I have a Studer A810. Using an MLR Reproducer calibration tapes for 3.75", 7.5" and 15" I performed the level setup, azimuth and EQ. The 7.5" and 15" EQs are fine, but when I attempt to EQ the 3.75" speed the high-end drops almost 8db. I've tried to adjust, but the HF adj is at max. I've looked at it with two different tapes, so I know the tapes are good. The adjustments are through the MPU with 256 steps, so I don't believe there is a way to change the resistance. I'm not sure why the higher speeds are OK. I've tried setting azimuth using both an oscilloscope and an RTW TM3 Primus meter and both are consistent. Other than relapping the heads are there any suggestions how to get the 3.75" EQ in spec? Everything else with the deck is good. Any suggestions would be appreciates.
Studer A810 3 3/4" HF
- Thread starter kfalls
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My guess is that the electrical response in your play amp is way off at 3.75ips due to a defect or incorrect setting. With a loop generator, verify that your electrical HF response is actually 90 usec (NAB 3.75ips) or close to it. 90 usec with a loop will give you a 15.2 db boost at 10KHz (vs. 315Hz).
Can you provide more details. Are you saying I should build a loop, connect it to a signal generator set to 10KHz and view the output to see if it's at 90usec? If not please specify. I have electronics and computer knowledge, just new to reel to reel and broadcast quality players.
Correct. Build the loop generator and inject two tones into the play head. When inputting 315 Hz and 10K to the loop, 10k should be at least +15.2 db relative to 315Hz. Actual measurements will be in the +15.2 to +16db range (due to the addition of head gap compensation). This is to verify that the play EQ amps are set to 90 usec EQ (NAB 3.75 ips).
Correct. Build the loop generator and inject two tones into the play head. When inputting 315 Hz and 10K to the loop, 10k should be at least +15.2 db relative to 315Hz. Actual measurements will be in the +15.2 to +16db range (due to the addition of head gap compensation). This is to verify that the play EQ amps are set to 90 usec EQ (NAB 3.75 ips).
First, is there a way to do this without fabricating a loop? I noticed in section 4/21 of the service manual there is a way to vary the time constant up or down by switching off JS7, holding the TRANS key and REPRO TREBLE keys until the LED flashes then adjusting the time constant using the up or down buttons. Press Down to shift it toward the treble. I'm having trouble determining which switch is the JS7 program switch. Is it on the underside of the keyboard panel, switch 7 of the first set of 10 position switch blocks?
Yes, as I indicated in the first post, your deck's internal settings may just be incorrect for the lowest speed. I don't have the manual in front of me right now. I will get it and see if it helps in locating that switch for you.
Is it on the underside of the keyboard panel, switch 7 of the first set of 10 position switch blocks?
In the upper right should be 8 "DIP" switches. JS7 is the second from bottom. Switch to off to check/set repro EQ.
Section 4/21 states that theoretical 90 usec value is A3 (163 in decimal). You should set the EQ to that if it isn't. EQ should be left at 90 usec. When fine tuning HF with your test tape, use repro treble.
Section 1/20 has "standard calibration values". For 3.75 ips it lists 70 for repro treble and 90 for repro bass. These should be starting points for adjusting play treble and bass. It also lists 95 (149 in decimal) for repro EQ which is different than the EQ value stated in section 4/21 (value A3). Might be a typo? See what value your deck is set to.
In the upper right should be 8 "DIP" switches. JS7 is the second from bottom. Switch to off to check/set repro EQ.
Section 4/21 states that theoretical 90 usec value is A3 (163 in decimal). You should set the EQ to that if it isn't. EQ should be left at 90 usec. When fine tuning HF with your test tape, use repro treble.
Section 1/20 has "standard calibration values". For 3.75 ips it lists 70 for repro treble and 90 for repro bass. These should be starting points for adjusting play treble and bass. It also lists 95 (149 in decimal) for repro EQ which is different than the EQ value stated in section 4/21 (value A3). Might be a typo? See what value your deck is set to.
Sorry to be so dense. Are you talking about the upper right of the Periphery Control board? I had asked about the underside of the keyboard panel and the 20 switches there. The Periphery board is all I can see with 8 switched. I just want to verify it's the Periphery Control PCB we're talking about. I know what you mean about different parameters, The text on the periphery board states switch 7 is for selection of NAB/CCIR (to use the same or different parameters), elsewhere it state switch 7 has no effect.
SJ7 is on the Periphery Control board. See photo in section 4/16 where the SJ8 switch is indicated.
SJ7 is on the Periphery Control board. See photo in section 4/16 where the SJ8 switch is indicated.
Yes, I found it. It was already set to A3 for both channels. I tried raising and lowering the values to see what changes it would make to the EQ. The EQ didn't change, so I set it back to A3. This player had a bad capstan controller some time ago which caused the capstan motor to run away at high speed. It was changed out with a direct replacement. It appears to be working well, PLL light flashes then syncs on all speeds. Using the MRL tape and a frequency counter I checked the speed. There were only slight variances. I don't think it's a speed issue. I can't think of anything else which would cause his except for worn heads, yet the 7.5ips and 15ips Eqs are good. Ant other ideas or suggestions for me? This has me scratching my head.
Yes, I found it. It was already set to A3 for both channels. I tried raising and lowering the values to see what changes it would make to the EQ. The EQ didn't change, so I set it back to A3.
Well the HF level not changing for you when you raised and lowered the EQ values is a defect. You should be able to change the HF level when changing EQ. Perhaps see if you can change the HF level for the other speeds when changing EQ. For 7.5 ips NAB, the base EQ value should be 61 (50 usec). See if changing that value changes the EQ (and therefore the HF level).
You could check the loop response, but I'm guessing it's not correct for 3.75ips (not 90 usec).
And you earlier said the repro treble adjust at 3.75 ips works fine? It raises the HF up and down?
I can't think of anything else which would cause his except for worn heads, yet the 7.5ips and 15ips Eqs are good. .
Just check the loop response as I initially suggested (to see if it's 90 usec). That will tell you for sure if it's a defect in the electronics or the head. Put all playback adjustments to the default/standard settings before measurement (bass, treble, EQ).
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