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Old 16th April 2013, 03:04 AM   #1
Sprags is offline Sprags  United States
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Default DIY Newbie...Passive Preamp question.

Hello.
I'm new here and would like to learn a little about electronics. A new tube amp built by a small company that specializes in Dynaco type ams is being delivered tomorrow. The builder is installing stepped attenuator on the amp that I can use if I'm connecting just one sound source on the amp.

I'm trying to build up the courage to build one of his other kit amps but before I do I thought perhaps something such as a passive preamp may be something simpler that I could try out.

I've been a mechanical engineer, tool designer and CNC programmer all my life and really have a very basic knowledge of electronics.

The passive preamp that caught my eye and seems simple to build was one being marketed as a Polish built preamp by Akustyk.

To me it looks like its sorta like B1 preamp being sold in the DIY store. Is it?
Can someone help get me started with the other components I would need such as the attenuator and source selector and perhaps schematics that will help me understand how it all goes together.

Perhaps this request is way beneath others here and if so i won't be offended if I'm told that. But if someone could help I'd appreciate it.

Thank you...Blake
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Old 16th April 2013, 07:47 AM   #2
Zen Mod is offline Zen Mod  Serbia
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start searching on forum for list of useful books

there are several threads about that
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Old 16th April 2013, 09:01 AM   #3
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one of these - covering many topics , from scratch

Audio Electronics, Second Edition: John Linsley Hood: Amazon.com: Kindle Store

edit : plenty of info here , too : http://firstwatt.com/articles.html
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Old 16th April 2013, 09:12 AM   #4
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by Sprags View Post
.................
The passive preamp that caught my eye and seems simple to build was one being marketed as a Polish built preamp by Akustyk.

To me it looks like its sorta like B1 preamp being sold in the DIY store. .................
If the attenuator has active electronics associated with it then it is not a passive pre-amplifier.

A passive pre-amplifier is simply a mechanical assembly of resistor/s to attenuate the signal.

The advantage of apssive is ti's simplicity and how little it affects the signal passing through it.

The disadvantage of passive is the output impedance.
This output impedance generally cannot drive cables and the Rin/Zin of the receiver.

Adding a buffer (B1) after the attenuator allows the pre to drive a cable and Zin.
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Old 16th April 2013, 01:45 PM   #5
Sprags is offline Sprags  United States
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Thank you.
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Old 16th April 2013, 01:54 PM   #6
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If your amp already has an input attenuator, your "passive preamp" might be nothing more than a selector switch for different inputs.

IMO, most preamps with active output stages have way too much gain and the output stage is rarely necessary, at least not one with gain. I've been very happy with passive preamps having no buffer at all. If you have a turntable you'll need an active RIAA stage in there too.
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Last edited by Conrad Hoffman; 16th April 2013 at 01:56 PM.
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Old 16th April 2013, 02:43 PM   #7
Sprags is offline Sprags  United States
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Actually it does have a stepped attenuator. I just want to build a passive preamp as a way to start learning a little about electronics and perhaps use on another amp kit if I get to the point of building one myself.
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Old 17th April 2013, 10:24 PM   #8
6L6 is offline 6L6  United States
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Don't bother with a 'passive preamp' Just build a B1. It's a great project, and great for first-timers.

https://www.passdiy.com/store

https://www.passdiy.com/project/prea...-buffer-preamp
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