Valve Itch phono

[Salas]

Salas it's normal more gain using the SHURE V15 type III or have I to look for the need of more gain in other place?

With 3.5mV output you should not need more than 43dB in any case. Many MM preamps have 37dB for 5mV carts as standard. 40dB for 3.5mV equals them. The Itch has at least 43dB on healthy tubes. Either the V15 has gone weak (usually its rubber suspension) or it needs more load capacitance to liven up or you need gain elsewhere in the system's chain.

 

[merlin el mago]

Thanks Salas, I suspected the same. I will try 1st with more load capacitance. The tubes are ok. The Itch it's connected to 26 preamp with Sic bias, Bartola hybrid Mu-follower, 15K-300R OPT & Dave Slage AVC.

 

[Salas]

Is the power amp's voltage gain and the speakers sensitivity loud enough as well?

 

[merlin el mago]

Power amp Mono block Erno Borbely 75W RMS Class A, speakers DIY 86dB or less because the passives filter.

I'm using the 26 with OPT to listen with headphones HD600

 

[merlin el mago]

Salas what about if I use a bypass capacitor at R9 330R?

 

[Salas]

It would not add anything much. 0.3dB or so. Full Mu stage gain is already achieved. Its a Mu follower.

 

[merlin el mago]

Thanks Salas

 

[merlin el mago]

Could be the load capacitance? Shure V15 III best load capacitance 400-500pF if so have I to add in parallel to 47K 430-440pF?

 

[merlin el mago]

Mine stylus it is older than 10 years, it should be replaced as the stylus bushing (made of an elastic material) has likely stiffened with age. Do you know how can do it?

 

[Salas]

Try higher load capacitance first.

 

[merlin el mago]

Ok thanks Salas.

 

[Salas]

There are economic needle replacements for V15 type III to check if that's the problem. And there are also expensive profiles when you know the main cart is ok.

 

[merlin el mago]

Wich value to start?

 

[Salas]

450pf target total i.e. include what you measured for your cabling and what you measured for your build's input capacitance

 

[merlin el mago]

I measured Linn Ekos cable 220pF + 65pF average Valve Itch input capacitance + my inside cable of the phono pre have 47pF= 332pF

450pF - 332pF = 118pF

I have on my stash 100pF & 18uF // = 118pF great!

 

[merlin el mago]

Salas also coud be an incorrect 47K loading?

LC resonant tank. Ignoring the effects of the resistances, the resonant frequency is given by:

Inductance: 500 mH, Capacitance: 332 pF, Frequency = 12.4 kHz

Load resistor = √L/C

5000000000000 ÷ 332 = 15.060.240.963,85542

√( √( 15060240963,85542 ) ) = 38.807,52628531664

So 38.8K load resistor in place of 47K?

 

[Salas]

Load resistor value play in MM is valid to try

 

[merlin el mago]

What do you think the calculated value get from Hagerman Hagerman Technology LLC: Cartridge Loading?

 

[Salas]

Logical

 

[merlin el mago]

I have on hand 39K, I wil try & let you know. Can affect the gain?