Technics RS-B965
- Thread starter Alex SE
- Start date
I'm on my phone traveling, I'll try to find time to download the service manual on desktop once I get home and look. But I haven't owned a cassette in years and never had a real deck, so don't know much about them.
"Fr" may be frequency response.
My experience using soundcard based testing software leaves me wondering how accurate it really is.
If you need a oscilloscope to test this, now might be a good excuse to get one and learn how to use it.
"Fr" may be frequency response.
My experience using soundcard based testing software leaves me wondering how accurate it really is.
If you need a oscilloscope to test this, now might be a good excuse to get one and learn how to use it.
yes, VR301 and VR302 are the bias trimpots (overall frequency response) while for example VR5 and VR6 are Rec gain trimpots (overall gain adj.)
Technics manuals use the word "overall" for the recording parameters, also on the older models from the RS-M series.
And i understand this word "overall" can be confusing.
the PB freq. response needs to change parts values to be modified, for example.
Technics manuals use the word "overall" for the recording parameters, also on the older models from the RS-M series.
And i understand this word "overall" can be confusing.
the PB freq. response needs to change parts values to be modified, for example.
Actually, I am not able to reply to this... simply because both of my 965 were modified by Alex himself.
What I do know for sure is that both of my 965 play and record just lovely.
Anyways, the above plot shared by Alex, from an untouched 965 in source mode, shows only about half dB roll-off from 100Hz down to 20Hz and less than half dB roll-off from 20Khz to 40Khz.
While your plots at the beginning of this thread show several dBs of roll-off from about 300Hz down to 20Hz which, IMHO, would be easily noticeable by ears if that measurement plot is what actually happens into your 965 decks.
So, do you also feel that lack of bass by ears or are you only seeing it while measuring?
What I do know for sure is that both of my 965 play and record just lovely.
Anyways, the above plot shared by Alex, from an untouched 965 in source mode, shows only about half dB roll-off from 100Hz down to 20Hz and less than half dB roll-off from 20Khz to 40Khz.
While your plots at the beginning of this thread show several dBs of roll-off from about 300Hz down to 20Hz which, IMHO, would be easily noticeable by ears if that measurement plot is what actually happens into your 965 decks.
So, do you also feel that lack of bass by ears or are you only seeing it while measuring?
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Crazy. Isn't it?
Level at decks is slightly lower then level at soundcard, it doesn't matter.
Loop at card in/out is a little bit higher (0.5db) over the 800Hz, doesn't matter too.
727 is about 2 db lower up to, say, 800Hz, not a big deal (not huge in any case).
965 is about 13db lower than soundcard loop up to 800Hz and about 11db lower than 727. Not a big deal. It's a disaster! It have to be something that is killing low frequencies. Some capacitor or I don't know what.
Level at decks is slightly lower then level at soundcard, it doesn't matter.
Loop at card in/out is a little bit higher (0.5db) over the 800Hz, doesn't matter too.
727 is about 2 db lower up to, say, 800Hz, not a big deal (not huge in any case).
965 is about 13db lower than soundcard loop up to 800Hz and about 11db lower than 727. Not a big deal. It's a disaster! It have to be something that is killing low frequencies. Some capacitor or I don't know what.
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Alex SE.... this latter plot of yours is making me thinking about something else...
Don't know if what I am going to say here can apply or not... but I remember such kind of filtering on the bass while experimenting with some external filters added at decks' inputs and outputs to be able to record Cr tapes at 120microseconds (as suggested by Alex/ANT at that other place in the past) when decks used to have different input or output impedances...
I understand that, maybe, impedance mismatches between devices should only change the levels but, hey, if there is some kind of (unwanted) capacitance in the middle then also the response will change and, usually, just with similar shapes as you are showing there in your latest plot, making the impedance mismatches joined with some capacitance acting just like EQ filters.
At this point, it might be interesting to measure the input and output impedances of your soundcard and your decks.
Anyways, it's just a wild guess... because, really, I don't know which your exact problem actually is.
