Adjusting signal with resistor

Alex SE

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#21
Yes, with 200nWb tape I have 245mV on Dolby chip and if I remember correct more than 570mV on output instead of 545mV.
Will do as Skywavebe said, that will fix the problem.
 

Makymak

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#22
My two cents: don't mess with the meters circuit. You should find out why your output is higher than it should be. It has to be something with the ic 5 & 6. Fix this and I bet your meters will show correctly. Do both your RS-B965 act the same?

I have two of these and no one has the problem you describe. I have over 10 Technics decks and all give me ~545mV output at Dolby level. And all of them are modified with ANT's "prescription".
 

Alex SE

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#23
Both 965 have the same mods, one is peaking to +5 the other to +6 if I remember correct. Both have NJM2114 for IC5 and IC6, and it was the same with NE5534. There is nothing between Dolby IC and IC5/IC6 than can be a problem.
 

Alex SE

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#25
Have replaced R41 and R42 with trimmers and adjusted output to 545mV using ANT test tape (200nWb), which is equal to 400mV with 160nWb as stated in SM. Peak meters are at +4db instead of +3db. Interesting thing is that resistance on those 2 trimmers is 10.80k and 11.75K (10k from factory). And yes, Dolby level is 245mV (oscillating +/-3mV)

Regarding resistors, they are removed. That way it doesn't matter if you are using single channel 5534 or dual channel 5532 or 2114. A-class is "disabled" by removing those resistors as they are responsible for "digital" color of sound, IARC.
 

Makymak

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#26
Indeed, there is nothing between trimmer vr3 & vr4 and ic5 & ic6 inputs to be a problem. So, if you have 245mV at Dolby then the level arrives correct at njm2114 (ic5 & 6). I'm not an electronics engineer so I can't calculate the impact of the resistors removed, on paper; I go try and error, have to say. If I were in your case, I would try to reset ic5 & 6 circuit at the factory state (re soldering r31, r32, r37, r38) and starting from the beginning. Not a chance I want to be offensive and I definitely don't question your knowledge but it's quite strange both decks act the same when neither should. If it was only one, I could accept it's something else but since it's both of them, it must have to do with the mods. Sometimes, the simplest way is the best!
 

Makymak

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#27
Update:

I was curious about the above so I replicated your mod. Yes, it makes no difference. My levels are the same with either the ne5534 or the njm2114.

More interesting: I recalibrated my decks with ANT's test tape and I took these interesting measures:

RS-TR333 (x3), RS-B565, RS-B655, RS-B665, RS-BX606, RS-BX707, RS-BX808.... 545mV output, meters spot on

RS-B755, RS-B965 (x2).... 600mV output, meters on +4dB.

Something is wrong with the design of the 755 and 965. In first place I suspected that we have wrong voltages for the Dolby chips. This is not the case as the 565, 655, 665 and 755 use the same Philips chip but the 755 gives different output (and vu level).

I adjusted the vr3 & vr4 on my 965 to have 545mV output and my meters (on detailed scale) still gave me +4dB... same as your case. But to achieve 545mV at output, I had to give about 215mV to Dolby chip...

So, I have to admit you're in the right path. Some resistors need to be recalculated.

What I have not done is to resolder the r31, r32, r37, r38 and turn back the output amplifier to AA class state to see if the output level is going to normal 545mV.

But, again the 755 hasn't discreet amp. It's still on AA class and gives wrong (high) output...
 

Makymak

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#28
Sorry, Alex. At Dolby level, the output of these decks is about 545mV. The 400mV are for the 160nWb test tape and is something 2.8 dB below the Dolby level.

Edit: sorry for stating my 965 gave me 545mV. Now, recalling, I think I didn't bothered to measure the outputs on these decks since I bought them last and I was always confident that they give the same as all the other Technics I had calibrated so long...
 

Alex SE

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#29
Hey, no worries Makymak, I was (and still am) confused about this. Feels better that I'm not the only one who noticed this. My 555 and 565 are just fine (IARC), 727 is at +2 which is acceptable since that 200nWb tape gives +2.8db so 0.2db is missing to turn on that third peak. Anyway, 965 is strange. SM states that pb level should be 400mV (545mV) at outputs, but if you adjust dolby level with 200nWb tape to 245mV it will give you higher voltage at the output and if you adjust output to 400mV (545) it will give you about 25-30mV lower voltage on dolby IC. It will work but tapes recorded at that deck are not going to be compatible with other decks. So, for me, the best solution is to adjust correct voltage on dolby IC, than adjust resistance at R41 and R42 to get 545mV at the output and at the end adjust peak meter by replacing those R555 and R565 as Skywavebe explained.
Don't have time to play with it now as I have to study (no, I'm not going to school but have some test at work), but after Tuesday I'll have a time to disassemble a deck. Of course, I'll share everything :) Than I have to solve the other problem with adjustment of rec EQ but that's another post, let's not mix the things :)
The deeper we going in to this, the more interesting it is.

