AG-1970/60 linear track device?

[dpalomaki]

Not exactly a repair item, but: Found a Carlson-Strand CS250 Audio Controller, which I believe is a device used to break out the linear track audio on the Panasonic AG-1970 (and AG-1960?) independent of the Hi-Fi audio.

This box inserts itself in the lead to the audio/control track heads, passing the control track signal and providing separate record/playback amps for the linear audio heads, thus providing a third audio recording independent of the Hi-Fi heads (a feature that was added to the AG-1980), and probably making linear time code (LTC) possible as well.

Have not tried it to determine whether or not it works, but an interesting device.

Anyone familiar with it?

[latreche34]

Interesting, I know some prosumer VCR's offered separate INs and OUT's for linear audio on the back of the machine but never heard of an add on gadget, Any pictures? Is it a plug and play with a breakout cable or requires de-soldering/soldering?

[dpalomaki]

12 VDC, 200 ma wall wart power supply required.
Molex connectors with a couple feet of cable to allow mounting outside the case.

Four images attached. The plastic case w/paper labels appears to be a garage industry product, obviously for a niche market. The circuit board looks neat except for a bit of an after-board-design add-in (cap, resistor, 2 diodes) just to the right of the "P" on the label in photo 4.. I will try power it up later this coming week if I find a chance.

[latreche34]

Funny that back in the VCR hay day I did a similar MOD to a friends VCR (non HiFi VCR) where the linear track audio no longer works, I suggested that a Walkman playback preamp PCB can be inserted inside the VCR for playback and he accepted, So I had a small Walkman PCB laying around and connected the audio head to it and found a 4.5V point in the main board to power it up and connected the headphones output to the RCA jack isolating the center pin from the main board and tweaked the volume wheel to a proper level, He was very happy. Off course I did not have the repair skills to actually fix it the right way and it was a mono only model, but he was very happy to keep watching his favorite porn tapes, LOL.

[dpalomaki]

Quote:

...but he was very happy to keep watching his favorite porn tapes, LOL

The driver for HD video sales. Some would argue moans and panting sound much better in stereo.

[latreche34]

You forgot to mention the 3D experience.

[dpalomaki]

I did some testing of the CS250 P linear track adapter mentioned above after finding the Installation and Operation Manual in a box of old documentation I have.

The manual indicates it was developed for the AG-1960, it also works with the AG-1970 which is how I tested it. Not needed with the AG-1980 because it provides a separate linear track I/O already. My tests were playback of an existing VHS tape, record/record to a blank tape, and insert to a previously recorded tape.

It connects to the A/C head, separating the audio erase/record/playback signals and passes the control track signals. Connecting wires are passed out of the AG-1970 case to the device via provided cables. (The linear track is no longer available via in the AG-1970 outputs or recorded by the AG-1970.) It has a wired remote control to select Record and Insert mode

It offers three modes, Green (Play), Yellow (Record) and Red (Insert)
- In play mode it gives the linear track output.
- In Record mode it passes audio connected to the input jack to its audio output jack.
- In insert mode it records its audio input to the linear track. Recording is independent of the AG-1970 record/playback mode.

It uses a 12 VDC wall wart supply similar to that used by the BVP-4; i.e., negative voltage at the center pin.

I see this as of value to anyone who wants to access the linear track from an AG-1960 or AG-1970 independent of the HiFi tracks. It may directly work with other Panasonic (and perhaps other brands of VCR) that use a similarly wired 6-pin connection to the A/C head. However a quick check indicates the common JVC S-VHS units use a 7-pin connector (although the signals may be similar).

I may offer it for sale later this month .

[latreche34]

Before you sell it could you provide clear pictures of the PCB, copper traces and components labels, I might be able to reverse engineer it and make a modern PCB with different connectors for different VCR's, If we double the PCB it will have stereo capability, Although stereo is rarely found in any HiFi VCR after the mid 80's. Very useful for JVC's where the linear audio preamp fails with the dreaded buzz noise and low level.

[dpalomaki]

I PMed a link to higher res photos. Good luck reading the component values. It might be easier to just read the schematics from the AG-1960, 1970, or 1980 and then use modern components. This box dates back perhaps 30 years.

[dpalomaki]

A correction to #7 above to cover the "OFF" case.:

It connects to the A/C head, separating the audio erase/record/playback signals and passes the control track signals. Connecting wires are passed out of the AG-1970 case to the device via provided cables. When the CS250 is ON the linear track is no longer available via in the AG-1970 outputs or recorded by the AG-1970. When OFF the linear track operates normally. It has a wired remote control to select Record and Insert mode

[hodgey]

The part that would be the most problematic for such a reproduction these days will be the main audio IC, as those aren't going to have been made for the last like 20 years (on pretty much any vcr from the 2000s linear audio was part of the main video ic). (Well unless one wants to handle Dolby NR but that would probably not be worth the bother...) So either one will have to try to source some commonly used audio ICs used/NOS or one would need to replicate it's functions. Maybe one could get away with something simpler if recording is not needed, and just use some sort of tape amp + switching logic to switch between deemphasis depending on tape speed. (Maybe there are some still produced ICs for audio tape recorders that could be utilized, idk)

[latreche34]

You're right, Some of the components are not easy to identify especially IC2, plus all capacitors has to be identified individually by tilting them.

Isolating the audio pre-amp from the VCR schematic is not that easy as it is usually tied to other circuits in the VCR and the controls are all digital from the main control chip, So I figured that one is as close as possible to replicating.

An audio engineer could design such thing from scratches but there ain't any left that know how to properly design an audio pre-amp taking into consideration the tape equalization for VHS based on tape speed and magnetic formulation, On top of that there isn't any Dolby IC's available on the market.

[dpalomaki]

IC2 is marked C1513HA.

Probably could find schematics for a simple cassette recorder. Tape speeds are similar, although VHS is a bit slower. Some of the old transistor manuals and audio IC data sheets and application notes had playback amp examples for both disc and tape (variations on RIAA and NAB and what ever is popular today). Its a matter of adjusting the equalization components as needed to approximate the right curves.

Record pre-emphasis could be reverse engineered by reading the signal to the record heads in a a vcr as audio signals are fed it.

[latreche34]

Writing is easy, doing it is another thing, Lol.

[dpalomaki]

It is a matter of having the skill set, tools, time, and motivation to do it.

We are discussing legacy gear and methods. A niche demand at best, and a fair amount of effort to research and design a circuit, layout a board, find parts including chassis, and doing it (while still having a life).

While I know how I would go about it (I've done similar projects in the past) I have no need for one now and other projects beckon. Once I put it back together and run a couple more checks I will offer it for sale.

The owner manual describes how to install and use it, but does not cover the internal adjustments (e.g., record bias, gain).