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May 22, 2019, 10:03:50 pm

Author Topic: Let's try this again: converting SII to Power Amp for BeePre  (Read 104 times)

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Offline Deke609

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I started a thread yesterday about this, to which Tom-s and PB responded, but it disappeared. So here goes attempt #2. New or only partially answered questions in yellow.

But first:

IMPORTANT PUBLIC SERVICE ANNOUNCEMENT: The mods I have in mind are completely "unnecessary" and are just for fun and experimentation. If you turn the volume pot all the way up, or alternatively, if you have the Mourquiet upgrade, set the attenuators to 0dB attenuation, the SII will function as a power amp. And you can jumper the input selector switch to take it it out of the equation. Making the mods contemplated below will kill the resale value of your amp, and will likely limit the help that BH can provide if something goes wrong. (The foregoing is stated in the hopes that it obviates the need for PB, PJ or Doc. B to advise of same).

My plan:

(A) remove all three pairs of rca inputs, the input selector switch and the Mourquiet volume attenuators (and if I still had the vol. and balance pots instead of the MQ upgrade, I'd be removing those)

(B) install 1 pair of rca inputs in the mounting holes for the MQ attenuators towards the front of the amp (same holes used for vol. and bal. pots).

My Original Questions:

(1) Input resistors - what values and where?

          Tom-s responded (IIRC - please correct if wrong): 50K 1/4 or 1/2W tantalum resistors between each positive input and
          ground.

              My Follow-up Questions:

              (1-i) Does this result in a 50K input impedance or a 100K impedance (assuming that setting input impedance is one of their effects)?

              (1-ii) Is the 50K value optimal or are there other values that will work equally well? 50K tantalums are hard to find -- can I use anything
              between 50K and 100K or even 200K? (I anticipate that the answer depends in part on the answer to question (1-i) above)


(2) Optimization for BeePre: what if any mods would make the SII power amp optimal for use with the BeePre?  This may be covered by Question (1). Whereas the SII is stated to have an input impedance of 50K, I thought I read that the BeePre prefers to see 100K.

             PB's response: The BeePre is fine with any amp with an input impedance of 1.8K and up.

                    Follow-up question: Just to be clear -- while the BeePre may be happy with anything over 1.8K, is there an input impedance with which it is happi-est?

                Tom-s' unanswered question (IIRC): Can one put a 100K vol. pot in the SII?

MTIA,

Derek





« Last Edit: May 15, 2019, 07:50:32 am by Deke609 »
Derek
______

Roon Intel NUC ->  Yggdrasil DAC -> BeePre (w/ BeeQuiet and JJs)  -> Stereomour IIs (2A3 and 45 Conversion - both fully upgraded)  -> Audeze LCD4

Offline Tom-s

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Re: Let's try this again: converting SII to Power Amp for BeePre
« Reply #1 on: May 17, 2019, 06:17:50 am »
1-i: 50K
1-ii:I'd search around 50K (Shinkoh 43K or 62K is also fine).

Follow-up question: I don't know. But can imagine, anything 1.8K and up.
My unanswered question: Yes, i think i can. Original stereomour had 100K.

Edit: In my SRII manual it shows 249K input impedance.
« Last Edit: May 18, 2019, 05:38:10 am by Tom-s »