#26 pre amp

[Vinylsavor]

Hi Pek

Is transformer LL 4725 little better , than LL 1660 ?

That depends on how you are using the preamp. The LL2745 has a higher step down ratio that the LL1660. If you want to drive a low impedance volume control like most TVCs or a power amp with low impedance input, the LL2745 will be the better choice.

Best regards

Thomas

 

[Pek Zenay]

Thank you Thomas for answer !

 

[merlin el mago]

Any success? Problem solved? 🙂 (just curious)

Now I'm just connected the TVC at the output and sounds horrible, very sharp without mids and bass.....

 

[Vinylsavor]

Hi!

Now I'm just connected the TVC at the output and sounds horrible, very sharp without mids and bass.....

Seems like it is not driven correctly. Did you wire the transformer 4.5:1?
Did you test the TVC itself with scope and signal gen to make sure each step is working correctly?

Thomas

 

[merlin el mago]

Yes the TVC is working OK because I measure with the scope before to use it. Before I used a simple Alps RK27 100K and sounded very good so I assume I wired well the LL1660, attached pics

 

[merlin el mago]

Thomas can be I wired the RCA outputs incorrectly?

 

[Vinylsavor]

Hi!

Yes the LL1660 is wired correctly on the photos. How did you connect the TVC to the secondary and from there to the output? Did you measure the preamp with TVC and how does it look like?

Thomas

 

[merlin el mago]

The TVCs are in separate box, I'm sorry to insist: can be reversed polarity in the output RCAs of the 26 the cause of the issue?

 

[merlin el mago]

No I don't measured the preamp with TVCs.

 

[Vinylsavor]

Hi!

can be reversed polarity in the output RCAs of the 26 the cause of the issue?

No unless you did some other mistake. Maybe with the ground connections?

Thomas

 

[merlin el mago]

I connected pins 10+9+3+2 to signal+ and pins 4+5+7+8 to signal-, so I assume I reversed the RCA polarity....

 

[merlin el mago]

Attached 26 insides pic

 

[merlin el mago]

I use this schematic except the LL that mine are config Alt.Q 4.5:1 SE to line output

 

[Vinylsavor]

Hi!

As mentioned the LL1660 is not sensitive to polarity. Best is to do some measurements over the whole preamp.

How does it look like at full volume setting how at lower settings.

Also a schematic would help with all ground connections

Thomas

 

[Vinylsavor]

Hi!

That schematic does not show how the TVC is wired in

Thomas

 

[merlin el mago]

TVCs

 

[merlin el mago]

TVC wiring

 

[merlin el mago]

TVC pic

 

[vgeorge]

Just out of curiosity, did you put a grid resistor after removing the pot at the input?

 

[merlin el mago]

Yes Georges are the Mills 100K.