Studer A710-need HELP in audio adjustment

[ijurcevic]

Hi,
I recently got deck from service but I am not sure that calibration is made correct, so I would like to check, but I have a questions and asking for help.

From Service manual;

5. AUDIO ADJUSTMENTS
(A suitably adjusted tape transport is a prerequisite for all audio adjustments. All line outputs must be terminated with 600 Ohms).
What does this mean? I meant doing measurement on line output with converter XLR to RC. Should I connect resistor of 600 Ohm between HOT and GND wire on RC connector, in parallel with milivoltmeter for each channel?

5.2.2 Checking and adjusting the signal path without tape
General: The line level (at 250nWb/m) corresponds to peak level, i.e. the operating level according to US-standards is lower by 6dB.
What does this mean? Which peak level, which voltage? Isn't dolby tape 200 nWb/m for level adjustment?

The buttons INPUT CAL and OUTPUT CAL must be released.
Set switches DOLBY NR and MPX*FILTER to OFF position.
Set MONITOR switch to SOURCE position.
Feed in 315Hz with line level to the two inputs LINE INPUT.
Which voltage should be on line out?
Turn R14 on NA-Encoder 1.710.489 to center position.
connect millivoltmeter on P3 (P4) on Dolby Encoder 1.710.485 (High Com 1.710.483).
adjust to 730mV (High Com to 755mV) with R 104 ( R204) on Stereo Balancing Unit.
Connect millivoltmeter to LINE OUTPUT.
Adjust line level with R110 (R210) on stereo balancing unit.
Two potmeter/channel for level adjustment? Which voltage for level adjusting with R110 (R210)?

5.2.3 Checking and calibrating the PEAK READING METER
Feed in 315Hz with 2dB below line level at LINE INPUT.
Which voltage should I have on line out?

Vary the generator level with in the range 0 to -0.5 dB.
Both segments to the left of the Dolby marker (0 dB) must turn on or off simultaneously. Should this not be the case, the display requires recalibration.

5.3.1 Adjusting the reproduce level
Carefully demagnetize and clean all metal parts that come in contact with the tape.
Mount Hi- Fi reference cassette 4.75 (Fe). Set MONITOR switch to TAPE position and press TAPE SELECTOR IEC1
Set DOLBY NR switch to OFF position.
Start reference cassette, level tone section 250 nWb/m, 315 Hz, in PLAY mode. Adjust reproduce level with trimmer potentiometers REPRODUCE LEVEL L and R in such a manner that the desired line level is available at the LINE OUTPUT (Fig 54).
Which voltage on line OUT? What with peakmeter, 0 or 2 dB? Which potentiometers? Like in 5.2.2?
What If I use tape 200 nWb/m, 400 HZ, 0dB? (Teac test tape)?

Thats for now, I hope somebody will help me.

Thanks,
Ivica

 

[jlb2]

Hi, and welcome to Audiokarma.

5. AUDIO ADJUSTMENTS
(A suitably adjusted tape transport is a prerequisite for all audio adjustments. All line outputs must be terminated with 600 Ohms).
What does this mean? I meant doing measurement on line output with converter XLR to RC. Should I connect resistor of 600 Ohm between HOT and GND wire on RC connector, in parallel with milivoltmeter for each channel?

This is correct, you insert a 600 ohms resistor in parallel between the hot and cold wires of the outputs. That's pins 2 and 3 on the XLR connector, or center pin and body on the RCA or XLR if your millivoltmeter has an unbalanced input. Both mountings are equivalent, you choose according to what's more convenient for you. Note that the closest actual resistor value you can buy is 604 ohms, which is close enough for practical purposes.

5.2.2 Checking and adjusting the signal path without tape
General: The line level (at 250nWb/m) corresponds to peak level, i.e. the operating level according to US-standards is lower by 6dB.
What does this mean? Which peak level, which voltage? Isn't dolby tape 200 nWb/m for level adjustment?

This is the one sentence in that manual that got me thinking for a while. In fact you mostly don't need this information to adjust the deck, and I don't know why they added it there. Maybe to fool the enemy? Or so you are not surprised that the meter reads +6dB on the 250nWb/m section? Just disregard this bit for the moment, and you will be fine.

The buttons INPUT CAL and OUTPUT CAL must be released.
Set switches DOLBY NR and MPX*FILTER to OFF position.
Set MONITOR switch to SOURCE position.
Feed in 315Hz with line level to the two inputs LINE INPUT.
Which voltage should be on line out?

