new 80-Column Display on Modern Hardware - Options 2 and 3

I wanted to report about using the Ambery adapter.  I originally posted you could use either the CV-04 (aka AV-04) or the Ambery adapter.  This is because they both sound like they do the same thing (RGB to S-Video and Composite), and others have reported use of the Ambery adapter.

However, I did not try the Ambery adapter myself until recently when I was unable to obtain another CV-04.  Well I had problems and started peeking around various CBM forums, and found that most posts claim the Ambery doesn't work at all.

Well, I eventually made it work, so I want to give everybody the details to save them a load of grief.  It was pain for me because the documentation with the product is quite pathetic.  It tells you acceptable INPUT FREQUENCY, Power Supply, and Output Voltages.  But it does not tell you input voltages (or impedance)...

So first problem was the video sync.  Although I used Ambery's 9-pin RGBI to 15-pin adapter (which has inputs for H-Sync and V-Sync), the Ambery adapter will not work with separate H and V sync.  So I tried combining them with various methods.  Using a XOR gate works with the GBS-8220, but not with Ambery!  This is because the VDC produces Positive sync signals while the Ambery requires Negative sync (it seems the GBS-8220 works with either).  Anyway, the solution was to use a second XOR gate to invert the combined sync.

With a stable display, I was still disappointed by the color of my Pull-Both circuit for 16-colors (without it, you only get 8 colors).  The problem was the dark colors looked almost identical to bright colors, even when I tried cutting the resistor values in half...  This was strange to me because my Pull-Both circuit worked fine for the CV-04 (S-Video adapter) and the GBS-8220 (VGA adapter).  What changed?

The Ambery adapter has a much lower input impedance than the other adapters, as far as I can tell (I don't have the equipment to measure impedance).  This means the Ambery was pulling on the output so "hard" that modification to voltage by my "Pull-Both" circuit had very little effect.  The solution I used was to add a 220 Ohm resistor on each R/G/B line going out from circuit before it gets to the Ambery... this reduces the "pull" (increase the impedance) of the Ambery.

This produced a nice 16-color display, but I always like the color of my prototype "Pull-Down" circuit more than the previously (see first post in this thread) mentioned "Pull-Both".  (Pull-Down is missing dark gray so only 15 colors... but the bright colors of "Pull-Both" are a bit "washed out".)

Anyway, I wanted to include a "brown fix" too.  This is done by 74LS138 (previously published and used by others).  I discovered a way to use the same chip to also generate signal for dark gray!  This means with new circuit I could have better quality of "Pull-Down" and still get 16 colors like "Pull-Both".  I hope you agree resulting quality is excellent....



The Ambery adapter needs Power Supply of 12V, but the chips I used (74LS138 decoder and 74F86 Quad-XOR) require 5V.  This means another detail was to add a 5V power converter to my circuit (this is not needed with GBS-8220 which naturally uses 5V).  So the final circuit is about 3x or 4x more complicated than original Pull-Both shown in first post of this thread.... in summary the extra factors are:

• Need extra 220 Ohm (x3) resistors for Ambery impedance
  
• Need 2 XOR gates to create Negative Composite Sync for Ambery
  
• Used decoder (74LS138) for "brown fix" (also used for "dark gray" to give better color for all "light" colors) [not strictly needed]
• Need 5V regulator circuit to use Ambery power supply
  

Below is a sample schematic... please note it is a bit buggy!  I labeled the pin numbers from some of the XOR gates wrong (swap pin# 8 and 10, and pin# 13 and 11 to be correct) and forgot to label a resistor (left of the top XOR gate... the resistor should say "1KΩ").



Sorry the posted schema is a bit buggy, but this laptop only has generic JPG image of the schematic... I will (actually have) corrected the source file but it is on another computer at the moment.  I will post the corrected version on my website along with additional images as I find the time (also awaiting feedback from user who requested this adapter).

Also interlace text mode and monochrome bitmap mode is confirmed working with the Ambery adapter.  Because I only have 16K V-RAM, I have not (yet) tested color bitmap or interlaced bitmap.  But I think it should work fine...

I guess the important thing to know is that Ambery adapter is more trouble than either the CV-04 or the GBS-8220.... in fact, I would say it has the problems of both added together (double trouble).  I have created and shared with you a working circuit that gives excellent results (hope you agree), so it is possible to use Ambery S-Video converter with C128 (despite some comments on the web to the contrary), but I would use a CV-04 or GBS-8220 if they were available....

(P.S., you can use either the CV-04 or the Ambery adapter as a basis for a SCART converter... ask if you want details... I know there is a thread somewhere on this forum about it...)