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Ribbon Microphone Preamp
Ribbon Microphone Preamp
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Old 9th July 2013, 03:16 PM   #251
woodrough is offline woodrough  United States
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Haha, Dang, I was going to use the ps-1 schematic (point to point) with an antek toroid transformer. Read my mind!

As for the cathode bypass caps, I have a few nice os-con 16v organics, what is a safe voltage rating to work with down there?

Also, I wouldn't be opposed to the idea of paralelling tubes (for the sake of heater elevation).
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Old 9th July 2013, 03:24 PM   #252
ruffrecords is offline ruffrecords  United Kingdom
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Quote:
Originally Posted by mm7 View Post
Hmm. The upper heater at -100V should generate some noise, shouldn't it?

Would it be better to use separate envelopes utilizing pairs for stereo, or for paralleling tubes as you said for some noise suppression?
The upper tube will not generate noise if you use dc heaters.

Cheers

Ian
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Old 9th July 2013, 04:16 PM   #253
ruffrecords is offline ruffrecords  United Kingdom
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Quote:
Originally Posted by woodrough View Post
Haha, Dang, I was going to use the ps-1 schematic (point to point) with an antek toroid transformer. Read my mind!

As for the cathode bypass caps, I have a few nice os-con 16v organics, what is a safe voltage rating to work with down there?

Also, I wouldn't be opposed to the idea of paralelling tubes (for the sake of heater elevation).

16V working should be fine. If the cathode ever gets near 16V the tube will be pretty much cut off.

Cheers

Ian
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Old 9th July 2013, 04:49 PM   #254
mm7 is offline mm7  Canada
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I read some negative things regarding toroid mains transformers. ( Toroidal vs EI type Power Supplies [Archive] - AudioKarma.org Home Audio Stereo Discussion Forums )
Probably I will better go with EI one and put some more iron screening around it and around input stage.
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Old 9th July 2013, 04:51 PM   #255
mm7 is offline mm7  Canada
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Originally Posted by ruffrecords View Post
The upper tube will not generate noise if you use dc heaters.
If same is applicable to lower tube, do we need heater elevation at all?
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Old 9th July 2013, 05:00 PM   #256
ruffrecords is offline ruffrecords  United Kingdom
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Quote:
Originally Posted by mm7 View Post
I read some negative things regarding toroid mains transformers. ( Toroidal vs EI type Power Supplies [Archive] - AudioKarma.org Home Audio Stereo Discussion Forums )
Probably I will better go with EI one and put some more iron screening around it and around input stage.
Perhaps a more important consideration is the enclosure in which you put the preamp and power supply. It is essential that this is NOT steel. If it is you will almost certainly have problems with stray flux from an EI type transformer being transmitted through the case work to the microphone input. I had exactly this problem once and the only solution was to take the power supply external. If you are going to build this all in one box put the mains transformer at one end of the box and the mic transformer at the other. Preferably use an all aluminium enclosure. I personally have never had any problems with toroidal transformers.

Cheers

Ian
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Old 9th July 2013, 05:08 PM   #257
mm7 is offline mm7  Canada
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Ian, thanks for another good advice! I was hesitating deciding which case to use, steel or aluminum. Now I see that aluminum one is better.
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Old 9th July 2013, 05:27 PM   #258
ruffrecords is offline ruffrecords  United Kingdom
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Originally Posted by mm7 View Post
If same is applicable to lower tube, do we need heater elevation at all?
You do need heater elevation to ensure you do not exceed the specified heater cathde voltage Vhk as I explained earlier.

Cheers

ian
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Old 9th July 2013, 05:40 PM   #259
mm7 is offline mm7  Canada
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Originally Posted by ruffrecords View Post
You do need heater elevation to ensure you do not exceed the specified heater cathde voltage Vhk as I explained earlier.
Oh yes, I see.

Regarding a toroid trans, what mains power do you have? 2 or 3 phase?
I know in Russia it is 3 phases by 220V 120 degree shift (regular residential receptacles use 1 phase), in US and Canada it is 2 phases by 120V 180 dgr shift. It looks like toroids should work without problems in North America, but may be problems in Russia because of DC bias. What type of power do you have?
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Old 9th July 2013, 06:47 PM   #260
woodrough is offline woodrough  United States
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I always feel inconclusive with the EI vs Toroid debate. It looks like the emi field of a toroid is a small fraction (1/8) of a EI core. So the question is, what is the minimum acceptable distance I should keep the input transformer from? *(with either version)?

I envision putting this in an all in one multi story enclosure.
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