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No-global-loop amplification
No-global-loop amplification
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Old 9th February 2018, 05:22 AM   #171
pinnocchio is offline pinnocchio  Canada
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It has been a while without updates. Anything new?

Ciao!
Do
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PREAMPs : Bal AMB α10 + JC-80 | Bal DCB1 | Bal LDR3x | AMPs: AMB β24 | ExtremA | FO v1.4 | USSA5 | TSSA | Telos 390 Clone | NX Amp | FC-100
DACs : TPA Buffalo II + OPC's NTD1 I/V | JLsounds | Mirand AK4490 + Discrete Output Speakers : Troels Gravesen ATS-4 | Sagwee LT V3
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Old 9th February 2018, 11:50 AM   #172
vzaichenko is offline vzaichenko  Russian Federation
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No-global-loop amplification
I continue listening to my single channel prototype - running nicely, slowly building the 2-nd channel, thinking about the point raised by Brian about the best balance between the gains of the front-ends.

My approach right now - if I want an overall gain of the power amplifier to be 29db, I set the gain of the "main" (high swing) OPS to 29db. The opamps (or some other error correction circuit) adds 18db on top, that is "balanced" by 18db NFB loop. I believe, around 20db is a reasonable value, assuming the "main" front-end is linear enough.
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Old 15th February 2018, 05:53 PM   #173
vzaichenko is offline vzaichenko  Russian Federation
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No-global-loop amplification
Default Better spectrum measurements

I've set up my recently received RTX audio analyzer in the lab - now I can show better measurements.

The first picture - note the noise floor with no signal - no noise / hum components above -120db line. Then THD for 1KHz and 20KHz, and IMD 14+15KHz go.

Listening to the amp - also through the analyzer's DAC - I would characterize the sound as "smooth and delicate" - no highlighting of anything, very comfortable listening in the near field (speakers are placed on the corners of a big table).

One 10pF bandwidth-limiting capacitor is added to prevent possible "ringing" when touching the input with something not grounded.

The design is rather mature now - easy to reproduce.
I'm thinking about a servo option for those who like rock solid zero offset, although right now possible fluctuations don't exceed +/-10mV.
Attached Images
File Type: jpg 00 RTX6001.jpg (103.1 KB, 222 views)
File Type: jpg NGNFB 10 Floor.JPG (170.3 KB, 219 views)
File Type: jpg NGNFB 12 01KHz.JPG (186.9 KB, 215 views)
File Type: jpg NGNFB 13 20KHz.JPG (169.0 KB, 209 views)
File Type: jpg NGNFB 15 IMD.JPG (581.8 KB, 203 views)
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Old 19th February 2018, 06:26 PM   #174
vzaichenko is offline vzaichenko  Russian Federation
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No-global-loop amplification
A fully tuned-up, mature version of Simpelstark.
I will update the post#1 with amended schematic and corrected layout (one additional capacitor is underneath the board now).
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File Type: jpg IMG_20180219_211430.jpg (123.6 KB, 90 views)
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Old 20th February 2018, 09:47 AM   #175
traderbam is online now traderbam  Europe
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Looks good. What capacitor did you add? Did you settle on 20dB global NFB?
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Old 20th February 2018, 10:19 AM   #176
vzaichenko is offline vzaichenko  Russian Federation
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No-global-loop amplification
Arrow V1.1

The one I have added is C20 (10pF). It closes the loop around the front-end at HF, preventing possible local oscillation when the input is touched with no ground reference.

The 2-nd picture shows the real board view from the top (ground plane), the 3-rd picture - the ground plane is shown transparent to see the routing.

I have stayed with 18db loop gain in ODNF mode. If somebody wants to use the circuit in a pure no-global-loop mode - he can drop all the components within the red box, shorting TP2 and TP3 with a wire.

P.S. Added the bottom view of the board with the proper copper pours.
P.P.S. What still amazes me in this amplifier - the noise / hum level. This is the quietest amplifier I've ever designed - dead silent at idle. To be honest, I didn't expect it to be that quiet when I just started thinking about this design.
Attached Images
File Type: jpg @1.1_Schematic.jpg (405.5 KB, 85 views)
File Type: jpg @1.1_PCB_01.jpg (1.02 MB, 83 views)
File Type: jpg @1.1_PCB_02.jpg (714.0 KB, 56 views)
File Type: jpg @1.1_PCB_03.jpg (447.5 KB, 55 views)
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Last edited by vzaichenko; 20th February 2018 at 10:26 AM.
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Old 20th February 2018, 10:56 AM   #177
vzaichenko is offline vzaichenko  Russian Federation
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No-global-loop amplification
Post #1 is updated with the links to this page.
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Old 20th February 2018, 08:43 PM   #178
pinnocchio is offline pinnocchio  Canada
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Will you have some PCBs available?

Thanks
Do
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Old 20th February 2018, 08:48 PM   #179
jwilhelm is offline jwilhelm  Canada
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I have a couple of the original boards in stock. Valery sent me corrected files but was hinting that a new more compact layout is coming so I'm going to wait for that before having more boards done.
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Old 20th February 2018, 08:52 PM   #180
pinnocchio is offline pinnocchio  Canada
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I'll wait for the new board

Do
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PREAMPs : Bal AMB α10 + JC-80 | Bal DCB1 | Bal LDR3x | AMPs: AMB β24 | ExtremA | FO v1.4 | USSA5 | TSSA | Telos 390 Clone | NX Amp | FC-100
DACs : TPA Buffalo II + OPC's NTD1 I/V | JLsounds | Mirand AK4490 + Discrete Output Speakers : Troels Gravesen ATS-4 | Sagwee LT V3
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