Low cost compact power supply for sub-mini tube preamp

johnmac0117 · 30th April 2011, 11:22 PM

Hi, I'm interested in building a guitar tube preamp using sub-mini tubes. Some are max plate 60V and some are 165V. Any thoughts on the best approach for compact low cost power supplies for these two different voltages (two different projects, so a 60V PS for one, and a 165V PS for the other). The power supplies need to be compact as they need to fit into guitar pedals, and they need to be low cost otherwise I might as well use a lower voltage tube to start with. Thanks in advance for any thoughts.

mastodon · 2nd May 2011, 09:37 AM

Due to the limited space, you might try something like this: heesch.net - Schaltnetzteil für Röhren It's a small form-factor and very simple SMPS using a microcontroller to generate the switching frequency and to drive the switching mosfet. You can easily adapt the design to your needs by adjusting the transformation ratio (you'll probably wind the transformer yourself anyway).

johnmac0117 · 2nd May 2011, 03:53 PM

Hi Mastodon,
That looks interesting. I don't speak German, but I used Google Translate to read the website, it's not perfect, but I get the idea, with the schematic as well.
Not sure about the transformer pot core though, I haven't wound my own before.
Have you built this circuit yourself? Can you specify a suitable pot core? Maybe a supplier as well if you know one :-)
Thanks for your time. John

Boofers · 2nd May 2011, 04:11 PM

If you put 120VAC straight to a bridge rectifier and filter cap you end up with around 170VDC. You could then use series resistor and second filter cap to drop the voltage down to 65VDC. Just make sure you fuse the 120VAC lol.

johnmac0117 · 2nd May 2011, 04:30 PM

Quote:

Originally Posted by Boofers

If you put 120VAC straight to a bridge rectifier and filter cap you end up with around 170VDC. You could then use series resistor and second filter cap to drop the voltage down to 65VDC. Just make sure you fuse the 120VAC lol.

Hi Boofers
Slight problem there, I live in the UK & the mains voltage is 240VAC!

Boofers · 2nd May 2011, 07:14 PM

Quote:

Originally Posted by johnmac0117

Hi Boofers
Slight problem there, I live in the UK & the mains voltage is 240VAC!

I see... Move to Canada? LOL. I guess that a step down transformer will take up too much space for you?

alfiax · 2nd May 2011, 07:22 PM

If you put 120VAC straight to a bridge rectifier and filter cap you end up with around 170VDC. You could then use series resistor and second filter cap to drop the voltage down to 65VDC. Just make sure you fuse the 120VAC lol.

No no no no no no no no no no no no no no no no no no bad bad bad. Transformer isolation or nothing. I don't think whoever finds you will be loling while he/she breaks your ribs in a (futile) attempt to get your heart started again.

Boofers · 2nd May 2011, 08:06 PM

Quote:

Originally Posted by alfiax

No no no no no no no no no no no no no no no no no no bad bad bad. Transformer isolation or nothing. I don't think whoever finds you will be loling while he/she breaks your ribs in a (futile) attempt to get your heart started again.

If you have a 1:1 isolation transformer you'll still have the risk of 120VAC on the secondary.

alfiax · 2nd May 2011, 08:25 PM

120 VAC on the secondary, yes, but 120 isolated VAC which will not form a circuit through you if you become connected to ground. Isolation is an absolute requirement for any line-powered DIY device.

Boofers · 2nd May 2011, 10:16 PM

Hey I agree safety first always, but most amps still have the common on the secondary tied to earth/chassis.

30th April 2011, 11:22 PM	#1
johnmac0117 diyAudio Member Join Date: Mar 2011	Low cost compact power supply for sub-mini tube preamp Hi, I'm interested in building a guitar tube preamp using sub-mini tubes. Some are max plate 60V and some are 165V. Any thoughts on the best approach for compact low cost power supplies for these two different voltages (two different projects, so a 60V PS for one, and a 165V PS for the other). The power supplies need to be compact as they need to fit into guitar pedals, and they need to be low cost otherwise I might as well use a lower voltage tube to start with. Thanks in advance for any thoughts.

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2nd May 2011, 09:37 AM	#2
mastodon diyAudio Member Join Date: Jan 2011	Due to the limited space, you might try something like this: heesch.net - Schaltnetzteil für Röhren It's a small form-factor and very simple SMPS using a microcontroller to generate the switching frequency and to drive the switching mosfet. You can easily adapt the design to your needs by adjusting the transformation ratio (you'll probably wind the transformer yourself anyway).

2nd May 2011, 03:53 PM	#3
johnmac0117 diyAudio Member Join Date: Mar 2011	Hi Mastodon, That looks interesting. I don't speak German, but I used Google Translate to read the website, it's not perfect, but I get the idea, with the schematic as well. Not sure about the transformer pot core though, I haven't wound my own before. Have you built this circuit yourself? Can you specify a suitable pot core? Maybe a supplier as well if you know one :-) Thanks for your time. John

2nd May 2011, 04:11 PM	#4
Boofers diyAudio Member Join Date: Oct 2008 Location: Ontario Blog Entries: 1	If you put 120VAC straight to a bridge rectifier and filter cap you end up with around 170VDC. You could then use series resistor and second filter cap to drop the voltage down to 65VDC. Just make sure you fuse the 120VAC lol.

2nd May 2011, 07:22 PM	#7
alfiax diyAudio Member Join Date: Oct 2005	If you put 120VAC straight to a bridge rectifier and filter cap you end up with around 170VDC. You could then use series resistor and second filter cap to drop the voltage down to 65VDC. Just make sure you fuse the 120VAC lol. No no no no no no no no no no no no no no no no no no bad bad bad. Transformer isolation or nothing. I don't think whoever finds you will be loling while he/she breaks your ribs in a (futile) attempt to get your heart started again.

2nd May 2011, 08:25 PM	#9
alfiax diyAudio Member Join Date: Oct 2005	120 VAC on the secondary, yes, but 120 isolated VAC which will not form a circuit through you if you become connected to ground. Isolation is an absolute requirement for any line-powered DIY device.

2nd May 2011, 10:16 PM	#10
Boofers diyAudio Member Join Date: Oct 2008 Location: Ontario Blog Entries: 1	Hey I agree safety first always, but most amps still have the common on the secondary tied to earth/chassis.

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