12 replies to this topic

[Willsy]

Thought I'd post a few pictures to show that the F18A can indeed be fitted neatly into the console:

This first pic shows the F18A VGA connector fitted into the case of the console. It is necessary to remove the steel support from the VGA connector that is supplied with the F18A, and also the black plastic shroud around the VGA connector pins. Use a sharp knife to cut away the plastic to make a snug fit, then drill two holes for the VGA connector screws to hold the connector in place on the case. De-solder the original analogue video out connector from the mother board. You can also see the cartridge cover has been removed to expose the grille in the top of the console. A 45mm Mylar speaker fits just great. Use two little spots of Uhu glue to glue it in place:
 IMAG0262.jpg   843.89K   56 downloads


This picture shows the VGA connector in-situ. Note that the UPPER case is cut and drilled, not lower case!
 IMAG0264.jpg   832K   73 downloads


Make sure to use washers and a split washer to hold the nut tight; it's a pain in the ass when they come loose and you have to open the console up to tighten them again:
 IMAG0269.jpg   715.44K   63 downloads


Cartridge cover back in place. Solder the cables to the speaker before you put the cover back on!
 IMAG0270.jpg   835.3K   52 downloads


I took the power supply for the internal amplifier (a kit from Velleman) from the mother board. As can be seen, I've tapped into the +12V supply:
 IMAG0271.jpg   1.19MB   56 downloads


Here's the F18A taking pride of place. Obviously the 9929 has been removed! Take care to fold the video cable so that it exits towards the back of the circuit board.
 IMAG0272.jpg   1.06MB   61 downloads


Re-assembling the motherboard case. The F18A fits inside the steel case just fine. You can see the amplifier, which as yet to be stuck down. It's very small, measuring about 35mm by 45mm.
 IMAG0274.jpg   737.83K   51 downloads


The amplifier is stuck to the 'roof' of the console, just to the side of the joystick port. It fits in there just perfect, the steel case on the mother board doesn't foul it!
 IMAG0275.jpg   1.06MB   39 downloads


All re-assembled - all fits together just fine!
 IMAG0278.jpg   714.03K   41 downloads


The VGA connector looks quite neat and is the only clue that something different lurks within!
 IMAG0279.jpg   824.42K   40 downloads


Oh, and the speaker! If you have some thin black plastic anti-static gauze (the type that is supplied with ICs sometimes) then you put that between the grille and the speaker to cover the speaker up.
 IMAG0280.jpg   588.2K   38 downloads


The final test: Beautiful crisp display on my 1024x768 LCD VGA monitor:
 IMAG0281.jpg   548.24K   34 downloads


The amplifier works fine too, and is as loud as hell! It's rather noisy though; there is an awful lot of noise picked up - you can 'hear' the 9900 processing. Of course, speech also comes from the internal speaker now, too. I'm going to add a rotary volume control to the side of the console next.

I took the audio output from the original audio out at the video connector. I understand that at this point, the audio signal has already been amplified a little for sending on to the UHF modulator. I'm open to suggestions as to alternative locations that I could pick up the audio signal from (somewhere less "noisy" I hope). Maybe I can just connect directly to the audio out pin on the sound chip?

My next little project is to add a two-stage flip-flop to the clock input on the sound chip to drop the sound by two octaves to give proper bass notes, giving a much more usable audio range.

Mark

[Stuart]

Willsy, on Sun Apr 29, 2012 2:04 PM, said:

I took the audio output from the original audio out at the video connector. I understand that at this point, the audio signal has already been amplified a little for sending on to the UHF modulator. I'm open to suggestions as to alternative locations that I could pick up the audio signal from (somewhere less "noisy" I hope). Maybe I can just connect directly to the audio out pin on the sound chip?

Mark

Hi Mark, very neat work!

Regarding the audio, there is no amplification of the sound chip output within the console. I've done the same mod and simply found that by the time you turn the volume down to something sensible, the noise is pretty much inaudible.

Stuart.

[marc.hull]

Willsy, on Sun Apr 29, 2012 2:04 PM, said:

Thought I'd post a few pictures to show that the F18A can indeed be fitted neatly into the console:

This first pic shows the F18A VGA connector fitted into the case of the console. It is necessary to remove the steel support from the VGA connector that is supplied with the F18A, and also the black plastic shroud around the VGA connector pins. Use a sharp knife to cut away the plastic to make a snug fit, then drill two holes for the VGA connector screws to hold the connector in place on the case. De-solder the original analogue video out connector from the mother board. You can also see the cartridge cover has been removed to expose the grille in the top of the console. A 45mm Mylar speaker fits just great. Use two little spots of Uhu glue to glue it in place:
IMAG0262.jpg


This picture shows the VGA connector in-situ. Note that the UPPER case is cut and drilled, not lower case!
IMAG0264.jpg


