Bada Ph12 headphone amp rebuild idea

pftrvlr · 12th May 2007, 03:57 AM

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?

pftrvlr · 12th May 2007, 07:48 PM

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?

xaviery · 12th May 2007, 08:21 PM

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.

pftrvlr · 13th May 2007, 04:36 PM

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,

Black Stuart · 26th February 2008, 11:34 AM

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.

pftrvlr · 27th February 2008, 02:54 AM

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.

26th February 2008, 11:34 AM	#5
Black Stuart diyAudio Member Join Date: Aug 2005 Location: Aveyron	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. __________________ Black Stuart

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12th May 2007, 07:48 PM	#2
pftrvlr diyAudio Member Join Date: Feb 2007 Location: SoCal	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?

12th May 2007, 08:21 PM	#3
xaviery diyAudio Member Join Date: May 2007	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.

13th May 2007, 04:36 PM	#4
pftrvlr diyAudio Member Join Date: Feb 2007 Location: SoCal	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,

27th February 2008, 02:54 AM	#6
pftrvlr diyAudio Member Join Date: Feb 2007 Location: SoCal	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.