Re: NewYorkDave Mila Dual Tube Preamp Help Thread
« Reply #340 on: February 02, 2019, 04:07:57 PM »
R1 (on the psu board) burns out. This happends when i connect the main board with the psu, powering on the psu unconnected doesn't make any smoke :P

Without the main board your PSU is stabil and with reasonable voltage output? This could be a sign for excessive current flow in your amp, due to a short to ground, wrong components (wrong biasing of the tubes) or faulty tubes on the main board. Please show a good photo of your amp.


bernatvm

Re: NewYorkDave Mila Dual Tube Preamp Help Thread
« Reply #341 on: February 03, 2019, 05:22:54 PM »
Without the main board your PSU is stabil and with reasonable voltage output? This could be a sign for excessive current flow in your amp, due to a short to ground, wrong components (wrong biasing of the tubes) or faulty tubes on the main board. Please show a good photo of your amp.

Yes, when amp unplugged everything seems ok. Voltage is 380V when its supposed to be lower, but without the tubes I read is normal.
« Last Edit: February 03, 2019, 05:38:49 PM by bernatvm »

bernatvm

Re: NewYorkDave Mila Dual Tube Preamp Help Thread
« Reply #342 on: February 06, 2019, 06:47:05 AM »
Input TX was backwards, corrected it and still smoke. R1 in psu is 4.7k instead of 2.2k (need to buy some 2.2k). Anyone seeing any kind of short? The problem is too much current flowing on b+ even with no tubes.

Re: NewYorkDave Mila Dual Tube Preamp Help Thread
« Reply #343 on: February 06, 2019, 08:50:50 AM »
Hi, your build is pretty messy, I do not know where to start. You must avoid in any case that your wires have unintentional contact with each other or against the case. The resistors at the sockets are very suspicious, your PSU PCB seems to have no save isolation against the case, this one screw in the second photo is not enough. Is this your layout?

- check all the components
- avoid any unintentional contact, find the short
- isolate suspicious contacts
- work safe and don´t kill yourself

Your layout will probably have problems with hum after you have established basic function, but first things first.
« Last Edit: February 06, 2019, 08:54:23 AM by rock soderstrom »

ruffrecords

Re: NewYorkDave Mila Dual Tube Preamp Help Thread
« Reply #344 on: February 06, 2019, 03:09:50 PM »
The most likely fault is the PSU baord shorted to the chassis due to improper fixing.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

bernatvm

Re: NewYorkDave Mila Dual Tube Preamp Help Thread
« Reply #345 on: February 06, 2019, 06:19:05 PM »
That's not it. Psu has 1 cm of rubber between it and the chassis, plus the psu alone is stable. Problem appears when I connect it to the amp board

scott2000

Re: NewYorkDave Mila Dual Tube Preamp Help Thread
« Reply #346 on: February 06, 2019, 07:00:49 PM »
Have you checked yet that c3 isn't backwards too?

The B- is to the left ???
« Last Edit: February 06, 2019, 07:05:45 PM by scott2000 »

bernatvm

Re: NewYorkDave Mila Dual Tube Preamp Help Thread
« Reply #347 on: February 07, 2019, 04:04:49 AM »
Yes, it was, I fixed it and still the same. C3 is heater filter and psu is stable when heaters are connected

scott2000

Re: NewYorkDave Mila Dual Tube Preamp Help Thread
« Reply #348 on: February 07, 2019, 10:35:21 AM »
What are your values at R18 and R19????

Kinda hard to decipher the build from pictures.....

You'll get it.....

bernatvm

Re: NewYorkDave Mila Dual Tube Preamp Help Thread
« Reply #349 on: February 07, 2019, 01:44:21 PM »
R18 and R19 ended up like this. Is a mod to vary the feedback and have more "range" control options.


Re: NewYorkDave Mila Dual Tube Preamp Help Thread
« Reply #350 on: February 07, 2019, 02:21:59 PM »
I would undo the mod. Start with the basic circuit, make it work first. Have you measured resistance between B+ and B- (without tubes and PSU)?

bernatvm

Re: NewYorkDave Mila Dual Tube Preamp Help Thread
« Reply #351 on: February 08, 2019, 07:33:07 PM »
No more smoke! The rubber spacers I was using happend to be a bit conductive (they give a reading on the ohmeter). The one on the superior right corner of the amp was shorting b+ with b-. Changed them for plastic spacers, smoke is gone.

Re: NewYorkDave Mila Dual Tube Preamp Help Thread
« Reply #352 on: February 09, 2019, 01:27:00 PM »
No more smoke! The rubber spacers I was using happend to be a bit conductive (they give a reading on the ohmeter). The one on the superior right corner of the amp was shorting b+ with b-. Changed them for plastic spacers, smoke is gone.

That´s good news! Check for further security related issues, make it safe. ;-) How is the sound, any hum problems?

bernatvm

Re: NewYorkDave Mila Dual Tube Preamp Help Thread
« Reply #353 on: February 09, 2019, 02:22:41 PM »
Didn't wire the mic input yet, but instrument input sounds very good! I only have hum with very high gain and higher range positions, but it's soft, so I think  it's the normal behavior.

bernatvm

Re: NewYorkDave Mila Dual Tube Preamp Help Thread
« Reply #354 on: February 09, 2019, 04:15:09 PM »
Wired the mic input and sounds ok but maybe hum is a bit over what would be desirable... Where do I start?

bernatvm

Re: NewYorkDave Mila Dual Tube Preamp Help Thread
« Reply #355 on: February 27, 2019, 05:18:05 AM »
I have some problems with phantom power. With the same configuration in the preamp (gain and range). I get more volume from my sm57 than my condenser AT2050. I checked it with my interface preamps and in that case the condenser gives more volume as you'll expect.

Also tested the 57 with the phantom power on and, as expected, nothing changes with it.

What could be the problem here?

Also, do I need to block phantom power with capacitors? Or the Lundahl LL1935 in the input stage is already doing the job?

Thanks guys!

Re: NewYorkDave Mila Dual Tube Preamp Help Thread
« Reply #356 on: February 28, 2019, 09:18:18 PM »
Wired the mic input and sounds ok but maybe hum is a bit over what would be desirable... Where do I start?

Rotation of the toroidal power transformer and keep AC wiring maximum away from high impendance inputs and DC wiring.
« Last Edit: February 28, 2019, 09:30:03 PM by rock soderstrom »

Re: NewYorkDave Mila Dual Tube Preamp Help Thread
« Reply #357 on: February 28, 2019, 09:27:51 PM »

What could be the problem here?


No idea. Stange phenomenon, maybe impedance mismatch due to wrong wiring of the input transformer section.

No, you don´t need blocking caps as long you use thigtly matched 6k81 "phantom" resistors (R2/R3), There is no DC at the primary side of your Lundahl.

Check you wiring, take the Jensen standard input circuitry as reference.
« Last Edit: March 01, 2019, 02:25:05 AM by rock soderstrom »

bernatvm

Re: NewYorkDave Mila Dual Tube Preamp Help Thread
« Reply #358 on: March 03, 2019, 03:01:36 PM »
I had a recording session with the preamp and realized it's not only volume problem. Whatever condenser mic I plug the sound gets very distorted


 

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