[wakibaki]

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Just as a quick update: board arrived fine. Thanks very much.

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Got my board today...Thank you!

 
Good. Let me know any problems such as identifying parts. You have some options, you don't have to build it exactly as the schematic. For example, if a regular (say OPA277) precision opamp were used for the DC servo instead of the chopper-stabilized one then the RC filter at the servo output could go.
 
 

@ wakibaki
 
You officially have a following...

 
Let's hope those turn out to be participants rather than followers. 

 
w

 

[sek@]

Hi,
 
Quote:

You have some options, you don't have to build it exactly as the schematic. For example, if a regular (say OPA277) precision opamp were used for the DC servo instead of the chopper-stabilized one then the RC filter at the servo output could go.

 
Have you tried this option? Do you recommend it over the chopper amp?

 

[wakibaki]

Quote:

Hi,
 
Have you tried this option? Do you recommend it over the chopper amp?

 
No and no. The chopper amp will give the lowest output offset. I'm about to test a build (TPA6120 amp) that uses a dual OPA2277, however. It should come close to the chopper. The chopper-stabilized opamps are the single most expensive component apart from the case.
 
I just mentioned it to point out that you still have some freedoms as to exactly how you build it, how much gain, how much servo authority, how much input offset will cause the relay to drop out, what rail voltage you pick, values for the CRCRC PSU filter, wallwart voltage. The last 3 will affect how much the regulators will dissipate, you might want to bolt them to the case and connect them with wandering leads to 3-way headers on the PCB.
 
Here's a BOM. Prices are approximate in UKP.
 

 
This is the DC power jack http://www.ebay.co.uk/itm/DC-Power-PCB-Socket-Connector-2-5mm-Pack-5-/290637034182?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item43ab5132c6#ht_1799wt_906
 
These are the 3.5 stereo jacks http://www.ebay.co.uk/itm/4-PCB-3-5mm-mount-Stereo-Jack-Socket-Connector-3-5-mm-/220488902014?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item335629a57e#ht_1930wt_955
 
I think that's most of the awkward components (from a fiting POV) dealt with.
 
If you're having trouble getting parts to fit, I may be able to help. 
 
w

 

[J-Pak]

Quote:

 
Good. Let me know any problems such as identifying parts. You have some options, you don't have to build it exactly as the schematic. For example, if a regular (say OPA277) precision opamp were used for the DC servo instead of the chopper-stabilized one then the RC filter at the servo output could go.
 
 
 
Let's hope those turn out to be participants rather than followers. 

 
w

 
Hoping to be a participant, will there be another run of boards? Cheers
 
Maybe this goes against the philosophies of the design, but I'll mention it if you are open to suggestions- IMO the option to use whatever pot/attenuator the user wanted would be a nice feature (given the high transparency of the amp). And perhaps the headphone connector off the board, I personally prefer 4 pin XLR over TRS even for single ended amps.

 

[wakibaki]

I have loaned my working amp to a friend to get his listening impressions.
 
There were 10 boards. I built 1, I gave away 3.
 
Nebby has asked me for a board, I told him he can have one as long as he really intends to build it. Not that I have any reason to think that he won't, but obviously, at this stage, the more amps working out there in the wild, the better from the point of view of getting some feedback.
 
I want to keep 3 boards.
 
I will give away another 2 to the first responders to this thread who will undertake to build them in the next couple of weeks.
 
In about 3 weeks (hopefully) I will respin the board on the basis of what has been learned, (about the ground plane, if nothing else). Realistically, most people will take a couple of weeks to get the components.
 
I can't continue to give away boards ad infinitum, at some point I will be obliged to set up a facility to take payment. If people like the amp I may supply a semi-kit or even complete amplifiers.
 
@ J-Pak
 
The intent with this board is to produce an integrated amp in a small, off-the-shelf case and which will run off a wallwart. There's no reason, however, why the board can't be installed in a larger case and flying leads used to permit the connection of any attenuator or connector the builder wishes.
 
Both Avro_Arrow and I have shown some designs for PCBs using the LME49600 in a simpler stand-alone amp earlier in the thread. Perhaps you would find one of them more suitable, but you'll have to push to get something done, there's a lot of demand on our attention ATM.
 
w

 

[J-Pak]

Quote:

I have loaned my working amp to a friend to get his listening impressions.
 
There were 10 boards. I built 1, I gave away 3.
 
Nebby has asked me for a board, I told him he can have one as long as he really intends to build it. Not that I have any reason to think that he won't, but obviously, at this stage, the more amps working out there in the wild, the better from the point of view of getting some feedback.
 
I want to keep 3 boards.
 
I will give away another 2 to the first responders to this thread who will undertake to build them in the next couple of weeks.
 
In about 3 weeks (hopefully) I will respin the board on the basis of what has been learned, (about the ground plane, if nothing else). Realistically, most people will take a couple of weeks to get the components.
 
I can't continue to give away boards ad infinitum, at some point I will be obliged to set up a facility to take payment. If people like the amp I may supply a semi-kit or even complete amplifiers.
 