At this point you don't care about the output level, you will set it at a later step. Just set the input level at your chosen reference level. This is usually +4dBu, but you can set a different level depending on your local standards (for instance the CCIR standard that applied in many European radio stations called for +6dBu. The machine is designed to allow such adjustment without problem but, unless you have a reason, I'd just use +4dBu. It is important to measure this level with both inputs connected, as the loading by the A710's inputs has an influence on the level somewhat.

Turn R14 on NA-Encoder 1.710.489 to center position.
connect millivoltmeter on P3 (P4) on Dolby Encoder 1.710.485 (High Com 1.710.483).
adjust to 730mV (High Com to 755mV) with R 104 ( R204) on Stereo Balancing Unit.
Connect millivoltmeter to LINE OUTPUT.
Adjust line level with R110 (R210) on stereo balancing unit.
Two potmeter/channel for level adjustment?

Not exactly. R104/R204 adjust the recording level. Once you have set them to read 730 mV at P3 and P4 (the 755 mV value is only for the ultra-rare HighCom version), use R110/R210 to read the reference output level (usually +4dBu) on both outputs.

R14 is the channel balance adjustment, just a reminiscence of the Revox B710 which is mostly the same as the A710, but not quite. You set the wiper roughly at the centre, and then you just forget it. In fact, unless you had to replace R14, you don't even need to adjust it at all. On a B710 you would need to adjust it, but on your A710 it is unimportant.

Which voltage for level adjusting with R110 (R210)?

The output level is your reference level, usually +4dBu, but as said above you can change it as required for your application.

5.2.3 Checking and calibrating the PEAK READING METER
Feed in 315Hz with 2dB below line level at LINE INPUT.
Which voltage should I have on line out?

At that point you don't need to measure the output level since it is independent of the meter reading. Just adjust the meter reading. The output levels are adjusted in the previous section so the output voltage should be the reference output level minus 2 dB, but that's just if you want to reassure yourself: for the calibration, you have to measure the input level, not the output level.

5.3.1 Adjusting the reproduce level
Carefully demagnetize and clean all metal parts that come in contact with the tape.
Mount Hi- Fi reference cassette 4.75 (Fe). Set MONITOR switch to TAPE position and press TAPE SELECTOR IEC1
Set DOLBY NR switch to OFF position.
Start reference cassette, level tone section 250 nWb/m, 315 Hz, in PLAY mode. Adjust reproduce level with trimmer potentiometers REPRODUCE LEVEL L and R in such a manner that the desired line level is available at the LINE OUTPUT (Fig 54).
Which voltage on line OUT? What with peakmeter, 0 or 2 dB?

As the manual says you are supposed to read the desired line level, i.e. usually +4dBu.

Which potentiometers? Like in 5.2.2?

No, those called "repro level" on the motherboard (section 7/3) aka R38 and R39 (section 7/7 and 7/8).

What If I use tape 200 nWb/m, 400 HZ, 0dB? (Teac test tape)?

200 nWb/m is 2dB below 250, so you just take the difference into consideration. 400 Hz instead of 315 should not make a difference.

 

[ijurcevic]

jlb2,
I don't know what to say, except many many thanks

Just one thing, because I am not sure;

As the manual says you are supposed to read the desired line level, i.e. usually +4dBu.

If 200 nWb/m = 0dB = 0,775 V, is than +4dBu = 1.227653 V?

If I use, for repro level, Teac 200 nWb/m, 400 Hz, 0dB test tape and adjust voltage on lineoutput at 0,775 V, peak meter on Dolby mark, is that adjustment OK?

Best Regards
Ivica

 

[ijurcevic]

Jlb2 if I understood you correct, procedure will be like:

5.2.2. I will fed 315 Hz with line level (+4 dBu) from Audacity...
With R104 (R204), measure on P3 (P4), I will adjust voltage to 730 mV...
With R110 (R210) I will put voltage of 1,23 V (measure on line out, SOURCE mode). This is +4dBu?

5.2.3. I will feed 315 Hz with 2dB below line level
I must adjust peak meter to show +2dB?

5.3.1. Tape deck in TAPE mode, level test tape 250 nWb/m, 315 Hz...
With R38 (R39) I must adjust voltage of 1,23 V on line output (+4dBu)? Peak meter must read +4dB?

And If I check everything with test tape 200 nWb/m, 400 Hz, TEAC DOLBY tape MTT150 I think, what I must have?
0,775 V on line out and 0dB (Dolby level) on peak meter? But this is than 4 dB less, not 2 dB. I think I will have 0,975 V on line out and +2 dB on peak meter....Is this correct?
I am really confused, I think just need one answer more

Best Regards
Ivica

 

[jlb2]

Jlb2 if I understood you correct, procedure will be like:

5.2.2. I will fed 315 Hz with line level (+4 dBu) from Audacity...
With R104 (R204), measure on P3 (P4), I will adjust voltage to 730 mV...
With R110 (R210) I will put voltage of 1,23 V (measure on line out, SOURCE mode). This is +4dBu?

