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Jrp27 1st September 2016 07:43 AM

Transistor Preamp
 
Any good small, easy, high fidelity transistorised preamplifier circuit that i can build ? Plan to use it with my DIY power amp. The preamp should be able to accept ipod level input.

Any help would be appreciated.

Richidoo 1st September 2016 08:55 AM

iPod 5G makes 1V output level. What is the input voltage that drives your DIY amp to full power? You probably only need 6dB voltage gain (2x.)

An opamp with 10k resistor in feedback loop will give you the +6dB gain, and is adequate performance for iPod source quality. I like ST Micro MC33079 dual opamp.

Something like this from Rod Elliott:


Also, see his full page of preamp circuits, some are discreet (not opamp)
ESP Projects Pages - DIY Audio and Electronics

Nikolai Petrenko 1st September 2016 09:40 AM

Quote:

Originally Posted by Jrp27 (https://www.diyaudio.com/forums/analog-line-level/296144-transistor-preamp-post4817637.html#post4817637)
Any good small, easy, high fidelity transistorised preamplifier circuit that i can build ? Plan to use it with my DIY power amp. The preamp should be able to accept ipod level input.

Any help would be appreciated.

Try Rod Elliott P37A, may be not as good as OPA2132, but at least you should try once in your life :D
An externally hosted image should be here but it no longer works. Please upload images instead of linking to them to prevent this.

You shouldn't use capacitors in the output if you can trim the VR1L to set output as close to 0V as you can or the following stages already have AC coupling caps. If must use, you should use film or paper or PIO cap like WIMA MKP10 (2x 10uF in parallel) or Mcap or K40U.... Avoid bipolar capacitors since they are not good if long-term stable is required.

franzm 1st September 2016 10:50 AM

For ipod and other devices with headphone output on can use step-up transformers.

Nikolai Petrenko 1st September 2016 12:26 PM

Quote:

Originally Posted by franzm (https://www.diyaudio.com/forums/analog-line-level/296144-transistor-preamp-post4817733.html#post4817733)
For ipod and other devices with headphone output on can use step-up transformers.

High fidelity coupling transformer are expensive and clumsy, especially in stereo mode, if two transformers are placed close together as result of space problem, cross-talk will appear because magnetic field of one transformer will affect the other.
Cheap or medium transformers will sound like crap! Distortion and weak of very low AF.
I think solid-state preamp will be the best choice for: money, space and sound performance.

Struth 1st September 2016 04:06 PM

Hi Guys

I know there are different file formats that one CAN use, but who using an ipod will use the highest fidelity format? The source fideltiy is already low, so no circuit suggested is likely to impair the sound.

What circuit is the PA? Is it a chip amp? Any opamp preamp will provide performance better than the ipod output quality. The circuit in post-2 should have a cap in series with the resistor to ground in the feedback loop. This will assure minimum output DC offset. otherwise, there could be a tiny DC voltage at the output that could upset the PA input.

NEVER use paper dielectric capacitors. They dry out over time and change their characteristics and cause high signal loss. A customer brought me an old amp that had very low output. I replaced the paper coupling caps with modern plastic types and the amp had its full power again. So, actually i stand corrected by myself: paper capacitors will impair the sound of even an ipod.

Digital audio can sound quite amazing but no such system I've ever heard used an ipod.

Have fun

xrk971 1st September 2016 04:22 PM

I like Apex designs - they are easy to make, work, and sound good.

BJT:
https://www.diyaudio.com/forums/atta...bjt-preamp.jpg

FET:
https://www.diyaudio.com/forums/atta...fet-preamp.jpg

https://www.diyaudio.com/forums/atta...-20-284-29.jpg

More here:
http://www.diyaudio.com/forums/solid...plifier-6.html

Project16 1st September 2016 07:11 PM

Quote:

Originally Posted by xrk971 (https://www.diyaudio.com/forums/analog-line-level/296144-transistor-preamp-post4817971.html#post4817971)
I like Apex designs - they are easy to make, work, and sound good.

https://www.diyaudio.com/forums/atta...-20-284-29.jpg

Hello xrk971
I like your work, the files (.pdf or gerber) are available?

Regard's.

xrk971 1st September 2016 07:27 PM

That is Apex Audio's work - I just re-posted. I asked him in his thread if pcb files are available. He will let us know if he has pcb files. I am looking for a good preamp as well.

http://www.diyaudio.com/forums/solid...ml#post4817973

Project16 1st September 2016 07:46 PM

Thank you for the reply and congratulations for the good work of amplifiers achievements proposed on the forum.


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