• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

AD797 Phono Stage Build and Help Desk Thread

Glad you got a refund GreatTone. Just received my replacement today. Measured 12.76 volts. Will test it out later this evening.
 
I see that Mouser is out of the 2.2uf Wima caps at the moment in 5% tolerance.

Anyone can use these if they don't want to wait, they are 10% tolerance.

505-M102.2/250/10 Film Capacitors 250V 2.2uF 10%

They are DC Blocking caps and not in the RIAA section, any roll off they do produce is below the audible range.
 
So I imagine for the power LED you want to draw from both sides and drop with a resistor? I am going to be using a left over Bulgin ring illuminated pushbutton switch for power, and it is designed to operate at 12v (I imagine there is an internal resistor) so it would be easy to just have it run off of one of the 12v sides, but this would drain the batteries too unevenly?
 
OldSch00l said:
So I imagine for the power LED you want to draw from both sides and drop with a resistor? I am going to be using a left over Bulgin ring illuminated pushbutton switch for power, and it is designed to operate at 12v (I imagine there is an internal resistor) so it would be easy to just have it run off of one of the 12v sides, but this would drain the batteries too unevenly?
Click to expand...

It depends on how it's wired up, is it DPST, in other words it has two circuits?

Can you show a pic or some specs for it?

If it's this type it shouldn't be a problem and you should add an external resistor for the LED circuit to run it off 24v, try around a 5k and work up or down from their IMO.

http://www.amazon.com/mod-smart-Illuminated-Bulgin-Latching/dp/tech-data/B005LEOH0E/ref=de_a_smtd
 
Last edited:
HypnoToad said:
It depends on how it's wired up, is it DPST, in other words it has two circuits?

Can you show a pic or some specs for it?

If it's this type it shouldn't be a problem and you should add an external resistor for the LED circuit to run it off 24v, try around a 5k and work up or down from their IMO.

http://www.amazon.com/mod-smart-Illuminated-Bulgin-Latching/dp/tech-data/B005LEOH0E/ref=de_a_smtd
Click to expand...

Yes it is a Bulgin, slightly different model, an MP0045/1E2/RD/012 specifically. And yes it is DPDT, I plan on running the + and - through the respective poles on the switch, so I guess I will be taking the 24v from the 2 terminals on the switch...
 
I'm just getting ready to set the impedance on my phono-stage and the manufacturer recommended impedance is 47k ohms. This seems way outside the range mentioned early on in the thread. The cart is a HO Sumiko Blackbird. I know this stage was designed for LO carts but I changed the trimmers according to the recommendation of The Great Toad and thought I'd see what happened. Am I reading the impedance figures correctly?
 
WntrMute2 said:
I'm just getting ready to set the impedance on my phono-stage and the manufacturer recommended impedance is 47k ohms. This seems way outside the range mentioned early on in the thread. The cart is a HO Sumiko Blackbird. I know this stage was designed for LO carts but I changed the trimmers according to the recommendation of The Great Toad and thought I'd see what happened. Am I reading the impedance figures correctly?
Click to expand...

I think that's a generic figure to suit MM phono stages, it would sound better with something a lot lower.

I would start in the 1k area.
 
Well, hooked things up and set the impedance to 47k ohms just as a reference. Figured I'd set the gain by ear and then adjust for balance. Within a few seconds things sounded fine. Question when it comes to the gain setting.


Getting the right gain and impedance is the main problem.

You would have to get higher value impedance trimmers like this:

http://www.digikey.com/product-detai...3LF-ND/1088188

You would then have to lower the gain a lot with trimmers like this:

http://www.digikey.com/product-detai...1LF-ND/1088186

Not sure what your noise levels would be though as you would not have much gain in the first stage, try it and see.

