Search found 10 matches

by montemcguire
Fri May 03, 2019 12:33 am
Forum: Pro Audio Design
Topic: Op amp matching
Replies: 44
Views: 6057

Re: Op amp matching

I forgot to mention, but the 'end of the day' offset using this DC servo on actual amplifier circuits is about 7µV in simulation, and I can't honestly measure anything better or worse on real circuits with a Keysight 34461A meter. I get numbers around 5-10-20µV, but when looking at the numbers I get...
by montemcguire
Fri May 03, 2019 12:05 am
Forum: Pro Audio Design
Topic: Op amp matching
Replies: 44
Views: 6057

Re: Op amp matching

I think a more fruitful approach is to not expect low leakages from the PCB assembly and components, and instead orient the design toward lower node impedances while still achieving the desired time constants. The benefit of this is that you can easily use chopper (auto zero) op amps, which have fan...
by montemcguire
Sun Apr 28, 2019 11:09 pm
Forum: Pro Audio Design
Topic: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
Replies: 483
Views: 175059

Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

I found some deep drawn steel pans made for a buffet steam table that work pretty well as a magnetic shielding chamber. A pair of those clamped lip to lip using spring document binder clips with some dollar store lasagna trays inside as extra EMI shielding works pretty well. The theory is that each ...
by montemcguire
Wed Apr 03, 2019 3:09 pm
Forum: Pro Audio Design
Topic: Op amp matching
Replies: 44
Views: 6057

Re: Op amp matching

mediatechnology wrote:
Mon Apr 01, 2019 4:34 am
Are the inverting/noninverting inputs reversed on U3/U4?
OOPS! Yes indeed. Sorry for the mistake and good eyes catching it. I "cleaned up" one of my simulations, replacing the auto-generated yellow blocks with triangle amps and got the polarity wrong. It's always something... :)
by montemcguire
Sun Mar 31, 2019 9:16 pm
Forum: Pro Audio Design
Topic: Op amp matching
Replies: 44
Views: 6057

Re: Op amp matching

I use a non-inverting integrator. Here's a picture of a Superbal amplifier with a dual servo for reference: superbal-with-servo.jpg This has the advantage of a 'pre-filter' RC lowpass filter, which keeps fast stuff out of the integrator amplifier. The disadvantage is that you need twice as many capa...
by montemcguire
Thu Mar 28, 2019 9:37 pm
Forum: Pro Audio Design
Topic: Op amp matching
Replies: 44
Views: 6057

Re: Op amp matching

The OPA2189 is a relatively new amplifier - it had 'preview' status in its datasheet up until 12-2018 with the rev-D datasheet, when it finally went into production status. So, you're not sleeping - it's new! I've been using the Analog ADA4522-2 for dual DC servo uses, and it's roughly equivalent to...
by montemcguire
Thu Apr 05, 2018 8:38 pm
Forum: Pro Audio Design
Topic: Dielectric Absorption
Replies: 53
Views: 24103

Re: Dielectric Absorption

In my searches it seemed as if most are using simple linear model to characterize it which hasn't seemed very satisfying. Then I found this paper, and see now that more complex models have indeed been proposed: https://cdr.lib.unc.edu/indexablecontent/uuid:9548dfd5-f6b3-48de-aa97-c562c379949c It wa...
by montemcguire
Mon Apr 02, 2018 10:23 pm
Forum: Pro Audio Design
Topic: RFI protection concepts
Replies: 48
Views: 82163

Re: RFI protection concepts

Honored to join the group, and a hearty welcome to all here! Since I'm using the LM4562 heavily for my current project, that thread about DECT rectification certainly caught my eye. I've had good luck avoiding RFI problems using the LM4562, but maybe it's been through pretty meaty 4 layer PCBs that ...
by montemcguire
Sun Apr 01, 2018 2:37 am
Forum: Pro Audio Design
Topic: RFI protection concepts
Replies: 48
Views: 82163

Re: RFI protection concepts

A great thread! I’d like to add that there are some specialized MLCCs that are designed for specific RF uses, such as base station amplifiers, which have impedance nulls placed near commonly used transmitter frequencies. The point of this is probably to reduce device dissipation in transmitter circu...
by montemcguire
Sat Mar 31, 2018 10:33 am
Forum: Pro Audio Design
Topic: THAT 202XL recreation
Replies: 26
Views: 15098

Re: THAT 202XL recreation

I'm trying to use a THAT RMS detector for a project, and also discovered that the Panasonic 3300ppm/K resistors are now EOL and unobtainable. The solution I settled on was to use a Platinum 500Ω RTD along with a conventional resistor to adjust the Pt tempco of 3850 down to 3300. The idea is that if ...