PL7000S2

[George S.]

Yup, but too much $ for what I'm doing. At this point though, I'm definitely considering getting one.
There was a cheap used one on eBay a couple months back. But the photo showed one of the spring ends had been pulled loose and poorly reattached.
Got the transport ready to drop back in. I now do better understand some of the finer points on how it works.

 

[George S.]

Back up and running.
Clutch is good, Issue was a slipping drive tire.
Cleaned the old original glaze off the reel drive hubs and drive.
Adjusted the DC motor drive.
Ran the mirror cassette, and the cut-away cassette.
Been monitoring VDC at the reel motor on a Fluke and frequency of the direct drive AC capstan motor on the scope.
Been playing SA's no problem, voltages and frequency are stable.
I'll readjust azimuth and redo alignment from the beginning.
Later, listening to the Allman Brothers.

 

[George S.]

Finished the initial alignment. Fortunately the Microscan board appears to be good as I can see the comparator switching on, off, on.
I do have EQ issues that further alignment may or may not resolve.
Here's the first frequency response taken at the decks output jacks
This is a automated test using the QuantAsylum QA403 to generate the tones and process the data. Target is -20 dBV, tape is a TKD D90.
Clearly the response needs improvement, but a good start.

 

[Chris Cables]

Finished the initial alignment. Fortunately the Microscan board appears to be good as I can see the comparator switching on, off, on.
I do have EQ issues that further alignment may or may not resolve.
Here's the first frequency response taken at the decks output jacks
This is a automated test using the QuantAsylum QA403 to generate the tones and process the data. Target is -20 dBV, tape is a TKD D90.
Clearly the response needs improvement, but a good start.

Pretty envious of your QuantAsylum. Been lusting after one for a while now but haven't pulled the trigger. There's quite a mark-up on them over here in the EU (€800) but at least no supply issues.
Currently using a Wavetek 75A through the target to a Scarlett into REW for FR analysis but would love to start measuring for noise and distortion on decks and cables at some point.
You going to be measuring that too?
Everyone seems to use NAKT100 for decks but fkd if MS gets any of my money!

 

[George S.]

Yeah Chris, eventually w+f, noise, distortion, etc.
I do like REW.
Used it to set up the MiniDsp active crossover in the main system.
It's very cool how the REW measurements drop directly into the MiniDsp software and REW is configured to use the MiniDsp USB microphones.

 

[Chris Cables]

I'm using WFGUI for W&F but would be really interested to see an accuracy performance comparison between that and the QuantAsylum if you have the scope/time?
Many comment and complain about the different weighting between WFGUI/NakT100 and other devices. Personally I take the WFGUI figures with a pinch of salt and am usually satisfied with a +/-0.010%RMS deviation from specs.

 

[George S.]

The QA40X software, which is a free download, has a w+f meter , but they haven't finished it. It works, but has no weighting options.
They're in the middle of rewriting all the software to make the units more compatable with other software that the pros use. Hopefully they'll sell more units and develop more products.
Personally, the current software more than meets my needs and is bug free.
If I'm using the Leader millivolt meter, I generally add a BNC T and tie the QA403 to the meter. Very easy to see the tape and voltage levels. Helps me visualize and hopefully better understand what I'm doing and what the Service Manual wants.
I'll post a screenshot of the w+f meter and results once I get to that point.

 

[George S.]

A little more tweaking of the Playback and Record EQ trimmers last night got me this.
The treble on the D falls off at 17K, the MA-X at 20K.
This may look acceptable, but it's not.
The Playback EQ trimmers are maxed out and the 10K and 14K levels are low, missing the target. These are adjusted using the HPR frequency response tape, and the Record EQ circuit isn't involved.
I surmise that by recording a signal and playing it back (the QA403), the Record EQ is compensating for the Playback EQ's low treble levels.
So board level component changes are needed to bring the Playback EQ into spec, using the HPR frequency response tape.
Then, I can look at the Recording EQ, using the QA403.
I have looked extensively at Alex's documents about swapping the head on the CT-F1250, and sort of see why he made the changes.
Going to study the schematics for the next years models that used the Sendust head and see what they changed.
Probaly just resistor and cap values.

 

[laatsch55]

Now its getting technical...

 

[J!m]

I agree with your analysis of the issue.

Tapes recorded and played back on the same deck often hide problems...

 

[George S.]

That's my understanding Jim.
Commercially recorded tapes are recorded with a specific EQ.
Therefore those tapes should play correctly on all decks that have a correctly aligned Playback EQ section.
In my case, the Playback EQ is out of spec due to the head swap.
I'm missing hitting my targets at the higher frequencies, even with the trimmer at its limits.
Just did a resistor swap between the head and Playback EQ section, copying what Pioneer did on the next models that used this head.
Hopefully this will work for this issue.
If it works, I'll post the plot the HPR tape generates.

 

[George S.]

So I need a additional tape to properly set the Playback EQ,
A Pioneer STD341A equivalent has been ordered from Genlabs.
I'll resume once I get the tape.
Everything is looking very good after the resistor swap.

 

[George S.]

The SM is calling for a 120usec tape to calibrate the Playback EQ, specifically the Pioneer STD341A.
All the HPR tapes are 70usec.
I can get the Playback EQ alignment close with the HPR tape and some juggling, but I want this accurate.

 

[George S.]

Still waiting on the tape.
Been playing around with digital and analog test equipment to make measurements of the Playback EQ.
If the SM alignment step requires playing a tape, I get best results with the old Leader Millivoltmeter and HP 1742A CRT scope.
They are contemporary with the deck and the test equipment being used when they wrote the service manuals.
Found a nice Excel program to TH's to plot the FR.

 

[George S.]

Got the Gennlab GL-341 tape.
Got the tones indexed to my tape counter and noted using the scope and QA403.
Then got head azimuth adjusted for this tape, it was close to the HPR tape adjustment, but definitely a difference.
The 10 KHz signal is more consistent and stable on the GL-341 than the HPR tapes.
I'm impressed so far.

 

[George S.]

Been reading about parallel and serial LCR circuits last several weeks.
Currently the play back heads self resonate frequency is too low to properly adjust the play back EQ.
It's currently resonating at about 1.5 kHz.
There's not a lot of information out there about this, but Nortronics says the resonant frequency must be equal to or above the maximum play back frequency.
There is 191 mH of inductance on each play back channel. Nortronics recommends setting the resonate frequency to 25 kHz for 200 mH of playback head inductance.
Think I can get from 1.5 to 25 kHz resonance with a small cap change.
Another issue is the damping, but I'll get the resonate frequency set first.
The graph was generated with the QA403, injecting the signal directly into the play back head through a adapter.
I see a very similar hump of +5 dBV over the -20 dBV base line at 1.5 kHz when attempting playback EQ adjustment.
Waiting on caps.

 

[laatsch55]

Damn....

 

[George S.]

Yeah Lee! Got the time and tools to hopefully figure this out.

 

[George S.]

Testing some styrene caps.
The deck came with 100 pF parallel to the playback head, while the schematic calls for 220 pF.
Calculations call for a 330 pF.
These melt easily while soldering or desoldering,

 

[laatsch55]

Yes they do. Gotta be quick. I have desoldered and salvaged 150 or so and only burnt 2. Figured that was pretty good.