DIY Simple Active Preamp

SuperSimplePreamp.jpg
 
That 15k resistor is the resistance from the non-inverting input to ground. For minimum offset it should be the same resistance as from the inverting input to ground. But with an output cap then offset is no problem.

I would eliminate the 100 ohm and the 100k ohm at the output. Just turn on the amplifier 10s after the preamp so any DC that leaks through the output capacitors is dissipated across the input resistance of the power amp. Thus no thumps.
 
That 15k resistor is the resistance from the non-inverting input to ground. For minimum offset it should be the same resistance as from the inverting input to ground. But with an output cap then offset is no problem.

I would eliminate the 100 ohm and the 100k ohm at the output. Just turn on the amplifier 10s after the preamp so any DC that leaks through the output capacitors is dissipated across the input resistance of the power amp. Thus no thumps.

The 100 ohm is to stop oscillation of some op amps. The 100k is to drain the output cap.
 
Its nice to be associated with smart people. I am a hobbyist/builder and have no idea what you guys are talking about. LOL.

Just to make sure adding an input switch to something like this would be simple right? I mean really simple or is a normal switch going to detract from the whole concept?

Reason I ask is over the years I seem to be going back to simpler things. No EQ first then I bought a simple Krell Pre with no base and treble. It sounds better all the time.

I love to build and all I need is two inputs. One for CD and one for my phono stage. And of course a volume control.

Appreciate the efforts in this thread. The engineering aspects are beyond me but I am intrigued with a potential project :)

I would love to make something into machined billet aluminum block with exposed components, etc for my audio rack.

I am using DQ-10s for speakers so I still need to drive with big power. No minimalist stuff in the amp section !
 
Its nice to be associated with smart people. I am a hobbyist/builder and have no idea what you guys are talking about. LOL.

Just to make sure adding an input switch to something like this would be simple right? I mean really simple or is a normal switch going to detract from the whole concept?

Reason I ask is over the years I seem to be going back to simpler things. No EQ first then I bought a simple Krell Pre with no base and treble. It sounds better all the time.

I love to build and all I need is two inputs. One for CD and one for my phono stage. And of course a volume control.

Appreciate the efforts in this thread. The engineering aspects are beyond me but I am intrigued with a potential project :)

I would love to make something into machined billet aluminum block with exposed components, etc for my audio rack.

I am using DQ-10s for speakers so I still need to drive with big power. No minimalist stuff in the amp section !

I assume you mean no bass or treble "knob" not the frequencies!:D Yes many mods to the old dyna pas included removal of those circuits. Simple can be good in audio, but always remember what Einstein said about simplicity: "Everything should be as simple as possible, but NO simpler." Genius!

Russellc
 
The 15k resistor was part of the original level/balance control network and just screws up the level control's linear action here as Phillip found, it needs to go. The 100^ series resistor also acts as a minimum load limiter at HF into what-ever the shunt capacitance may be as well as stabilization, just good practice I've been told by someone a lot smarter than me.
 
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I am a hobbyist/builder and have no idea what you guys are talking about. LOL.

Just to make sure adding an input switch to something like this would be simple right? I mean really simple or is a normal switch going to detract from the whole concept?

I love to build and all I need is two inputs. One for CD and one for my phono stage. And of course a volume control.

I have no idea what I am talking about either.

You can use a switch setup with a led like this for the on/off part, whether using batteries or a PSU:

BatteryLED.jpg


You can connect two inputs using a DPDT switch. Connect the + inputs from each pair of RCA's to the upper and lower terminals of the switch and the two center terminal go to the inputs of the preamp. So you can switch between the two.
 
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OK on the DPDT. Didnt know if a simple switch would cause any issues with loss, etc.

Carry on. Excellent thread.
 
The 100 ohm is to stop oscillation of some op amps. The 100k is to drain the output cap.

The 100 ohm needs to be on the other side of the capacitor. Where it is the Op-Amp doesn't interact with it.

The 100k does the same thing your amplifier input resistor would do with the DC that leaks through at turn on. But if your amp is on the thump is heard.
 
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