HF loss - general

Makymak

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#61
I've done a same try with RS-B965. It didn't made any difference with or without the pad on playback but the recording was suffering.

@Skywavebe these Aiwa heads are quite beaten!!! I haven't seen any cassette head with such a deep groove. I wonder if they have their gaps open or they have some more juice (if lapped accordingly), but I highly doubt it...
 

Alex SE

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#62
To remove pads from a cassette would be wrong approach to a problem I think. Even if that gives better results, it would be like a deck with wrong pb level. It can sound great but tapes recorded on it would not be compatible with other decks.
What I don't get is how someone can use a deck until a heads becomes so worn as on pictures. Those decks have lost good sound long before heads ended in that condition.
 

Skywavebe

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#63
This is the same question I have with Akai open reel heads that I have tested. The owners of the deck even though I fixed his channel out problem did not know there was any fidelity problem. I could not calibrate the deck with the heads he had on it that were those life time heads. You know people play machines until they drop sometimes regardless of the quality of sound. Here is a head as John Candy would say just needs to be lapped.-
1647770661311.png
 

Alex SE

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#64
Before I say something, let me remind that I'm a learner/amateur so lot of things you are talking about are Sci-Fi to me, but I'm trying to understand.
Now, as long as I know, ground for good working deck is condition of head and mechanics (including tape path and pinch rollers). If those are not as they should, there is no meaning to do adjustments. Wear of a heads can be compensated by adjusting electronics but only in case that it's not a groove wear. Even if small wear, adjustments should be done only as a temporary solution. Not less important is that all capacitors are up to specs (other components are not degrading). Conclusion is that mechanics should be served, tape path clean and demagnetized, rollers in good condition and head adjustment is OK. Next thing is to check all caps, replace if needed. First then the one can start with other adjustments.

Skywavebe, what are you using for taking a pictures of heads? There is some cheap USB microscope on the market but I doubt if it is good enough for this.
 

derek92994

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#65
Well that groove in the Aiwa 7000 head is quite bad, I do wonder if it was heavy use or an incorrect tape tension setting throughout the life of the head.

To remove pads from a cassette would be wrong approach to a problem I think. Even if that gives better results, it would be like a deck with wrong pb level. It can sound great but tapes recorded on it would not be compatible with other decks.
Good point, thats why I didnt go removing the pads from my tapes, mainly so they would play on single capstan decks. I generally stick to the Naks, dual capstan with the pad lifter. But sometimes play the occasional tape in the other decks.

Does anyone know if tape wear increases when played on a deck without a pad lifter compared to one that does?
 

Skywavebe

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#66
Tape path is important but so are some other things like OIL. People put 3 in 1 oil in their decks and expect good results when what they are using is a garbage oil- I have said what to use many times still people will go out of their way to use the wrong oil. Pinch rollers- they do not have to be changed all he time like a lot of amateurs do. In some deck I have worked on I clean and recondition the rollers and they are as good as new. Those rollers that are cracked and or soft mushy must go which is why Marion's Do It Yourself site in Slovakia is of great help. Demagnetization- stop listening to wives tales and hype as no one has ever showed me any proof that it is needed and I have not seen it either in my test experiments.

The pictures I take can be from a Nikon 8700 that then is cropped using a program called Thumbs plus. I do not have any USB microscope devices here.
People seem to be lazy and want to leave in 40-50 year old Electrolytics. This is almost as large a battle as with these lapping guys and then Demagnetization. Get rid of any capacitors or the electrolytic type that are past 35 years old. It is not so much if they are degraded now or shorted now and they do not have to puff or blow up to be bad- many of them are bad just being old with no other sign. If you put a deck in play with no tape and look at the scope patterns of output DC coupled and see the lines jumping around that is low frequency noise being generated by old leaking caps- all you should see is two straight lines with a little noise on it.
 

Skywavebe

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#67
Here is another wives tale to put to rest- grooves in a tape head will occur from 50 hours to the end of life and most heads will operate well the entire life with out any worry about them. Those people that make a big deal with the fingernail test on any machine are clearly amateurs following more sooth sayers from I don't know what planet- stop listening to all these clowns that do not know what they are talking about. They only want to look smart by making a big deal over nothing and those experienced Technicians will be able to deal with grooves without an issue. Cassette heads usually do not have a lot of vertical adjustment but some do. This is why a M300 gauge must be used- think about all those people out there adjusting heads without them to make the deck better. Also the tilt of a head either by bent head mounts or mis-adjustment can affect the left channel. Also dirt and corrosion on the head can also- this is why I polish heads with Nu Finish when I encounter a problem and most the time it goes away- there is crap that sticks to the head over many years and then people with the piss poor Isopropyl alcohol will never get it off. Thus come abrasive needs such as Nu Finish or Brasso in reel deck heads. Why do I use such stuff? Because it gets results.
 

