Spencerleehorton

Re: Neumann U47FET Clone: D-U47 FET Microphone Project PCB Build thread
« Reply #780 on: July 07, 2019, 05:26:23 AM »
T3 looks like you have a problem as more than 0.6 between E and B.
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!


duantro

Re: Neumann U47FET Clone: D-U47 FET Microphone Project PCB Build thread
« Reply #781 on: July 07, 2019, 04:06:39 PM »
 ::)
T3 looks like you have a problem as more than 0.6 between E and B.
That's right!, I'll switch it out and see if it helps.
Edit: Swapped T3 out and same measurements.  Checked all connections, and component values. Would a fake 2n3819 cause this? I've read about people getting fake ones? Not sure what is up here...
« Last Edit: July 07, 2019, 08:42:26 PM by duantro »

Spencerleehorton

Re: Neumann U47FET Clone: D-U47 FET Microphone Project PCB Build thread
« Reply #782 on: July 09, 2019, 06:48:21 AM »
I would change T1 and remeasure
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!

duantro

Re: Neumann U47FET Clone: D-U47 FET Microphone Project PCB Build thread
« Reply #783 on: July 09, 2019, 04:52:57 PM »
I changed T1 and same voltages everywhere.  I get get a pretty quiet signal on the mic, which I'm assuming from the low polarization voltage. What the hell is going on here?!

duantro

Re: Neumann U47FET Clone: D-U47 FET Microphone Project PCB Build thread
« Reply #784 on: July 12, 2019, 09:48:17 PM »
Still banging my head against the wall on this one. Do the outer screw holes have to be grounded for the circuit to work? The mouser cart has 4/40 screws that are way to big for these holes, ...without drilling. I'm using Spencer's bodies that have flat rails and don't work with the mounting hardware, without some  fabrication. I'm noticing that the holes on the hiZ side don't have continuity to the opposite boards mounting holes. Would this have any affect on it working?

duantro

Re: Neumann U47FET Clone: D-U47 FET Microphone Project PCB Build thread
« Reply #785 on: July 13, 2019, 04:13:01 PM »
Since I had concern with Pad "A" being shorted out and damaging something, I swapped out the pcb's for the 2nd set of boards that I've populated the same,  and still really low output. So frustrating.  What now....The telefunken transformer has a bit higher resistance than the others have posted here 2k2: 120r. Would that affect the circuit adversely? Trying to think outside of the box here.
« Last Edit: July 14, 2019, 04:58:10 PM by duantro »

Spencerleehorton

Re: Neumann U47FET Clone: D-U47 FET Microphone Project PCB Build thread
« Reply #786 on: July 13, 2019, 06:02:59 PM »
I’ve got 4 of these circuits on the bench, when I get some time I’ll help, anyway you could just have capsule in headbasket and test circuit out of body?

Also continuity test all connections as much as you can, I’m sure you’ve probably done this!

I’ve got a working version so will get some voltages for you,
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!

duantro

Re: Neumann U47FET Clone: D-U47 FET Microphone Project PCB Build thread
« Reply #787 on: July 13, 2019, 08:03:49 PM »
Thanks Spencer.
I put it down for a minute and built my second pair  km84’s  that just showed up. I finished them and will calibrate tomorrow. I used the same 2n3819’s and figured I’d at least see if the batch I received were suspects in the fet47’s.

duantro

Re: Neumann U47FET Clone: D-U47 FET Microphone Project PCB Build thread
« Reply #788 on: July 14, 2019, 04:56:35 PM »
Ok, so the Km84s work like a charm (3 hour build with zero head scratching!) with 2n3819's from the same batch, so that doesn't seem like the issue. In comparison, the idle room noise with the gain cranked up on my Neve pre is -10db on the km84's, and -60 on the fet47. When checking polarization voltage on r8 starts out at around 38vdc and drops to 15 vdc when meter is applied. The only thing I can guess is something is dragging polarization voltage down.
edit:
Changed T1 yet again, changed capsule wires, and checked component values again.  Same results. Maybe this would sound good on a 100db kick drum? :o
« Last Edit: July 14, 2019, 08:32:25 PM by duantro »

Spencerleehorton

Re: Neumann U47FET Clone: D-U47 FET Microphone Project PCB Build thread
« Reply #789 on: July 14, 2019, 07:13:29 PM »
Dodgy capsule maybe?