Yes, this is correct.

5.2.3. I will feed 315 Hz with 2dB below line level
I must adjust peak meter to show +2dB?

No, you adjust the meter calibration trimmers so that the segment just to the left of the Dolby/0dB mark just lights up, on both channel, as explained in the manual. Make sure that the two channels light up simultaneously as you slightly increase the input voltage. It is important to remember that the peak meter does not tell you the output voltage, but the difference between the current level and the reference level. With the usual input/output level of +4dBu, an input voltage of +4dBu will give you a meter reading of 0dB. For an input voltage of +2dBu (2dB below line level), you get a peak meter reading of -2dB. Note that the 2dB step on the A710's meter is fairly coarse, hence the intricate adjustment procedure to accurately set the light-up voltage.

5.3.1. Tape deck in TAPE mode, level test tape 250 nWb/m, 315 Hz...
With R38 (R39) I must adjust voltage of 1,23 V on line output (+4dBu)? Peak meter must read +4dB?

You must adjust for +4dBu at the output. The peak meter should read 0dB, but at this point it is already calibrated so don't touch it.

And If I check everything with test tape 200 nWb/m, 400 Hz, TEAC DOLBY tape MTT150 I think, what I must have?
0,775 V on line out and 0dB (Dolby level) on peak meter? But this is than 4 dB less, not 2 dB.

Your 200 nWb/m reference tape is just 2dB below the nominal 250nWb/m, so you will adjust for +2dBu (or, more generally, 2dB less than whatever line level you choose) at the outputs, and the peak meter will read -2dB (but again, don't touch it). Note that +2dBu is 976mV, and +4dBu is 1.228V (the "u" after "dB" means that the 0dB reference is 775mV).

I am really confused, I think just need one answer more

No problem, this is not such an easy notion to grasp. With experience you will get used to it

One last thing: at some point you will wonder why the mention of 250nWb/m as the 0dB level, whereas your TEAC reference tape is 200 nWb/m. This is because different manufacturers used different standards, Teac went for Dolby's 200 nWb/m and Revox/Studer chose to use the DIN standard which was 250. Which is best? Both, of course You can use the same reference tape to calibrate either make of deck, as long as you know and compensate the differences.

 

[ijurcevic]

jlb2, ones more....many thanks!
In yours two posts I learned a lot.

When I do calibration I will post here my experience.

Best regards from Croatia
Ivica

 

[jlb2]

You are welcome Ivica By all means feel free to let us know.

BTW in my previous post I told you to set a line level of +4dBu and a voltage 730mV at P3/P4, which was a mistake. By default, the A710 is calibrated for a line level of +6dBu for 250 nWb/m (this is written on the last page of the service manual) and that's why the service manual calls for 730 mV. This is strictly equivalent to a line level of +4dBu for 200 nWb/m, corresponding to 580 mV at P3/P4, as stated in the A721 manual. I don't know for sure why Studer chose to say it this way for the A710, but +6 dBu and 250nWb/m are more in line with the CCIR/DIN standards in use in the European public radio stations (for some reason the levels tend to be 2dB hotter in Europe than in the US), so that may well be the reason.

I've seen that you have received answers to your question on Tapeheads as well. I am not a tapeheads member so I won't answer there, but I have to clarify a mistaken advice that was given to you there, namely not to terminate the outputs on 600 ohms. Clearly, the author of the quoted article could use a course on transmission lines, but the important point is that any transformer-coupled output (e.g. the Studer A710) will ring if it is not properly terminated. In other words, the frequency response will not be flat in the trebles, and it is a very measurable effect - I know because I measured it myself. A transformerless output would be much less sensitive (albeit not insensitive) to loading, but with an A710 you definitely need the 600 resistors. Walter66 is the knowledgeable one on this.

 

[ijurcevic]

You are welcome Ivica By all means feel free to let us know.

BTW in my previous post I told you to set a line level of +4dBu and a voltage 730mV at P3/P4, which was a mistake. By default, the A710 is calibrated for a line level of +6dBu for 250 nWb/m (this is written on the last page of the service manual) and that's why the service manual calls for 730 mV. This is strictly equivalent to a line level of +4dBu for 200 nWb/m, corresponding to 580 mV at P3/P4, as stated in the A721 manual. I don't know for sure why Studer chose to say it this way for the A710, but +6 dBu and 250nWb/m are more in line with the CCIR/DIN standards in use in the European public radio stations (for some reason the levels tend to be 2dB hotter in Europe than in the US), so that may well be the reason.

