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DC power source for DIY preamp
Old 27th August 2014
  #31
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LeeYoo's Avatar
 

Not sure about the hash at this (dead-bug) stage.
THIS module with an XL6009 works on 400Khz. Far away from audio anyway.
I suppose the negative output will be the same as the normal out, if the final cap is the same value/quality.
If you want to use these modules for audio, it is wise to add L/C filtering anyway.
And put the whole thing in a metal box, with ferrite beads on all in/out wires.
The negative rail can't be loaded as much as the positive.
I just tried 100mA, and that was not a problem.
When loading +15 and -15 with 100mA, efficiency was surprisingly high (almost 90%).

I made P48 with four diodes and four caps.
Two ceramic! 1uF caps to tap from the switching point, and two 100uF/25v finals.
As in the top picture on this page.
http://en.wikipedia.org/wiki/Voltage_tripler
Only D1/C2 not to ground, but to the +15 rail.
+15 and a doubler gives about 48volt.
Before adjusting the module to 48volt, I loaded that rail with a 10k resistor (5mA).
The 15 volt rails were about 15.5volt after adjusting P48.

Looks like this module is using the same technique.
http://www.prodctodc.com/dc-35v30v-t...l#.U_5JuWMUOOu
http://www.aliexpress.com/item/DC-DC...716086944.html
Single coil, double rails.
Too bad the input range does not include 12volt.
Leo..
Old 3rd September 2014
  #32
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This, added to those cheap boost converters, seems to work ok.
Depending on parts and module, up to 300mA or so.
Ignore the part on the right of the vertical line. That's the simulated load.
But do use ferrite beads. They, plus the rail caps, lower the ripple to a few milivolts.
15.6v on L1, -15.6v on L2 and 48v on L3.
Use 25v ceramics for C1 and C3. And 50v ceramics for C5 and C7.
Smaller values can be used for higher switch frequencies/ lighter loads.
Low ESR 25v lythics or tantalum for the rest. Watch polarity.
SW comes from the switch point (anode) of the module.
+Out from the DC out. Set module to about 15.6v for P48v out with light load.
Will work between about 5v and 12v in. Tested on 7.2v lithium battery pack.
Leo..
Attached Thumbnails
DC power source for DIY preamp-triple-supply.jpg  
Old 3rd September 2014
  #33

So, this will work with the non-synchronous (like a buck converter that uses a single FET and a diode with the inductor)?

For pre-amp designs that use fairly heavy bias current - where transient power-supply loads are minimal, this seems like a good approach.

You could use a FET and an oscillator instead of a full-on SMPS driver too.



-tINY

Old 3rd September 2014
  #34
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I used it with the boost (step-up) module from post #19.
That also provides the regulation.
It keeps the switch output at a constant 16volt t/t.
Load regulation is not that great, but ok for my needs.
e.g. P48 dropped 1volt between 10mA and 40mA load.
And the 15v rails dropped 0.4v between 50mA and 250mA.
One advantage of this circuit is that the 15v rails both come up symetrically from 0volt.
Not so when you tap the +15v from the module itself.
There it starts up from almost the battery voltage, while the neg. rail is still 0volt.
And it's ends 0.5v higher than the negative rail.
Old dog learning new tricks playing with these circuits.
Maybe next I'll convert it into a 300v valve supply.
LTspice is nice to simulate these circuits.
The zip file contains a simm with a very small switcher.
Leo..
Attached Files
File Type: zip LT1935_2x15_1x48.zip (1.6 KB, 127 views)
Old 3rd September 2014
  #35

The caps you'd need for a 15w tube amp supply scares me a little.

Ever seen a big tantalum cap go?




-tINY

Old 3rd September 2014
  #36
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Yep, I have seen many caps explode, most of them were my fault
But only the first cap after the rectifying diode has to be able to handle the switching frequency.
Only small values are needed there.
That could be a few ceramic caps stacked.
After the ferrite bead, normal caps can be used.
Most of these converters are 10w max.
I was more thinking of a small supply for a valve pre.
Leo..
Old 25th September 2014
  #37
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Quote:
Originally Posted by LeeYoo View Post
This, added to those cheap boost converters, seems to work ok.
Depending on parts and module, up to 300mA or so.
Ignore the part on the right of the vertical line. That's the simulated load.
But do use ferrite beads. They, plus the rail caps, lower the ripple to a few milivolts.
15.6v on L1, -15.6v on L2 and 48v on L3.
Use 25v ceramics for C1 and C3. And 50v ceramics for C5 and C7.
Smaller values can be used for higher switch frequencies/ lighter loads.
Low ESR 25v lythics or tantalum for the rest. Watch polarity.
SW comes from the switch point (anode) of the module.
+Out from the DC out. Set module to about 15.6v for P48v out with light load.
Will work between about 5v and 12v in. Tested on 7.2v lithium battery pack.
Leo..
This is nice! +-15 and +48 from a battery source! I've been following this thread with interest as well as another on the Preamp here: https://www.gearslutz.com/board/geek...caps-pots.html

I thought this might be a great way to power a portable mic preamp, but I can't figure out how to get the full 15V swing to the rails and +48V to the phantom power without the two grounds interfering with each other.