Using the above gain pots, there seems to be no change in the gain as I try and balance things out either measured or by ear. Left channel seems lower than the right one. Despite running the trim pot in or out dozens of turns, sound remains the same. What could I put in there that might increase the sensitivity to adjustment? The output of the Blackbird is 2.5mV. I'm sort of unsure about ordering a bunch of new trimmers. For instance, what is the difference between the 3296Y series and the 3299Y series? Just can't seem to get my mind wrapped around this stuff.
__________________
 
Last edited:
Sort of wondering that myself. I just set my Digital meter to 200k ohms and wound that puppy in until the meter read 47.1. Did the same on the other channel. That seemed OK.
 
Pio1980 said:
Wouldn't the "Super-High-End, No-Expenses-Spared" phono stage be more appropriate for this cart?
Click to expand...

Yes, I already built that one and wanted to try something else. I'm sort of a phono stage maniac. Phonoclone 3 still bests them all but I'm thinking this Ad797 may outdo it once dialed in. The PC3 is supposed to be for LOMCs too but sounds about perfect with my Blackbird much to the designer's surprise.
 
WntrMute2 said:
Sort of wondering that myself. I just set my Digital meter to 200k ohms and wound that puppy in until the meter read 47.1. Did the same on the other channel. That seemed OK.
Click to expand...

Was that 47.1k on an autoranging DVM? If not you need a 50k-or larger trimpot.
 
Yeah, I was wondering if it had a name yet. I ordered a black anodized aluminum enclosure and I was going to at least get the jack lettering on the back engraved, might engrave the name on the front!

Maybe I will just have "The Best" engraved on the front... :D
 
WntrMute2 said:
Well, hooked things up and set the impedance to 47k ohms just as a reference. Figured I'd set the gain by ear and then adjust for balance. Within a few seconds things sounded fine. Question when it comes to the gain setting.


Getting the right gain and impedance is the main problem.

You would have to get higher value impedance trimmers like this:

http://www.digikey.com/product-detai...3LF-ND/1088188

You would then have to lower the gain a lot with trimmers like this:

http://www.digikey.com/product-detai...1LF-ND/1088186

Not sure what your noise levels would be though as you would not have much gain in the first stage, try it and see.

Using the above gain pots, there seems to be no change in the gain as I try and balance things out either measured or by ear. Left channel seems lower than the right one. Despite running the trim pot in or out dozens of turns, sound remains the same. What could I put in there that might increase the sensitivity to adjustment? The output of the Blackbird is 2.5mV. I'm sort of unsure about ordering a bunch of new trimmers. For instance, what is the difference between the 3296Y series and the 3299Y series? Just can't seem to get my mind wrapped around this stuff.
__________________
Click to expand...

For the impedance trimmers you could try these from Digikey:

3296Y-104LF-ND 100k

For the gain trimmers try the 1k trimmers they are the same ones used in the impedance spot for the AD797:

3296Y-102LF-ND 1k

The difference between the 3296Y series and the 3299Y series is just the size.

Another thing you can do is increase the value of the 560 ohm resistors, R11 & R12, you can use 1k in these spots, this will reduce the gain of the second stage by around 6db.

Also you can replace the 47 ohm resistors R15 & R16 with 100 ohms which will reduce the gain in the first stage by 6db.

Then even with the stock 2k trimmers you should be able to screw them down so you have around the 45db you need.

Then you will probably be tempted to try it with MM carts, but be aware that the AD797 won't like the higher resistance of these carts.
 
Last edited:
I just got done populating my PCB a bit ago... Still a ways to go before I get this done as I need the opamps, adapters, suitable power supply and an enclosure but I should get that stuff together in the coming weeks.

I noticed a couple things that might be able to be improved for future runs though, first was that the lead spacing on the Dale precision resistors is a little wider then the standard 5mm pitch making them a tightish fit. Also, the .015uf Wima cap (the one in the mouser BOM) and 200k resistor are a bit too close together to mount without having to bend the resistor out of the way. Lastly, the input pads are not the same distance apart as the out pads and I can't use the screw clamping connectors there. The power in and the outputs fit fine but I'll probably just straight solder this so everything matches up. :)
 
Last edited:
You must log in or register to reply here.
Back
Top Bottom