Superbal input 5k impedance. There is a tone control board (with switchable bypass) in front of the volume control input. The pcb interconnects (on the huge baseboard carrier) are always balanced.
Looks good
Now that’s what I call a prototype
Fair bit of led current I, for those bar graph LEDs, non- multiplexed I assume
Now that’s what I call a prototype
Fair bit of led current I, for those bar graph LEDs, non- multiplexed I assume
You are using a 24 position dual/stereo switch for tone control. Is it a make before break type? What type do you use? Another question: tone control in front of volume control or after volume control?
The LEDs show the port state. If low, led is on, because I'm using resistor arrays.
The many resistors I have used are 12R instead of wires...
Tone control be4 volume control with bypass relay.
Switches: make be4 break. The ccw last 2 positions are short circuit to get a correct center value. haven't found 23 position switches...
The many resistors I have used are 12R instead of wires...
Tone control be4 volume control with bypass relay.
Switches: make be4 break. The ccw last 2 positions are short circuit to get a correct center value. haven't found 23 position switches...
Yesterday I have got a used Rohde & Schwarz UPL - unfortunately without the B1 and digital option, but the Analyzer itself is far better as the Levear VP-7723D
Quickchecked the VP-7723D generators qualtity and here you can see the THD+N limits. During development I often had such values measured with the VP-7723D.
I often said to my THD+N 20kHz measurements "as good as or better than" ...
BR, Toni
Quickchecked the VP-7723D generators qualtity and here you can see the THD+N limits. During development I often had such values measured with the VP-7723D.
I often said to my THD+N 20kHz measurements "as good as or better than" ...
BR, Toni
Test setup of new optoMOS volume control...
Input frequencies sweep from 21.5 kHz to below 100Hz
Input voltages SE from 50mV sweep to 7V RMS
This analog volume controller can be stepped digitally from -63.5dB to +12dB in 0.5dB steps ...
Maybe I should open a building thread for the "SA2022 - Precision analog preamplifier digitally controlled"... 😉
BR, Toni
Input frequencies sweep from 21.5 kHz to below 100Hz
Input voltages SE from 50mV sweep to 7V RMS
This analog volume controller can be stepped digitally from -63.5dB to +12dB in 0.5dB steps ...
Maybe I should open a building thread for the "SA2022 - Precision analog preamplifier digitally controlled"... 😉
BR, Toni
Attachments
Looks not so bad - a PGA2320 performs similarily. The Analyzer loopback shows my measurement limits especially at freqencies above 10kHz and below 100Hz.
Attachments
-
Analyzer_loopback_SE_output_to_balanced_Input.png -
Volume_controller_output_+12dB.png -
Volume_controller_output_+9dB.png -
Volume_controller_output_+6dB.png -
Volume_controller_output_0dB.png -
Volume_controller_output_-3dB.png -
Volume_controller_output_-6dB.png -
Volume_controller_output_-9dB.png -
Volume_controller_output_-12dB.png
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more progress... most pcb's developed, produced and tested.
First picture:
Base board left side: two slots are free for headphone amp.
Baseboard right side: only 2 of 6 input slots are inserted.
The white acryl locks the inserted cards.
The red pcb is carrying the digital supplies.
Second image:
+/- 17V supply for analog circuits. A second one for the headphone only.
Maybe time to open a thread in analog line...
Have fun, Toni
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It's on the plan for this week... 😎
I will announce it here too and add an index update, so one can easily find the corresponding preamp project for all SA20XX amplifiers.
Thx to all for your kind words!
Have fun, Toni
First powering - success! No noise, no hum, just pure sound.
D. Self Tone control with selectable bass/mid frequency and +/-10dB works absolutely clean, no clicks between selections. No click and pop switching from tone control to direct. No clicks and pops selecting volume or switching inputs.
Input gain selection can be selected during music without clicks and pops (range from -15 to +10dB) using the 16 position hex switches on backside.
Have fun, Toni
I can't believe it. All measurements are at the limits of VP-7723D ...😉
Even the homebrew carefully designed opamp/diamond buffer based headphone amp exceeds my measurement limits. Only headphone amp output 20 kHz / 10Vrms / 32R is about 0.005% THD+N. Below 10Vrms I see only the limits of my THD analyzer...
Need really immediatly to open a thread in "analog line level" ...
Noise is well below -120dB A-w. in reference to 2Vrms input vs all outputs (standard, headphone, monitor=tape record)
Switch on tone control and all knobs set to center offer nearly the same good noise and THD values. The tone control is very well designed - thanks goes to Douglas Self for all his hints to do it right!
Have fun, Toni
Even the homebrew carefully designed opamp/diamond buffer based headphone amp exceeds my measurement limits. Only headphone amp output 20 kHz / 10Vrms / 32R is about 0.005% THD+N. Below 10Vrms I see only the limits of my THD analyzer...
Need really immediatly to open a thread in "analog line level" ...
Noise is well below -120dB A-w. in reference to 2Vrms input vs all outputs (standard, headphone, monitor=tape record)
Switch on tone control and all knobs set to center offer nearly the same good noise and THD values. The tone control is very well designed - thanks goes to Douglas Self for all his hints to do it right!
Have fun, Toni
If you need a preamplifier for your SA20XX amplifier series - see this thread SA2022 - Modular High End Precision Preamplifier
Have fun, Toni
Have fun, Toni
Hello Toni
I have been reading your thread with increasing interest and I am planning to build a power amp with four pairs of exicon 125W devices.
As my PSU will deliver 63VDC and I believe the drivers should be fast (KSA1381 / KSC3503) I need to have two pairs of drivers.
In your BIG amp, you used two pairs of drivers in parallel.
1st you started with 47ohm base stoppers and 1ohm Emitter resistors
2nd you changed the emitter resistors to 0.47ohm
3rd you chose 10ohm base stoppers and 4.7ohm in the emitters.
Why did you make the last change ?
In my simulation, increasing the emitter resistors also increases 20THD.
Hope you have the opportunity to explain me how to choose the correct emitter resistors for these paralleled drivers.
Best
Ricardo
PS: So you can better analyse it I am posting here the schematic and my models. (You must include this file in the schematic so to be able to run it)
I have been reading your thread with increasing interest and I am planning to build a power amp with four pairs of exicon 125W devices.
As my PSU will deliver 63VDC and I believe the drivers should be fast (KSA1381 / KSC3503) I need to have two pairs of drivers.
In your BIG amp, you used two pairs of drivers in parallel.
1st you started with 47ohm base stoppers and 1ohm Emitter resistors
2nd you changed the emitter resistors to 0.47ohm
3rd you chose 10ohm base stoppers and 4.7ohm in the emitters.
Why did you make the last change ?
In my simulation, increasing the emitter resistors also increases 20THD.
Hope you have the opportunity to explain me how to choose the correct emitter resistors for these paralleled drivers.
Best
Ricardo
PS: So you can better analyse it I am posting here the schematic and my models. (You must include this file in the schematic so to be able to run it)