I recently managed to obtain some pairs of Tamura STU-001 (150:100K) input transformers that were ubiquitous in Sakuma-san’s designs.
I’m trying to think of where is the best place to add a potentiometer to these designs? Probably after the secondary of the STU-001 to the tube’s grid?
I want a really simple, straightforward setup, DAC (2Vrms output, very low output impedance) -> amp with input transformers + volume pot. No preamp involved.
Any insight would be much appreciated.
Thank you!
I’m trying to think of where is the best place to add a potentiometer to these designs? Probably after the secondary of the STU-001 to the tube’s grid?
I want a really simple, straightforward setup, DAC (2Vrms output, very low output impedance) -> amp with input transformers + volume pot. No preamp involved.
Any insight would be much appreciated.
Thank you!
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On the output seems logical - keeps loading constant for the transformer (and actually loads it of course, so use 100k pot).
I agree. Also use a lower pot resistance, so you flat the bandpass response. Leaving the trafo unloaded make the resonance of it very sharp.
I normally try to use a zobel after input transformers, or if not desirable a load of about 0.8x of rated output loading. This means for a typical 600:10k SUT used as a 150:10K 1:8 gain ratio, the apparent input load is around 120 ohms.
For most headphone style outputs this is a non-issue. Regular DACs with line outputs have problems driving it, even if their output impedance is low. There is significant degradation in the sound quality.
For most headphone style outputs this is a non-issue. Regular DACs with line outputs have problems driving it, even if their output impedance is low. There is significant degradation in the sound quality.
Yes, low output impedance does not necessarily include the ability to drive an unusually low impedance load. For that you also need low minimum load impedance. A typical source may say something like '100 ohms output impedance, minimum load 10k'.
this is very special sakuma design, he used stepup tr to add more gain.
150:100k= 1:25
which is like 9/230v tr backwards... you need strong signal source to drive this.
something like dac+small amp. not only on bass freq, this small winding will look like almost short. not a big inductance.
dac alone will not drive that....
The second issue with this sort of a setup is transformer loading and voltage swing into a given load.
Though this may not be a problem in this case, there is a limit to how much the secondary side can actually swing into a given load. High ratio transformers are usually employed for MC, MM or microphone preamplifiers where the expected input signal is very small and output signal is moderate, or line level at the most.
This sort of transformer will distort badly when used with a line level input. You need to verify what the actual application is. The few references I found either said nothing or specified it as a MC input SUT.
Though this may not be a problem in this case, there is a limit to how much the secondary side can actually swing into a given load. High ratio transformers are usually employed for MC, MM or microphone preamplifiers where the expected input signal is very small and output signal is moderate, or line level at the most.
This sort of transformer will distort badly when used with a line level input. You need to verify what the actual application is. The few references I found either said nothing or specified it as a MC input SUT.
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