J!m

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#68
To use a car engine analogy:

No point adjusting the carburetor when the timing chain is not on correctly.

Corrwct the major things first, and then dive deeper. My KX-1080 was done like this- step by step to avoid throwing money into a bonfire. Once the Dolby chips were found to be corroded, no further work was done to try and work around that handicap and “make” it record. Every recording will have noise. Playback is great, and ESL did align everything properly.
 

Alex SE

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#69
One week later I've found a little time for myself (read: my decks). Here is what I got by marginally adjust VR302 and adjusting resistance on R95 and R96, from 15K to 5.4K. Result is much better, recording is now almost perfectly flat from 1.5kHz and up.
Question is now, is it possible and if it is, how to make it flat between 200Hz and 1.500Hz? Would really appreciate is someone have a solution.
Once again, roll off between 20Hz and 200kHz have to do with resistance mismatch between a sound card and a deck, don't think about that.

1648353970398.png
Regarding a head, purchase of new one and lapping of those two which are in my decks now is coming. Waiting for an answer from a seller.
 

vince666

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#70
Not having tried to tweak it by myself, I wonder which is the actual frequency range affected by R95 and R96...
Alex had described those two resistors as a treble shelving filter control... a shelving filter is such a filter which boosts (or cuts) all the frequencies below or above a certain frequency in an equal way (sorry if my language isn't properly technical, but I never actually studied electronics)... then, for example, if that treble shelving filter starts to work just as low as the 500Hz - 1Khz zone, then it will be useful to move up and down the whole zone from 500Hz - 1Khz and on...
So, if for example, that filter start working from where I've described (or so) then you would be able to flatten the recording even more by simply trying changing R95 and R96 once again and without even touching the bias setting.

While, if you go and raise the bias in order to lower the mid-hi zone by that 1dB you have there in your plot, then, most likely, the treble (and especially the extreme treble) will go down by more than that... and you will get again the roll-off at the treble side as you had in the very first moment.

anyways, your plot now is just a lot better than before... how does it sound while recording music just this way, compared to the source?
 

Alex SE

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#71
Problem with things like this is that the one have either to do a whole job under the same day or write down observations :) I didn't done either first or second. IARC, frequencies from about 1K was going up and then there was a roll off with about 10K. Lowering resistance on R96 and R96 made it not going up and down but stay flat. I'm wondering if is there is some kind of filter that can be re-adjusted (by changing resistance) to push low frequencies up, in my case about 1.5db OR if there is something than can simply balance low and high like boost low for about 1db and lower highs for about 1db, but first option sounds more logic. Will see what experts are gonna say.
 

vince666

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#72
do consider that boosting the EQ curve below 1Khz or reducing it above 1Khz will bring you more or less at the same result, save for an overall level difference which is simply a matter of adjusting Rec gain a bit.

if, like I can see at now, you have both channels equal with the same value at both R95 and R96, to see what exactly changes with the values of such resistors is as easy as trying a different value only on one channel and, without touching the bias setting, checking how the two channels differ just because of the change applied only at R95 or R96... in fact, trying things only on one channel (and only one kind of thing at once, to not add unwanted confusion) while leaving the other channel untouched as a reference of the "before" situation is helpful while investigating what happens just "in practice".... not being that good at the theory or by calculating anything related to electronic circuits, I usually tend to work with a typically empirical method.... sure, it's time consuming and it involves several try and error work, but at least it's something I am quite able to do... otherwise I should give-up just in the first moment.
 

Skywavebe

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#73
It had been my observation over time to consult a guy like Alex Nikitin to see what he says. He had some head preamp section that were better noise wise using FET's but boosting the low end I don't think is all that important as what is there below 60 Hz but sounds from Pipe organ or some kinds of synthesizers. Low end audio due to head bumps often times are high than they are suppose to be like it or not. Now of course you could design in a low pass circuit to make an adjustment here but then once done the cross talk might suffer from the additional low end. Things have trade offs.
 

vince666

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#74
actually, I am a bit surprised about all of these weird issues our friend is experiencing on his RS-B965.

on both of my RS-B965, which were overhauled and modified by ANT himself, i can easily get flat response.

