Remove resistence to A75 for unbalanced use?

Danyele82 · 5th December 2004, 10:24 AM

To A75 amplifier for unbalanced use I can remove R28 , R5.
R29 and R2 can be romoved?

Danyele82 · 5th December 2004, 11:52 AM

look here the circuit A75

Alain Dupont · 5th December 2004, 12:52 PM

Danyele82,

>> To A75 amplifier for unbalanced use I can remove R28 , R5.
Yes, you can...

>> R29 and R2 can be romoved?
Well, I don't think so.

For the cost of 4 resistors, 2 XLR's and 2 switches, it's a shame to
remove the Balanced inputs of the A75.!! Who knows, you'll probably
build a balanced preamp sooner or later...

PS: Now with my CCS-X-Bosoz preamp I use my A75 balanced, and I prefer this type of connections, the balanced mode has great advantages...
And using Belden 89207 twinaxial cable, its not so costly to have balanced cables..

Alain.

Danyele82 · 6th December 2004, 12:47 PM

For unbalanced use the gain is determinated by (R81 + R3//R27)/(R2//R29)?
If it's right the input resistence (R4) can be eliminated (or it's necessary for the low-pass with C1)?.
The quality of C7 and C5,C6 are important to the final result?

Alain Dupont · 6th December 2004, 10:57 PM

Danyele82,

>> If it's right the input resistence (R4) can be eliminated (or it's necessary >> for the low-pass with C1)?.
>> The quality of C7 and C5,C6 are important to the final result?

Keep R4, it wont interfere in the 75 K Ohms unbalanced impedance,
but globaly there must be symetry between positive and negative input's.

Norman Thagard and Nelson Pass tells: the only requirement being that corresponding values on the positive and negative input networks be matched.

For the quality of C3,4,7 4.7uF, 16V, electrolytic
C5,6 220uF, 16V, electrolytic

I have used Panasonics, quite standard types...

Regards.

Alain.

5th December 2004, 10:24 AM	#1
Danyele82 diyAudio Member Join Date: Mar 2004 Location: Como	Remove resistence to A75 for unbalanced use? To A75 amplifier for unbalanced use I can remove R28 , R5. R29 and R2 can be romoved?

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5th December 2004, 11:52 AM	#2
Danyele82 diyAudio Member Join Date: Mar 2004 Location: Como	look here the circuit A75

5th December 2004, 12:52 PM	#3
Alain Dupont diyAudio Member Join Date: Sep 2003 Location: Paris - France	Danyele82, >> To A75 amplifier for unbalanced use I can remove R28 , R5. Yes, you can... >> R29 and R2 can be romoved? Well, I don't think so. For the cost of 4 resistors, 2 XLR's and 2 switches, it's a shame to remove the Balanced inputs of the A75.!! Who knows, you'll probably build a balanced preamp sooner or later... PS: Now with my CCS-X-Bosoz preamp I use my A75 balanced, and I prefer this type of connections, the balanced mode has great advantages... And using Belden 89207 twinaxial cable, its not so costly to have balanced cables.. Alain.

6th December 2004, 12:47 PM	#4
Danyele82 diyAudio Member Join Date: Mar 2004 Location: Como	For unbalanced use the gain is determinated by (R81 + R3//R27)/(R2//R29)? If it's right the input resistence (R4) can be eliminated (or it's necessary for the low-pass with C1)?. The quality of C7 and C5,C6 are important to the final result?

6th December 2004, 10:57 PM	#5
Alain Dupont diyAudio Member Join Date: Sep 2003 Location: Paris - France	Danyele82, >> If it's right the input resistence (R4) can be eliminated (or it's necessary >> for the low-pass with C1)?. >> The quality of C7 and C5,C6 are important to the final result? Keep R4, it wont interfere in the 75 K Ohms unbalanced impedance, but globaly there must be symetry between positive and negative input's. Norman Thagard and Nelson Pass tells: the only requirement being that corresponding values on the positive and negative input networks be matched. For the quality of C3,4,7 4.7uF, 16V, electrolytic C5,6 220uF, 16V, electrolytic I have used Panasonics, quite standard types... Regards. Alain.

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