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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

Pre Amp Basics Questions
Pre Amp Basics Questions
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Old 28th December 2017, 05:17 AM   #1
SyncTronX is offline SyncTronX  United States
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Pre Amp Basics Questions
Default Pre Amp Basics Questions

Maybe y'all can give me some pointers. I'm considering moding some older 70s - 80s pre amps that I have sitting around. I'm thinking the first stage is critical, we have the input into the first differential pair of transistors. Parts Recommendations for the input cap & Resistor (phono stage). Then another differential pair for each channel, L, R.
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Old 28th December 2017, 10:45 AM   #2
DF96 is offline DF96  England
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Audio circuits are 70% circuit, 29% implementation and 1% components. Can we assume you have sorted the first 99%?
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Old 28th December 2017, 11:53 AM   #3
r_merola is offline r_merola  Brazil
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Quote:
Originally Posted by DF96 View Post
Audio circuits are 70% circuit, 29% implementation and 1% components. Can we assume you have sorted the first 99%?
Totally agreed! I also can say:
Simulation only gives you a reference to start work. Real circuits show real results. Correct compensation do more effects than good components. Simple DIY circuits always lacks some important detail to best performance. It is real electronics.

Happy New Year to all
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Old 30th December 2017, 12:33 AM   #4
SyncTronX is offline SyncTronX  United States
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Quote:
Originally Posted by DF96 View Post
Audio circuits are 70% circuit, 29% implementation and 1% components. Can we assume you have sorted the first 99%?
Yes.

So wondering if RPR or MELF with leads would help. parts around the voices has krinkly type sound at start, then becomes smoother.

I haven't even toyed with phono section. Haven't even replaced the electrolytics. It works and sound pretty good, but It's old. From late 70s early 80s. It's a single pre amp from Marantz and has been well cared for, no sign of cap changes either, so all original. So yes the cap change first to freshen her up.

Then, I"m wondering what next?

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Old 6th January 2018, 10:26 PM   #5
SuppressorGrid is offline SuppressorGrid  Netherlands
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Hi Sync,

When I work on vintage audio, I go through three stages. First is bringing the amp (or any equipment) back to the original factory spec. That includes recapping, cleaning all switch contacts and potmeters, replacing relays and generally clean or replace all components that are subject to aging. Second stage is finding and fixing where the manufacturer has been cutting corners, e.g. by using non-matched pairs for transistors resulting in offsets, the use low-precision parts resulting in poor RiAA response or inequality in left/right channel etc. Part of stage 2 is also replacing parts with modern equivalents with better behaviour, like low noise transistors, better quality opamps, proper dimensioning of the power supplies, using more precise clocks in DACs etc. The result of a stage 1 and stage 2 treatment can be quite astonishing. Stage 3 is about changing the original design. But be aware that designers of high end 70-s and 80-s audio worked mainly with their experience and ears, not with datasheets. All parts of their creations are inter-related and typically the result of years of experimenting and listening. Changing the design also changes the character of the amp and in my experience, that rarely is an improvement.

It is generally true that improving the first stage has the largest effect but that is by no means an iron law. If you are not happy with the potential of a vintage amp in the first place, my bet is that you are not going to be happy with the sound of a modded version.

And also be aware that many vendors distributed schematics for repair purposes only that do NOT match the real life amp. This was often done to protect their intellectual property rights.
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Old 21st January 2018, 07:27 PM   #6
SyncTronX is offline SyncTronX  United States
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Pre Amp Basics Questions
That is as good an explanation as I've read SupressorGrid.

Good, I'm moving along the correct path with this. First getting
a good feel for the sound of the pre amp. I'm in no rush as I'm
reworking and redoing my bench. Adding shelving separate from
the actual bench top along with additional shelving for test gear,
parts, close storage (in bench room as opposed to garage or remote storage), etc.

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