TDA7052A for compressors etc

[StephenGiles]

http://www.ee.bilkent.edu.tr/~eee211/data%20sheets/IC/TDA7052.pdf
This looks promising, Elektor have a compressor circuit using this chip in their summer circuits issue.

[Mark Hammer]

haven't seen the summer issue of Elektor, but I gather this chip can be conceived of as a 2073 where one output can be haressed as a source of signal to be rectified and then fed to the DC control input?

[merlinb]

That article interested me too, and at 80p each, they're hardly more expensive than the LM13700 dual-OTA at £1.47!
The TDA does require about three times more supply current though, and appears to be at least twice as noisy. The small package could be very useful though.

[Lurco]

http://www.ee.bilkent.edu.tr/~eee211/data%20sheets/IC/TDA7052.pdf
This looks promising, Elektor have a compressor circuit using this chip in their summer circuits issue.

Wonder why they invert the signal from pin 5 with a T3 when the chip itself provides an opposite phase on pin 8!

[StephenGiles]

Frankly I couldn't care less if they cost £5 each if they do the job

I had a look at the circuit lunchtime and it's very basic - well it is Elektor Summer Circuits!!! A good one for modificaton I should think.

Oh yes, it must be the 7052A and not the 7052.

[Gurner]

http://www.ee.bilkent.edu.tr/~eee211/data%20sheets/IC/TDA7052.pdf
This looks promising, Elektor have a compressor circuit using this chip in their summer circuits issue.

Wonder why they invert the signal from pin 5 with a T3 when the chip itself provides an opposite phase on pin 8!

In this implementation, the phase/polarity of the signal on pin five is not relevant (vs pin eight) - they simply want to use both the positive & negative swing of the signal from pin 5 to derive a DC control signal for the TDA7052A pin 4, else they'd only be able to use half of the signal swing - it's a (little) akin to half wave vs full wave rectification - a smoother (less ripply) DC-ish control signal on the top of C9 is the end result (vs not using T3 & T5).

It's a basic compressor variant - the attack time & release time are fixed ...and if you mess with the 'R' of the CR release chain, you also mess with the DC control voltage on pin 4 - you could of course change the value of C9 to change the compressor release, but that's not exactly available as a rotary control for the guitarist!

[Lurco]

Nevertheless I`d try to control T5 (which was not at all doubted by me!) through C10 directly from pin 8 and control T4 through C8 directly from pin 5 to save on components.

[Gurner]

Aahh...got what you mean ....agreed, they mention 'separation', but that sounds a little feeble.

I'm sure it must work (they tested it - right?!) , but I'd always thought the TDA7052A DC Vol pin needed a resistance to ground generate the control voltage (vs the way they've implemented it - by presenting an externally derived varying DC voltage to the control pin)

Figure 7 & 8 of the TDA7052A datasheet kind of alludes to this.

I also read of one dabbler's experience here....

http://fab.cba.mit.edu/classes/MIT/863.07/people/charlie/final/

(scroll down the page a bit chapter headed "2, Speaker" )

"Rather than acting as a sink, the volume control pin actually sources current, and the resistor you put between it and ground governs the volume level (shorted to ground means no volume, infinite resistance means maximum volume"

[merlinb]

I'm sure it must work (they tested it - right?!) , but I'd always thought the TDA7052A DC Vol pin needed a resistance to ground generate the control voltage (vs the way they've implemented it - by presenting an externally derived varying DC voltage to the control pin)

They have arranged it so that the current from the vol pin 4 charges up the cap to a high voltage, resulting in max gain when there is no signal (or a very small signal). With large signals the cap gets drained by the transistors, pulling the voltage of pin 4 down, and with it the gain. The pull-up resistor has been added to speed up the release time, since it supplies additional current to the cap.

[petemoore]

  Voltage range between 4.5 [kinda low for signal swings] up to 18v [perfect for these 18v portable amps].
  Hot output, looks like a cool chip to mess around with. My little amps like compressors, they turn 'further up' when compression is preventing the high peaks that can destroy what would otherwise be good amplification. 

[Gurner]

I'm sure it must work (they tested it - right?!) , but I'd always thought the TDA7052A DC Vol pin needed a resistance to ground generate the control voltage (vs the way they've implemented it - by presenting an externally derived varying DC voltage to the control pin)

They have arranged it so that the current from the vol pin 4 charges up the cap to a high voltage, resulting in max gain when there is no signal (or a very small signal). With large signals the cap gets drained by the transistors, pulling the voltage of pin 4 down, and with it the gain. The pull-up resistor has been added to speed up the release time, since it supplies additional current to the cap.

I'm possibly interpreting the circuit wrong, but surely when those trannies are off the cap will charge up towards VCC (it'll never get there as the incoming signal on the trannies will see to that) & when the trannies are on, the cap gets discharged to gropund. Therefore, all pin 4 gets is a varying  (somewhat averaged) DC voltage resulting from that tranny switching action - I don't see where the current from pin 4 comes into charging up the cap? The TDA7052A datasheet talks of microamps through pin 4 (fig 5) - with such low pin 4 current, there's not a hope that the current will charge C9 up to a 'high voltage'

From Elektor's schpiel...

