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DIY Simple Active Preamp

sachu888 said:
Does anyone have experience with Burson Audio type Opamps? A Hifivision member posted a SSP review with Burson Audio opamps here http://www.hifivision.com/preamplifier/57775-burson-supreme-sound-dual-opamp-review.html
Those Opamps are costly. Can we design our own opamps?

Regards
Sachin
Click to expand...

linuxguru has designed the LF series of discrete op amps and folks
over on diyaudio have reported some good results in certain applications.

http://www.diyaudio.com/forums/vend...-discrete-dip8-opamp-myref-rev-c-similar.html

There is also a giant thread on the topic -

http://www.diyaudio.com/forums/analog-line-level/218373-discrete-opamp-open-design.html
 
I´m planning on building one of these in the near future.

I have a question regarding the volume control pot. I can only get a 10K or 50 K Alps pot. I understand that 10K puts a higher load on the source and 50 K might pick up some noise. Which one should I use?

I´ll be using an USB DAC as a source.

Another question: Is the output impedance low enough to drive my amp and an active sub?
 
Depending on how robust the line driver in the stage feeding it is. 50k might accept a greater variety of line drive sources but 10k might yield better SQ on sources that can adequately drive it, depending on the quality of the pot.

Sent from my SM-N900V using Tapatalk
 
I´ll probably go with the 10K pot.

I want to build a 15 V or 12 V symmetrical power supply and not run this with 2 batteries. The transformer shouldn´t normally need a lot of power. One watt should be enough, right?
 
I think I´ll order a 5w transformer, just to be sure. I´m surprised how much this preamp is going to cost me. I thought I could throw it together for 20 Euros:banana:

I am at a total of 70 Euros right now. That´s including a case, transformer, voltage regulators, PCB material, an ALPS pot, RCA connectors, etching solution and, and, and.....

I ordered more resistors and capacitors than I need, because it´s good to have some spares, and they are cheaper the more you buy :)
 
So, this is the PCB layout I´ve come up with. The 2 separate pots are just for CAD design purposes; I´ll be using a single, stereo Alps pot.

The cut outs at the corners are a mistake. I just wanted to leave those empty for the mounting holes. I don´t know why it came out like that.
 

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cary said:
Does anyone have a board for sale?
Click to expand...

This is simple enuff to do on perf board, but you'd lose the ground plane. That might matter if you were going to crank out higher gain from it tho' 12-15 dB should be plenty.

Sent from my SM-N900V using Tapatalk
 
So, I got 127 Euros for my C-80; more than enough to pay for this project.

On the other hand, I paid 430 dollars back in 1986 for it. That was in the base exchange in Germany, so no sales tax. The C-80 sold for around 2000 marks on the German market. That would have been a good thousand bucks.
 
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I ordered a board from Sachin,
(This is the SSP right?)
I was putting together order from Bom . The part # listed for pot is linear but described as Log in description in list. Am I misunderstanding something.
Next,
I have a CNC preamp in an enclosure already. I've been led to believe the PS is adequate for both. I know I'm going to have to up the size of the enclosure to fit it all. I'd love to find an IR module that would switch sources through a relay board and control volume through a motorized pot but so far I haven't seen anything that might work. It may just be the pot and a selector switch. Has this been pursued much. Any tips greatly appreciated . Thanks
 
Thanks Grainger,
That seems to fit the bill. In the Bom I think they're looking for 47k pot. These appear to be 100k I'm curious what the difference in sound would be
 
Steve is right, but he and I don't hear the really high frequencies, we are both over 60. With low capacitance cable, under 20pF/Ft and under 12 feet of cable you will never hear a difference between 47k Ohms and 100k Ohms.
 
I think the plan now , which is fluid. Is build board ,Jerry rig it into system (no offense Jerry). Do some listening and then decide whether I want to go with the remote and the big enclosure. Sachin suggested a stepped attenuator (50k) , so for now I'll go with that. Mouser order is in , attenuator coming from china and board coming from India ( I think). I haven't melted solder in while (a couple of months anyway) I'm looking forward to the build and the outcome. Thanks for the info and the tips.
 
Going with the stepped attenuator is probably a good move if you like balanced sound.

I am chasing down some possible oscillations in a Sansui G-6700 and fed a signal into the front end and measured it at the input to the driver board with the o’scope. Then I used the volume control to adjust the signal level. That was when I saw that the left channel was noticeably higher than the right when the volume was lower than 3:00. I was chasing another problem and did not record any qualitative data.

The dual ganged pots in a volume control are rarely ever exact duplicates, resulting in channel imbalances that vary with the position of the knob, and often annoyingly audible. The stepped attenuator ‘should’ have matched resistors at each step, giving matched volume (at least at that point in the chain).

Component variances throughout the rest of the system could also cause a channel imbalance. That should be constant and you can compensate with the balance control.
 
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