Make sure to use washers and a split washer to hold the nut tight; it's a pain in the ass when they come loose and you have to open the console up to tighten them again:
IMAG0269.jpg


Cartridge cover back in place. Solder the cables to the speaker before you put the cover back on!
IMAG0270.jpg


I took the power supply for the internal amplifier (a kit from Velleman) from the mother board. As can be seen, I've tapped into the +12V supply:
IMAG0271.jpg


Here's the F18A taking pride of place. Obviously the 9929 has been removed! Take care to fold the video cable so that it exits towards the back of the circuit board.
IMAG0272.jpg


Re-assembling the motherboard case. The F18A fits inside the steel case just fine. You can see the amplifier, which as yet to be stuck down. It's very small, measuring about 35mm by 45mm.
IMAG0274.jpg


The amplifier is stuck to the 'roof' of the console, just to the side of the joystick port. It fits in there just perfect, the steel case on the mother board doesn't foul it!
IMAG0275.jpg


All re-assembled - all fits together just fine!
IMAG0278.jpg


The VGA connector looks quite neat and is the only clue that something different lurks within!
IMAG0279.jpg


Oh, and the speaker! If you have some thin black plastic anti-static gauze (the type that is supplied with ICs sometimes) then you put that between the grille and the speaker to cover the speaker up.
IMAG0280.jpg


The final test: Beautiful crisp display on my 1024x768 LCD VGA monitor:
IMAG0281.jpg


The amplifier works fine too, and is as loud as hell! It's rather noisy though; there is an awful lot of noise picked up - you can 'hear' the 9900 processing. Of course, speech also comes from the internal speaker now, too. I'm going to add a rotary volume control to the side of the console next.

I took the audio output from the original audio out at the video connector. I understand that at this point, the audio signal has already been amplified a little for sending on to the UHF modulator. I'm open to suggestions as to alternative locations that I could pick up the audio signal from (somewhere less "noisy" I hope). Maybe I can just connect directly to the audio out pin on the sound chip?

My next little project is to add a two-stage flip-flop to the clock input on the sound chip to drop the sound by two octaves to give proper bass notes, giving a much more usable audio range.

Mark

Looks good Dr. Frankenstein .  Please explain the flip flop approach.

[Willsy]

Stuart, on Sun Apr 29, 2012 3:47 PM, said:

Willsy, on Sun Apr 29, 2012 2:04 PM, said:

I took the audio output from the original audio out at the video connector. I understand that at this point, the audio signal has already been amplified a little for sending on to the UHF modulator. I'm open to suggestions as to alternative locations that I could pick up the audio signal from (somewhere less "noisy" I hope). Maybe I can just connect directly to the audio out pin on the sound chip?

Mark

Hi Mark, very neat work!

Regarding the audio, there is no amplification of the sound chip output within the console. I've done the same mod and simply found that by the time you turn the volume down to something sensible, the noise is pretty much inaudible.

Stuart.

Stuart, have a look at Theirry's web site, on the audio page.

There's a description of the audio out pin on the sound chip, as follows:


AUDIOOUT This pin carries the sound data to the monitor's speaker (pin 3 of the connector). It is connected to an internal analog audio amplifier.

			 												
--+
#7|--------+----||---+--uuu---+----< pin 3 monitor port
   |		|  100uF  | ?uH	|
   |  0.1uF =	10nF =		= 10nF
   |		|		 |		|
   |		+--www---Gnd	  Gnd
--+ 10 Ohm

The circuit isn't reproduced very accurately here, it's clearer on the website.

One of the problems (in my particular console) is that the the audio input cables to the internal amplifier are quite long, and run very close to the 50hZ AC power - as you know, the console takes in 18V and 5V power rails, and they are AC. They must be noisy as hell! I think I'll physically de-solder the audio out pin from the mother board, lift the pin and solder it to the audio input of the amplifier.

I went and got me a 220K potentiometer yesterday from Maplins. If there is space somewhere at the side of the console I will fit it as a volume control. Jens-Eike also mentioned (and I thought it was a good idea) fitting a 3.5mm jack socket to the console, so that you can run the audio to PC speakers!

[Willsy]

marc.hull, on Sun Apr 29, 2012 4:50 PM, said:

Looks good Dr. Frankenstein .  Please explain the flip flop approach.

Just using a flip-flop (74LS74) to effectively divide the clock input to the sound chip by two. The '74 is a dual flip-flip, so you can feed the output of one flip-flop into the input of the other, for a divide by 4. Jens-Eike can probably comment more than me - he gave me the idea

[matthew180]

Willsy, on Sun Apr 29, 2012 2:04 PM, said:

Maybe I can just connect directly to the audio out pin on the sound chip?

If you take the audio directly from the sound chip, your amp should probably provide a low-pass input filter and impedance matching.  But if you are going to go through all that trouble, you probably want some speakers that are more substantial, and maybe some tone controls.  The idea of providing an standard external audio connector is good IMO.

