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AD797 Phono Stage Build and Help Desk Thread

Depends on the cart. My Benz Glider recommended 100 ~ 47K ohms, in my system it was too plump at anything less than 47K.
 
jimreeves said:
Depends on the cart. My Benz Glider recommended 100 ~ 47K ohms, in my system it was too plump at anything less than 47K.
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I gotcha. I would say mine is pretty right on in terms of tonality, so I think I'll stick with 100 ohms. I know it wouldn't be that hard to pop the top and squonk the pots, but I've been doing a LOT of fiddling recently. I'm tired of it and ready to listen.

Add to the normal vinyl headaches the fact that I've only just discovered that many (maybe most) of my full collection of Music Matters Blue Note reissues have inner sleeves that need to be replaced. Those pink inners from RTI emit a nasty sticky white powder over time that can only be removed from the vinyl by vacuum cleaning. Then I have to replace them with inners at my expense. Nearly 100 albums. And they're all doubles. That means 400 album sides to clean, and 200 inner sleeves. Awesome.

So yeah, I'm ready to stop working and start having fun.
 
Pio1980 said:
I've finished stuffing the board and contemplating a temporary mock-up while I decide the final casing. I have a couple LOMC carts on-hand to try thru it for gain and SQ. I need enuff quiet gain to work with a passive controller if possible.
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Got it up and running w/the O'fon MC20MkII at full gain into the passive, just enuff gain checking Leo Kottke, Dreams And All That Stuff, side 1 tho' it'll never play loud-loud like this.
I tried tweaking the loading by ear and the 10^ rec was close to spot-on by ear, came a couple ^ close both channels by ear so variable loading on-the-fly is a real bonus. Best yet I've heard from this cart FWIW, probably partly thnx to proper loading as much as anything.
 

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The Ortofon MC20 MkII is a super low output cart at 0.09mV, so I would be surprised if there is enough gain, you can always lower the 47ohm resistors in the feedback loop to 33ohm.
 
HypnoToad said:
The Ortofon MC20 MkII is a super low output cart at 0.09mV, so I would be surprised if there is enough gain, you can always lower the 47ohm resistors in the feedback loop to 33ohm.
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Yep, I knew that, so this was sort of a stress test for the thing which it did well. There is more hum from the lack of shielding than noise, I'd also agree about lowering the series resistors tho the ratio for gain is pretty high already. So far tho' there is a wonderfully natural sense of textural contrasts here and remarkable transparency without being analytical. This cart sounded lush toward somewhat bloated on some records with the Marcof/P-06 (probably sub-optimal default loading) whereas the DL-103M sounded pretty much spot-on with that set-up. I haven't tried it with this thing yet, I will have to change loading for it of course. It is a pleasure hearing the O'fon sounding this good tho'.
Also am considering getting an A-T OC9-II as my "Sunday-Best" MC.
 
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Pio1980 said:
Is there a suggested properly sized case for this project? I thought I'd ordered it but what arrived from Context Engineering was plainly too small and otherwise inappropriate.
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It appears I am f.o.s. on this, the enclosure was 'telescoped' to pack and only appeared to be too small as such and I won't have to it return for credit. I unwrapped after determining it was indeed the proper-sized split enclosure, so packaging this project is the next step. I'tll be good to audition it shielded at full "rock and roll" gain setting.
 
So here we are with remote battery power, comparing it to a recapped Marcof PPA-1 into an Elliott P-06 with a Denon DL-103M. Output is notiably greater than with the O'fon MC-20MkII. What I'm hearing first-off with just side 2 of Joni Mitchell THOSL replayed is greater precision and directness/immediacy and with quieter background than with the Marcof/P-06 combo., Marcof combo is more 'tube-like' except bottom end which is solid.controlled and seems to go down forever. The 2,2uF of the AD797 stage is loaded into a 10k controller so we'll see how it's bottom end subjectively compares, the P-06 has the output cap defeated/bypassed due to essentially no offset present. Dunno abt offset on the AD797 stage as I didn't think to check, perhaps its blocking cap could be optional as well.
As always, time will tell with further auditioning.
 

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Nice looking build. I'm curious about the mounting of your LME49710 opamps though. In HT's pic of his build in Post #1 (looks like he's using the same adapters), his opamps are oriented in the other direction (dot/dimple is on the top on his, bottom on yours). I don't doubt that yours work, I just thought that these had to be soldered in a specific orientation.
 
dodog said:
Nice looking build. I'm curious about the mounting of your LME49710 opamps though. In HT's pic of his build in Post #1 (looks like he's using the same adapters), his opamps are oriented in the other direction (dot/dimple is on the top on his, bottom on yours). I don't doubt that yours work, I just thought that these had to be soldered in a specific orientation.
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I had expert help with these chip mountings so cannot give a proper answer tho' I did the rest of the build stuffing and casing the board.
FWIW, I don't recommend packaging the unit with the batts due to possibility of outgassing, a simple elegant remotely powered approach like this with a twin-lead shielded mic cable as the power umbilical is probably the best way to go IMO. I'd also recommend direct-soldering the power umbilical under the board to using a connector for lo-noise longevity.
 
