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Old 12th May 2007, 04:57 AM   #1
pftrvlr is offline pftrvlr  United States
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Default Bada Ph12 headphone amp rebuild idea

I have a hybrid Bada ph12 headphone amp with blown MOSFET, which I want to rebuil/mod. I don't want to deal with MOSFET any more. I am going to rebuilt it as all tubes.

The ph12 has three 6SN7 mounte on PCB. B+ power supply is 230v. Heater are from 3 7806 regulators.

I want to re-use as much as possible what is on the PCB. Any suggestions?
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Old 12th May 2007, 08:48 PM   #2
pftrvlr is offline pftrvlr  United States
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OK, I did a quick test today to connect my HT600 headphone dirctly to the 2.2uf cathode follower output capacitor, and I got loud enough volume - about 11:00 o'clock for normal listening.

So if I replace the 2.2uf CF output cap with a larger one, it should be OK for my high impedence headphone.

To get more amp to headphone. I am thinking to put a small output transformer between the CF and headphone. Anyone has a schematic for a parafeed tranny?
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Old 12th May 2007, 09:21 PM   #3
xaviery is offline xaviery  France
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If you want to increase output power with 100% tubes, two ways can be studied:

The first solution: add grid coupling capacitor betweem u7 and u8, convert ub8 into a commun-cathod amplifier, add a transformer in the anode to adapt any headphone impedance.

The second solution: don't touch the three present tubes, just add one extra tube as last stage amplifer with transformer. The impedance of the transformer will be defined by the added tube.
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Old 13th May 2007, 05:36 PM   #4
pftrvlr is offline pftrvlr  United States
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All I need for 300 ohm headphone is 3v-10ma output. I am thinking I can skip the CF and add output transformer to U7 stage.

Thanks,
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Old 26th February 2008, 12:34 PM   #5
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I have a Bada PH12, which I find with a few mods to be excellant, however as I will be moving to somewhere that I won´t have neighbours to molest with my sound system, a h/amp is not something i will require in the future, so this is what I propose to do - turn it into a power amp.

My only experience up to now is with all valve amps, so what I am proposing maybe a non-starter.

As I understand it - the output of the mosfets (rated at 125W each) are dictated by the paralleled resistors in front of them.

These presently total 200 Ohms per side - if I want to have an output of 20-25W per channel what value do I need to change these resistors to?

I also intend to use Welwyn W23/9W wirewounds so they will total 36W per channel. I will fix PC coolers to the aluminium top plate, to which the mosfets are already screwed and as I already use a Papst fan for cooling, which is very effective, I forsee no problems there apart from fitting speaker binding posts - what other changes do I need to make.

I also intend to use some exotic caps, which will later be used in the Moskido that I shall build. This project I think is a good way for me to get to understand hybrid amps.

Looking forward to answers as if the Bada sounds as good as a power amp as it does as a h/amp then it will mean no more all valve amps for me.
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Old 27th February 2008, 03:54 AM   #6
pftrvlr is offline pftrvlr  United States
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After a few iteration, my current PH12 is all tube head amp:

one 6SN7 common cathode direct coupled to two 6BX7 white cathode follower

Not my favorite one - none of my WCF amp is my favorite - but I have a lot of tubes I can roll.
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