Don't know if what I am going to say here can apply or not... but I remember such kind of filtering on the bass while experimenting with some external filters added at decks' inputs and outputs to be able to record Cr tapes at 120microseconds (as suggested by Alex/ANT at that other place in the past) when decks used to have different input or output impedances...
I understand that, maybe, impedance mismatches between devices should only change the levels but, hey, if there is some kind of (unwanted) capacitance in the middle then also the response will change and, usually, just with similar shapes as you are showing there in your latest plot, making the impedance mismatches joined with some capacitance acting just like EQ filters.
At this point, it might be interesting to measure the input and output impedances of your soundcard and your decks.
Anyways, it's just a wild guess... because, really, I don't know which your exact problem actually is.
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An now something really weird:
When I go to Set up for sweep testing (see picture) and choose "Mono, right/left ch. ref" instead for "Stereo, no ch. ref.", results are totally different. Interesting is that signal have always the same level no matter how I turn Rec level potentiometer on a deck. What is to be trusted?
When I go to Set up for sweep testing (see picture) and choose "Mono, right/left ch. ref" instead for "Stereo, no ch. ref.", results are totally different. Interesting is that signal have always the same level no matter how I turn Rec level potentiometer on a deck. What is to be trusted?
That's what I have posted in #33. Question is only if that measurements are relevant/correct. Differences between frequencies +/-1db are OK for me. Doesn't have to be ruler flat, within 1db I think it's OK.
As I said, question is only if last measuring I did is correct.
One more thing. RS-BX727 have 5.2 kOhms on output, 965 have 100Ohms (when turned off). Is it possible that it can be such a difference? Should I measure when decks are on?
As I said, question is only if last measuring I did is correct.
One more thing. RS-BX727 have 5.2 kOhms on output, 965 have 100Ohms (when turned off). Is it possible that it can be such a difference? Should I measure when decks are on?
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Depends on if you've calibrated the software to your sound card output voltage. This is normally mV. One of the reasons I use REW software is it auto calibrates to the soundcards mV output. Of course I check this with a 60 Hz test tone (U.S.) and a voltmeter. If all parameters are properly set such as bit depth, windows sound settings, etc, and software voltage calibration, then that's as good as it gets. Is it somewhat accurate? Probably good enough for home use. Laboratory accurate? Don't think so, maybe probably close enough.
Best we can do is try different software and compare, or spend big bucks for real equipment.
Best we can do is try different software and compare, or spend big bucks for real equipment.
This is one of the issues why I use REW, and I have searched for the answer many times, finally got that part working, but it was a good while ago. ARTA is very similar. Pretty sure the voltage calibration determines how far from the 0 dB line the generated traces are drawn. Right now this isn't a real issue for you, as your just doing comparisons. You can work on this later
The real issue for you is not to under drive or over drive the unit with the built in tone generator output. Luckily you should have built in VU meters so you can monitor the level and adjust the tone generator output to a good usable level as shown by your meters.
For comparison, on the Phase Linear preamps I was working on last several months, I was using a 142 mV 2 kHz sine wave tone to do spectrum analysis. That seemed to be comparable to the 18 Db sweep function that REW has built in.
But you'll have to experiment. Set your tone generator output low, all potentiometers on the unit as normal, and do a sweep watching the VU meters. Bring the mV up until the meters look good. There you go.
I'm working today, have to run.
The real issue for you is not to under drive or over drive the unit with the built in tone generator output. Luckily you should have built in VU meters so you can monitor the level and adjust the tone generator output to a good usable level as shown by your meters.
For comparison, on the Phase Linear preamps I was working on last several months, I was using a 142 mV 2 kHz sine wave tone to do spectrum analysis. That seemed to be comparable to the 18 Db sweep function that REW has built in.
But you'll have to experiment. Set your tone generator output low, all potentiometers on the unit as normal, and do a sweep watching the VU meters. Bring the mV up until the meters look good. There you go.
I'm working today, have to run.