Record and playback calibration

[frpe12]

Hi Mampfi,

Still waiting for my level test tape.
In the meantime, could you explain the role of R1/R3/R5 and R2/R4/R6 trimmers on board Y for recording ?
Thanks in advance.
Regards.
François

[mampfi]

First of all you have to adjust the recording azimuth to the playback head. In hope the playback azimuth is correct.
Because you need a azimuth testtape to adjust it. Give a 10kHz -20dB signal to the machine and measure it with oszillograph.
Set the sinus curves on top of each other on the screen, so you can see if the sinus curves matches each other.

If you do so, you can adjust the recording level and the pre magnetisation for 19cm and 4,75cm speed.

Choose a type of recording material that you like. LPR35 or something like that.
Put a 1kHz Signal to the machine and record it with 19cm @ 0dB ---> approx. 1,3V at the output from the monitor socket.
Turn the prerecording/recording switch to record and adjust R1/R2 that you have the same level in prerecording and in recording position.

Don't move the recording slider/controller. Put a -20db Signal with 10kHz into the machine and switch also from prerecording to recording.
Adjust R5/R6 so that you have the same level between prerecording and recording.

Do the same with R3/R4 @ 4,75cm

Note:
The recording level @0dB will be adjusted only once @ 19cm or 9,5cm/sec
Grundig wrote to do so @9,5cm. I do this @ 19cm/sec. and optimate the frequency response for 19cm/sec
There is only one adjustment for 9,5 and 19cm/sec
You can use R5/R6 and R3/R4 to optimate the frequency response

[frpe12]

Ok, if you playback the testtape, you have to adjust the internal level to 675mV (with this 250nWb tape) @9,5cm/sec
The internal level you can measure at the adpapter board

Adapterplatte TS 1000.jpg

or on the input plug for the phones amplifier

Kopfhörerverstärker TS1000.jpg

Or the output from the monitor socket. If you do so, you have to put the output gain poti to maximum.

You have to adjust the internal level with gr53/gr54 on board G to 675mV.
After that adjust the VU Meters with GR61/GR62 on board D to -6dB, what corresponds to 514nWb@0dB

...that's it

Hi Mampfi,

Job is done : playing this 250nWb test tape at 9,5cm/s allowed me to set 675mV on the read output level (measured on adaptator board) with trimmers on board G. I then set the VU meters level to -6dB with trimmers on board D.

I also set the capstan speed to get 1kHz signal @9,5, 2kHz @19 and 500Hz @4,25.
Heads have benn cleaned and demagnetized before proceeding.

I noticed an issue on the left channel : it is lower than the right channel of about 80mV. Selecting mono2 gives well a very stable 675mV signal with both VU meters @-6dB. But selecting mono1 gives a fluctuating 590mV average signal with both VU meters @-7dB.

I assume that the reading head has to be aligned with an azimuth test tape.
What do you think about that ?

Best regards.

François

[mampfi]

The left channel is on the outer side of the tape. So have to look first for tapetension, tape contact to the head and the correct position for the metal role between the erase head and the record head.
Also you can have a look to the left play system of the playback head. The lower edge of the playback headsystem has to match with the lower tape edge. Easy to test with an transparent tape.
Another thing is the quality of the pinch roller. There is a test described in the service manual for checking the tape run without heads.
Last but not least.....cleaning, cleaning, cleaning

Good luck

[frpe12]

Hi mampfi,

I'm back with some news !
I checked the tape path and it seems to be ok, just by watching the tape contact with the heads with a transparent header tape.
I then tried to tune the screws for playback head alignment, using my level calibration tape.
I succeeded in getting a better result on the left channel : the level is no more fluctuating, but it is still lower than the right channel (around -1dB) on the VU meters and oscilloscope.
The screws are at their maximum course and I cannot get any better than this. Maybe another issue with the pinch roller or something else.
The test tape provides a 1KHz signal @250nWb.
Switching to "Mono 1" (left channel on both VU meters) gives -7dB.
Switching to "Mono 2" (right channel on both VU meters) gives -6dB.
This shows that my playback amplifier settings on board G are the same for both channels.
I also aligned the phase shifting between the channels. Now they are perfectly synchronized.

Then I switched to the recording part.
Recording a 1Khz sine wave (from YouTube) then a 10KHz sine wave signals allowed me to align the record head azimut to the playback head one.
Now the recorded signals are perfectly aligned and synchronized at playback with the different frequencies.
But I noticed that playing back the recorded signal gives different left and right levels : the left channel playback level is almost the same as the recorded level, but the right channel playback level is much higher than the recorded level (+3dB).
The difference is the same whatever the recorded signal frequency. Same also when recording a song.
Please note that I use a brand new LPR35 tape from RTM.
How do you explain this delta ? Do you think that board Y trimmers need to be tuned as you described in your previous comment ?

Kind regards.

François

[mampfi]

Sorry for the late news. We were out for a short Holiday.

Yes i think you have to align the trimmers like i described in my earlier post.
1. First use 1khz @ 0db to get no difference between record and playback.
2. Then use 10kHz @ -20dB to get no differnce between record and playback.

If you do so, repeat step 1 and 2 until you have (almost) no difference for both alignments.
Because the results influence each other somewhat

Use R1/R2 on Y board to calibrate the 1khz level.
Use R5/R6 on Y board to calibrate the 10kHz level for 9,5/19cm speed
Use R3/R4 on Y board to calibrate the 10kHz level for 4,75cm speed