Chip amp modification to current drive

[dkfan9]

Here, this is the proper way.

* you keep DC NFB , DC unity gin (so minimized offset)

* you have 100% current drive

* Now current into speaker is Vin/0.22 ohm

* Gain is RL/0.22 ohm

* Have been using this in my Guitar amps since 1972

Musicians call them "bold, brash, aggressive" or "Fahey amps have bite"

View attachment 1089141

Simple, huh?

If speaker is disconnected, it looks like AC voltage gain becomes 56k/.22 (assuming amp can provide this), is this problematic?

 

[JMFahey]

Yes, it will practically become open loop.

That´s what current drive implies. [shrug]

Either be careful to always have a load connected (what Tube guys do anyway) or place a "safety" resistor, such as 220 ohm suggested earlier, across speaker out terminals.

 

[dkfan9]

Yes, it will practically become open loop.

That´s what current drive implies. [shrug]

Either be careful to always have a load connected (what Tube guys do anyway) or place a "safety" resistor, such as 220 ohm suggested earlier, across speaker out terminals.

Thanks 😊

 

[Freedom666]

Hello, because of availability I bought two STK4241 Mk5 just to begin with a current drive amplifier.

One question, is the MK5 Version for a conversion to current drive functional, too? (The other one was the MKII Version optimized for current drive).

As far as I can see there are only minor differences in the schematic. Basically its all the same.

 

[Freedom666]

The data sheet mentions pin compatible versions. Is it basically possible to use these amplifier chips, too?

It is STK4201II and STK4141X series.

Shall I use two separated transformers for each amplifier chip?

 

[Freedom666]

Existing amplifier with STK4152_II is Technics SU-Z250 amplifier. In germany easily to be found as used item. And not expensive. Usually for 30 to 50 Euros.

I own two of them. Would be nice to see how to transform it to a current driven amplifier as you do not need to build an amplifier from the scratch.

https://www.radiomuseum.org/r/technics_su_z250.html

https://pdf1.alldatasheet.com/datasheet-pdf/download/41592/SANYO/STK4152.html

 

[Freedom666]

Hello, I found this statement on TDA2003 chipamp which is claimed to be current drive without modification, can that be true?

ivanlukic​

Member​

2013-05-17 5:43 pm
#2

Well,i have a tda2003 amp and im very happy with it,probably the best chip amp ever,i like the sound.
Its a class b amp but there is no distorion at all.What i dont like is the clipping sounds very bad.
Its much better than tda8560 or lm1875T,which are my other amps.
Now please tell me,what experiences have with tda 2003.
Here is my amp,i dosent look very good since i dont spen much time designing the looks,it is also powered by an 12v 250ma old cell phne charger which is ok for 2 ohms but only at low-ish volumes
Click to expand...

It is my favourite chip amp. Great sound is due to current feedback topology which is rare in chip amps. It is designed for car radio and for battery supply. If you use it with 8 ohm speakers it will deliver only about 5W and will clip badly if you push it hard. If you like it's sound as much as I do, I suggest you to try TDA2005 which is the same amp but in bridge mode. You won't need output cap for it. It offers twice as much power as TDA2003. But in any case you should use some kind of regulated supply and avoid supplies of over 12V.

 

[Freedom666]

I found no hint on current drive in the datasheet

 

[Freedom666]

If it's standard voltage drive, can this chip be modified to current drive?

 

[MarcelvdG]

It is an amplifier chip that does not work in bridge tied load mode and that has an external feedback network, so it should be possible. The single supply and peculiar way of biasing complicate things somewhat.

 

[Freedom666]

Would like to hear about it if someone finds it out how to convert it

 

[Freedom666]

In the datasheet I found this here:

 

[PRR]

claimed to be current drive without modification,
Great sound is due to current feedback topology

"Current drive" is not same-as "current feedback". (I could debate if 2 Ohms is really "CFB" here but why?)

Try this:

 

[Freedom666]

Thank you, looks easy to do it.

 

[Baffless]

I use that 220 ohm just as precaution if there is no speaker connected. If there is no load, current drive amp will raise the voltage to produce current, but nothing will flow. Than someone will plug the speaker and get surprise.
If you are sure you will not mistreat the amp, you can omit it. I would not.
Good luck. You will need it.

Never saw any oscilasions without that 220 ohm resistor on lm3875 , lm3886 chips. They just raise voltage to maximum if nothing connected. No surprises when pluging speaker.just faint click. Why are you expecting surprise? There is no technical reason for surprise to accur i think.

 

[adason]

Good. Do not use it then.

 

[Freedom666]

I will start to try out the TDA2003 in current drive. I have nice Pioneer 13cm fullrange driver in a marvelous old enclosure from the 70ies.

This driver needs added hi and lows to work properly.

If current feedback works it will make the frequencies without assisted EQ.

I have measurement equipment and will measure the result.

As a preamp functions a Bluetooth module for 3 euros. I will look for a 9 Volt dc source for it as it has a LM7805 regulator.

I will ad some small Cs between its legs like mentioned in the data sheet. I do not see them on the pcb.

As DC source for the TDA2003 I have 15 Volt SMPS.

 

[Freedom666]

As a heat sink I will use a piece of marble the TDAs glued onto it. Is this functional? For the electronic parts I will use old ones from defect electronics.

 

[Freedom666]

Does anyone know something about these Bestonesound speakers? Never found something on them on the web.

 

[Freedom666]

DC source for the TDA