Do you have a technical question that doesn't really fit a specific console? Want some general info on electronics, hacking, making cookies, etc? Here's the place to ask! Go nuts.
Well I have been thinking of that 7800 mod I have been working on. At the moment it is mono audio only (where as the 2600 mod is stereo). I would like to make it stereo by lifting pins 12/13 on the TIA just like the 2600 mod but the problem is that the 7800 also has a EXT audio signal that comes from certain carts with the pokey chip. This signal is mixed very far down the line.
I could just lift the pins and add the EXT to just one of the signals (like the left signal) but I would like to have EXT mixed into both sides at the same time while keeping the TIA stereo well stereo.
Anyone got a clue? One of my friends was like use a diode! But we all learned from that other thread you can't do that . Technically diodes would work if you DC offset all the signals diode then take the DC offset of but thats allot of work and a potential way to destroy your audio quality.
The wood master
"I was under the impression Mac owners don't actually USE their machines, they just parade them around trying to evangelize the masses."
Basically what I want to do but the L and R can not be mixed at all. I could add resistors at a high enough value that they wont mix but im afraid of loosing some quality there.
The wood master
"I was under the impression Mac owners don't actually USE their machines, they just parade them around trying to evangelize the masses."
Usig resistors will really only degrade the quality if they block the current so much that you have to amplify the signal a lot. That way you also amplify the noise floor which is always present. With something as noisy as the TIA, using resistors for mixing will be the least of your problems.
Values in the range 10k-50k are frequently used in professional mixing equipment without causing any problems. So using four 10k or even 4.7k resistors should work fine. You won't get signal degradation, but keep in mind however that it will lower the output impedance, so you can't drive a speaker directly with that connection, not efficiently anyway. You need some sort of driver circuit, like two LM386's or why not the TPA6021A4N as recommended by Ben himself.
nitro2k01 wrote:Usig resistors will really only degrade the quality if they block the current so much that you have to amplify the signal a lot. That way you also amplify the noise floor which is always present. With something as noisy as the TIA, using resistors for mixing will be the least of your problems.
Values in the range 10k-50k are frequently used in professional mixing equipment without causing any problems. So using four 10k or even 4.7k resistors should work fine. You won't get signal degradation, but keep in mind however that it will lower the output impedance, so you can't drive a speaker directly with that connection, not efficiently anyway. You need some sort of driver circuit, like two LM386's or why not the TPA6021A4N as recommended by Ben himself.
I tried this last week and I couldn't get the single separation that I wanted. 7800 mod will stay Mono only.
The wood master
"I was under the impression Mac owners don't actually USE their machines, they just parade them around trying to evangelize the masses."
What do you mean by "far down the line"? I checked the schematic (bottom right) It seems they are mixed "on the same depth". (Ie one capacitor and one resistor leading up to a common bus)
By duplicating the schematics for each channel, I got this:
If this is what you did, are you sure that...
You cut the trace between the TIA pins properly?
That the 7800 version of the TIA actually supports stereo?
nitro2k01 wrote:What do you mean by "far down the line"? I checked the schematic (bottom right) It seems they are mixed "on the same depth". (Ie one capacitor and one resistor leading up to a common bus)
By duplicating the schematics for each channel, I got this:
If this is what you did, are you sure that...
You cut the trace between the TIA pins properly?
That the 7800 version of the TIA actually supports stereo?
Thats exactly what I tried. Yes the TIA in the 7800 is exactly the same TIA that is in the 2600. Cut the trace? I have the TIA pins desoldered and lifted completely ftom the board . The problem is that 90% of the time there is no EAUD so the signals just blend.
The wood master
"I was under the impression Mac owners don't actually USE their machines, they just parade them around trying to evangelize the masses."
. Technically diodes would work if you DC offset all the signals diode then take the DC offset of but thats allot of work and a potential way to destroy your audio quality.
. The problem is that 90% of the time there is no EAUD so the signals just blend.