DAVID GRANT'S 625 TO 405 STANDARDS CONVERTER

 

A review by Jeffrey Borin 12 June, 1993

Published in 405 Alive Issue 19, dated Summer 1993

 

Suddenly the world is full of standards converters! David Grant's converter has existed for a little while but I have only recently obtained a sample for review. Inevitably this review will compare his design with the Pineapple unit reviewed in the last issue of 405 Alive.

 

A FAMILY OF CONVERTERS

This is not one design but a whole family. This ranges from a kit without interpolation at 180 to a unit built in a very professional 19" rack case for over 800.

 

At the time of writing not all prices had been finalised but here is some idea:

 

Kit without interpolator: 180

Kit with interpolator: 250

 

The kits come with all tricky assembly such as surface mount components done. The analogue parts are pre‑aligned so no test equipment is needed. Assembly is not difficult but remember that soldering chips to PCBs is a rather different task to wiring valveholders. You will need to provide your own box and power supply. Instructions are provided along with circuit diagrams etc.

 

Ready built unit including box and power supply: Add 80 to above.

Broadcast grade video filters, 19" rack case etc are by individual quotation.

 

There is no intention to add a modulator. Refer to my review of the Pineapple converter for information on modulators.

 

FIRST THOUGHTS

Operation could not be simpler. The only control is the mains switch! BNC sockets are provided for 625 video in and 405 video out.

 

The construction quality is excellent. There are two PCBs for the main converter and a further one for the interpolator. These all plug into a small PCB mother board. Unfortunately this means that access to the lower boards is very limited so faultfinding and repair might be tricky. On the other hand it all runs cool and should be very reliable.

 

The review sample used a small switchmode power supply. This was not shrouded and would make working inside the box quite hazardous. With the outer cover in place the converter is perfectly safe. I am assured that all future converters will have their live parts adequately covered. Future units will probably also have a linear power supply since the total consumption is under 10 watts.

 

INTERPOLATION
David Grant's converter uses conventional line store technology and its concepts are based on the BBC CO6/509. This contrasts with the Pineapple and its frame store. The two line interpolator uses successive lines from the same field. It is fully digital unlike the Pineapple design. The interpolation is excellent and difficult to distinguish from the CO6/509 which uses four lines.

 

RADIO INTERFERENCE
The converter contains much high speed digital circuitry which is a potent source of RF interference. If you buy a kit you must house it in a metal box. The review sample did not cause any significant interference.

 

ENGINEERING NOTES

All the circuitry has been designed and built to a very high standard. It is difficult to find even the most minor fault with the performance of the converter. In the absence of video input the converter produces 405 line sync at the wrong frequency. This is comparable to the BBC CO6/509. With very poor quality inputs it is possible that the Pineapple converter with its frame store might produce usable pictures where David Grant's might not. Certainly the Pineapple converter is incapable of producing bad 405 sync pulses however grim the picture looks.

 

PICTURE QUALITY

The subjective picture quality is very good. I compared the converter with a BBC CO6/509 using a professional video monitor and several receivers both pre‑ and post‑war. It was difficult if not impossible to tell the difference. In particular there was no ragging of verticals. (NB this effect is still present on a production version of the Pineapple converter that I saw recently) The unit copes well with VHS replay.

 

CONCLUSIONS

For many people the Pineapple converter will be the right choice. It is cheaper, has some nice tricks like picture freeze and gives good pictures. If you want the very best results or if you enjoy building a kit then David Grant's converter offers outstanding performance and is recommended.