I've seen that you have received answers to your question on Tapeheads as well. I am not a tapeheads member so I won't answer there, but I have to clarify a mistaken advice that was given to you there, namely not to terminate the outputs on 600 ohms. Clearly, the author of the quoted article could use a course on transmission lines, but the important point is that any transformer-coupled output (e.g. the Studer A710) will ring if it is not properly terminated. In other words, the frequency response will not be flat in the trebles, and it is a very measurable effect - I know because I measured it myself. A transformerless output would be much less sensitive (albeit not insensitive) to loading, but with an A710 you definitely need the 600 resistors. Walter66 is the knowledgeable one on this.

Many thanks jlb2,

yes in meantime I am OK with resistor of 600 ohms, i.e. I will terminated output of deck with that resistor.

Yes I am on TH forum, but I didn't find what I need, so thanks again

Ok, now I will have change only in item 5.2.2. (only P3 and P4)? Everything else stay a same?

With R104 (R204), measure on P3 (P4), I will adjust voltage to 580 mV...
With R110 (R210) I will put voltage of 1,23 V (measure on line out, SOURCE mode).

Best Regards
Ivica

p.s. I will do that when I find a time...two small kids... . And after that recording part will be on the way...

 

[jlb2]

Many thanks jlb2,

You are welcome.

Ok, now I will have change only in item 5.2.2. (only P3 and P4)? Everything else stay a same?

With R104 (R204), measure on P3 (P4), I will adjust voltage to 580 mV...
With R110 (R210) I will put voltage of 1,23 V (measure on line out, SOURCE mode).

Yes, except in 5.2.3: you feed 315 Hz at the line level (here +4dBu) instead of 2dB lower, because you are already at the level that reads 0dB on the peak meter. All the rest is the same.

p.s. I will do that when I find a time...two small kids... . And after that recording part will be on the way...

Have a good time with the kids See you soon.

 

[twiiii]

It depends on the capability of the tape deck and the tape your using whether 250 n/web is your peak level your - 3db level or 0 db level. MY old Ampex professional machines, even with tube electronics could easily put higher levels on Maxells best high output tapes with less than 3 % distortion. Observing the signal with an oscilloscope I have seen + 18 db levels above 185 n/ web using Scotch 201 back in the late 60's. With Maxell and Ampex Grand Master and some TDK tapes, + 18 db levels above 250 N/web were common too as long as compression wasn't used. ATR series decks were just amazing at. the levels they could put on tape and take off at 30 Ips. Studer machines could be an equal too. Dynamic ranges approaching 85 db were easily observed. Remember professional VU meters that were used on professional tape decks could easily lie by 18 db. So when the meter hit + 3db it might be a + 21 db peak. This why later Ampex professional decks had over 30 db head room. Now you know why they had to compress signals to make LP's with less than 55 db dynamic capability and much less for consumers with console stereos.

 

[jlb2]

Hi twiii, we are talking about very different things. One major difference is that the A710 is a cassette machine, not a RTR. I strongly doubt that you can reach 18dB above 250nWb/m before saturation on a cassette, at least I've never seen this happen. Another big difference is that we are discussing the reference level (aka the level for which the peak meter reads 0dB) whereas you are talking about saturation level. The Revox/Studer cassette recorders are set for a 200 nWb/m reference level and that's all we need to know in this thread. Maximum achievable levels are a completely different issue.

Re. the VU meters reading 18dB below the peak level - yes, it happens depending on the waveform's shape, but the A710 has peak meters (for a reason) so this consideration does not apply here.

 

[ijurcevic]

Hi jlb2,
thanks to you I finished with reproduction part of adjustment and I am 100% OK now. Now I made recording part and I am not satisfied with results, so I need one more help . From service manual:

5.4.2 Adjusting the azimuth of the record head (not used for units from no. 2521 )
Caution:
When making this adjustment, use only high quality cassettes that have been spooled forward and backward once. The tape must not show
any mechanical damage or deformations along the edges.
— Clean all parts that come in contact with the tape with a moist felt stick (included in the REVOX cleaning kit) and subsequently demagnetize these parts.
— Load cassette and press the TAPE SELECTOR button that corresponds to the type of cassette. For cassettes coded according to the IEC scheme, the AUTO position can be used.
— Feed in line level —20dB, 10kHz, at LINE INPUT; line level —20dBu should be available at the LINE OUTPUT ( MONITOR switch in SOURCE position).
77,5 mV?
— Start record in play mode ( press REC and PLAY ).
Set MONITOR switch to TAPE position.
With screwdriver size 00 for cross recessed head screws adjust screw Y (Fig. 5.5) in such a manner that maximum level is obtained for both channels (minimum phase difference) .
When I done azimuth I had difference in voltage value between L and R channel (85 mV and 135 mV), but they were in phase (and in XY plane it was 45 degree). I just made a little turn to right side and I got 120 mV on both channel, but chanel were not in phase (in XY plane it was not much less than 90 degree). Is this correct? I used TDK D90 tape.

