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PostPosted: 24 Jan 2012, 23:55 
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Odd (not watt) that you do this Bruce, ever since I built "Paris" as an integrated tube amp, I have been thinking of a preamp with phono section built in. Possibly one of the 4S Tube preamp but with jFet phono stage (still on batteries) in the one case.

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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: 25 Jan 2012, 13:11 
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Nice work Bruce. An advantage to this is that you also eliminate one set of interconnects.

How are you cutting and bending the sheilding cage?

Cheers

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PostPosted: 25 Jan 2012, 13:41 
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Hi Gio, Thanks for the kind words. The shielding is easy to work with. It is copper plated aluminum that is available from hardware stores in the form of kick plates for screen doors. It cuts easily with sheers and bends on the perforations quite easily. Great stuff for shielding.

I am waiting for a few more hours on the preamp and then will go over it thoroughly to make sure it is as good as it sounds. Then I'll put together a write up on how to go about it. The key is in spacing the parts out and having a high quality power supply. There are 1500uf of caps in the B+ (separate lines go to each board and to each stage) and about 50uf of polys at key locations.

Good listening
Bruce

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PostPosted: 25 Jan 2012, 17:42 
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Gio wrote:
Nice work Bruce. An advantage to this is that you also eliminate one set of interconnects

This is what I feel made a difference with Paris that there was no inter-connects from preamp to amp. Anytime you can cutout a connection or length of lead it has to be good. It just limits flexibility in the system.

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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: 02 Feb 2012, 13:23 
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I am in the completion stages of thiis project, it is my first from scratch, I think I have it built as in the schematic, voltages are all good on the power supply and heaters, but I have ~100 volts on output jacks, input is nominal. Is this something you have seen before? Thinking it is best not to hook up to amp quite yet... I am sure I have made an error somewhere, as I tend to rush things.


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PostPosted: 02 Feb 2012, 14:40 
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Ledbellyhead wrote:
I am in the completion stages of thiis project, it is my first from scratch, I think I have it built as in the schematic, voltages are all good on the power supply and heaters, but I have ~100 volts on output jacks, input is nominal. Is this something you have seen before? Thinking it is best not to hook up to amp quite yet... I am sure I have made an error somewhere, as I tend to rush things.

Bruce will probably guide you here but 100V on the output doesn't sound right.

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PostPosted: 02 Feb 2012, 21:44 
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Hi, There should be no DC on the output jacks. I suspect your final coupling capacitor is faulty. It blocks the dc voltage on the cathode of the final stage which is in the 100-150 range. What type of capacitor value/voltage rating/brand did you use for this part?

Good listening
Bruce

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PostPosted: 03 Feb 2012, 20:00 
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Man, had the last caps installed backwards, nichicon aluminum electrolytic. On a budget. Flipped them over and this thing kicks some major butt. I can't wait until I can move it upstairs and give a good listen. You were dead on with diagnosis. Thanks a bunch for the help and the entire project it has been an awesome one. Thanks for everything man!


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PostPosted: 04 Feb 2012, 16:40 
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Hi, I like happy diyers. :) having them backwards will certainly do that. On A budget, you can use Jantzen CrossCaps. About $4 each and they work pretty well in this application.

Good listening
Bruce

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PostPosted: 20 Feb 2012, 10:44 
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Hi Everyone, If you want to use the preamp with a low output MC cartridge I recommend using Lundhal 1678 input transformers. Very nice sound and they don't add any noise. I used a gain of 8 on the trannies. I get noise levels in the -90dbv or better range on both MC and MM now. Getting the low output MC portion that quiet with just tubes will require at least one more gain stage and then the preamp would invert the signal. So really two extra stages would be needed. Not cost effective. The trannies are about $85US each from K&K audio (sole importers in the US). If you really want to splurge there are higher cost ones with different cores and Cardas wire. :$: :$:

Good listening
Bruce

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