So, i believe that for our friend it's more a matter of tweaking/optimizing what's just into the deck... or, at least, i hope so.

anyways, the preamp section in this model is just made with JFET from the factory.
 

Alex SE

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#75
I was thinking, regarding audio tester, in section Measurement what is a difference between Mono left/right ch. reference and Stereo no ch. reference ? Are you guys using mono or stereo when measuring FR?
1648974275542.png

Here is what I got when testing with settings as above (observe that scale is 0,5db):
1648974545361.png
 
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vince666

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#76
interesting.

i never touched those settings and mine are set as defaults.

anyways, now roll-off on bass disappeared and source and tape are substantially the same... just, i would expect the head bumps on bass in the tape curve.

but, can you also do both channels with these settings?

must give a look at audiotester's manual to know the actual meaning/purpose of those settings.

as soon as i am at my PC, i will take a screenshot of that settings page here
 
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Alex SE

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#77
Default is Stereo, no ch. reference.
As concluded earlier, that readings of bass roll off have to do with deck's resistance as roll off appearing in source mode.
When testing in Stereo, no ch. reference mode, readings looks like this.
Here is what AT manual says, but I don't have a clue what it means:
1648983716043.png
 
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vince666

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#78
these are the settings I use there in the Sweep dialog... I will use the numbers of the above pic from the manual to identify the various settings.

1) Step Count = 60 (you can use larger numbers with no problems, the software will check more frequency steps and will take more time... but for the purpose of setting up the deck I believe that 60 steps are just enough... and the measurement needs noticeably less time than when I had set this parameter to 150 !)

2) Digital Level... I change this parameters very often, depending on the actual level into the deck I want to test the sweep... of course, I never set it as high as 0dB FS... but the value here depends on how you setup the input levels also in your deck and on the deck itself... for example, on last deck I've checked, to get the sweep at -20dBVU on tape, I had to set that parameter to -47dB FS... anyways, it strictly depends on how the levels are going on there at you... for example, to not struggle just anytime in setting the deck's input level knob with care at a "somewhere in the middle" setting, I directly set the deck's input level knob to the max (which is fast!) and then I need to set lower levels there at the audiotester's sweep signal... but, to avoid overloading the soundcard's inputs with the signal which returns from the deck's output to the soundcard's input (which would especially happen when I test the deck at high levels, like when I do measure the distortion/MOL on tapes), I use a cable with some resistors to simply lower the signal level just there in the "return" cable... which works just like a fixed potentiometer inbuilt in the cable.

3) Frequency Generating = logarithm

4) which is the frequency range of the sweep... again, you are free to choose which range you wish to investigate... here, I usually go with a range from 30 Hz to 30000 Hz.... of course, my soundcard/audiotester are both set to work at 96Khz samplerate, otherwise I cannot go over 22050 Hz... and, as far as bit resolution, i did choose the 24/32bit option... the soundcard I use on this "measurements" PC is an old M-Audio Delta Audiophile 24/96 which turned out to be VERY compatible with audiotester, unlike the Echo Audiofire 4 i am using on my "music" PC and which never really got to work properly with this software.
Also, unless I have a very good reason to start the sweep at 20 Hz or even below (and sometimes I need to check this), I prefer to start from 30 Hz because the whole sweep measurement work needs quite less time.
And, sometimes, i.e. when I am tweaking bias and Rec EQ on a deck and need to get faster results from audiotester to just work a bit faster, I start the sweep from a higher frequency, say from 300-400Hz, as I only need to see what happens at the treble side of the frequency range.

5) Measurement = Stereo, no ch. ref.

6) Phase is totally disabled here, but I believe that if you choose Stereo at the above setting then the Phase is automatically disabled.

7) Mode = sync

8) Pause = 0

9) Tracking Filter isn't even visible here... maybe you see it there because of how you've set some previous parameter?

10) Graph... that option new curve / meas. is not selected there in that small box, just like on both screenshots you shared here above.

11) default... never pushed it, but it might simply be a button to set the default settings, i guess.

12) wait before meas. ... i've set the Start Sine option at 193 ms (or maybe it was like that in the first moment? I don't really remember) and the max. single Meas. Time Stop Sine number I see here is 666ms... Don't know/remember where it does come from (certainly not from my own nickname! :p).


Ah, I did not perform any kind of "calibration" there in audiotester... I am not interested in getting the real millivolts values and, as far as frequency response (i.e. while doing a loopback test between soundcard's outputs and inputs), it was just OK in the first moment.

I hope it helps.
 
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