Attenuating high gain amplifier (Class D) for the purposes of bi-amping

[Jacob29]

I have a 6SN7 (tubes4hifi sp14) running into pass labs Aleph J, powering, troels gravesen Faital 3WC-15 (96db) I would like to bi-amp the woofer with moderately high-power class D (I was looking at ICEpower 700AS2) there’s a couple issues and questions I’m running into

• My preamp is single-ended, and the Ice power module is a balance differential amplifier. Can I go from RCA to XLR by connecting pins one and three of the XLR. Or do I need to use absolutely use an active device/transformer
• The Aleph J has about 19.6DB of gain the ICEpower has 27.4DB, to get the gains to match. Can I simply add a potentiometer between the preamp and the class D amplifier to reduce gain. Or this will cause impedance issues and do I need an L pad?
  • Preamp output impedance 600 ohms
  • Aleph J input impedance 242 Kohms (RCA input)
  • ICEpower Input impedance, 36 kW Kohms(xlr )

Sorry for the somewhat novice questions.

 

[HrAberg]

I think what you you need is an l-pad to match the gain. Troels has an article about this. There is also calculators online to find suited values for resistors.
I run my hypex ucd from an aikido 6sn7 single ended .
If running it single ended dosent work you could get one off these.

https://neurochrome.com/products/universal-buffer

 

[rayma]

The Aleph J has about 19.6DB of gain the ICEpower has 27.4DB, to get the gains to match. Can I simply add a potentiometer between the preamp and the class D amplifier to reduce gain.

You don't really want the amplifier gains to match. You want the acoustical outputs of the Faital and woofer to match.

 

[Jacob29]

rayma I'm not trying to do a active speaker, I already have a passive speaker with crossover so the acoustical output is already matched?

 

[rayma]

So you mean the woofer in the Faital.
This is only possible if the internal crossover is a parallel design.
Some are not, but this one is parallel.

The 7.8 dB difference can be made with an L pad before the woofer amplifier.
Or an H pad if the woofer amp input is balanced.
But you have to take into account the source and load impedances involved.
Two precision resistors can make up the attenuator, and will be better than a pot.

 

[Jacob29]

Would something like this work

I was trying to follow this old thread
https://www.diyaudio.com/community/threads/connecting-single-ended-to-icepower-modules.359131/

 

[rayma]

Remember:
L pad for unbalanced input
H pad for balanced input.

 

[Jacob29]

Would that still be true (h pad) if I am running this from a single-ended preamp and connecting pins one and three

 

[rayma]

If you use only one phase, the system gain will be 6dB less, unless the amp has an internal unbal to bal converter.