Willsy, on Sun Apr 29, 2012 2:04 PM, said:

My next little project is to add a two-stage flip-flop to the clock input on the sound chip to drop the sound by two octaves to give proper bass notes, giving a much more usable audio range.

The 9918A generates the GROM clock which drives the sound chip.  Thus, the F18A generates the GROM clock as well, and I'll just make the frequency programmable.  That way you can adjust the sound chip's frequency range via software.

[Willsy]

matthew180, on Mon Apr 30, 2012 9:11 AM, said:

[The 9918A generates the GROM clock which drives the sound chip.  Thus, the F18A generates the GROM clock as well, and I'll just make the frequency programmable.  That way you can adjust the sound chip's frequency range via software.

Swooooooon

[matthew180]

Keep in mind though, that the GROM clk also drives the system GROMs, and any GROMs found elsewhere in the system.  They do have a "wait" output so things should still work, but it might make BASIC and XB even slower!  Adjusting the GROM clk specifically at the sound chip would probably be the better solution since it would not affect the rest of the system.

[Stuart]

Willsy, on Mon Apr 30, 2012 4:01 AM, said:

Stuart, on Sun Apr 29, 2012 3:47 PM, said:

Willsy, on Sun Apr 29, 2012 2:04 PM, said:

I took the audio output from the original audio out at the video connector. I understand that at this point, the audio signal has already been amplified a little for sending on to the UHF modulator. I'm open to suggestions as to alternative locations that I could pick up the audio signal from (somewhere less "noisy" I hope). Maybe I can just connect directly to the audio out pin on the sound chip?

Mark

Hi Mark, very neat work!

Regarding the audio, there is no amplification of the sound chip output within the console. I've done the same mod and simply found that by the time you turn the volume down to something sensible, the noise is pretty much inaudible.

Stuart.

Stuart, have a look at Theirry's web site, on the audio page.

There's a description of the audio out pin on the sound chip, as follows:


AUDIOOUT This pin carries the sound data to the monitor's speaker (pin 3 of the connector). It is connected to an internal analog audio amplifier.[code]

I think what Thiery means is that the audio amplifier is internal to the sound chip. All those components between the sound chip pin and the monitor output are just filtering.

[Stuart]

matthew180, on Mon Apr 30, 2012 11:44 AM, said:

Adjusting the GROM clk specifically at the sound chip would probably be the better solution since it would not affect the rest of the system.

I would think though that on the sound chip the clock is also used for the processor interface (the sound chip data manual says that a write operation to the sound chip takes (can't remember the number) clock cycles, but doesn't show the connection in any diagrams). So reducing the clock speed might result in the sound chip keeping the READY line pulled low for longer? But as writes to the sound chip are relatively infrequent compared to what's going on in the rest of the system, may be it won't be noticeable?

[matthew180]

I have not checked the sound chip recently, but the GROMs do have a ready pin, so they will hold up the CPU.  The side affect is slowing down anything that uses the GROM and possibly the sound chip.  The feature is easy enough to add, and I can see what happens.

[marc.hull]

Willsy, on Mon Apr 30, 2012 4:09 AM, said:

Just using a flip-flop (74LS74) to effectively divide the clock input to the sound chip by two. The '74 is a dual flip-flip, so you can feed the output of one flip-flop into the input of the other, for a divide by 4. Jens-Eike can probably comment more than me - he gave me the idea

Will dividing the clock by 4 get you two octaves lower and lower the rest of the octaves by two?   Is it that simple  or will you have to recalculate the half steps ?   Wonder what that will do to the noise generators ?    Neat and simple  idea.  Please you tube some results.

[matthew180]

Ok I just tested the GROM clk divider in the F18A and it works fine with the handful of carts I tried (Tombstone City, Pole Position, and XB).  It is not quite as impressive as I was hoping, but the tones were lower (I only tried n=13 (0Dh) which is half the original freq).  The console beep sounds strange for sure, and the Pole Position "motor running" sounds like you are going to stall.

So there are now 10 programmable frequencies in the F18A you can set the GROM clk to:

gc = 1 / ((>nF + 1) * 2 * 10^-9)
min = gc / 2 / 1024 / 2

n	   GROMclk		Min Freq
-------------------------------------------------
0 - 6 = 446,428.57Hz = 108.99Hz original min freq
7	 = 390,625.00Hz = 95.37Hz min freq
8	 = 347,222.22Hz = 84.77Hz min freq
9	 = 312,500.00Hz = 76.29Hz min freq
A	 = 284,090.91Hz = 69.36Hz min freq
B	 = 260,416.67Hz = 63.58Hz min freq
C	 = 240,384.62Hz = 58.69Hz min freq
D	 = 223,214.29Hz = 54.50Hz min freq
E	 = 208,333.33Hz = 50.86Hz min freq
F	 = 195,312.50Hz = 47.68Hz min freq