@ J-Pak
 
The intent with this board is to produce an integrated amp in a small, off-the-shelf case and which will run off a wallwart. There's no reason, however, why the board can't be installed in a larger case and flying leads used to permit the connection of any attenuator or connector the builder wishes.
 
Both Avro_Arrow and I have shown some designs for PCBs using the LME49600 in a simpler stand-alone amp earlier in the thread. Perhaps you would find one of them more suitable, but you'll have to push to get something done, there's a lot of demand on our attention ATM.
 
w

 
I'm in a GB at Diyaudio for some 49600, so I will take a board. Thank you for the kind offer, pm coming.

 

[shadow419]

If I didn't have so many unfinished projects on my plate, I'd take your offer.  With 3 O2 builds for friends and 2 "The Wire" builds all in different states of completion, I have too much to finish one of your boards in the near future.  When/if you do a re-spin, I'd buy a pcb or perhaps a kit from you for sure though.

 

[wakibaki]

OK, the 3 spare boards are going to Nebby, J-Pak and tcpoint. I'll post them tomorrow (Monday).
 
Remember that the boards have 2 known problems, detailed earlier in the thread. They need the relay transistor mounted upside-down and rotated to make B, C & E line up correctly and they need the ground planes cut top and bottom as shown in the pictures. Cutting the planes shouldn't be a problem, but remember that the intent is to prevent current flow, so the cuts need to separate the sections completely.
 
I still haven't checked that the relay drops out when the input offset gets too great.
 
w
 
Edit: Post offices are closed here for the Diamond Jubilee until Wed. 6 June. Sorry.

 

[J-Pak]

Thanks! Working on a Mouser BOM now, will share once it's done.

 

[J-Pak]

Looking through Mouser and some of the SMD thin films are obscenely priced, ie Panasonic 1206 package resistors for $1.73 each or the 10 ohm 2512 package- Vishay 2.5w at $6.57 each

 
I haven't checked Digikey yet, but I might as well go with Farnell if they will ship to the US.

 

[ujamerstand]

Newark is farnell's US branch. Get a raspberry pi while you're at it.

 

[Avro_Arrow]

I thought they were all sold out of Raspberry Pi...
 
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Newark is farnell's US branch. Get a raspberry pi while you're at it.

 

[J-Pak]

Quote:

I thought they were all sold out of Raspberry Pi...
 

 
Yeah none in stock at the moment. Newark is also out of stock on several resistors that Farnell still has.
 
If the other 2 people that are getting boards want me to buy most of the parts and distribute at cost I am happy to do this. As Newark has minimum purchases of 5 or 10 on SMD resistors.

 

[tcpoint]

J-Pak,
 
I probably have 35% of the parts, already.  I'll have to check.  Some of the resistors can be thick film (esp. in power supply section).  I'll see what parts I have in the next day or two and I'd be happy to go in on an order.

 

[wakibaki]

Quote:

Looking through Mouser and some of the SMD thin films are obscenely priced, ie Panasonic 1206 package resistors for $1.73 each or the 10 ohm 2512 package- Vishay 2.5w at $6.57 each

 
I haven't checked Digikey yet, but I might as well go with Farnell if they will ship to the US.

 
OK, there's an error there (mine), the 10R resistors are 1210. I have amended the BOM to show this.
 
The 10R resistors aren't in the signal path, they're in the PSU CRCRC filters, thick film are probably adequate there. I used a Panasonic part from Farnell, described as an anti-pulse or anti-surge resistor, rated 0.5W 5%. There are pads on the board for 2 in parallel so you could use 2 * 22R, The actual value is dependent on the wallwart you use (how much voltage you can afford to drop) and the dissipation (how hot they get). I've got 1 * 10R in each position, the amp should draw ~50mA quiescent which is 0.5V dropped across each, you can feel that they're above ambient but they're not hot.
 
R17, 18, 23 - 28, the voltage setting resistors round the regulators again don't need to be anything special, 1% is nice but I just selected some matching values from 5% thick film. I have a selection kit, 50 each of numerous values, only a few dollars from ebay. The values shown, 150R and 1k5, result in +/- 13.75V rails. You could parallel a 10u 1206 cap with the voltage-setting resistor to reduce ripple by piggy-backing it, but I found the hum inaudible once I cut the board. Similarly, the voltage dividers for the protection circuit and the switch-on delay can be thick film. This just leaves the gain-setting resistors in the amplifier proper and the integrator. I used Panasonic ERA series metal film 0.1% for this first build. These are rated low current noise, excellent non-linearity and are 27 pence here, not too bad.
 
All the ICs in the amp are rated +/-18V, so you can run it this hot if you feel the need and you have a suitable wallwart.  I have some 16V ones. These provide ~22V after the diode drop. Lose 2V in the CRCRC filter, the LM317/337s have a dropout voltage of 2V, that would allow 100mA before the supply would begin to sag, a good compromise keeping the dissipation in the regulators from getting too high. You can see that you could get 200mA by reducing the 10Rs to 5R at the cost of some supply ripple, or go for an 18V wallwart at the cost of having the regulators run a bit hotter. You might want to bolt them to the enclosure and bring wandering leads to the board in that case.
 
w