Re: Armor Attack sounds and rom versions

>what do the opamps do? What actually amplifies the audio to send to
>speakers?

The opamps IC19,20,21,22 are voltage-controlled current amplifiers
(transconductance amps). They output a current signal proportional to the
sum of the noise generator and the voltage envelope signals that are
generated by 5 groups of R, C, and Q components. Each of the current
signals represents a shaped-noise sound effect. These current signals
comprise group one of sounds (Tank fire, Lo explosion, chopper, jeep fire, &
hi explosion). These current signals then all pass through a resistor R90
(100k) where the sum of the currents is converted into a voltage signal.

The voltage signal representing the group one sounds then goes through opamp
IC25 which is nothing but a buffer (unity gain amp) and then is coupled by
cap C43 into another opamp IC26. The resistors R91 and R92 set the gain of
the opamp IC26 to about 2.4.

Resistors R7 and R14 bring the Tank engine & squeak sounds into IC 26 also.
Resistor R7 sets the gain for the tank engine to about 0.8. If the value of
R7 is too low, the engine sound will be too loud. R83 brings into IC26 the
beep signal from the 555 oscillator IC23. The tank engine, squeak, and beep
sounds comprise group two of the sounds. IC26 has summed together both
groups.

The output of opamp IC26 represents the sum of all sounds but it is a
relatively weak signal. It goes out through the volume pot and returns to
the input of opamp IC24 (at pin 3). Resistors R25 and R84 basically set the
DC gain to about 26. C39 limits AC gain to reduce noise and to keep the
amplifier from oscillating. The output of IC24 through R85 and R87 drive
the bases of the final power amp stage transistors Q12 & Q13 which then
drive the speaker through R88 & R89. The two diodes D6 & D7 protect the Q12
& Q13 base-emitter junctions from damage from reverse-bias voltage that
would otherwise occur during the half-cycle at which the transistor is off.

William Boucher

----- Original Message -----
From: "andre" <livnfree_can@yahoo.com>
To: <vectorlist@vectorlist.org>
Sent: Thursday, June 04, 2009 10:19 AM
Subject: Re: VECTOR: Armor Attack sounds and rom versions

> 28. Since your [engine/squeak/morse] group of sounds
> are all much louder than the [tank fire, jeep fire, hi
> explosion, lo explosion, and chopper] group, I am wondering

I don't think anything is louder really.. i mean the chopper and everything
is loud as well (proper volume.. not cranked up) but the tank engine drowns
those noises out. If I turn down the volume as you suggested, they all go
down at those same levels so when it is barely audible, I can still hear all
sounds but the engine noise overpowers all the others. And when the tank
speed is at its max, or even close to that, it sounds like you have a bad
channel on a car radio with HUGE engine noise interference comming thru yur
speakers as well.

> if the capacitor C43 (0.33uF) is bad and is not passing the
> output signal from IC25 pin 6 through to R91 (8.2k).

This meters out ok.

> Also, if the value of R91 has gone way up, it would reduce

Within range... actually on the down side but in spec.

> other group? If that is true, then the problem could
> be either C43 or R91 or maybe one of the transconductance
> opamps (current amps) at IC19/20/21/22 is leaky and pulling
> all of the sounds from that group down. Anyways, I am
> getting the impression that there's a gain problem between
> the two groups of sounds. It may also be possible that
> the cap C14 (0.4y uF) is shorted and shoving a big DC bias
> into the TL081 at IC26 pin 2.

Replaced that cap and no go.. what do the opamps do? What actually amplifies
the audio to send to speakers? There really isn't too much left on these
other than those opamps.. even replaced the 555's and a couple more logic..
think only 2 or 3 chips left outside of the opamps.

>
> I wish I had your board on my bench for a little
> while. Why don't you pop it into your transporter and
> beam it over here?
>
I may end up doing that..

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Received on Thu Jun 4 17:49:39 2009