luckily I have 2 SRD7s. one modded, one stock. so I did some further tests this time with a more detailed side panel and some comparisons.
I don't trust that my instrument (R&S UPD from late 80s) has super accuracy when measuring impedance for non standard speaker Items. it goes up to only 600ohms and is only extremely accurate below 50 ohms and starts to very upwards from that and its sat for ages without service calibration. but it definitely is enough to show acceptable correlation. I did see this in measurements of other devices I did and compared to what can be found online which were quite accurately comparable. and the graph here just seems worlds apart from mine. Don't know what's the explanation for such.
here are the results:
INPUT Z
Modded SRD7 with SR303 headphones (set as REF for comparison on the faded trace and dB deviation scale on right side):
Modded SRD7 without any headphones pugged in:
Stock SRD7 with SR303 headphones:
I don't trust that my instrument (R&S UPD from late 80s) has super accuracy when measuring impedance for non standard speaker Items. it goes up to only 600ohms and is only extremely accurate below 50 ohms and starts to very upwards from that and its sat for ages without service calibration. but it definitely is enough to show acceptable correlation. I did see this in measurements of other devices I did and compared to what can be found online which were quite accurately comparable. and the graph here just seems worlds apart from mine. Don't know what's the explanation for such.
here are the results:
INPUT Z
Modded SRD7 with SR303 headphones (set as REF for comparison on the faded trace and dB deviation scale on right side):
Modded SRD7 without any headphones pugged in:
Stock SRD7 with SR303 headphones:
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Registered to share that I modded my SRD-7 MK2. Can confirm the MK2 has two 10Ohm thermistors in parallel for each channel unlike the MK1 with a single 4.7Ohm. I just replaced them with a single 4.7Ohm 5W resistor for each channel and it seems to be working fine. Also interestingly the 27Ohm resistor that the MK1 has is missing on the MK2. I didn't add one, should I?
Also what is the best way to measure bias? If I measure from bias to the chassis I get about 330V instead of 580V. Are the caps in my bias circuit going bad perhaps?
Also what is the best way to measure bias? If I measure from bias to the chassis I get about 330V instead of 580V. Are the caps in my bias circuit going bad perhaps?
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Sorry for the delayed reply, I've been taking a break from audio. If those resistors have magnetic material in the body (most do), I'd bend the leads upward to get them both as far away from the xfmrs as possible.
Yes.
Measure it before the series resistor.