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Commercial Gainclone kit- building instructions

No problem, I'm always willing to help ;)

Here's wiring done for inputs and outputs. By proper internal layout we can minimize cables length. This is not critical, but won't hurt either ;)

Next, versin with potentiometer.
 

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I've been using Noble pots for years; while they are not perfect, for the price they offer great value. Available from percyaudio and partsconnexion.

Most suitable value is either 25k or 50k (log taper, stereo). Picture below shows the connections, pin 1 & 5 are not being used in normal application (those are for loudness option)
 

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And here how it's implemented in the amp.

I use SG (signal ground) on amp board as star ground for input signal. The ground wire from RCA and from ground pin on the pot (pin4) connect to SG. Signal wire from RCA goes to pin 2 on the pot, from pin 3 it goes to IN on amp board.

Those are the connections for one of the channels, the other channel is done exactly same way. Please note that so far the grounds are kept separately.
 

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Peter Daniel said:
The amp basic schematic shows only 4 resistors per channel.
R1 is optional and its value can be anything between 200R and 1k (or so). I usually don't install that resistor at all, placing piece of wire in its place. Alternatively, if you need coupling capacitor to protect the amp from DC that may be produced by a source component, a small electrolytic cap can be installed here: 4.7uF or bigger.


Hi Peter,

This is a great thread!;)

I have built myself a gainclone based on your schematic with R1 (220 ohm) installed. Can you give some comments on the sonic difference when we put a piece of wire in place of R1, for this particular design?

Thanks,

Joshua
 
Without R1 the sound will be more neutral and transparent, especially with Premium kit.

I supply that resistor "just in case", to provide some isolation for amp's input.

I had a case when DAC was connected to the amp (without series resistor) and some RF interference was occuring when pot was completely turned down. With a resistor in place, the problem was gone.
 
Talking about interferences, there are certain instances, I guess mostly due to location and local house wiring, where the amp is sensitive to switching appliances and house lights, and may also pickup quite heavily radio frequencies. In my experince, this is some 5% of users that need to deal with that problem and the cure is quite simple, by installing small polystyrene capacitor (300pF or so) between inverting and non inverting amp inputs (pin 7 and 8 in attached diagram).

That issue was also discussed here:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=55300&highlight=
 

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Peter Daniel said:
Without R1 the sound will be more neutral and transparent, especially with Premium kit.

I supply that resistor "just in case", to provide some isolation for amp's input.

I had a case when DAC was connected to the amp (without series resistor) and some RF interference was occuring when pot was completely turned down. With a resistor in place, the problem was gone.


Very useful information, thanks Peter!

Joshua
 
yes, one transformer secondary to each PSU input pair.

That's the beauty of twin secondary windings, they are isolated from each other. Separating the transformers simply follows the same isolation. Unfortunately twin transformers also increases the regulation unless you choose very large transformers which have lower regulation.
 
casiomax said:
I believe i have post this question on other thread, but I want to know about single or split supply, what are the benefits?

The explanation can be found on 47Labs site: http://sakurasystems.com/faq.html


Q. What kind of improvement do we get by adding an extra power supply?
A. By adding another power supply, you make it into a complete mono structure. It also adds more power (does not double though) and current capacity. The result is an airier, deeper soundstage and more authotity through the entire frequency range.
 
Lets start with a transformer. I use Plitron 300VA, 2 x 22V AC in all my amps, both stereo and dual mono. It is is approx $100 for a single unit. Getting similar Avel transformer from Partsexpress will cost you $50/pc.

If I order custom transformers, I prefer secondary at the core with wire diameter 1.8mm (for 300VA unit). I tested some amorphous core custom transformers and they sounded marginally better than standard core.
 

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If your transformer comes with a standard mounting hardware, that's what you use.

Plitrons are epoxy filled and hardware is not included. I increase the hole to 3/8" size and install ancor nut with a matching screw, available from Home Depot. The screw hole size, in a bottom of a chassis, is 1/4".
 

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