How would one go about adding this circuit to a pre similar to the one in the link?
Old 25th September 2014
  #38
Gear Head
Quote:
Originally Posted by LeeYoo View Post
...
I was more thinking of a small supply for a valve pre.
Leo..
I was gonna ask about this, because I've been wishing they made a version w/ a higher voltage range. I had it them mind as a regulator for a mic preamp and/or tube LDC mic B+ supply/bias supply.

What would you do to increase the output voltage, sit it on top of a string of HV zeners?

My requirements: An adjustable regulated B+ of 100 to 250VDC @ up to 50mA; a regulated capsule bias supply of 120VDC (miniscule current); and a 6.3V @ 300mA regulated DC filament supply. (I don't ask for much 8>)

Do you see these booster/regulators as this kind of universal building block, or am I getting carried away? 8>] I guess you could end up pushing the practical/safe design limits on these things (not that I'm unfamiliar with electronic smoke. 8>)

Dave
Old 25th September 2014
  #39
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Hi Dave.
As far as I know, there are two ways of generating a higher voltage with these cheap modules.

A: replace the coil with another one with two windings.
The main winding with the same inductance as the one on the module, and a second winding that makes the high voltage.
That can be an autotransformer (three pins).
Apart from that, you need a high voltage fast recovery diode and a high voltage cap.
Been there, done that, but it's not easy for a beginner.

B: Doubler/tripler/quadrupler... Easy.
You just need to solder an extra wire to the anode/coil/switch point of the module, and add the tripler.
With SMD components, it can be very small. See schematic and board.
Choose a module with 50volt caps and a 40volt diode. See previous posts. Use 50v caps and 40v schottky diodes for the tripler.
With a tripler (3x) on top of the existing voltage (+1), you can generate up to 160volt. More if you use more stages.
I only made a tripler for 48v so far. If you want to go higher, you're on your own. Take care. High voltage can kill...
Leo..
Attached Thumbnails
DC power source for DIY preamp-tripler.jpg   DC power source for DIY preamp-tripler_board.png  
Old 25th September 2014
  #40
Gear Head
Quote:
Originally Posted by LeeYoo View Post
Hi Dave.
As far as I know, there are two ways of generating a higher voltage with these cheap modules.

A: replace the coil with another one with two windings.
The main winding with the same inductance as the one on the module, and a second winding that makes the high voltage.
That can be an autotransformer (three pins).
Apart from that, you need a high voltage fast recovery diode and a high voltage cap.
Been there, done that, but it's not easy for a beginner.

B: Doubler/tripler/quadrupler... Easy.
You just need to solder an extra wire to the anode/coil/switch point of the module, and add the tripler.
With SMD components, it can be very small. See schematic and board.
Choose a module with 50volt caps and a 40volt diode. See previous posts. Use 50v caps and 40v schottky diodes for the tripler.
With a tripler (3x) on top of the existing voltage (+1), you can generate up to 160volt. More if you use more stages.
I only made a tripler for 48v so far. If you want to go higher, you're on your own. Take care. High voltage can kill...
Leo..
Thanks Leo - No worries about the HV, one hand in pocket always - home-built guitar amps, you know 8>]
Can you describe the 'switch point' on the module. Maybe it's obvious, but I'm never too sure with this SMD stuff. I'll take another look tomorrow...

cheers
Dave
Old 25th September 2014
  #41
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Boost converter - Wikipedia, the free encyclopedia
The diagram shows a coil, switch and diode.
The switch point is where the coil, diode and FET/IC are joined.
Find the diode with it's cathode to the +out.
The anode of that diode is the switch point.
Leo..
Old 25th September 2014
  #42
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Quote:
Originally Posted by Dathead View Post
This is nice! +-15 and +48 from a battery source! I've been following this thread with interest as well as another on the Preamp here: https://www.gearslutz.com/board/geek...caps-pots.html

I thought this might be a great way to power a portable mic preamp, but I can't figure out how to get the full 15V swing to the rails and +48V to the phantom power without the two grounds interfering with each other.

How would one go about adding this circuit to a pre similar to the one in the link?
I have made a dual 15volt/+48volt supply with a module and a doubler.
And a dual 12volt/+48volt supply with a module and a tripler.
Shared grounds ofcourse.
If you want exactly 48volt, you have to accept +/- 15.6volt.
Not a big problem I think.

