Unusual amp from 1987

[minek123]

Nice rounded tracks!

 

[minek123]

With LTP input slew rate is 50V/us. УНЧ-ВВС-2011 has 100V/us.

You can see my sim of LTP Vhex several posts ago
Unusual amp from 1987
Check the numbers...
Doesn't look like I'd be building it anytime soon...

 

[egra]

can you please share the asc file you are building?

 

[egra]

Nice rounded tracks!

Thanks. BTW the slew rate is limited by opamap IMO. Most of them have 15-25V/ms. I forgot to mention earlier that it would be worth trying OPA1656. As far as I know, it uses Denis Monticelli's patent for "non switching" bias, considered by many to be the most neutral sounding opamp.

https://hu.mouser.com/ProductDetail/Texas-Instruments/OPA1656IDR?qs=vLWxofP3U2ztlJVp%252BbIcnQ==

 

[egra]

If you add another transistor, the oramp becomes redundant.

Looks very good, Maxim. What do you think about CFP/Sziklai output?

 

[stanislav1957]

Can I put it more simply? Do you want to install field-effect transistors?
I'm sharpening my teeth on an AD829 variant with a single OOS and a very large loop gain.But for now I'm doing PCB

 

[egra]

I was surprised that my measured slew rate was about 15V/us.
Was expecting more...
And even worse, it seemed to be the same for all op-amps I tried, even fast ones.
So it means it is limited by VAS...

Another option try AD843. In ASR Emitter you can see this IC. Slew Rate: 250 V/ms, Power Bandwidth: 3.9 MHz.

https://www.analog.com/media/en/technical-documentation/data-sheets/AD843.pdf

 

[minek123]

Thanks. BTW the slew rate is limited by opamap IMO. Most of them have 15-25V/ms. I forgot to mention earlier that it would be worth trying OPA1656. As far as I know, it uses Denis Monticelli's patent for "non switching" bias, considered by many to be the most neutral sounding opamp.

https://hu.mouser.com/ProductDetail/Texas-Instruments/OPA1656IDR?qs=vLWxofP3U2ztlJVp%252BbIcnQ==

I don't think so.
I tried fast op-amps (e.g. LT1056, LT1357). No difference in slew rate.
TL071 is slow (max 10uV/s), but op-amp in this topology works on the low voltage (700mV or so), it doesn't amplify voltage like VAS does,
so it doesn't need to be fast...

 

[stanislav1957]

this is how RRCRC correction works

 

[minek123]

Another option try AD843. In ASR Emitter you can see this IC. Slew Rate: 250 V/ms, Power Bandwidth: 3.9 MHz.

https://www.analog.com/media/en/technical-documentation/data-sheets/AD843.pdf

This kind of amp will need fiddling with compensation to avoid oscillations,
PCB has to be designed right, with guard tracks.
Lots of things to care of....
I tried fast op-amps before, always troubles, need time to tune the compensation RCs..
Sim is not going to help with this.
And in my opinion it's not gonna improve slew rate anyway.

 

[minek123]

this is how RRCRC correction works

The one in your schematic? It would improve slew rate?

 

[stanislav1957]

No, this is about early schemas

 

[minek123]

If you add another transistor, the oramp becomes redundant.

Tried to sim it. Not sure if this is better than op-amp.

Don't like the resistor pot to bias the base of VT1 (Q7).
Thd and symmetry will depend on it...

 

[stanislav1957]

The introduction of the EP into the voltage amplifier gives a positive result. Even in the composite with Oramn.
Added a local OOS to the emitter of the second transistor.A completely different amplifier has become. Of distortion decreased

 

[minek123]

Impressive...
So your design is still "work in progress", I guess this PCB will not get done anytime soon

 

[stanislav1957]

In December, I will order. By the way IMD with 2 pairs

 

[minek123]

The best so far!
Maybe there is a way to use 2 op-amps, and less transistors?

Wouldn't it be nice, if all of us were using the same software for simulations...

 

[stanislav1957]

Two oramps are real, but the details will not decrease .And on my link in PM did not look at the amplifier?

 

[stanislav1957]

Wouldn't it be nice, if all of us were using the same software for simulations...

I'm too old to retrain.

 

[egra]

This kind of amp will need fiddling with compensation to avoid oscillations,
PCB has to be designed right, with guard tracks.
Lots of things to care of....
I tried fast op-amps before, always troubles, need time to tune the compensation RCs..
Sim is not going to help with this.
And in my opinion it's not gonna improve slew rate anyway.

The driver between opamp and VAS appears to limit the SR. (simple or cascaded equally). Using emitter follower + common emitter arrange (Maxim version) gives significantly better Square wave. (10 kHz)