sampleaccurate wrote:
switched mode power supply
HI.
That exactly what I thought it is. I just want to you to confirm to me.
The last PS I would use to power any audio amps is switch mode, a hugh generator of RFI, let alone heating tubes.
Here what I am using to power the 6.3V tube heaters of my tube phonostages:- a digital power pack comprising a 6V sealed lead acid cell, rechargeable by a 7.5V SMPS.
Yes, I've chosen SMPS for its
constant regulated voltage O/P, extremely efficient, cool running &
very small size. I scrapped the SMPS board from a redundant charger sleeping in my parts bin & used it to build an small outboard 6.3V heater pure DC power pack for my phonostages.
So pure DC heating means no hum from the tube heaters/filaments, which is crucial for DHT like 300B & the likes. I have the heater circuit
floated from the phonostage circuit to ensure zero ground loop from the PS.
Knowing SMPS is a well-known RFI generator, it must be
100% isolated from any audio circuitry, including their AC powerlines. To ensure no RFI generated from the digital power pack affecting my auido rig, I've so design/built this digital heater power pack that when the SLA cell inside the power pack is heating the tube heaters when I am playing LPs, the digital charger is always switched off & electrically 100% isolated from the SLA cell.
Under no circumstances the digital charger & the SLA cell work at the same time by proper switching circuitry incorporated in the power pack, which is built in a small plastic equipment box, 7.5" x 3.5" x 2.5". Thanks to the miniature 7.5V 4ADC digital PS board, only 2.5" x 2". which permitted me to build the entire PS (digital charging board + 6V SLA cell + all switching gears, LED indictors & voltage measuring points etc etc) in such a small box !!!!
To further ensure no RFI leaking via its AC powre cord & battery DC cables hooked up to the phonostages, they both have RFI ring suppressor snapped on.
I enjoy the pure DC heating sound let alone cute looking of the small power pack, which sits right beside my super-upgraged Dynaco PS-2 pre-amp.
c-J
PS: IMO, you are playing with (RFI) fire !
The Oddwatt amps on this website feature switched mode power supplies for the heaters and everyone who has built one seems satisfied with it.
When I put my scope on the amp I'll know exactly how much and exactly what kind (if any) of RFI is leaking into my amp from the SMPS. I'll let you know the results.
Your solution to the RFI "problem" sounds quite clever, although slightly elaborate. If the SMPS is indeed making noise I'll take steps to eliminate it.