Search found 30 matches

by terkio
Mon Mar 18, 2019 11:43 pm
Forum: Pro Audio Design
Topic: Op amp matching
Replies: 6
Views: 96

Re: Op amp matching

In my quest for low Input Voltage Offset, a key point for an integrator circuit, I lost hope in matching op amps. What is better than OPA2277 ? Are they better ones, at low input voltage offset ? Is chopper op amps the way to go, in audio applications ? EDIT chopper op amps like: Zero-drift amplifie...
by terkio
Sun Mar 17, 2019 5:49 pm
Forum: Pro Audio Design
Topic: Op amp matching
Replies: 6
Views: 96

Re: Op amp matching

I found, offset voltage matching does exist:
https://www.analog.com/media/en/technic ... LT1002.pdf
Guaranteed LT1002A 60µV max offset voltage
Guaranteed LT1002A 40µV max offset voltage matching
This data is disapointing, I was expecting much better from matching. :(
by terkio
Sun Mar 17, 2019 12:42 pm
Forum: Pro Audio Design
Topic: Op amp matching
Replies: 6
Views: 96

Re: Op amp matching

An interesting paper about Vos Ios Ibias, how they come in the output offset of a FDA circuit using THS4551. https://e2e.ti.com/blogs_/b/analogwire/archive/2016/12/08/what-you-need-to-know-about-input-bias-current-and-why This shows, on the given example: Vos is the major contributor onto the output...
by terkio
Sat Mar 16, 2019 4:45 pm
Forum: Pro Audio Design
Topic: Op amp matching
Replies: 6
Views: 96

Op amp matching

In the design of an integrator circuit whether it is a Deboo or another implementation, a most important op amp characteristic is low Vos. For a balanced integrator that uses two op amps, the two Vos, if exacly equal, would provide an integrator with 0 Voltage input offset. Does it make sense to mat...
by terkio
Fri Mar 15, 2019 7:47 am
Forum: Pro Audio Design
Topic: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
Replies: 347
Views: 144443

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

Great to see you have a final proto with final measurements.
What about the noise from the servo ?
At the op amp output
At C6
The effectiveness of noise removal by the 100 nF cap.
by terkio
Thu Mar 14, 2019 11:13 am
Forum: Document
Topic: Cohen OM1556 Mic Preamplifier Schematic
Replies: 8
Views: 146

Re: Cohen OM1556 Mic Preamplifier Schematic

An after thought about my statement: "A peak led is a must on a preamplifier board". When not implemented on the preamplifier boards, adding peak led and vu meter drivers afterward gives a not so clean chassis wiring. OTOH, there are many variants about what users like to add or not. To keep modular...
by terkio
Wed Mar 13, 2019 6:45 am
Forum: Pro Audio Design
Topic: Dielectric Absorption
Replies: 53
Views: 17466

Re: Dielectric Absorption

In page 7 and 8 Assuming phantom power has once been turned on, dielectric absorption impacts the circuit’s behavior when phantom power is off for a very long time. In one experi- ment, after being charged to 48V for a few minutes, we turned off all power for over one hour. Coming back to the circui...
by terkio
Wed Mar 13, 2019 5:56 am
Forum: Pro Audio Design
Topic: Dielectric Absorption
Replies: 53
Views: 17466

Re: Dielectric Absorption

You scared me with dielectric absorption. I did encounter DA, years ago, while debugging a water pump electric moteur. Checking the motor starting cap ( 20uF 400V AC ). I was amazed to read DC after I had shorted it to make sure it was discharged, and see that DC coming back. Recently, interested in...
by terkio
Tue Mar 12, 2019 6:21 am
Forum: Pro Audio Design
Topic: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
Replies: 347
Views: 144443

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

I see, good catch. For some odd reason I thougt the OPA2277 was a JFET input, so I did not care about Ibiais.
OPA 2277, Ib spec: 0.5nA typ, 2.8nA max. This widespread between Typ and Max is pretty anoying.
by terkio
Mon Mar 11, 2019 6:34 pm
Forum: Pro Audio Design
Topic: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
Replies: 347
Views: 144443

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

At higher currents, about 5.5 mA nominal in this front end, there's a thermal effect that delays final measurement. With Ian's jig, at lower currents, I was able to get a settled measurement pretty quickly. I handled the transistors with tweezers to keep from heating them up and then covered them b...