Would you recommend the MOFI C-3850 preamp for this IRS2092 power amp?
https://www.aliexpress.com/item/1005006668312496.html
If so, what gain of preamp would be suitable?
https://www.aliexpress.com/item/1005006668312496.html
If so, what gain of preamp would be suitable?
Thank you. I have read all pages. 🙂
Also watched YT videos about this preamp. Looks great so I would like to use in my project.
Also watched YT videos about this preamp. Looks great so I would like to use in my project.
Where should I put volume potentiometer?
At preamp input as usual or batter at output between preamp and power amp?
What is better in this case of very powerful amp?
At preamp input as usual or batter at output between preamp and power amp?
What is better in this case of very powerful amp?
I have two Protodacs, and definitely enjoy them. I also have a Dorati NOS DAC, so you could say I'm a bit of a 1387 weirdo at this point.
Please would someone direct me to the latest revision of this board and possibly a link to it.
I find it very confusing reading all the past links that include lots of suggested mods that may or may not be good.
Many thanks.
I find it very confusing reading all the past links that include lots of suggested mods that may or may not be good.
Many thanks.
Here is one
Here is another
Yet another
Another
The little yellow/orange board is the main focus.
That's up to you and you have to read from the beginning to sort that out but I can tell you there are people here that bought the boards stuffed from China and others that bought the boards blank(like me) from China.
Changes like A,B & C would be mandatory to drive the smaller load impedance. The other changes for Class A current and a bit more heat.
Download LT Spice from Analog Devices and use the Chalky schematic and tinker around with it. You can use TIP outputs or OnSemi MJEs etc.
You got to drop those emitter resistors to a smaller value and the series output resistor should go. I'm not sure that series output resistor was ever needed. But that can be said about the entire design. It seems to present as redundant and superfluous in structure. The most obvious question: what is the purpose of the opamp? Flavor? Something to tinker with? It sure ain't no balance line convertor like you might expect it to be...
Driving lower impedances, like 20 ohms headphones, incurs heat and current. Those need to be looked after and embraced for such modifications. Bigger power on the emitter resistors? Heatsinks on the output devices? Does the power supply need to be beefed up?
Attachments
I simulated the schematic in post 595 with a 20 ohm load and it functioned very well. Just so you don't think it is a total waste of your time.
For various reasons and other projects and work, I have yet to try out my Chinese C-3850 preamplifer line stage. Crazy, I know. I will get to it soon....
Hello,
here is a little report about the C3850:
I use this board inside a DIY remote controlled preamp to drive two Grundig Aktiv 30 speakers.
About the setup:
Transformer: 2x15V Toroidal
Volume Control: Alps 50K log with motor
Mods to the board: Gain resistors changed to 680 ohms and input capacitors changed to 22pF
How it sounds:
Very clean, no distortion noticable, also very quiet with no signal.
My active speakers seem to get along with this board pretty well.
The old Grundig preamp, which the speakers were made for, puts a lot more bass out though…typical 70s loudness.
With the C3850 the highs are crystal clear and the bass is not booming but it is there when it has to be…
So all in all I am pretty happy with this thing…would be nice if there was a version with tone controls.
here is a little report about the C3850:
I use this board inside a DIY remote controlled preamp to drive two Grundig Aktiv 30 speakers.
About the setup:
Transformer: 2x15V Toroidal
Volume Control: Alps 50K log with motor
Mods to the board: Gain resistors changed to 680 ohms and input capacitors changed to 22pF
How it sounds:
Very clean, no distortion noticable, also very quiet with no signal.
My active speakers seem to get along with this board pretty well.
The old Grundig preamp, which the speakers were made for, puts a lot more bass out though…typical 70s loudness.
With the C3850 the highs are crystal clear and the bass is not booming but it is there when it has to be…
So all in all I am pretty happy with this thing…would be nice if there was a version with tone controls.
Hello! The question was already asked/ proposed by STOXX, but I wonder what the opamp's function is in the circuit? Thank you!
It seems to be there to...
... clever.
- match source output impedance to the correct low output impedance (out of that IC) required to drive Q5/Q7 properly
- it is part of the negative feedback loop, providing DC offset correction, and the gain setting while ensuring stability through phase compensation
- it also isolates the influence of power supply ripple from directly affecting the Q5/Q7 (poor-ish CMRR due to simple R12/R16 current control...); the IC at the input takes care of power supply noise rejection, by means of pseudo-balanced input (actual input at NON INV + feedback "input" at INV) and IC's high CMRR figure.
... clever.
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Thank you for taking the time Extreme_Boky. I am exploring the idea of using this preamp as a make up stage for summing - does it seem reasonable to sum into the opamp somehow? It would be a non-inverting summing configuration i assume. The sources in this case are identical (two phono preamps).