The following adjustments apply for one type of tape only.
For other tape types, proceed in the same manner. The position of the corresponding trimmer potentiometers can be determined from Fig 5.4
All of settings first I do for normal tape (bias, level, equalization) and after for chrom and metal, or I change tapes in each setting (bias, level, equalization)?

5.4.3 Adjusting the tape bias
Same preparations as described in 5.4.2. (mean I must record tone 10 kHz, -20 dB?) and...
Adjust the corresponding trimmer potentiometers on the oscillator PCB (refer to Fig. 5.4) in such a manner, that maximum output level is obtained for both
channels. Write down the actual values (in dB) and deduct from this valuetheamount shown in Fig. 5.8.
My deck has serial number 1391 and I think that I have Sony heads, because I can adjust records head azimuth. Which column for delta U is mine; left or right? I think left (for example delta U for TDK MA is 4 (dB?).
Should I have same max value for both channel, or just max value which can be different for each channel? I made with max but different voltage between channels (probably wrong!)Set this calculated value with the corresponding trimmer potentiometers.
For max value and for value according to table in fig 5.8 I use same potmeters? (R37-R42)
Caution:
The channels influence each other. When adjusting for maximum level, the optimum compromise must be found.


5.4.4 Adjusting the record level and equalization
Feed in line level —20dB, 315Hz, at LINE INPUT.
77,5 mV?
The INPUT CAL button must be released. Set DOLBY NR switch to OFF position.
Start tape transport in record mode. Adjust trimmer potentiometer LEVEL (potmeters R39-R44?) (record equalization 1.710.486) in such a manner that no level jump occurs
when changing the MONITOR switch setting from SOURCE to TAPE.
That was OK.
Preadjust the trimmer potentiometer EQUALIZATION (R45-R50?) (record equalizer 1.710.486) with the following frequencies relative to 315 Hz:
IEC 1 10 kHz 0 to +1 dB
IEC 2+4 14 kHz 0 to +1 dB
Here I had a problem. I could not made enough voltage for 10 kHz and 14 kHz. 315 Hz was 77,5 mV but with equalization I had up to 60 mV, more or less.
Check the frequency responses for all three tape types and adjust for best possible linearity with the aid of trimmer potentiometer EQUALIZATION.
Again R45-R50?
Load IEC2 cassette and start tape transport in record mode.
Feed in Dolby level OdB, 250Hz. When
changing the MONITOR switch setting
from SOURCE to TAPE, the indication
at the PEAK METER should not vary. In
case of a difference adjust trimmer LEVEL (1.710.471).
After these adjustments check the azimuth of the sound heads.

i dont know where is a problem with equalization. I turned potmeters all the way but without results. Maybe in bias adjustment because I had different voltage. Maybe my line in voltage (77,5 mV) was to high?

Hope that this has simple answer and solution

Best regards
Ivica

 

[jlb2]

Hi Ivica! Sorry for not replying sooner, it's been a busy week and I've just seen your post.

Hi jlb2,
thanks to you I finished with reproduction part of adjustment and I am 100% OK now. Now I made recording part and I am not satisfied with results, so I need one more help . From service manual:

5.4.2 Adjusting the azimuth of the record head (not used for units from no. 2521 )
Caution:
When making this adjustment, use only high quality cassettes that have been spooled forward and backward once. The tape must not show
any mechanical damage or deformations along the edges.
— Clean all parts that come in contact with the tape with a moist felt stick (included in the REVOX cleaning kit) and subsequently demagnetize these parts.
— Load cassette and press the TAPE SELECTOR button that corresponds to the type of cassette. For cassettes coded according to the IEC scheme, the AUTO position can be used.
— Feed in line level —20dB, 10kHz, at LINE INPUT; line level —20dBu should be available at the LINE OUTPUT ( MONITOR switch in SOURCE position).
77,5 mV?

No, it's line level minus 20dB, i.e. -16dBu, or 123 mV - unless you chose to use a line level different from the standard +4dBu.

