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DIY preamp

Naveenbnc

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hydrovac

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As per the title I've started work on a new pre to pair with my DIY power amp.

Sadly not much work on this project recently due to other demands on my time... and also partly because my soldering equipment went kaput.
The manufacturer took 6 weeks to deliver… (as he was executing a big order)

New solrdering stn:








The purpose of the thread is threefold

1] To keep a record of the project.
2] To perhaps encourage others to have a bash at an easy DIY project.
3] To perhaps get some input as the project progresses.


Some hardware for the project:



 

yogibear

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How good is this soldering station ? I have been looking for one. Could you mention price and source link ?

Thanks.
 

hydrovac

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How good is this soldering station ? I have been looking for one. Could you mention price and source link ?

Thanks.
Back when I started out, we did not have such a wide range of cheap imports from the Far East to lead us astray.
I bought this soldering stn made by a local company just around the corner in our IDA.

I was just reviewing this and thinking how lucky I was, because it was a good call. I could very easily have bought something cheap and nasty that would have put me off this hobby altogether.
It saw me through many projects in the past decade... so, i bought another of the same make.

Old analogue stn:
1548872797627.png
 

hydrovac

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@hydrovac, RCA sockets look good, would you mind sharing the source...
@har297 The RCA sockets were procured quite some time back... i am not able to recollect the source.


Made a little progress last night and got the power switch installed and wired up… the flush fitting 5 amps illuminated power switch was bought online.



And a shot of the rear:
RCA sockets are gold plated. I've used these previously on my Power Amp build and really like them.








The only tools used so far have been a Screwdriver, Spanner, Pliers, Electric Drill, Dremel.
All that's required is a little care and patience.

It's worth spending a bit of time to get the connector rod between the knob on the front panel and the pot aligned properly as this has a pronounced effect on the feel of the pot in operation.





Once again, spending a bit of time to get the extension lined up correctly for the volume control is worthwhile for that silky smooth quality feel.
 

jls001

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Question: is power supply circuitry included in the preamp board? I see a direct connection from transformer to the preamp board.
 

Hari Iyer

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Crosstalk is less than -95dB, i beleive that no humar ear can hear that.
How was that measured? Curious to know.

Hello!

Just starting on a new preamp - which I recently procured from fellow DIYer Aniket, who designed it.
Luckily I found a spare cabinet and 18-0-18 1 Amp, R-core trafo from my earlier projects... here is the log of the build.

Preamp module:

View attachment 32061


View attachment 32062


The cabinet:

View attachment 32063


View attachment 32064


...
NIce layout and clutter free installation (in comparasion to my setup. Mine is a wiring mess). Btw, any pointers to schematics or is that top secret?
 
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hydrovac

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Btw, any pointers to schematics or is that top secret?
Thanks Hari,
I presume, this is for Aniket.

When doing a project like this, the easiest place to begin (for me, anyway...) is the mechanical. Drilling, hardware, things that touch the chassis. Owing to prefab, not a lot of drilling was involved, the switch hole and power inlet module was pre-cut… i just added the holes and screws for the circuit board and transformer.

I'm only using 1 input, so selector switch is eliminated… the signal wiring is RG-174/U coaxial cable… if you just need to get signal from here to there, cleanly, you will love this cable! It's extremely thin and flexible.

Nothing exciting here but so far so good.






All wired, powered it for a brief period and voltages checked... will fire it up and post updates tomorrow.

 

Aniket

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How was that measured? Curious to know.
my audio measurement system. Audiomatica Clio QC.

NIce layout and clutter free installation (in comparasion to my setup. Mine is a wiring mess). Btw, any pointers to schematics or is that top secret?
this is a push pull design, which operates completely in Class A, with symmetrical input stage, this improves PSRR and linearity. The output stage operates at 20mA of quiescent current. actually this is a Headphone amp, capable of 11V rms output.

Regards,
Aniket
 

Hari Iyer

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my audio measurement system. Audiomatica Clio QC.



this is a push pull design, which operates completely in Class A, with symmetrical input stage, this improves PSRR and linearity. The output stage operates at 20mA of quiescent current. actually this is a Headphone amp, capable of 11V rms output.

Regards,
Aniket
I had built a similar preamp couple of years ago, as in LM4562 original datasheet from National semiconductor.

For the crosstalk- wanted to know process of measurement.
 

Aniket

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I had built a similar preamp couple of years ago, as in LM4562 original datasheet from National semiconductor.

For the crosstalk- wanted to know process of measurement.
LM4562 equivalent circuit is totally different
 

Hari Iyer

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LM4562 equivalent circuit is totally different
I am not referring to internal chip block diagram of LM4562. If you open the datasheet of this chip published by TI/ National semiconductor you will notice that, there is a circuit idea for a "Line Preamplifier". What i am saying is i implemented that particular class A preamp. Hope this clarifies.
 

Aniket

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I had built a similar preamp couple of years ago, as in LM4562 original datasheet from National semiconductor.
I am not referring to internal chip block diagram of LM4562. If you open the datasheet of this chip published by TI/ National semiconductor you will notice that, there is a circuit idea for a "Line Preamplifier". What i am saying is i implemented that particular class A preamp. Hope this clarifies.
even that is totally different. no where near similar.
anyways, the one which i have designed is both a headphone amp and a pre-amp, and it can drive impedance as low as 4 ohms.
 

Hari Iyer

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even that is totally different. no where near similar.
anyways, the one which i have designed is both a headphone amp and a pre-amp, and it can drive impedance as low as 4 ohms.
Ok, I had driven my 32 ohm headphone with this preamp with decent output. I had used a BC550, BD139/BD140 complimentary pair mounted on a heatsink.
 
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