MeToo2
Well-known member
As the title says. I'm looking for a recommendation for a (line) input transformer with split center tapped secondary for use on the input of a variable mu tube compressor (approx -60V dc on the centre tap, approx +4dBm input level)
Impedance and other specs would be something like the Edcor XSM600/10K, but with a magnetic shield.
I'm currently using this Edcor transformer and the frequency response is great down to low f and high input levels, but I have traced back some undesirable low level hum and coupling to the input trannie. Currently measuring about -60dBm at the output but I'd like -70dBm or better
Yes I'll try to reduce the hum at source (suspect very strongly it's due to DC heater current rectification of a 15V AC supply for 12.6V DC heaters) so relocating mains transformer and redressing leads might be an option too that I'll look at in the meantime. Also adding some resistance to the bridge rectifier might also reduce the source.
Another alternative is to shield the existing transformer, although that could work out expensive too, without any guarantee of success.
I tried an OEP A262A3e with mu-metal shield series connected (600:25K) as a temporary test to prove where the noise coupling was (after searching all over in the HT grounding etc.). Worked absolutely fine and removed the hum entirely, but suspect it will saturate too easily at higher input levels? [spec is 1mW at 30 Hz for 1% THD]
The Jensen JT-115K-E (60) looked like the sort of thing I'd like, but it has no centre tap on the secondary.
Any recommendations of an off-the-shelf reasonably priced (±70USD) transformer for input on a vari mu?
Sowter 8540? 9062? Don't see a whole lot of love for Sowter on the DIY sites .
Lundhal LL1922 perhaps? although that's a bit more expensive.
Impedance and other specs would be something like the Edcor XSM600/10K, but with a magnetic shield.
I'm currently using this Edcor transformer and the frequency response is great down to low f and high input levels, but I have traced back some undesirable low level hum and coupling to the input trannie. Currently measuring about -60dBm at the output but I'd like -70dBm or better
Yes I'll try to reduce the hum at source (suspect very strongly it's due to DC heater current rectification of a 15V AC supply for 12.6V DC heaters) so relocating mains transformer and redressing leads might be an option too that I'll look at in the meantime. Also adding some resistance to the bridge rectifier might also reduce the source.
Another alternative is to shield the existing transformer, although that could work out expensive too, without any guarantee of success.
I tried an OEP A262A3e with mu-metal shield series connected (600:25K) as a temporary test to prove where the noise coupling was (after searching all over in the HT grounding etc.). Worked absolutely fine and removed the hum entirely, but suspect it will saturate too easily at higher input levels? [spec is 1mW at 30 Hz for 1% THD]
The Jensen JT-115K-E (60) looked like the sort of thing I'd like, but it has no centre tap on the secondary.
Any recommendations of an off-the-shelf reasonably priced (±70USD) transformer for input on a vari mu?
Sowter 8540? 9062? Don't see a whole lot of love for Sowter on the DIY sites .
Lundhal LL1922 perhaps? although that's a bit more expensive.
![Electronics Soldering Iron Kit, [Upgraded] Soldering Iron 110V 90W LCD Digital Portable Soldering Kit 180-480℃(356-896℉), Welding Tool with ON/OFF Switch, Auto-sleep, Thermostatic Design](https://m.media-amazon.com/images/I/41gRDnlyfJS._SL500_.jpg)