What is you phantom volts on pins 1/2?

Do you have a frequency generator and a scope?
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!


Re: Neumann U47FET Clone: D-U47 FET Microphone Project PCB Build thread
« Reply #790 on: July 14, 2019, 07:46:05 PM »
See Page 1    4th picture allthe requirement ,
also ake sure you have the backplate connected on the right side of the connector there is only one side of this connector that goes to gnd ,

Backplate is ground in this case , just to make sure ,
Best,
Dan,




duantro

Re: Neumann U47FET Clone: D-U47 FET Microphone Project PCB Build thread
« Reply #791 on: July 14, 2019, 08:05:17 PM »
Unfortunately my tek 465 just died, so I'm kind of shooting from the hip here, until I can get another one.  I tossed it on a kick drum, and think it may be working, but possibly a transformer issue. The signal is clean, just real quiet. I'm going to check the wires on it.

edit: Thanks guys, Back plate is correctly connected. Getting phantom power as T7 collector is showing 44.74. What are you getting for voltage at r8? Is this transformer's impedance an issue? Could the polarity of the transformer cause a drop in level if not connected correctly? This transformer has all clear coated wires. Output phasing is correct with my beta 52.
If I boost the clip gain by 15db in pro tools, the signal is great. 
« Last Edit: July 14, 2019, 09:02:34 PM by duantro »

Spencerleehorton

Re: Neumann U47FET Clone: D-U47 FET Microphone Project PCB Build thread
« Reply #792 on: July 15, 2019, 01:42:15 AM »
If it sounds right and it’s just your level, it could be your transformer, try it the other way round?
Quick fix to try.
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!

Spencerleehorton

Re: Neumann U47FET Clone: D-U47 FET Microphone Project PCB Build thread
« Reply #793 on: July 15, 2019, 06:44:03 AM »
do you have another transformer you can try? i have some OEP 6.5:1 ratios ones that i've used to test before, ideally a 9:1, 9.5:1 or 10:1 will work nicely.
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!

duantro

Re: Neumann U47FET Clone: D-U47 FET Microphone Project PCB Build thread
« Reply #794 on: July 15, 2019, 11:08:15 AM »
Yeah, I’ve switched the primaries and secondaries around the other direction, and it gets quieter.  Can anyone verify voltage at r8?

Spencerleehorton

Re: Neumann U47FET Clone: D-U47 FET Microphone Project PCB Build thread
« Reply #795 on: July 15, 2019, 12:44:55 PM »
I’ll have a look in the morning, I’m knackered now after 2 full van loads of crap from the garden, monster dog walk then football practice!!!
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!

duantro

Re: Neumann U47FET Clone: D-U47 FET Microphone Project PCB Build thread
« Reply #796 on: July 15, 2019, 01:37:45 PM »
I’ll have a look in the morning, I’m knackered now after 2 full van loads of crap from the garden, monster dog walk then football practice!!!
That sounds like a full day! Let me know what you find out when you get a minute to check. I plan on saving up for a pair of capsules and transformers that match at some point, so if my voltages are on with yours here, maybe that's my next step.

Spencerleehorton

Re: Neumann U47FET Clone: D-U47 FET Microphone Project PCB Build thread
« Reply #797 on: July 16, 2019, 12:03:31 AM »
Could you email me some photos or post up some?
Do you have any other transformers you could try?
Most of the time it’s not about finding the fault but eliminating the possible problems.
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!

duantro

Re: Neumann U47FET Clone: D-U47 FET Microphone Project PCB Build thread
« Reply #798 on: July 16, 2019, 12:14:32 AM »
I posted photos of the build  a page back. The only other mic transformer I have is a 2:1 mxl, and a 3:1 lomo 19a9, so nothing that I think would work.
I agree about finding a possible problem, that’s why I was asking about polarization voltages  at r8
Edit: I forgot, I do have a t14 transformer that I can try. It has about the same impedance as the telefinken.
« Last Edit: July 16, 2019, 12:22:12 AM by duantro »

Spencerleehorton

Re: Neumann U47FET Clone: D-U47 FET Microphone Project PCB Build thread
« Reply #799 on: July 16, 2019, 10:54:23 AM »
T14 is 12:1 so would work and if level is better would then prove your txf is faulty.
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!


 

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