Aleph5 question - always ground -in if using unbalanced inputs?

[Michael Vogel]

hello to all passlabs forum members,
I have build an aleph 5 running it unbalanced directly from marantz cd67 se. Now I have read in the service manual of aleph 30 and in some of passlabs threads, that you have to ground negative input of balanced input. Is this true to aleph5 also? It changes sound considerably in my ears. Grounded its sounding more open, but with weaker bass, ungrounded its more closed in but has more controll in bass.
As I understand there is a difference in feedback due to paralleling R5 and R3 when grounding -in.
As there is an input wiring difference between aleph5 and aleph30 as R6 (same as R5 in aleph5 schematics) is 68K. Grounded this would give an feedback somewhere between aleph5 grounded and ungrounded.
Would someone help me to determine correct wiring of input circuitry for unbalanced use and best sound?

thanks
michael

P.S.
I have changed C7 0,047mü to aleph2 wiring C7 0,001mü to open sound. Does this effect bass?

 

[wuffwaff]

Michael,

with the Aleph5 you can choose between grounding or not. The difference is 6dB in gain (and also in feedback). The 30 or 60 won´t work unbalanced without grounding pin2.

Using the 5 grounded gives you more gain and less feedback (6dB) wich could be the cause for the change in bass you here. Due to the rel low input impedance there can also be some effect when feeding this from a rel. high output impedance.

William

 

[SGregory]

I also found a similar sonic difference between grounding and ungrounding. In my case I was using my BOZ todrive the amp wit only 5k impedance.

I solved the problem by building a X-SOBOZ. This intern created another problem whether or not to ground the input to the X-BOSOZ. I gues I will have to build a balanced DAC and ONO to solvethis problem.

 

[Nelson Pass]

Without grounding the negative input, you get 6 dB less
gain, which is translated into 6 dB more feedback, and the
corresponding improvement on a number of specs. I leave it
to you to decide whether it sounds better or not.

 

[Michael Vogel]

Thanks for your replies. Than how was original aleph input factory wired? That should be the "official" version, I think.

 

[Holger Barske]

There should have been a plug for shorting the two corresponding pins of the XLR input jack when using the unbalanced input.

 

[Michael Vogel]

Sorry that I'm so lazy.

I've read the owners manual of aleph 5 once again carefully. Should have done it before posting my question. Yes, it was shipped with shorted -in but it was left to customers ears to decide which way sounds better.
Thank you for your help