the scematic?

 

[PKI]

Am I correct that DN2540N5 are impossible to get? Looked everywhere -- out of stock

 

[mrdave45]

It looks like that at the moment, but I don't think it's just that chip. There's a global chip shortage at the moment caused by higher demand due to lockdown etc and I think there's been a pretty major fire at one of the chip factories. I thought I had a load spare but I don't seem to be able to find them at the moment.

 

[PKI]

Thank you!

Also, anyone knows how you could get those Cinemag transformers? Could not find a store online? Or you get them directly contacting Cinemag?

 

[6L6]

Directly from CineMag. Order now, they have long lead times.

 

[PKI]

Thanks, got it! Will email tomorrow.

 

[jackinnj]

Am I correct that DN2540N5 are impossible to get? Looked everywhere -- out of stock

DN2535N5 is in stock at Mouser -- 350V, not 400V.

If not happy and stuck, I have 3 tubes of DN2540N5.

You can always just use a resistor -- with a regulated power supply the prodigious impedance of the DMOS ccs may be a bit of overkill.

 

[nkostop]

Is it possible to use a shunt attenuator?
I don't have any ladder type and I find it difficult to buy one in europe. Does anyone have a clue about it?

 

[nkostop]

The pcb worked!
Here is the ImPasse with a Salas input selector and sowter 3575 trans on top of an F4!

The first of the DN2540N5 on every side seems to get too hot, I cannot touch it. The second one seems ok.
Any suggestions here?

For anyone interested on the PCB I haven't heard from SY so I do not know if it is good to publish it...

 

[6L6]

Use a heatsink on the hot DN2450s

 

[jackinnj]

Yeah, wrt the heat-sinks note that the drains are at different potential so you MUST use an insulator and thermal compound

 

[nkostop]

One newbie question here:
If the transformer has a center tap can i use it for balanced input?

 

[nkostop]

Added the heatsinks and everything seems ok.
I am still puzzling my head how can I add one balance input with the salas selector or maybe a second selector. The goal is to use an arduino to change the the inputs and the volumes with a remote...
The PCBs worked fine with no hiss or buzz or anything! The sound is good.

One issue that I cannot understand:
1) I measured the split load phase splitter voltages and found that with 15K for R11 and R12 the voltage drop on the resistors are about 90V and 170V on the tube instead of 120V and 100V as SY has said on his article.
2) I also checked with TubeCAD from glassware and seems that my measurements holds true.

What am I missing here?

 

[TonyTecson]

there is a 500k trimpot that you can adjust to get the voltages right ...

 

[nkostop]

Yes I will do that but trying to understand, why is there such a difference? It is tube related?
I reread the thread and found that lehmanhill had the same problem here
(ImPasse Preamplifier)

 

[Brinkman]

I’m excited to build this and the F4. Got some JAN 6592 tubes for the input and a couple ECC99 tubes for the output. Also ordered a pair of CineMag CMLI-15PC transformers per the instructions on this thread.

 

[Brinkman]

Anyone looking for a a power transformer, the XPWR051 from Edcor seems to be a better value than the Hammond 290CX mentioned earlier. It’s also somewhat overbuilt for the Impasse but nowhere near as overbuilt as the Hammond.