— Start record in play mode ( press REC and PLAY ).
Set MONITOR switch to TAPE position.
With screwdriver size 00 for cross recessed head screws adjust screw Y (Fig. 5.5) in such a manner that maximum level is obtained for both channels (minimum phase difference) .
When I done azimuth I had difference in voltage value between L and R channel (85 mV and 135 mV), but they were in phase (and in XY plane it was 45 degree). I just made a little turn to right side and I got 120 mV on both channel, but chanel were not in phase (in XY plane it was not much less than 90 degree). Is this correct? I used TDK D90 tape.

No, this is not normal, you must get both the same phase and level, but if you cannot get them both then adjust for phase.

The manual is not clear on this, but the equalisation adjustment, which basically a filter, changes the phase in the high frequencies. This means that the azimuth and eq adjustments interact to change both the relative phase and amplitude of both channels. You will need to set the adjustments several times in order to iteratively approach the correct azimuth, eq and level settings - When you can achieve the correct level and phase simultaneously, you're done..

In fact, you will probably need to run several times the whole playback & record calibration procedure to reach perfect adjustment, because both are somewhat interdependent. You will find this cubersome the first time, probably to the point of doubting your ability to do things right, but after a few times experience will help you considerably.

The following adjustments apply for one type of tape only.
For other tape types, proceed in the same manner. The position of the corresponding trimmer potentiometers can be determined from Fig 5.4
All of settings first I do for normal tape (bias, level, equalization) and after for chrom and metal, or I change tapes in each setting (bias, level, equalization)?

The procedure is exactly the same for all three types of cassettes, but the pots are different for each. You do the whole procedure separately for each type.

5.4.3 Adjusting the tape bias
Same preparations as described in 5.4.2. (mean I must record tone 10 kHz, -20 dB?) and...

20dB below the reference level, that is correct.

Adjust the corresponding trimmer potentiometers on the oscillator PCB (refer to Fig. 5.4) in such a manner, that maximum output level is obtained for both
channels. Write down the actual values (in dB) and deduct from this valuetheamount shown in Fig. 5.8.
My deck has serial number 1391 and I think that I have Sony heads, because I can adjust records head azimuth. Which column for delta U is mine; left or right? I think left (for example delta U for TDK MA is 4 (dB?).

You are correct, use the left column if you can adjust the playback and record azimuth separately. The deltas are in dB indeed.

Should I have same max value for both channel, or just max value which can be different for each channel? I made with max but different voltage between channels (probably wrong!)

It is not necessary to have the same maximum level on both channels, that's why the manual tells you to measure it separately. Because the bias adjustments of both channels are interdependent, you will need to find a compromise so that both channels are as close as possible to their maximum, but no need to ensure the same values. Of course,an excessive difference would indicate a problem, but a couple of dB is normal.

Set this calculated value with the corresponding trimmer potentiometers.
For max value and for value according to table in fig 5.8 I use same potmeters? (R37-R42)

Yes, you use R38 (right channel) and R42 (left channel) for type I cassettes.

Caution:
The channels influence each other. When adjusting for maximum level, the optimum compromise must be found.


5.4.4 Adjusting the record level and equalization
Feed in line level —20dB, 315Hz, at LINE INPUT.
77,5 mV?

No, 123 mV as above.

The INPUT CAL button must be released. Set DOLBY NR switch to OFF position.
Start tape transport in record mode. Adjust trimmer potentiometer LEVEL (potmeters R39-R44?) (record equalization 1.710.486) in such a manner that no level jump occurs
when changing the MONITOR switch setting from SOURCE to TAPE.
That was OK.

This is a good thing. But you still need to run the calibration several times until the other conditions (phase, 10 kHz level) are also met. Yes, it's R41 and R44 for a type I cassette.

Preadjust the trimmer potentiometer EQUALIZATION (R45-R50?) (record equalizer 1.710.486) with the following frequencies relative to 315 Hz:
IEC 1 10 kHz 0 to +1 dB
IEC 2+4 14 kHz 0 to +1 dB
Here I had a problem. I could not made enough voltage for 10 kHz and 14 kHz. 315 Hz was 77,5 mV but with equalization I had up to 60 mV, more or less.

This is normal the first time you try. It will improve in the following iterations. Yes, R47 and R50 for type I.

Check the frequency responses for all three tape types and adjust for best possible linearity with the aid of trimmer potentiometer EQUALIZATION.
Again R45-R50?

Yes.

Load IEC2 cassette and start tape transport in record mode.
Feed in Dolby level OdB, 250Hz. When
changing the MONITOR switch setting
from SOURCE to TAPE, the indication
at the PEAK METER should not vary. In
case of a difference adjust trimmer LEVEL (1.710.471).
After these adjustments check the azimuth of the sound heads.

i dont know where is a problem with equalization. I turned potmeters all the way but without results. Maybe in bias adjustment because I had different voltage. Maybe my line in voltage (77,5 mV) was to high?

