thermionic
Well-known member
- Joined
- Jun 3, 2004
- Messages
- 1,671
Hi,
I’ve fitted some Sowter 3603 transformers to the outputs of a 6-channel Phono preamp.
The preamp works fine and – although I haven’t measured the output impedance – I know it’s happy to drive loads down to around 200 Ohms without major issues (output drivers are BC461).
With an incorrectly terminated transformer, you usually expect to see “ringing”, creating spikes in the upper Khz region – famously noted by the Rupert Neve / Geoff Emerick story, where Emerick noted the artefacts from an incorrectly terminated transformer ringing at 54K.
In my case, I have the opposite… Instead of a rising HF response, an FFT suggests nearly 2dB roll-off by 20K compared to without the transformer. I have spoken with Brian Sowter and he thought the issue somewhat odd. He told me I shouldn’t need to terminate the 3603, but I could experiment with a 10K variable resistor if I wanted to.
When I listen to the preamp, the bass seems more bloated than without transformer (not that unusual – transformers in general are known for exaggerating bass), the HF slightly duller – but the most noticeable behaviour – from a subjective POV – is a kind of “pumping”, slightly like a poorly aligned Dolby NR system, but subtler…
I could be imagining this, but the HF seems to “pump” in sympathy with the slightly “bloated” bass… I can well imagine some people to like this sound for harsh-sounding pressings as it’s quite subtle, but I’d like to figure out what’s going on here.
The PSU is overrated btw, and could supply many preamps of this type.
My main issue is that the sound with the transformers seems to lack the “speed” you get when you bypass the transformers… Anyone got an idea as to what’s going on?
It should be noted that the preamp’s output is fixed at 300mV (from a 4mV cartridge), so there’s no chance of overloading the transformer - and it should also be noted that there’s absolutely no chance of any of the transformers being subject to DC (fed from a cap – DC measured) – all 6 preamps sound identical.
Here’s the Sowter data sheet: http://www.sowter.co.uk/pdf/3603.pdf
Thanks in advance.
Justin
I’ve fitted some Sowter 3603 transformers to the outputs of a 6-channel Phono preamp.
The preamp works fine and – although I haven’t measured the output impedance – I know it’s happy to drive loads down to around 200 Ohms without major issues (output drivers are BC461).
With an incorrectly terminated transformer, you usually expect to see “ringing”, creating spikes in the upper Khz region – famously noted by the Rupert Neve / Geoff Emerick story, where Emerick noted the artefacts from an incorrectly terminated transformer ringing at 54K.
In my case, I have the opposite… Instead of a rising HF response, an FFT suggests nearly 2dB roll-off by 20K compared to without the transformer. I have spoken with Brian Sowter and he thought the issue somewhat odd. He told me I shouldn’t need to terminate the 3603, but I could experiment with a 10K variable resistor if I wanted to.
When I listen to the preamp, the bass seems more bloated than without transformer (not that unusual – transformers in general are known for exaggerating bass), the HF slightly duller – but the most noticeable behaviour – from a subjective POV – is a kind of “pumping”, slightly like a poorly aligned Dolby NR system, but subtler…
I could be imagining this, but the HF seems to “pump” in sympathy with the slightly “bloated” bass… I can well imagine some people to like this sound for harsh-sounding pressings as it’s quite subtle, but I’d like to figure out what’s going on here.
The PSU is overrated btw, and could supply many preamps of this type.
My main issue is that the sound with the transformers seems to lack the “speed” you get when you bypass the transformers… Anyone got an idea as to what’s going on?
It should be noted that the preamp’s output is fixed at 300mV (from a 4mV cartridge), so there’s no chance of overloading the transformer - and it should also be noted that there’s absolutely no chance of any of the transformers being subject to DC (fed from a cap – DC measured) – all 6 preamps sound identical.
Here’s the Sowter data sheet: http://www.sowter.co.uk/pdf/3603.pdf
Thanks in advance.
Justin
