Pass Aleph P1.7 internal switches

[spersanti276]

I own on original P1.7 preamplifier.
I would need to know the right setting of the internal gain switches.
Different indications are given in the user manual from the service manual.

For example in the user manual:
-"The switch default position is 1,2,7,8 = ON and 3,4,5,6 = OFF.
For a 12 dB input attenuation, 1,2,7,8 = OFF and 3,4,5,6 = ON."-

The service manual says:
-"The input pad settings are as follows (only 3 settings)
1.3 dB 3,4 5,6 on
9.7 dB all off
15 dB1,2 7,8 on"-

I'm completely confused, will you help me?

Thanks

 

[SRMcGee]

Stefano:

Pick any one of the three options. I think the ideal is to have the gain set as low as possible, so start with the 1.3 dB setting (3, 4, 5, 6 on, the rest off). If at that setting you can get the volume you want, regardless of how far you turn the attenuator (the volume control), then you're done. If you decide you need greater volume, turn the Aleph P 1.7 off and set the switches at the 9.7 or 15 dB settings. Then turn the AP17 back on.

Regards,
Scott

 

[wayne]

Use default if you can it has least in the signal path. 1,2,7,8 on 3,4,5,6 off.

 

[spersanti276]

Hi Scott:
but 1.3/9.7/15 is the gain of the circuit with 15 the higher, as we read in the service manual?

And this is the same setting we read in the owner manual (the 'default' setting) with the lower attenuation?

So the owner man. speaks about gain and the service man. speaks about attenuation?

Why do you think it's better to have the gain as low as possible?

Thanks again.
Stefano

 

[spersanti276]

Use default if you can it has least in the signal path. 1,2,7,8 on 3,4,5,6 off.

This was in fact my idea but i'm not a technician.
The Pass preamp is driving two bridged Aleph3 for powering very inefficient loudspeakers (Eminent Technology lft8b almost 84 db eff. but with very high impedance always over 8 ohm, tipically 10 and excellent phase behaviour)

Stefano

 

[Zen Mod]

Stefano

Wayne is Pass Labs

just do what he told you

if you are not happy then, ask again

 

[spersanti276]

Thanks to everyone for the precious advices.
You have been very kind as always.

Regards,
Stefano

 

[ozorfis]

Those switches (I marked them red in the schematic) lower the input signal. The transistors and volume control still do there thing as before but with a lower input. So you can speak of it as a lower gain of the preamp as a whole or a higher attenuation of the input signal.

Switch 1 and 2 when off put the 10k resistor in series with the input signal = lower signal
Switch 3 and 4 when on put the 3.3k shunt resistor in parallel with the input signal = lower signal

It is just a resistive voltage divider like the volume control at the output. One of the manuals might actually be for the earlier Aleph P (not the 1.7 revision). I have my Aleph P 1.7 on the lowest gain setting, because of my hot DAC and plenty of gain in the BA-3 monos.

 

[spersanti276]

You said "One of the manuals might actually be for the earlier Aleph P (not the 1.7 revision)"

I think this is true, in fact on the net there is only the service manual of version 1.7. I have never seen the 1.7 user manual.

Thanks for your help.
Stefano