No, on the contrary it is too low, but this has no effect on the flatness of the frequency response. The calibration procedure is the same for type II and IV as for type I, including the need to iterate the adjustments.

Hope that this has simple answer and solution

"Simple" is not the exact word, but this is definitely feasible, and with experience you will do it faster and better. Just don't get discouraged.

 

[ijurcevic]

jlb2 many thanks, I was on short holiday and my answer is a little bit late. Now I have complete picture and I will make one or two iteration more.
Just today I found something strange. I made all test tones on audacity and I measured voltage on outputs of DAC. This test tones I put on tapedeck via DAC and foobar2000.
I made tones 250 Hz, 315 Hz, 1 kHz, 10 kHz, 14 kHz and 16 kHz, 128 mV, 0,775V,...(according service manual. Today i put all tones to tapedeck and measured voltages on output (monitor switch on SOURCE).
i measured all tones and all voltage were same like on DAC, except 14 kHz and 16 kHz. This two tones on tapedeck has voltage 103 mV, not 128 mV like on DAC. 315 Hz, 10 kHz were 128 mV on DAC and on tapedeck.
I dont have idea what is not good.

Best Regards
Ivica

 

[jlb2]

jlb2 many thanks, I was on short holiday and my answer is a little bit late. Now I have complete picture and I will make one or two iteration more.
Just today I found something strange. I made all test tones on audacity and I measured voltage on outputs of DAC. This test tones I put on tapedeck via DAC and foobar2000.
I made tones 250 Hz, 315 Hz, 1 kHz, 10 kHz, 14 kHz and 16 kHz, 128 mV, 0,775V,...(according service manual. Today i put all tones to tapedeck and measured voltages on output (monitor switch on SOURCE).
i measured all tones and all voltage were same like on DAC, except 14 kHz and 16 kHz. This two tones on tapedeck has voltage 103 mV, not 128 mV like on DAC. 315 Hz, 10 kHz were 128 mV on DAC and on tapedeck.
I dont have idea what is not good.

Best Regards
Ivica

Hi Ivica,

It's a good idea to create a test file with the levels and frequencies you need, it makes it easier to do a quick check of the deck.

First off, this is not the main point but I wonder why you set the signal level to 775 mV. The standard line level should be 1228mV, 2dB lower as discussed should be 976 mV, and I can't remember of a calibration step that requires 4dB below the standard line level. But, of course, this does not explain your abnormal frequency response.

I need to know more about what you are doing: if I get you right, you have a soundcard (let's call it like this for clarity, even if it's external) that you feed with Audacity, and you measure the voltage both on the output of the soundcard and of the A710. I have a few questions about your setup:

• Is your soundcard balanced or unbalanced? Unbalanced line outputs have a highish impedance and can easily give irregular frequency response when loaded by a complex impedance like a transformer.
  
• What is your voltage measuring instrument? An oscilloscope? A millivoltmeter? Something else?
  
• When you measure the voltage at the output of the soundcard, is it hooked to the recorder's input? If not, you may just be measuring the effect of loading the soundcard's output.
  
• When you measure the recorder's output, is the Monitor switch in the "Source" or "Tape" position? In the latter case, you may be measuring the cassette's response and it is not unusual to measure 1.5 dB irregularities, which is what you see.
  
• Is the recorder's output terminated by a 600 ohm resistor between pins 2 and 3 when you measure it? Poorly terminated transformers can ring and produce irregularities in the highs.
  
• Are pins 1 and 3 of the XLR connector shorted to make them unbalanced? Measuring just one leg and letting the other "in the air" can easily produce strange readings.

I don't see anything else to check for now, but once you have eliminated those common sources of problems and given me more details on your measuring setup I'm sure more questions will arise.

Best regards

 

[ijurcevic]

