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PostPosted: 29 Nov 2014, 18:15 
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Joined: 06 Jun 2008, 18:23
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Location: Australia
Yes OPAMPs, cheap and cheerful. I get them cheap from work at staff prices but if I shopped on eBay and bought a dozen I would probably get them cheaper again. I've propably used well over a dozen to this point anyway.

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Projects: "Lagoon" - tube preamp with cathode follower | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
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PostPosted: 30 Nov 2014, 02:18 
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Joined: 28 Nov 2014, 15:21
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Location: Queensland, Australia.
G'day mate, for what it's worth I have done a bit of op amp 'rolling' with this design and the OPA2134 comes out as best, and believe it or not it is actually slightly quieter than the supposedly 'ultra low noise' LM4562 in this circuit.

I can't work that one out, but the OPA2134 works superbly and sounds amazing in this design and is my recommendation! Regards, Felix.


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PostPosted: 30 Nov 2014, 19:51 
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Bruce would you please list the caps and where they go. The schematic is very hard to read.

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PostPosted: 30 Nov 2014, 22:45 
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Hi Mark, Mine shows up as quite clear.... which caps are you concerned with? I can send you a higher rez one to your regular email if you like.

Good listening
Bruce

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PostPosted: 30 Nov 2014, 22:50 
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Hi Everyone, first the schematic I posted was the wrong for for the combined phono tape preamp with line stage and second it has a couple of errors. Sorry folks. Here is the real deal. If you need capacitor loading for the cartridges then in would go at the input in parallel with the loading switch. My personal ones all have two 100 pf mica caps that I can switch in and out there as needed.

Good listening
Bruce

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PostPosted: 01 Dec 2014, 02:21 
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Bruce please send a high Rez image of the original schematic.

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PostPosted: 19 May 2015, 01:50 
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Here is another build of Bruce's LOMC and this time for MC only. On the proto brd I only need to add two wires which brought the power to the chip. The rest of the on board wiring is parts leads only. The output caps (4.7uf NP) are under neath. Neatest build so far. This is for a guy in Scandinavia who asked me if I would make one for him. The external wiring has been added and the board ready for assembly.
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Projects: "Lagoon" - tube preamp with cathode follower | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
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PostPosted: 30 May 2015, 22:10 
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Joined: 22 May 2013, 20:53
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Location: Yorktown, VA
Bruce,

I've built your Groovewattand it sounds wonderful. I'm building this OPAMP-based preamp as a project to compare with a buddy's commercial OPAMP-based preamp. I'm just curious to hear the difference between this and the GW and his $80 store-bought unit.

I will only be running MM cartridges with this "fun" project, so I don't need any of the LOMC switching or supporting caps/resistors. I also don't need the NAB equalization, so I've deleted those parts of the circuit.

The thing that's got me wondering is the difference between the DIP-switch-selectable resistors and caps in the Groovewatt and this OPAMP design. I'm guessing the Groovewatt's three resistors and two caps are a good mix of selectable components for MM, so I was planning on using those instead of the 400+400+100+100+51 in this design. Is this a mistake? What do you think?

Thanks!

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PostPosted: 30 May 2015, 23:48 
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G'day mate, I have done pretty well the same thing with my versions, just for MM cartridges and it is the one of the nicest sounding DIY phono stage that I've ever built. It's one of my two or three favourite phono stages at any price point. You'll love yours I suspect! Regards, Felix.


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PostPosted: 31 May 2015, 20:31 
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Hi, The IC based preamp has only one choice for loading the MM cartridges (47K) the tube based one has some choices that seem to be useful. The low value resistors in the IC one are for LOMC only. If you want a simle circuit just use the 47K in the IC one. If you more flexibility then add others and possibly 100 and 200 pf capacitors sometimes they are needed. In my system I have found that all the MI cartridges use 47K with no extra capacitance. The HOMC ones soetimes work better at slightly lower loading (about 28-33K) and with 100 pf extra. The LOMC ones I have all seem to work best at about 200 ohms and no caps in the IC version. Using Lundahl SUTs with the tube preamp the loading on the cartridges works best at about 150-180 ohms and again no extra caps. The loading issue is something that is hard to predict. Standard values are 47K and 0-220 pf for MM and MI. The standard LOMC is 100 ohms and 0-220pf. YMMV.

Good listening
Bruce

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