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The AMNESIS amp: a good amplifier, like a gentleman, has no memory.
The AMNESIS amp: a good amplifier, like a gentleman, has no memory.
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Old 12th December 2018, 09:13 AM   #351
FdW is offline FdW  Netherlands
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The AMNESIS amp: a good amplifier, like a gentleman, has no memory.
Why noot look at it like this?
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File Type: png Bootstrap.PNG (73.4 KB, 63 views)
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Old 12th December 2018, 10:25 AM   #352
maxlorenz is offline maxlorenz  Chile
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Quote:
Originally Posted by FdW View Post
Why not look at it like this?
Sorry FdW, I don't get it.
Are you referring to the bootstrap caps?

Cheers,
M.
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Old 12th December 2018, 10:51 AM   #353
JOSI1 is offline JOSI1  Germany
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Default Bootstrap Cap

Hi Max,

I made new measurements with my single Amnesis prototype (Darlington output stage):
Ups= +-44V
Sine wave 1KHz
Scope 20V/scale

The lower curve is the output signal (minus pole of cap) at clipping point (+-40V)
The upper curve is the voltage at plus pole of the cap connected to the middle of the two 1k resistors (+44V).
As you see the maximum voltage across the cap is below +30V.
The same is valid for the cap of the negative side.
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Old 12th December 2018, 11:54 AM   #354
JOSI1 is offline JOSI1  Germany
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Hi Max,

Quote:
Feedback resistors are good from 48K to 50k paralleled. Or 12k-12.5K single. Simulations do not show it but I commented before the work of an audio guru (which name now escapes me) that measures significant THD reduction with parallel or series-parallel (low tempco) equivalent resistors.
The layout contains 4 parallel resistors (0.25W) or 1 resistor 1-2W.

Quote:
IF you find the amp worthy, then it is recommended that all resistors on the signal path be swapped to high Q, low tempco units.
Which low tempco units do you prefer (brand). What is the component seize (datasheet), what is the price.

Quote:
Can you give the model/dimensions of the output relays?
I don't use output relais/protection circuits to separate the speaker from
the amp (no relais in the signal path)
The optional relais in my layout helps effectual to mute 'plops' in the speaker during power up and power down.
There are many relais possible with the correct make/break contact arrangement. I post examples later.

Quote:
You know BJTs on the input CFP could be swapped for equivalent (cbe pinout) with lower Ccb/lower V capability (BC550-560 for instance), as they face very low voltages...
You are the experts.

R27 of the Hagermann Vbe multiplier must be chosen given the behavior of the chosen BJT (T9) for that position, following the paper I posted before.
From a layout point of view this can be determined later.

Cheers
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Old 12th December 2018, 12:34 PM   #355
maxlorenz is offline maxlorenz  Chile
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Quote:
Originally Posted by JOSI1 View Post
Hi Max,

I made new measurements with my single Amnesis prototype (Darlington output stage):
Ups= +-44V
Sine wave 1KHz
Scope 20V/scale

The lower curve is the output signal (minus pole of cap) at clipping point (+-40V)
The upper curve is the voltage at plus pole of the cap connected to the middle of the two 1k resistors (+44V).
As you see the maximum voltage across the cap is below +30V.
The same is valid for the cap of the negative side.
You beat me to the clock
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Old 12th December 2018, 12:54 PM   #356
maxlorenz is offline maxlorenz  Chile
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Quote:
Originally Posted by JOSI1 View Post
Hi Max,

*The layout contains 4 parallel resistors (0.25W) or 1 resistor 1-2W.

*From a layout point of view this can be determined later.
Exactly.

Quote:
Originally Posted by JOSI1 View Post
Which low tempco units do you prefer (brand). What is the component seize (datasheet), what is the price.
I don't remember from memory. We will have to search and it will also depend on how cheap I feel at the time.
(size is standard 0.25W-0.5W)


Quote:
Originally Posted by JOSI1 View Post
I don't use output relais/protection circuits to separate the speaker from
the amp (no relais in the signal path)
The optional relais in my layout helps effectual to mute 'plops' in the speaker during power up and power down.
There are many relais possible with the correct make/break contact arrangement. I post examples later.

Cheers
Ah! Yes, now I remember you mentioned this already. So a low power one will do?
Anyway, if it works OK, offset shall be under 20mV, so no pops expected. On the contrary, I recommend speaker protection circuits on all DIY amps...at least on the development/optimization period

Best wishes,
M.
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Old 12th December 2018, 01:46 PM   #357
JOSI1 is offline JOSI1  Germany
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Default Resistors

Hi Max,

Quote:
low tempco units component seize
I don't remember from memory. We will have to search and it will also depend on how cheap I feel at the time.
(size is standard 0.25W-0.5W)
I just want the prevent that the layout has to be changed completely due to
more board space is required for many resistors.
For resistors in audio signal path I used a grid of 10.16mm (400 mil).
For standard resistors 0.25W metal film (e.g. current sources) I used
7.56 mm (300 mil).

For the bootstrap resistors 1K I used 3W types (grid 20.8mm) and for the 2k2 resistors (Driver stage) 2W types (grid 15.2mm) to avoid increasing the PCB length.

Cheers
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Old 12th December 2018, 04:05 PM   #358
FdW is offline FdW  Netherlands
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The AMNESIS amp: a good amplifier, like a gentleman, has no memory.
Quote:
Originally Posted by maxlorenz View Post
Sorry FdW, I don't get it.
Are you referring to the bootstrap caps?

Cheers,
M.
Yep, I was kind of in a hurry

What I wanted to show is, how you could determine a value for the bootstrap capacitor by observing the 'red'-line

A small sim goes a long way (I hope).
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Old Yesterday, 02:45 AM   #359
maxlorenz is offline maxlorenz  Chile
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Quote:
Originally Posted by JOSI1 View Post
Hi Max
I just want the prevent that the layout has to be changed completely due to
more board space is required for many resistors.
For resistors in audio signal path I used a grid of 10.16mm (400 mil).
For standard resistors 0.25W metal film (e.g. current sources) I used
7.56 mm (300 mil).

For the bootstrap resistors 1K I used 3W types (grid 20.8mm) and for the 2k2 resistors (Driver stage) 2W types (grid 15.2mm) to avoid increasing the PCB length.

Cheers
That seems OK.
Besides, legs can be bent.

I bought my quality R years ago. I don't remember where are the "bills". Any one with 50ppm (25ppm if you feel splendid) or less shall be good.

What is the pace for the PS caps' leads, BTW?


Dear FdW wrote:
Quote:
Yep, I was kind of in a hurry

What I wanted to show is, how you could determine a value for the bootstrap capacitor by observing the 'red'-line

A small sim goes a long way (I hope).
Yes, thanks for your interest and support.
I believe we can be confident on the minimal value we found: 35V standard or more. This can be bypassed also with good film cap.

I repaired my channel with the last configuration. It seems stable with 6R8 dummy load. No time to listening though...family obligations...

BTW, JOSI1, did you listened to your single channel? And, is it stable? Just curious...anyhow, at least 48hrs of burning-in are recommended before critical listening.

Cheers, guys,
M.

Last edited by maxlorenz; Yesterday at 02:49 AM.
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