Almost forgot to say, I believe that 965 have a wrong dolby level from a factory. If a deck is adjusted so that output level is 400mV as SM states, it's obvious that dolby level is lower than it should be. Why? That's a question only Matsushita can answer. Thanks god we have forums and our experts otherwise we would never notice this. 965 is a great machine when modified and properly adjusted.
 
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Makymak

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#30
I'm with you on this: most important is to have correct levels at the Dolby chip to make it encode and decode the noise reduction as it should. Everything else beyond the Dolby chips (and dbx in our case) is just a matter of amplification.

Now, if Matsushita had the Dolby level wrongly calculated, then it's an additional reason this deck was mediocre in it's oem state...
 

Skywavebe

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#31
Has anyone actually measured a resultant enhancement of performance or am I going to get the typical "It Sounds Better" response from this what they say is an obsolete NJM2114 IC.
 

Alex SE

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#32
Has anyone actually measured a resultant enhancement of performance or am I going to get the typical "It Sounds Better" response from this what they say is an obsolete NJM2114 IC.
I have 2114 in my decks. It should be enhaced version of 5532 but I can't tell a difference. Reason why I chose 2114 is because I couldn't find 5532 in SIL package.
 

Skywavebe

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#33
I don't think they make NE5532 in SIL neither does the LME49720 come in that package. If the use of these expensive Op Amps can not be noticed then why on earth put them in for peace of mind? I know in Tascam Mixers there were all these yahoos putting in NE5532 and other high frequency op amps and the only thing they did is oscillate and burn out because they never compensated for their different Poles and Zeros in the frequency domain. We ended up putting in the original chips. We had the knowledge at Teac to put in the higher quality parts but if it sat between two NJM4558D chips what would be the point?
 

Skywavebe

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#34
You could make a PCB to adapt a DIP IC on a stand up board to fit into a SIL pin out but it just adds to the cost of a restoration or repair. On this PCN then it might use an SMD part but if it were me doing it I would still use a DIP IC. You can socket these easier.
 

J!m

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#35
I might be the worst at soldering and I figured out how to do the SMD modern DIP8 replacements. Put those on a sub board after I put the eight stand-off pins into the board. Now you have a socket able SMD op amp.

Most of them in my phono pre are like this. They all got soldered, not socketed, regardless of package.

But the point is it’s not that bad to do it if I can do it.
 

Makymak

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#36
I preferred to put the 5534 on that position. I found it easy to solder a dip on a sip row of pins. Now, my 5534 can be removed and reinstalled like a sip opamp.

@Skywavebe I'm the last person who could take measurements. But to my ears it makes difference.

Edit: they don't make the ne5532 in single line but one can use the njm5532 which can be found in sip8 form.
 
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Alex SE

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#37
You could make a PCB to adapt a DIP IC on a stand up board to fit into a SIL pin out but it just adds to the cost of a restoration or repair. On this PCN then it might use an SMD part but if it were me doing it I would still use a DIP IC. You can socket these easier.
That's what I did from beginning, but found later 2114 and replaced all 5532 (Dual Channel) and 5534 (Single Channel). Only one which is still on home made adapter is one OPA2227, which Alex ANT recommended as better choice for just that position.
 

Alex SE

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#38
At last I have found some time to test R555 and R556 with trimmer and it is just fine with 52K instead if 82K. Don't have 52K resistors so used 47K and 5.6K from one cannibalized deck and got 51.87K and 52.09K. 220Ohm difference should not make a difference on such a values.
Now I'm more than satisfied, Dolby level OK, output level OK, peak meters OK.
Big thanx to all of you, specially to @Skywavebe for advice regarding resistors.
Makymak and other 965 owners, if you decide to do this mod, observe that you'll need to re-adjust VR9 and VR10. Easiest way is to do external calibration for some tape, before, and re-adjust VR9 and Vr10 with a same tape after replacing R555 and R556.

Now I have to adjust rec side to match or better than this (thanx Vince for pointing), and then I'm finished with first deck. The other one will be much easier to mod and adjust.
 
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Alex SE

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#40
Just a big Thank you!!!
Thank you, it's always much easier when more people participates in measuring, observing and discussing.
One more thing I forgot to mention is that, if the one wants to do those adjustments, start with output adjustment (R41/R42). Those are 15K by the factory and I have replaced them with 11.5K IIRC. Those affects peak meters, too, so measure & replace those two first and then play with R555/R556).
Those values I have used will guaranteed NOT be the same for the other deck as that one peaks 1db more than current one does (was). As said earlier, best way is to test first with trimmers.
 
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