I have found it takes at least a week of use for this to hit its straps.

Different adapters for the LME49990's have different orientation, so as long as it's followed all is fine.

I am with Steve on having the batteries separate, I have mine behind a speaker out of sight.
 
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HypnoToad said:
Different adapters for the LME49990's have different orientation, so as long as it's followed all is fine.
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Sure, I get that. I was commenting more on the fact that the adapters you two are using look identical. My adapter, although functional, looks a bit different (FWIW, and that's not much, the dimple on my opamp points in the same direction as HT and not Steve). All the more reason to be careful with the orientation when soldering I guess.
 
I finished up my 797 last night but it was too late to test it. I rushed home, fired it up and..... nothing. This ALWAYS happens to me. I swear I checked all continuity when soldering, tested the jacks last night, etc. So, I disassembled and took the opamps out. I checked continuity for all ground points. Check. L and R pos. in to pos. in on the boards. Check. L and R pos. out to pos. out on the boards. Check. Same with all negatives. I tested V+ to switch to board, same with V- and ground. Check. My last ditch was to check out all the DIp8 adapter sockets. I verified that pin 4 is V- on all four adapters, also that pin 7 is V+ for all four adapters. For the two left adpaters (closest to inputs), pin 3 is L or R+ input (depending on the channel). For pin 2 on the same adapters I get continuity to Ground (but not to each other (L-2 to R-2)). So, I was stumped and put it away for a while.

I got back to things and figured that the LME49990 might be the culprit. I swear that I followed the layout for both of these, I even verified the layout with some blank adapters that I have (mini opamp orientation matches the pritining on the adapter PCB and it was mounted correctly to the sockets). For fun, I decided to look closely at the PCB and follow the traces back to the pins. I used these adapters based on a recommendation in the BAP buy thread (no affiliation):

http://www.ebay.com/itm/2-Dual-SOIC...mplifier_Parts_Components&hash=item337e60c33b

I'm fairly certain, though, that these are NOT what should be used. I looked at a few other SO8 to Dip8 adapters (no affiliation):

http://cimarrontechnology.com/so8to8-pindipadapterpn970601-3.aspx
http://www.ebay.com/itm/5-Pcs-SOP8-...869?pt=LH_DefaultDomain_0&hash=item3f1429421d

The trace-to-pins definitely don't line up. Here is my crude diagram of what I have (on top) with what I should have (on bottom) along with the diagram from the opamp spec sheet:

adapterissue.jpg






So... unless something else is the culprit, I think I'm pretty well screwed. Is my reasoning sound? What is the kind of adapter I used? I see other examples of this adapter with opamp (again, no affiliation):

http://www.head-fi.org/g/i/655560/2-dual-soic-lme49990-on-dip8-adapter/

So, I'm really confused. What did I do wrong? Is there something else I can/should be checking?
 
HypnoToad said:
Dodog, this is the problem, unfortunately you purchased the adapters to mount two single circuit op amps on the one adapter making them into a dual circuit like these:

http://www.ebay.com/itm/1PCS-Dual-t...798?pt=LH_DefaultDomain_0&hash=item337cd3e9ae

You need to purchase ones like these:

http://www.ebay.com/itm/2x-SOP8-SO8...mplifier_Parts_Components&hash=item4ab2a7c05f



Can you desolder the chips you have?
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For the record, I would like to point out that you were the one who linked to the incorrect PCB's in post #81 of the group buy thread. :D Perhpaps you could edit your post so that no one makes the mistake that I did.

No worries, I should be able to mount some other LME49990's on the other side and run them in the CNC or the SSP, no?

I'll order some new opamps and the correct adapters and have at it again. The opamps are cheap enough, as are the adapters, that I'm not going to lose any sleep over it. At least I know why things didn't work correctly! :thmbsp:
 
dodog said:
For the record, I would like to point out that you were the one who linked to the incorrect PCB's in post #81 of the group buy thread. :D Perhpaps you could edit your post so that no one makes the mistake that I did.

No worries, I should be able to mount some other LME49990's on the other side and run them in the CNC or the SSP, no?

I'll order some new opamps and the correct adapters and have at it again. The opamps are cheap enough, as are the adapters, that I'm not going to lose any sleep over it. At least I know why things didn't work correctly! :thmbsp:
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I edited the post, my mistake, to make things right I will send you a pair of adapters as I ordered a bunch for myself.

PM me your postal address, I will send them out in the morning as it will take you a few weeks to get them from China.:thmbsp:
 
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