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AD815 preamp build thread

H

hacker

Delicious and nutritious
Ok, the last thread got enormous and was concentrating around the design and buying of bits. Let's have a thread just for building, asking questions, fixing bugs, tweaking, etc etc etc.

First up, I've copied this from the other thread:

IMPORTANT INFORMATION

SMD components are hard to recognise, so I colour-coded them. Here's a Kit 1:

DSCF2380.jpg


The 620R SMD resistors are coloured pink.

The 330R SMD resistors are coloured greenish-yellow.

The 0.1uF SMD capacitors are in the clear plastic, and they're not coloured at all.

The kit 2 is similar, but it contains an extra 4 caps an extra 2 resistors.

The kit 3 looks like this:

DSCF2395.jpg


The 0.1uF film bypass caps for the PSU are blue. You'll need a multimeter to measure the resistors I'm afraid.

The kit 4:

DSCF2382.jpg


The small tantalum beads can be identified as follows. 33uF/25V:
DSCF2383.jpg


The 10uF:
DSCF2391.jpg


The 0.22uF:
DSCF2394.jpg


The positive (+) legs are marked with a + symbol.

This is the schematic (the PCB doesn't have the protection diodes in the PSU circuit, they're not needed @ < 25V):
cfmad815preampcomplete_rev1.jpg


Cheers,
Carl
 
Has anyone got a link to that volume pot that Graham (Laverda) is now using in his ad815 preamp.

Just thought this would be handy to have it in this thread.
 
Anyone have a step by step guide to soldering those pesky smd components?

Might be useful to meatfited clutzes like me....
 
Easy way to solder multi-pin SMD device:

1) ensure soldering iron etc is clean
2) Use flux pen on pads of PCB
3) dab IC in place, hold with tweezers or superglue.
4)Wipe solder across pins with hot clean iron. Inspect with a lense.
5) If 5 not cleanly successful, just use clean solder braid to lift solder bridges.

Easy! Really, nothing to be afraid of.
 
Andy weekes did a guide years ago.

Coat the solder pad and component with flux (get a flux dispensing pen)

Put a nice blob of solder on your iron tip and drag it across the component/pad (use a screwdriver to hold down the component)

If you have applied too much solder, wipe the tip and drag it across again. .
 
As a suggestion, it would be good to include links here for any information related to the basis of design and construction if it is possible to condense it.
 
It's up and running and sounding very very good indeed. :D

It's taken me all day though. Most of the time has been spent trying to null dc offset which I can't. :mad:

I'm reading -50mv on output which only alters when volume is set to full then it goeas slightly positive. I suspect it might be because the impedance of the pot is low (2.5k ish).

The preamp is powered by an off-board linear supply, which also feeds the nulling circuit. I measure 9V at the test point. As the trim pots are adjusted I can read the voltage being changed just before the 390K resistors. However, just after the 390k resistors the voltage is almost zero whatever the voltage before. :confused:

BTW I am now no longer a SMD virgin. It wasn't as painful as I thought it was going to be. It's not pretty though. ;)
 
fatmarley said:
... use a screwdriver to hold down the component ...
Click to expand...

I've never SMD soldered myself, but I've heard said that blu-tak is a great way to hold down the component while you're soldering it without needing one of your precious two hands to do so...
 
I use Blu-tak for through hole components, but, because SMD components sit on the surface of the circuit board, and they are very small, it makes it difficult (if not impossible) to use blu-tak.
 
darwin006.jpg


darwin007.jpg


Below is my first simple AD815. It all fits in a tiny box. Only one input. There are two 33uf tants instead of a 68uf electrolytic. Some resistors and the 0.1uf caps are soldered directly onto the pins of the chip under the board. There is no nulling circuit but there's space and I intend to install it. The Alps pot doesn't like DC. It took some time to burn in so I expect the new board to do so.

darwin012.jpg
 
Big thanks to Carl and everybody involved with supplying us with the PCB's
I didn't get chance to finish mine yet but fitted a few parts, I already had most of the parts so just went for the pcb, thanks to a mate who added me one onto his order;)
I fitted little sockets for the coupling caps, allows for quick linking if the nulling circuit behaves

DSCF0442.jpg
 
Nice one, Ron. Very neat, especially around the 815. The sockets for the caps look like nice test point sockets, can you tell me the part number/supplier please?

Regards,

Mus
 
new naim boy said:
It's up and running and sounding very very good indeed. :D

It's taken me all day though. Most of the time has been spent trying to null dc offset which I can't. :mad:

I'm reading -50mv on output which only alters when volume is set to full then it goeas slightly positive. I suspect it might be because the impedance of the pot is low (2.5k ish).

The preamp is powered by an off-board linear supply, which also feeds the nulling circuit. I measure 9V at the test point. As the trim pots are adjusted I can read the voltage being changed just before the 390K resistors. However, just after the 390k resistors the voltage is almost zero whatever the voltage before. :confused:

BTW I am now no longer a SMD virgin. It wasn't as painful as I thought it was going to be. It's not pretty though. ;)
Click to expand...

Probably is the pot, the DC varies depending on the position of the vol pot which is why you set the nulling at your normal listening level

BTW it looks fine to me mate, long as it works is all that matters;) the pads for the AD815 is more awkward because it takes a bit more heat
 
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