A75 without preamp?

SteveG · 20th January 2002, 08:32 PM

I am in the process of building an A75, and was wondering if I could use the output of my SACD player to drive the inputs directly (no preamp) with a passive attenuator in between. If so, how would I go about choosing the value?

SACD player output specs

from owner's manual)
level: 2VRMS (at 50Kohm), minimum load- 10K

Since it is spec'd into a 50Kohm load, I was thinking of using a 100K pot. What do you think? I believe that the A75's input impedance in unbalanced mode is about 75K. I'm not sure how you go about determining the minimum impedance as seen by the output... is it the combination of the pot on the output paralleled with the amps input impedance?
When it is possible to connect this way, what is the point of using a preamp anyway (besides tone control)?
It dosen't make sense to me to build an active preamp, unless your amplifier is really demanding. Is there something that I'm missing here?
Thanks
Steve

jam · 20th January 2002, 08:57 PM

Steve,

I would choose a pot between 10k and 20k.
Cable length will be an important consideration. Keep the length of you interconnects as short as possible.

Jam

paulb · 20th January 2002, 09:12 PM

Assuming the sensitivity and impedance considerations are okay you don't require an active preamp. I prefer at least a buffer after the volume control but if you keep cables short it should be okay.
Many swear by passive preamps. Especially with a CD player, it shouldn't be a problem.
The impedance seen at the output of the CD player will be (at full volume) the parallel combination of the volume pot and the amp input impedance. At lower volumes, it will be higher until at zero volume it's just the pot.

audionut · 21st January 2002, 01:34 AM

I have built a number of Aleph 3 channels and use them in a Bi amped system...as in the Zen amps, I have been using air core 2mh inductors in the power supplies. I measure very low ripple on the Aleph rails, (20 mv), I wonder what other benefits there are to having these inductors in the Aleph power supplies. The inductors certainly reduced the hum in the Zens to almost nothing.
To my ears, the Aleph's are sweet and warm sounding.

20th January 2002, 08:32 PM	#1
SteveG Account Disabled Join Date: Jan 2002 Location: Newton Falls, Ohio	A75 without preamp? I am in the process of building an A75, and was wondering if I could use the output of my SACD player to drive the inputs directly (no preamp) with a passive attenuator in between. If so, how would I go about choosing the value? SACD player output specsfrom owner's manual) level: 2VRMS (at 50Kohm), minimum load- 10K Since it is spec'd into a 50Kohm load, I was thinking of using a 100K pot. What do you think? I believe that the A75's input impedance in unbalanced mode is about 75K. I'm not sure how you go about determining the minimum impedance as seen by the output... is it the combination of the pot on the output paralleled with the amps input impedance? When it is possible to connect this way, what is the point of using a preamp anyway (besides tone control)? It dosen't make sense to me to build an active preamp, unless your amplifier is really demanding. Is there something that I'm missing here? Thanks Steve

21st January 2002, 01:34 AM	#4
audionut diyAudio Member Join Date: Jan 2002 Location: Cleveland ohio	Aleph 3 I have built a number of Aleph 3 channels and use them in a Bi amped system...as in the Zen amps, I have been using air core 2mh inductors in the power supplies. I measure very low ripple on the Aleph rails, (20 mv), I wonder what other benefits there are to having these inductors in the Aleph power supplies. The inductors certainly reduced the hum in the Zens to almost nothing. To my ears, the Aleph's are sweet and warm sounding.

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Tube Preamp Popping on Source Input Change (?) / 6DJ8 Preamp On Chip Amps	MartyM	Tubes / Valves	3	16th October 2008 04:52 AM
Guitar Preamp = MIC Preamp = other preamp ,,are they all same?	Paswa	Solid State	1	12th March 2008 05:16 PM
twisted pear Preamp/other suggestions for Preamp kit	LukeDuke	Chip Amps	1	1st February 2008 09:57 PM
Electret mic preamp - will phono preamp work?	darthmullet	Analogue Source	6	12th October 2007 07:32 AM
wiring preamp outs on a preamp	bonsai171	Solid State	4	22nd March 2004 10:13 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

20th January 2002, 08:57 PM	#2
jam diyAudio Member Join Date: May 2001 Location: Charlotte,NC,USA	Steve, I would choose a pot between 10k and 20k. Cable length will be an important consideration. Keep the length of you interconnects as short as possible. Jam

20th January 2002, 09:12 PM	#3
paulb diyAudio Member Join Date: Jun 2001 Location: Calgary	Assuming the sensitivity and impedance considerations are okay you don't require an active preamp. I prefer at least a buffer after the volume control but if you keep cables short it should be okay. Many swear by passive preamps. Especially with a CD player, it shouldn't be a problem. The impedance seen at the output of the CD player will be (at full volume) the parallel combination of the volume pot and the amp input impedance. At lower volumes, it will be higher until at zero volume it's just the pot.