That Corp 1606 after Pot
« on: August 04, 2019, 10:50:16 AM »
Would I need a unity buffer amp between a 10k pot (fader) and a that Corp balanced line driver?


EmRR

Re: That Corp 1606 after Pot
« Reply #1 on: August 04, 2019, 11:24:59 AM »
I recall they want a low impedance source, so yes. 
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JohnRoberts

Re: That Corp 1606 after Pot
« Reply #2 on: August 04, 2019, 12:52:48 PM »
It is pretty common to put 10dB of gain in a post fader stage. That gain stage could be your low z buffer.
====
From the data sheet   http://thatcorp.com/datashts/THAT_1606-1646_Datasheet.pdf 

Quote from: THAT says
2. Both devices (1606/1646) must be driven from a low- impedance source, preferably directly from opamp outputs, to maintain the specified performance.

I find reading manufacturer data sheets useful.

JR
Visit https://circularscience.com to hear what properly "cleared" drums sound like.

Re: That Corp 1606 after Pot
« Reply #3 on: August 04, 2019, 01:54:21 PM »
It is pretty common to put 10dB of gain in a post fader stage. That gain stage could be your low z buffer.
====
From the data sheet   http://thatcorp.com/datashts/THAT_1606-1646_Datasheet.pdf 

I find reading manufacturer data sheets useful.

JR
useful indeed. Must've missed it. Thanks

Re: That Corp 1606 after Pot
« Reply #4 on: August 05, 2019, 04:18:07 PM »
So i was thinking something simple like this. Or would it be better as an inverting amp?

haven't worked out values yet but I think I'll only need 3-4db of gain since the 1646 has an additional 6db.



also, I don't think the  series resistors from  the wiper are doing anything  positive so disregard.


abbey road d enfer

Re: That Corp 1606 after Pot
« Reply #5 on: August 06, 2019, 04:20:10 AM »
Or would it be better as an inverting amp?
No. The days when inverting was better than non-inverting are long gone.

Quote
also, I don't think the  series resistors from  the wiper are doing anything  positive so disregard.
I would leave them and put a small (ca. 100pF) cap to ground.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

CurtZHP

Re: That Corp 1606 after Pot
« Reply #6 on: August 06, 2019, 08:23:44 AM »
I tried it recently with a THAT 1646, placing a pot right before the input.  The result was ugly to say the least.
Electrons don't read schematics.

Re: That Corp 1606 after Pot
« Reply #7 on: August 06, 2019, 10:48:58 AM »
I tried it recently with a THAT 1646, placing a pot right before the input.  The result was ugly to say the least.


makes sense. I little opamp buffer is the way to go i guess..

looking at resistor values:
G=1+r2/r1
4dB=1.58

so thinking R2=16.8k (or 16.9k seems to be a standard)
r1=10k

I understand there are a few things to consider regarding that ratio. Any benefit to going lower say 5k, and 8.4k?

what would I be looking at for R3? i guess I'm unsure as to what it would be doing.

abbey road d enfer

Re: That Corp 1606 after Pot
« Reply #8 on: August 06, 2019, 11:31:37 AM »
I understand there are a few things to consider regarding that ratio. Any benefit to going lower say 5k, and 8.4k?
It depends on the opamp. If you stick to OPA2134, it just doesn't matter. An opamp with significant Input Noise Current may want lower values. FET opamps have negligible INC.

Quote
what would I be looking at for R3? i guess I'm unsure as to what it would be doing.
I'd put anything between 1k and 4.7k. That's enough to ensure it imposes no restriction on HF response (is 200kHz enough?), whilst protecting the non-inverting input from whatever HF pollution.
Again, my answer would be different if the opamp was a 5532.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

Re: That Corp 1606 after Pot
« Reply #9 on: August 06, 2019, 01:46:10 PM »
ok so I think this should do it. Added filtering after the input resistors (100pf). Went with 3.3K for R3. should be ~48kHz filter I think.
Thinking an100pF cap in the feedback path. Can always omit if not needed.


Re: That Corp 1606 after Pot
« Reply #10 on: August 06, 2019, 05:23:41 PM »
No. The days when inverting was better than non-inverting are long gone.


When were those days? And why?, I mean I know that non-inverting can cause common mode distortion if driven with significant source impedance (this is still a problem today), but cant think of why inverting should be considered better at some point in time?

abbey road d enfer

Re: That Corp 1606 after Pot
« Reply #11 on: August 06, 2019, 05:53:35 PM »
When were those days? And why?, I mean I know that non-inverting can cause common mode distortion if driven with significant source impedance (this is still a problem today), but cant think of why inverting should be considered better at some point in time?
You answered your own question. Opamp designers have dealt with this issue over the last 50 years.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.


 

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