"P2 (sustain) varies how much effect the voltage on C9 affects the voltage on IC1 pin 4 and therefore controls the range of gain control."

It looks to me that they're taking it literally (as I did when I first had a dabble with this IC a while back), that by simply applying a varying DC voltage onto pin 4 will vary the gain of the IC - it doesn't ...only a variable resistance between ground & pin 4 works.

I look forward to someone making this one!

[Lurco]

Fig.7 of the datasheet looks like a typo to me (notorious for Philips). The other curves look like pin 4 expects an outboard voltage which doesn`t get loaded very much ("sinking"). Compare figs. 3, 5 and 6. That cap on pin 4 would just be there for noisesmoothing purposes,
while the clockwise end of the pot IMHO should be connected to an (external) controlvoltage.

[Gurner]

Fig.7 of the datasheet looks like a typo to me (notorious for Philips). The other curves look like pin 4 expects an outboard voltage which doesn`t get loaded very much ("sinking"). Compare figs. 3, 5 and 6. That cap on pin 4 would just be there for noisesmoothing purposes,
while the clockwise end of the pot IMHO should be connected to an (external) controlvoltage.

Well I can def confirm that a varying resistance works (as per their datasheet - a 1M resistor to ground) ...I'd have to dig the chip out again, but from memory a varying DC voltage applied to pin 4 has no affect on the IC's gain (nor did it for the chap I linked to further up ie http://fab.cba.mit.edu/classes/MIT/863.07/people/charlie/final/  who assumed the same as me & everyone else that it's just a matter of applying a DC voltage onto pin 4 to effect the gain  - )

Definitely one to revisit.

[StephenGiles]

Where does all this lead to - have you tried the Elektor circuit?

[Gurner]

Where does all this lead to - have you tried the Elektor circuit?

No, I've not, like I say, i'm sure they must have tested it, but having dabbled  with a TDA7052A a fair bit, I couldn't get the gain to alter by just aplying a varying DC level on pin 4 (neither could that other chap) - and looking at their circuit, that's all they're doing (a varying voltage on C9 fed onto pin 4 via a couple of resistors). Alas, the datasheet is poor wrt the DC Vol control workings (no IC internal info etc)

I've a few TDA7052As in my collection, but I'm a tad tied up with a certain widget to replicate my findings.

In obviously doesn't need the whole circuit replicating...and just to prove the point, all it really needs  is a simple manual config to prove one way or the other - ie a  pot between VCC & ground with the wiper to pin 4 with a sig gen into pin 2 - that'll show soon enough that applying a varying DC voltage alters the gain or not.

But hey, at the end of the day, this is just lil 'ole me ...a hobbyist wondering if it can work as they've implemented.

[Perfboard Patcher]

But hey, at the end of the day, this is just lil 'ole me ...a hobbyist wondering if it can work as they've implemented.

I myself have been called a doubting Thomas at some other forum.

I think you're right that a varying voltage doesn't affect the gain. What changes the gain is the varying resistance of the envelope filter. When T4 & T5 are cut off the resistance is 100k, when they are conducting the resistance is 100k||(P2+3k3).

PP

[StephenGiles]

Looks to be a non-starter to me - just like the England team currently 4-1 down to Germany (don't mention the 2 world war )

[Gurner]

But hey, at the end of the day, this is just lil 'ole me ...a hobbyist wondering if it can work as they've implemented.

I myself have been called a doubting Thomas at some other forum.

I think you're right that a varying voltage doesn't affect the gain. What changes the gain is the varying resistance of the envelope filter. When T4 & T5 are cut off the resistance is 100k, when they are conducting the resistance is 100k||(P2+3k3).

PP

Aah...that puts a new spin on it -  though it's not how they're describing it - they're implying its the varying DC that acts as the control to vary the TDA7052A gain.

(rightly or wrongly) I'm only seeing it as ....when the trannies are off the resistance to ground will be very high & when the trannies are fully on the pin 4 resistance to ground will be between 3k & 50k (depending on where p2 is set) - where does your 100k come into it?

PS As a brit, that was an ugly game...damn ugly.

[Perfboard Patcher]

Aah...that puts a new spin on it -  though it's not how they're describing it - they're implying its the varying DC that acts as the control to vary the TDA7052A gain.

Another possibility is that there is DC voltage at pin 4 and the resistor between pin 4 and ground will function as part of a voltage divider. 

where does your 100k come into it?

One leg of R9 is connected to + of the battery, the battery itself has a low resistance.

Yes the Germans got compensated for the battle of 1966 

[Gurner]

Another possibility is that there is DC voltage at pin 4 and the resistor between pin 4 and ground will function as part of a voltage divider. 

I just found an old cct with a TDA7052A in it - so just pulled all connections attached to pin 4 - there's about 1.1V on there (my VCC is about 8V)....so that's a likely possibility.