Sjöström Audio DIY forum

Projects => Phono RIAA amplifiers => Topic started by: Brambus on January 27, 2011, 08:35:12 PM

Title: QSXM3 with LTC1050 servo?
Post by: Brambus on January 27, 2011, 08:35:12 PM
Sorry for a stupid question, but i could not resist...  :?
 
I'm planning about building  QSXM3.
Before starting I was searching for a good substitute for MAX420 -
I know that it is possible to use OP07 etc. but having found the data sheet of LTC1050-CN8
i was thinking that maybe it would work.

Would it be enough to omit P7 P8 C79 C80 (i.e. the net around terminals 1-5-8) or am i totally out of way?
Thanks in advance.
Paolo

PS
I see now that 18 volts is the total  V+ to V-  power supply rating. Maybe this is the show stopper... :|
Title: Re: QSXM3 with LTC1050 servo?
Post by: peranders on January 27, 2011, 10:19:12 PM
LTC1050 could be used with some redesign but I'll recommend you a non-chopper type, like a medium speed, low noise type, capable of +- 15 volts. 5-15 V/us, 4 nV/Hz or less, 1 mV offset or less. Low input bias currents.
Title: Re: QSXM3 with LTC1050 servo?
Post by: Nugman on January 20, 2018, 01:50:51 PM
Hi Per-Anders,

I'm also looking for a substitute for the MAX420 in QSXM3. In another topic regarding the QSXM2 you were suggesting an OP07 instead. Would this work in the QSXM3 as a drop-in replacement with the same circuit around as with the MAX420? Could I use the OP07 just instead of the MAX420?

Many thanks in advance  for your advice.
Roland
Title: Re: QSXM3 with LTC1050 servo?
Post by: peranders on January 20, 2018, 09:49:49 PM
OP07 will work fine.
Title: Re: QSXM3 with LTC1050 servo?
Post by: Nugman on January 20, 2018, 11:49:11 PM
Hi Per-Anders,

thanks for the quick reply. I'm a little bit embarrased because I found that you already mentioned the OP07 in the original documentation. I was so focused on looking for a MAX420 and how to replace it, that I somehow missed that.  :oops:
You write that when using the OP07, P3/P7 should be used as well. How should the pot be adjusted then? Is there a measurement point that should have a certain voltage or current?
What value should the pot have? The datasheet of the OP07 recommends 20k, while the schematics show a 10k?

Thanks, Roland
Title: Re: QSXM3 with LTC1050 servo?
Post by: peranders on January 21, 2018, 10:24:48 AM
Start to use the OP07 without any trimming. I think it will work good. If you add a trim pot then the offset drift will be higher so it's good if you can avoid it. If you anyway want this pot use the recommended value in the datasheet.
Title: Re: QSXM3 with LTC1050 servo?
Post by: Nugman on January 21, 2018, 12:03:46 PM
Many thanks!