Hello
The phono socket is a miniature type from RS components part number 411-071 I have attached the PDF datafile for you. There are 2 types gold plated or nickel plated .. I used nickel because the gold version was out of stock. also this size phono socket fits this size PCB very well .. normally I use a standard size socket for large PCB designs. Plus I was building a test bed for this amp to make sure all was OK before I commit to a full size finished case
Ok a few pics of my little test bench before I commit to an expensive case, just to make sure all is ok. I have used a 300va 35v 0v 35v secondary winding toroidal transformer (5 amps on the sec) have used a k4700 protection module modified for single channel heavy duty. And a power supply that I have used for years with very good results and a old pair of nos MOSFETS .. please remember this is work in progress and not completed 100% yet will also add a earth lift switch to stop ground loops etc
Attachments
Hi all,
I recapped my old monoblocks while looking a little at this thread.
There's probably room for improvement, so I thought I'd show the amp..
I changed the stoppers to 220R.
Put in 470u low ESR caps.
Changed feedback cap to a Muse bipolar 47uF
Changed the input cap (used to be 1uF) to a 10uF poly (The input cap and 2.2k res are swapped to fit them onto the board).
Changed earthing to star in front of the board
Changed L1 from 10 turns to 15 (bifilar due to wire constraints).
Bias twiddle (clamp ammeter on the thick red wire) to 100mA
Some of the documentation varies... the original design has L1 10 turns and speaker ground to the main cap centers, and a 50mA bias..
Here:
Mosfet Amplifier (EMM Jun 81)
But the article in the thread states 15 turns for L1. I doubt it's critical..
The PSU is a soft start, but it's not big on fuses
. I designed and built it a while ago. I has an 'instant start' voltage reference, and only closes the relays (usually resistors feed the bridges) when the PSU voltage is close to what it should be. In this way it is safe to powercuts etc.
So the big caps go to the power mosfets only, the driver has it's own PSU. The idea was to help dynamics. It appears I liked caps back then, perhaps they were cheaper too
With the new changes, if I plug an DAC directly in (The brilliant Apple USB-C headphone adapter) it's perfect, very nice, silent as needed...
... But if I use an old Proton pre-amp I get some mains buzz - I need to investigate that, as i don't notice any problem individually.
I doubt it's an earth loop as mains earth currently comes in via a 4.7R resistor (that I had spare - please advice the best earth decoupling method), and persists even when the amp is switched off.
Cheers.
I recapped my old monoblocks while looking a little at this thread.
There's probably room for improvement, so I thought I'd show the amp..
I changed the stoppers to 220R.
Put in 470u low ESR caps.
Changed feedback cap to a Muse bipolar 47uF
Changed the input cap (used to be 1uF) to a 10uF poly (The input cap and 2.2k res are swapped to fit them onto the board).
Changed earthing to star in front of the board
Changed L1 from 10 turns to 15 (bifilar due to wire constraints).
Bias twiddle (clamp ammeter on the thick red wire) to 100mA
Some of the documentation varies... the original design has L1 10 turns and speaker ground to the main cap centers, and a 50mA bias..
Here:
Mosfet Amplifier (EMM Jun 81)
But the article in the thread states 15 turns for L1. I doubt it's critical..
The PSU is a soft start, but it's not big on fuses
. I designed and built it a while ago. I has an 'instant start' voltage reference, and only closes the relays (usually resistors feed the bridges) when the PSU voltage is close to what it should be. In this way it is safe to powercuts etc. So the big caps go to the power mosfets only, the driver has it's own PSU. The idea was to help dynamics. It appears I liked caps back then, perhaps they were cheaper too
With the new changes, if I plug an DAC directly in (The brilliant Apple USB-C headphone adapter) it's perfect, very nice, silent as needed...
... But if I use an old Proton pre-amp I get some mains buzz - I need to investigate that, as i don't notice any problem individually.
I doubt it's an earth loop as mains earth currently comes in via a 4.7R resistor (that I had spare - please advice the best earth decoupling method), and persists even when the amp is switched off.
Cheers.
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