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  #1  
Old 22nd September 2018, 12:01 PM
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Little Mick Little Mick is offline
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Default BADA PH12 head phone amp hum

Hello

I bought one of these years ago new have never used it (only for a few hours)when I first had it,having a clear out tried it the other day and noticed it has a very slight standing hum canít remember if it was like this new and is the normal, I know Stuart has extensive experience of these from previous posts, any comments advice would be appreciated.

Regards

Stuart
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  #2  
Old 22nd September 2018, 01:24 PM
Black Stuart Black Stuart is offline
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Default Re: BADA PH12 head phone amp hum

Mick,
I never had hum problems even when stock. This h/amp is worth persevering with. You had hum, please explain.The supplied Chinese tubes shouldn't be the source but try others. It should be worth doing a continuity check on all solder joints.

This amp has genuine Toshiba mosfets that don't even break into a sweat - 12.5 W / rated @ 125W. A soft start circuit, something WAD never bothered to implement.

The little fan supplied is a joke, get rid of it and don't replace the bottomplate. I was lucky living in Spain, I had a slate box made for Ä10 - no bottom and no back plate, used a Noctua fan in the base running @ 5V.

Just changing the 0.1uF and 1uFcoupling caps for K73-16 caps, shunting the pot with Z foils will shock you. The PSU caps and the power resistors can be changed for better. I mused the old Philips Blue and Mills resistors. There are signal path resistors that benefit from changing for Z foils. the h/phone socket can be changed as well. There are other mods but these are the important ones.

The beauty of this h/amp is the 6SN7 driver and o/put tubes - you can literally create the sound that you like. I use a 6F8G Tung Sol RP as driver and Russian 1578 as o/put, for me the endgame. The Toshiba mosfets will give you all the power,bass and sweet top end you could wish as o/put.

Blows away the WAD h/amp - definitely worth persevering with.
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Old 22nd September 2018, 03:29 PM
bob orbell bob orbell is offline
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Default Re: BADA PH12 head phone amp hum

But I bet it never gets close to Stax, . Bob
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  #4  
Old 22nd September 2018, 05:27 PM
colin.hepburn colin.hepburn is offline
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Default Re: BADA PH12 head phone amp hum

Canít comment on the BADA PH12 has anyone got a schematic for it as I may be thinking of building a hybrid H/amp with mosfet output over the winter or I may go for this one https://headwizememorial.wordpress.c...ic-headphones/ but using this schematic
see waarde image

Or the pmillett Wheatfield HA2
I am still using my mapletree 5751/12B4A triode h/amp I built years ago but i built it with external psu using a choke and oil caps there are no electrolytic in the amp anywhere all film caps and 1.5volts battery bias on the 5751 cathode
Attached Images
File Type: jpg Waarde (2).jpg (30.2 KB, 6 views)
File Type: jpg Orignal HD AMP.jpg (94.0 KB, 7 views)
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  #5  
Old 22nd September 2018, 05:47 PM
Black Stuart Black Stuart is offline
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Default Re: BADA PH12 head phone amp hum

Colin,
I'm just on the way out but tomorrow I'll post an Italian site that shows the layout. Very good idea to separate the power from the signal section, should be standard.

Hybrids can be the best of both worlds - don't forget to include a soft start module. ridiculous to use tubes for this, these modules can be bought cheap as chips on the net.

The Bada runs 200W, you'll need a big battery for that. Finding kosher Toshibas is difficult these days. Don't need to tell you how important a big beefy quality Tx is, potted makes sense.
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Old 25th September 2018, 10:12 AM
Black Stuart Black Stuart is offline
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Default Re: BADA PH12 head phone amp hum

Colin,
for what they cost try the K73-16 caps, I wouldn't touch PIOs ever again. I looked at the OTL you posted. Here's another idea - take a look at the Dark Voice 336, there are loads of visuals available on the web, so you can easily work out a schematic.

I was very impressed even in basic form at the soundstage it produced. As always the chassis is too small, why this obsession with cramming everything into as small a space as possible - completely irrational, especially for amps that produce a lot of heat.

The point-to-point wiring is very good and simple to replicate. The o/put caps are very important. In the D/V they are 30uF per channel, which is fine for 600 Ohm cans. If you have the skills to change the actual operating voltage at the o/put caps to 60V from 70V then this opens up the ability to use 4 x 22uF/63V K73-16 caps that greatly increase the range of cans and deepen the sound. Just a thought.

For Mick - you can raise the mains Tx from the chassis , the o/put wires are long enough. You will see that there is a big slot cut into the chassis directly over the mosfets so creating a conduction current to release the heat of the mosfets and power resistors, greatly helped of course if you have left off the bottom plate. Couple that as I do with a Noctua fan and the operating temperature is greatly reduced.

You can either suspend the Tx on vibration damping supports or use longer screws (there are 2) to support the Tx .
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  #7  
Old 25th September 2018, 05:52 PM
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Little Mick Little Mick is offline
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Default Re: BADA PH12 head phone amp hum

Hello Stuart

Thanks

Having now earthed the chassis the hum has reduced significantly,i now think although the valves are new one is very micro-phonic and could be a further cause, I built an original HD83 and it hummed badly, I shielded the mains tranny which was the cause to a reasonable effect,having had a quick listen to the ph12 it has a punchy detailed sound,i will next shunt the vol pot as you suggest I have done it many times before, as you say often with staggering results,from a little listening it does appear to get quite warm I will have to keep an eye on this it may need further attention.

Regards

Stuart
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  #8  
Old 25th September 2018, 06:43 PM
Black Stuart Black Stuart is offline
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Default Re: BADA PH12 head phone amp hum

Mick,
just remove the stupid little fan, it's a complete waste of time. If you undo the bolts that hold the mains TX you will be able to lift the tranny, that immediately allows the cut-outs above the 2 Toshibas to exit the heat.
If you ditch the first and second caps - 0.1uF & 1uf coupling caps and use K73-16 ones you will be gobsmacked I promise you.

There's a lot of schlerotics on this forum who can't bring themselves to shell out for Z foils - they will out live yo. Use these to shunt the pot and the K73-16 caps - you won't believe your ears.

I bought some little PCBs to use on the Alps, I have spares, if you want to use one for the shunt, they make life very easy, let me know by PM and I'll send you one.

I wouldn't remove the PCB to do these changes just cut the legs of the existing caps and solder to these, when your happy and if and when you choose to do other changes then you will have to remove the PCB.

THIS IS VERY INPORTANT - Do not try to tube roll with the Bada, it's a no-no - use one set per listening session.
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