D-EF47 Tribute To Oliver Archut U47 Build Thread.

[C12VR]

Ok so my power supply produces B+ and H+ voltage without any load but with the mic plugged in these values drop near zero--what could be the cause of this? Sorry for my ignorance.

 

[Silas]

Okay great thanks! Page 15 helpful reading

 

[oongbac]

Ok so my power supply produces B+ and H+ voltage without any load but with the mic plugged in these values drop near zero--what could be the cause of this? Sorry for my ignorance.

I don't know much about electricity, so the only answer I can give you is check the pinouts of cable. Sorry if you already do this... Let’s wait for the other answers!

 

[C12VR]

I don't know much about electricity, so the only answer I can give you is check the pinouts of cable. Sorry if you already do this... Let’s wait for the other answers!

Just fixed it--I idiotically miswired the 7 pin XLR inside the PSU, skipping pin 4 on the molex connectors and thus wiring the rest in order, but out of place by one pin. Now I have another problem--I can't get the B+ higher than 93v.

 

[oongbac]

Just fixed it--I idiotically miswired the 7 pin XLR inside the PSU, skipping pin 4 on the molex connectors and thus wiring the rest in order, but out of place by one pin. Now I have another problem--I can't get the B+ higher than 93v.

How about check the wiring of transformers first?

 

[TLRT]

Hi All,
I’m thinking of building the DEF47 in the UK - I wondered if anyone on here might know - are there any alterations I need to make to the PSU transformer to work with the UK voltage?
Many thanks
Silas

I have custom made 200V/20V transformers, so you dont need 2 transformers. Shielded, high quality, no noise. Write me PM if interested

 

[C12VR]

My microphone seems to work well right now but I measure a small voltage, about -35mv between cable ground and mic body, as well as a resistance of -22ohm. I can touch it without getting shocked but I am sure that I am doing something wrong here. Maybe the negative resistance and voltage could give clues as to what is wrong. When I turn off the psu, I measure about 1ohm in resistance.

 

[Silas]

Hi guys,

Can anyone help - I’m finding that the H+ pin in the mic body is contacting the two mounting holes either side of the transformer - detailed in the attached photo
Is this correct? It reads a slight resistance if roughly 138 ohms

I find this worrying as the h* voltage should not contact the mic body and by it contacting those holes it will do - have I miswired something?

 

[duantro]

How is that connecting to the body? Are the mic body rails wide right there? If so take a die grinder and carve out a spot.

 

[Silas]

Thanks Duantro - only because I’m using those through holes to mount the mic to the rails like in Dan’s build - see screenshot
Was wondering about not using them but surprised Dan had if there was connection to the h+ rail

 

[duantro]

The heater and B+ traces go north to the head amp and tube section, so shouldn't be active by those holes. Look at the pcb photo on page 1

 

[Silas]

Yes I thought that! - any thoughts as to why H+ has connection to those holes in that case? There is slight resistance so I suspect there are components between it and the holes - I’ve just been checking with a multimeter.

B+ nothing I don’t think, although I should double check that..

 

[duantro]

Are you getting voltage there? I'm thinking there might be a slight resistance as the heater goes to ground after the tube.

 

[Silas]

Are you getting voltage there? I'm thinking there might be a slight resistance as the heater goes to ground after the tube.

Ahh spot on - those holes are linked to the ground pin directly - zero resistance

Explains that resistance! Thanks

Could connecting those holes to the mic body could create a ground loop?
I was under the impression that having one point of chassis connection stopped the possibility of that
Thoughts?

 

[duantro]

Ahh spot on - those holes are linked to the ground pin directly - zero resistance

Explains that resistance! Thanks

Could connecting those holes to the mic body could create a ground loop?
I was under the impression that having one point of chassis connection stopped the possibility of that
Thoughts?

I don't recall exactly where the ground connects in this circuit, but the body and headbasket shields the circuit. It should only be connected to the ground wiring at 1 location to keep from having a loop.

 

[Silas]

Yes, perfect. I was in the process of checking the shielding connections when I noticed the ground connecting to the body - I will connect the microphone pcb differently to avoid connecting the ground at two points
Thanks!

 

[Silas]

Hmm so all the four holes connect to ground.

Out of interest what is the purpose of ground to chassis in the mic body as well as ground to chassis in the PSU?

 

[Silas]

Hmm so all the four holes connect to ground.

Out of interest what is the purpose of ground to chassis in the mic body as well as ground to chassis in the PSU?

Only that my understanding was that the existing shield connection to mic body and also the 0 ground + PSU chassis does the same thing - so to have both could cause ground loops, as effectively there would be two chassis connection points within the mic body - one via those through holes (0v pin effectively) and one via pin 3 of XLR (shield connection)

 

[Silas]

Only that my understanding was that the existing shield connection to mic body and also the 0 ground + PSU chassis does the same thing - so to have both could cause ground loops, as effectively there would be two chassis connection points within the mic body - one via those through holes (0v pin effectively) and one via pin 3 of XLR (shield connection)

I had a chat with a microphone engineer about this - they mentioned it is common place for microphones to have the 0 rail bonded to the mic body in several places - so all good on that front

 

[Silas]

I have built the PSU and have one other question around the voltages I'm getting. Can anyone help?

Firstly the 230v toroidal transformer is giving 270v at the output (I measured the input to be 240v - I based in the UK so this makes sense) - It's wired correctly in series and so I would expect roughly 240v at output - has anyone had this issue before - it mentions 12% regulation but 270 is right at the end of that - should I just replace for another one? Is there anything else in the circuit that could increase the voltage differential? 180k dummy load connected across B+.

I am getting a healthy 20v input and at the H+ rail output I'm getting 10v with 20hm res dummy load connected - this is as far as I can adjust it - I had hoped to hit the 5.3v mark. Any ideas these?

Is it worth placing a dummy load where the relay voltage would go?

Many thanks!

Silas