Something else is brewing here in the basement as well.
Boards for a small (3"x3.2") two channel THAT mic pre are ordered.
(double sided ground plane not shown for clarity)
Onboard XLRs, 4-LED peak metering, phantom and phase switch.
The critical parts are through hole.
Hope to test drive next month.
Plans for a double guitar DI are also drawn up.
Maybe next winter.
Leo..
Attached Thumbnails
DC power source for DIY preamp-mic_pre_x2.jpg   DC power source for DIY preamp-guitar_di.jpg  
Old 25th September 2014
  #43
Gear Head
Quote:
Originally Posted by LeeYoo View Post
Boost converter - Wikipedia, the free encyclopedia
The diagram shows a coil, switch and diode.
The switch point is where the coil, diode and FET/IC are joined.
Find the diode with it's cathode to the +out.
The anode of that diode is the switch point.
Leo..
Thanks Leo

Dave
Old 25th September 2014
  #44
Gear Head
Quote:
Originally Posted by LeeYoo View Post
I have made a dual 15volt/+48volt supply with a module and a doubler.
And a dual 12volt/+48volt supply with a module and a tripler.
Shared grounds ofcourse.
If you want exactly 48volt, you have to accept +/- 15.6volt.
Not a big problem I think.

Something else is brewing here in the basement as well.
Boards for a small (3"x3.2") two channel THAT mic pre are ordered.
(double sided ground plane not shown for clarity)
Onboard XLRs, 4-LED peak metering, phantom and phase switch.
The critical parts are through hole.
Hope to test drive next month.
Plans for a double guitar DI are also drawn up.
Maybe next winter.
Leo..
Great work on the preamp. Is it portable/12V battery supply? Will you be sourcing parts and supplying a complete kit?

cheers
Dave
Old 26th September 2014
  #45
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It has been designed with low power in mind.
So it could be mains powered or battery powered with a DC/DC module.
Only parts that are not the board are the supply, the output jacks and the gain switches (or pots).
I will have some spare boards, because they come in lots of 10.
Not sure at this stage. They haven't even been made or tested yet.
Picture of the front panel I'm also milling and engraving on my CNC router.
Also on it is a DUAL out DC/DC converter that looks promising.
All you have to add to that one is the 48v tripler.
Only downside is that you have to feed it with less than 6volt, e.g. 4 penlites or one LiPo.
I would have liked to use a 7.2v LiPo pack. Maybe I'll mod that one as well some day...
The picture of the +48v test tripler shows the two connections. The +out and the switch point. Ignore the cap values.
Leo..
Attached Thumbnails
DC power source for DIY preamp-mic_x2_front.jpg   DC power source for DIY preamp-test_dc_dc.jpg  
Old 26th September 2014
  #46
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Great work Leo. Is this still essentially the same amp as depicted in this schematic

I haven't done a board in almost 2 decades. I'm an old ham and used to build boards for amateur radio projects using sharpies, press-on decals and copper chloride solution. Things sure have come a long way.

I've been messing around with some of the PCB CAD programs out there and having a lot of fun. I'm playing with some designs more along the lines of the Sound Devices MP-2 portable Preamp (one of my favorites as far as aesthetics) where the XLR ins are on the left, the outs on the right and the controls on the front.
Old 26th September 2014
  #47
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Hi Dathead.
Yes, essentially two of the same circuits, but no onboard -20db pads. Not needed with a bigger gain range and a THAT1512.
Every IC counts when on battery power, so this time also without the extra offset opamp.
Trials will tell if the offset is within the 5.25mV stated on the THAT datasheets.
I started making my first circuit boards with tiny rolls of black etch resistant masking tape and etch pens.
Later decals on UV transparent raster paper. And making my own photosensitive blanks with a spraycan and baking them in the oven.
My mother did not like that part.
Now I'm using Eaglecad. I have a love/hate relationship with it, but with a lot of manual intervention I get what I want.
Then I email the Gerbers to a place in Hong Kong.
Perfect results for peanuts. Done in a few days, but postage takes 2-3 weeks.
Biggest problems I always had was with making my projects look good (case and front).
That changed with a tabletop CNC router.
. _ .. . _ _ _
Old 26th September 2014
  #48
Gear Head
Quote:
Originally Posted by LeeYoo View Post
Hi Dathead.
Yes, essentially two of the same circuits, but no onboard -20db pads. Not needed with a bigger gain range and a THAT1512.
Every IC counts when on battery power, so this time also without the extra offset opamp.
Trials will tell if the offset is within the 5.25mV stated on the THAT datasheets.
I started making my first circuit boards with tiny rolls of black etch resistant masking tape and etch pens.
Later decals on UV transparent raster paper. And making my own photosensitive blanks with a spraycan and baking them in the oven.
My mother did not like that part.
Now I'm using Eaglecad. I have a love/hate relationship with it, but with a lot of manual intervention I get what I want.
Then I email the Gerbers to a place in Hong Kong.
Perfect results for peanuts. Done in a few days, but postage takes 2-3 weeks.
Biggest problems I always had was with making my projects look good (case and front).
That changed with a tabletop CNC router.
. _ .. . _ _ _
Hey Leo - I remember doing the spray-on UV-sensitive resist, then the boards under a 'sun lamp'. God what a lot of trouble 8>/ After that I did mainly p-to-p guitar amps and vintage-flavored stuff. If I need PCBs I just let clever guys like you do it(!) But I have to learn Eagle/CAD now anyway, for a shared project I'm doing. All for the good 8>]
cheers
Dave
Old 8th October 2014
  #49
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While trolling eBay, I found a mic preamp kit based on the AD797. Seems to be from this site:

