Revisiting some "old" ideas from 1970's - IPS, OPS

[vzaichenko]

My pioneer SX-780 Lichtstark boards arrived from Express PCB.
just have to build and test !!
both channels on a express pcb mini board size.
780

Cool project!

 

[stocktrader200]

Hi Valery,
I will have to remove all componets from the original amp and jump some traces.
I want to drop it in where the driver transistors are on the main board as a daughter card
rerouting some pins on the main board for signal and power.

 

[vzaichenko]

Hi Valery,
I will have to remove all componets from the original amp and jump some traces.
I want to drop it in where the driver transistors are on the main board as a daughter card
rerouting some pins on the main board for signal and power.

OK, just keep all the high-current traces wide enough

 

[stocktrader200]

Hi Valery,Lichtstark amp loves to oscillate at 22mhz 30v p-p.
when the VAS capacitors are raised to 2 * 150pf the amp behaves well.
20k first stage resistors at 45v rails.

What does this do to the distortion specs?

 

[vzaichenko]

Hi Valery,Lichtstark amp loves to oscillate at 22mhz 30v p-p.
when the VAS capacitors are raised to 2 * 150pf the amp behaves well.
20k first stage resistors at 45v rails.

What does this do to the distortion specs?

That's ok - one of the other builders has experienced the same thing - also tamed with 2 x 150pF caps, so we have to consider this value as the right one for this design.
I will give you more details on the specs in a few days when I come back to my home workstation.

 

[jwilhelm]

TubSuMo

I'm putting the finishing touches on a new Modular NS-OPS amplifier with TubSuMo inputs. It's running +/- 56V rails with an output power of 150W RMS @ 8R. I tried a new finish on this one. It was buffed to a mirror state before anodizing, then lightly polished after dying. I like the results but it's definitely not good around kids, fingerprints are a problem.

 

[jwilhelm]

I've done some quick measurement on the amp. Sound is great! With open input you can faintly hear some 60Hz hum with your ear against the speaker. This hum disappears completely with the input shorted. My quietest amp so far, but I'm having some ground loop issues with my test equipment so it doesn't measure the best yet. All tests were done with a 8R dummy load.

 

[Kay Pirinha]

I'm putting the finishing touches on a new Modular NS-OPS amplifier with TubSuMo inputs. It's running +/- 56V rails with an output power of 150W RMS @ 8R. I tried a new finish on this one. It was buffed to a mirror state before anodizing, then lightly polished after dying. I like the results but it's definitely not good around kids, fingerprints are a problem.

What a pleasure to my eyes !
Best regards!

 

[thimios]

I'm putting the finishing touches on a new Modular NS-OPS amplifier with TubSuMo inputs. It's running +/- 56V rails with an output power of 150W RMS @ 8R. I tried a new finish on this one. It was buffed to a mirror state before anodizing, then lightly polished after dying. I like the results but it's definitely not good around kids, fingerprints are a problem.

I've done some quick measurement on the amp. Sound is great! With open input you can faintly hear some 60Hz hum with your ear against the speaker. This hum disappears completely with the input shorted. My quietest amp so far, but I'm having some ground loop issues with my test equipment so it doesn't measure the best yet. All tests were done with a 8R dummy load.

Nice very nice Jeff,perfect!
Wellcome to fft world.
If my memory serve well you are an RTX6001 owner?

 

[jwilhelm]

What a pleasure to my eyes !
Best regards!

Thanks

 

[jwilhelm]

Nice very nice Jeff,perfect!
Wellcome to fft world.
If my memory serve well you are an RTX6001 owner?

Yes I have an RTX6001. I've got the new Virtins software too but haven't had time to even install it yet. I still need to install the hardware and firmware updates in the RTX too. Racing season is done for the year so I'll have some time to play before it's time to rebuild the bikes for next year.

 

[vzaichenko]

Hi Valery,Lichtstark amp loves to oscillate at 22mhz 30v p-p.
when the VAS capacitors are raised to 2 * 150pf the amp behaves well.
20k first stage resistors at 45v rails.

What does this do to the distortion specs?

By the way - what OPS do you use it with?

 

[stocktrader200]

the irfp240, irfp9240. the test was done from the drivers (330 + 330 ohm to NFB. center point to scope) after 2 fets were ruined.

 

[vzaichenko]

Sorry for delay,

I have checked the parameters - 2 x 150pF look good. The difference in THD at 20KHz is around 0.002% - insignificant. No difference at 1KHz.
I also recommend trying to remove the lead compensation capacitor - 2.2pF, placed in parallel with 27K feedback resistor. Feedback loop response looks very good in this configuration.

Cheers,
Valery

 

[rhythmsandy]

Valery once I saw double driver stage to drive 6 pairs IN NSOPS I couldn't find that sch can you please re post it

 

[gannaji]

Please see post #2874.

 

[rhythmsandy]

I have question that why not use a bigger transistor with lower cob to drive than using dual drivers.. is this configuration stable?

 

[Kay Pirinha]

NO, you do not want to accuse vzaichenko and jwilhelm of publishing unstable amplifier designs, do you?
Best regards!

 

[jwilhelm]

In initial testing the Double Power output stage was very stable with my layout. I moved some components around and improved thermal stability, particularly warm up bias over the standard NS-OPS. When time permits I'm going to do a full build and do some more in depth testing. The NS series output stages, both in standard form and in Double Power are tricky to lay out. If done improperly they can be oscillators.

 

[rhythmsandy]

I think its better to have all the driver stage on the heatsink. as basically it will dissipate all heat and also thermal tracking for bias will also be effective as you have mentioned in the earlier posts.