Hi jlb2,
i had 0,775 V for other decks, I dont know why I put it to my text . I used for A710 315 Hz, 128 mV; 315 Hz, 1,228 V; 10 kHz, 128 mV and 14 kHz, 128 mV.
1.) My soundcard is unbalanced, with USB input for PC and RCA outputs for left and right channel
2.) Millivoltmeter with proper voltage measuring up to 100 kHz. Not cheap one.
3.) I connect a millivoltmetar direct on RCA outputs of soundcard, first left channel, then right. Mean not hooked on recorders input.
4.) Monitor switch is in SOURCE position, on recporder inputs i have connected soundcard, on recorder outputs i have connected a same millivoltmeter.
5.) My coleague made me two cables XLR to RCA (for input and output of deck). Hot of RCA is connected to pin 2 of XLR. Shield of RCA is connected to shorted pins 1 and 3 of XLR. Connectors (XLR and RCA) are from NEUTRIK. When I measured outputs of Studer I put on Male RCA connector another connector (female to female, also Neutrik) and then I connect a millivoltmeter, first left then right channel. I have RCA cable with open HOT and shield wire. That two wires I connect to millivoltmeter and in parallel I put 600 Ohm resistor ( I use a crocodile connectors for that). Input signals from soundcard (test tones) are always stereo, ie always has left and right channel on recorder inputs
6.) Yes, pins 1 and 3 of XLR are shorted.

Once more, for all test tones I have same measurement on soundcard and tapedeck, except on 14 kHz. For example 315 Hz, 128 mV has voltage of 128 mV on souncard output and on Studer output (monitor switch in SOURCE position). !4 kHz, 128 mV tone has voltage 128 mV on soundcard outputs and 103 mV on Studer output.

Best Regarda and thanks
Ivica

 

[jlb2]

Hi jlb2,
i had 0,775 V for other decks, I dont know why I put it to my text . I used for A710 315 Hz, 128 mV; 315 Hz, 1,228 V; 10 kHz, 128 mV and 14 kHz, 128 mV.
1.) My soundcard is unbalanced, with USB input for PC and RCA outputs for left and right channel
2.) Millivoltmeter with proper voltage measuring up to 100 kHz. Not cheap one.
3.) I connect a millivoltmetar direct on RCA outputs of soundcard, first left channel, then right. Mean not hooked on recorders input.
4.) Monitor switch is in SOURCE position, on recporder inputs i have connected soundcard, on recorder outputs i have connected a same millivoltmeter.
5.) My coleague made me two cables XLR to RCA (for input and output of deck). Hot of RCA is connected to pin 2 of XLR. Shield of RCA is connected to shorted pins 1 and 3 of XLR. Connectors (XLR and RCA) are from NEUTRIK. When I measured outputs of Studer I put on Male RCA connector another connector (female to female, also Neutrik) and then I connect a millivoltmeter, first left then right channel. I have RCA cable with open HOT and shield wire. That two wires I connect to millivoltmeter and in parallel I put 600 Ohm resistor ( I use a crocodile connectors for that). Input signals from soundcard (test tones) are always stereo, ie always has left and right channel on recorder inputs
6.) Yes, pins 1 and 3 of XLR are shorted.

Once more, for all test tones I have same measurement on soundcard and tapedeck, except on 14 kHz. For example 315 Hz, 128 mV has voltage of 128 mV on souncard output and on Studer output (monitor switch in SOURCE position). !4 kHz, 128 mV tone has voltage 128 mV on soundcard outputs and 103 mV on Studer output.

Best Regarda and thanks
Ivica

Hi Ivica,

The combination of points 1 and 3 is a plausible explanation. You need to measure the input and output in exactly the same conditions, otherwise the input voltage might change while you are not measuring it, and then you think you see a different gain in the recorder whereas you are really seeing a different input voltage. I always use a Y cable between the generator and the recorder input, and plug the millivoltmeter either on the input or the output: the input impedance of the millivoltmeter is very high so plugging it in and out does not change the measure, unlike the recorder which has a comparatively low and complex input impredance. One last thing; the 600 ohm resistor must be connected to the recorder, not to the millivoltmeter (not sure to understand what you wrote about this), otherwise what I wrote above would not be valid as you would have the equivalent of a millivoltmeter with an impedance of 600 ohms..

All the best,

Jean-Luc

 

[AlexMacPro]

Hi, and welcome to Audiokarma.

Not exactly. R104/R204 adjust the recording level. Once you have set them to read 730 mV at P3 and P4 (the 755 mV value is only for the ultra-rare HighCom version), use R110/R210 to read the reference output level (usually +4dBu) on both outputs.

Hi I’m new on Audio Karma with Best Regards to All. Sorry, but i need Help. Where can i locate P3 and P4 points?
In my manual i have nothing about where this points are exactly located. No picture or something like that.
Help me Please

 

[ijurcevic]

Hi and welcome,
P3 and P4 are on Dolby encoder board 1.710.489, in service manual section 7/16, near and left from IC2 and IC3.

Best regards,
Ivica

 

[AlexMacPro]

Hi and welcome,
P3 and P4 are on Dolby encoder board 1.710.489, in service manual section 7/16, near and left from IC2 and IC3.

Best regards,
Ivica

Thank you very very much for your help. One more question is there any ability to adjust repro equalisation?