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Old 18th July 2014, 07:36 AM   #1
konman is offline konman  Australia
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Default powering a class D amp with a tube pre amp. Please help.

Friend and I are building a DIY guitar amp.

We have the following parts

- 1 x300 watt sure amplifier Sure Electronics' webstore 1 X 300Watt Class-D Audio Amplifier Board - TAS5613

- tube pre amp - M-PRE - British Style Preamp Kit M-PRE - British Style Preamp Kit

the question is, what power supply should we use. We are looking at a meanwell power supply to power the amp. Also thinking of an unregulated pwoer supply, as in, a transformer to rectifier/capacitor board. This has also got me a little confused as the rectifier board outputs +,0,- voltages. Do i just connect the + and 0 voltages from the rectifier board to the class D amp? (if we were to go with this solution)

The problem (to us anyway) is powering the tube pre amp alongside the class D amp. The tube pre amp requires 12 volt, and 320 volts!.

We are relatively new at diy amps.. so any suggestions would be appreciated.

Last edited by konman; 18th July 2014 at 07:38 AM.
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Old 18th July 2014, 07:51 AM   #2
Mooly is offline Mooly  United Kingdom
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I'll delete your other thread
Installing and using LTspice. From beginner to advanced.
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Old 18th July 2014, 08:43 AM   #3
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So the tube preamp needs >300 V ( @4ma)and the 12 V for the heaters.
It's easily doable with a 50 W transformer which has the HV output and the LV one. 20 $ transformer plus the bridge rectifier, two 330 uF/ 450 V caps and a 3k3Ω resistor or better a 5-10 mH choke.
The amplifier works from 18 (12 ?) to 38 V so a SMPS 24 V DC @ 10 A
would be ok, I guess. Or...if you can find some big 24 ( 28 max) V AC transformer : then you need a bridge rectifier and about 10-20000 uF cap.
The DC after rectification and levelling is about x 1.5 the AC voltage outputted from the transformer so it should not surpass the 38 V suggested max voltage of the supply for the amplifier.
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Old 18th July 2014, 08:54 AM   #4
konman is offline konman  Australia
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Thank you.

I appreciate your response. I understand 1/3rd of what you said.

Were happy for a switch mode power supply, to power the amp, but are looking for an easy and affordable solution to power the tube pre amp, without noise etc.

Do you have a link to a specific transformer , or schematic to which we could easily put this together (for the tube pre amp?)
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Old 18th July 2014, 09:29 AM   #5
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the schematic is quite straightforward, as it represents a transformer with its primary and the two secondary windings.
The 12 V @ 1A ( how much does a single 12AX7 absorb ? multiply x 3 )
doesn't need rectification nor levelling, but it could be done also a DC heater supply...
For the high voltage, you need about 300 V AC or 150 V AC if you make a voltage doubler.

I was looking at some HK based traders but all the heaters voltages are 6.3 V!
You need 12 V.
The same manufacturer of your preamplifier offers also the PSU
PSU-PRE - Power Supply Kit for Tube Preamp
Which has one transformer for LV and one for HV; protection fuses on the primary; bridge rectifier, some resistors and caps ( no chokes)

Maybe if you can find an old tube radio which uses 12V heater supply...
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