noDAC DHT output stage

[merlin el mago]

What choke are you using now, amorphous?

 

[Koifarm]

Could you elaborate why you chosen two corner frequencies and what's the final Fc?

Fc about 37khz at 1260ohm output impedance.

 

[merlin el mago]

Isn't too low? Did you heard noise with the Fc higher?

 

[Koifarm]

I have with transformer no filter no noise but a little bit distorsion(0.8%).
With filter and transformer i had 0,1% distorsion. With isolator, filter and tube cathode follower i have 0.04% distorsion. No noise. Isolator has it ones power supply.

 

[merlin el mago]

What transformer do you use?

 

[Koifarm]

Lundahl LL1521B

 

[merlin el mago]

Have gain?

 

[Raj1]

ultranalog: CD enhancer II

 

[Koifarm]

Have gain?

2.3 times step up.

 

[merlin el mago]

Thant's very good numbers, could I ask how much cost?

 

[Koifarm]

They were used for € 25 a piece.

 

[merlin el mago]

ebay?

 

[Koifarm]

Yes, but they are not for sale at the moment.
On the web i saw some used ll1521 without the "B". I do not know the difference.

Lundahl LL1521 TRANSFORMER Analogue audio, PCB, line input (used)

 

[merlin el mago]

Lundahl web:

The LL1521B is a high impedance line input transformer, very similar to the LL1540 but with a slight step up. Turns ratio 1 + 1 : 2.28

But I can't get the data sheet of LL1521B or LL1521

 

[Koifarm]

ll1521B is obsolete. You can only buy used ones.

 

[merlin el mago]

OK thanks.

I have with transformer no filter no noise but a little bit distorsion(0.8%).
With filter and transformer i had 0,1% distorsion. With isolator, filter and tube cathode follower i have 0.04% distorsion. No noise. Isolator has it ones power supply.

I understood correctly that you don't use the filter & the isolator, are you using only the transformer?

 

[Koifarm]

At first i used only transformer, now i use isolator, filter and tubestage.
This config has for me the best sound and lowest distorsion.

 

[merlin el mago]

 

[Hearinspace]

Working on another solution, can you tell me what your 26' operating points are?
Thanks

 

[merlin el mago]

I'm using attached schematic but in place OPT I use the OPT as choke connecting all primary an output cap between the choke & plate, I don't know exactly the plate voltage but I guess something between 140-145V.