Ad797 Mic preamp Kit

(there's a PDF schematic link near the bottom of the page)

Anyway, I was wondering if instead of using the DRV135 line driver and OPA134 servo, just feeding both sides of the balanced signal through separate amps (or both amps in a dual op-amp chip) is a better idea. Is there an advantage to going dual to single, then back to dual with the DRV135?
Old 8th October 2014
  #50
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Hi Dathead.
There are line drivers with differential inputs (THAT1606?).
Maybe you don't need a line driver for just a short run of output cable.
Beware of the phanom protection of this board (it hasn't got any).
And the rather small (value) input caps.
Google "THAT AES129" and "Analog Secrets Your Mother Never Told You" and "AES7909 48v phantom menace"
Leo
Old 9th October 2014
  #51
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Thanks Leo. Great read.

Here's the article:
http://www.thatcorp.com/datashts/Ana...r_Told_You.pdf


I didn't realize that the gain pot could cause so much swing in the output balance. I like the last line: "Trimming is complex – let us do it for you." I haven't looked at the specs of the DRV135 yet, but I assume it works similar to the THAT1646/06 in the article.

I'm aware of the lack of phantom protection; I don't intend to buy that preamp. It just caught my eye in that it did things a little differently than most. I thought it might be a better option (less parts) for a balanced-in to balanced-out amp, but I realize now that the extra parts make a difference in performance.
Old 8th November 2014
  #52
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I finally got my boards back for the voltage inverter/tripler. I had a few hours to kill tonight so I soldered one up. I think it's working, but I need a load to be sure. When I adjust for 48V, I get +28 and -28 on the rails. Here's some pics of the work so far. Not the best soldering job, but far from the worst.
Attached Thumbnails
DC power source for DIY preamp-img_20141107_162425.jpg   DC power source for DIY preamp-img_20141107_180752.jpg   DC power source for DIY preamp-img_20141107_185518.jpg   DC power source for DIY preamp-img_20141107_184634.jpg  
Old 9th November 2014
  #53
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I put some 100K resistors in the circuit for a load and I'm getting some better values: +48.2, +16.3 and -16.3; but the o-scope shows a bit more ripple than I'd like to see.
Attached Thumbnails
DC power source for DIY preamp-img_20141109_112035.jpg  
Old 9th November 2014
  #54
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Hi Dathead.
Great looking board, and I see you have it working.
What are those long square SMD parts on the board.
Is the ripple on the +48v or on the +16s.
A simple LC filter could fix this ripple.
This is HF, so small caps (100n) and small inductors or ferrite beads.
Leo..
Old 9th November 2014
  #55
Gear Head
Quote:
Originally Posted by Dathead View Post
I put some 100K resistors in the circuit for a load and I'm getting some better values: +48.2, +16.3 and -16.3; but the o-scope shows a bit more ripple than I'd like to see.
100K doesn't seem like much of a load. What kind of current are your preamps drawing?
Old 9th November 2014
  #56
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Quote:
Originally Posted by LeeYoo View Post
Hi Dathead.
Great looking board, and I see you have it working.
What are those long square SMD parts on the board.
Is the ripple on the +48v or on the +16s.
A simple LC filter could fix this ripple.
This is HF, so small caps (100n) and small inductors or ferrite beads.
Leo..
Those are SMD ferrite beads. I'm measuring the ripple on the 48V tap (5 usec/div , 50 mV/div).
Attached Thumbnails
DC power source for DIY preamp-img_20141109_152646.jpg  
Old 9th November 2014
  #57
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Quote:
Originally Posted by groovon View Post
100K doesn't seem like much of a load. What kind of current are your preamps drawing?
Well, I had some 1k resistors and some 100k. I smoked the 1k but I wasn't going to admit that unless pressed.

I don't have a preamp yet. That's my next project.
Old 24th February 2017
  #58
mtr
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Hello,
Can someone check my design dc-dc converter based on LeeYoo idea?
Attached Thumbnails
DC power source for DIY preamp-xl6009.jpg  
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