Doug Self Preamp from Linear Audio #5

Jump to Latest
C

Carl_Huff

Member
Joined 2004
kadproducts.com
Cyberpup said:
To replace the "volume control" stage, I think you would want to leave C40 in place to prevent any DC offset from being imposed on the new resistive volume control element. C47 would not need to be kept in the circuit if the new resistive element is truly passive.
Click to expand...

I agree with you, which is why I wrote, "everything between ...". As to being completely passive, solutions often have a buffer inline.
 
fvzeppelin

fvzeppelin

Member
Joined 2016
Carl_Huff said:
You are right! That MCP41HV51-104E/ST part looks very interesting.
Click to expand...
There is also a 5k version available, i.e. MCP41HV51-502E/ST. Wouldn't this be a better match?
One thing which I miss with these parts is an NVM to remember the last setting before power down. But if you are planning to use a Nano or Teensy, you can use their internal voltage reference to recognize a shutdown and then save the settings to the inbuilt EEPROM.
 
G

geoffw1

Member
Joined 2014
fvzeppelin said:
There is also a 5k version available, i.e. MCP41HV51-502E/ST. Wouldn't this be a better match?
One thing which I miss with these parts is an NVM to remember the last setting before power down. But if you are planning to use a Nano or Teensy, you can use their internal voltage reference to recognize a shutdown and then save the settings to the inbuilt EEPROM.
Click to expand...
Preamp Controller
This runs an Arduino Nano with IR remote (RC5 protocol), rotary encoder, LCD display and SPI output to control the volume with an MAS6116 chip. I have this working for some time controlling my Pre-amp (Bruno Putzeys balanced design) which implements the same baxandall volume circuit as Doug Self uses here.

Pick the bones from it and modify so the I2C would control the MCP41HV51-502E/ST.

I seem to remember trying out the MCP41HV51-502E/ST and may already have a library written to run it. I'll have a look and post if it's of interest.
 
Last edited:
G

geoffw1

Member
Joined 2014
geoffw1 said:
Preamp Controller
This runs an Arduino Nano with IR remote (RC5 protocol), rotary encoder, LCD display and SPI output to control the volume with an MAS6116 chip. I have this working for some time controlling my Pre-amp (Bruno Putzeys balanced design) which implements the same baxandall volume circuit as Doug Self uses here.

Pick the bones from it and modify so the I2C would control the MCP41HV51-502E/ST.

I seem to remember trying out the MCP41HV51-502E/ST and may already have a library written to run it. I'll have a look and post if it's of interest.
Click to expand...
MCP41HV51-502E/ST looks to be on long lead time (expected March 2023) at Farnell and Mouser. Like lots of devices at present, they seem to be unobtainium!
 
G

geoffw1

Member
Joined 2014
geoffw1 said:
MCP41HV51-502E/ST looks to be on long lead time (expected March 2023) at Farnell and Mouser. Like lots of devices at present, they seem to be unobtainium!
Click to expand...
Ignore my previous post (#2025). Also, the last two sentences of the one before it - my library is for the I2C version of this chip.

The only thing needed in my Arduino code for interfacing to the MCP41HV51-502E/ST would be replacing the mas6116 files with MCP41HVxx version. They are both SPI bus devices. Code for this is fairly straightforward.

​

 
diyiggy

diyiggy

Disabled Account
Joined 2019
Hi,

Is someone still use the first PSU with 7515/7915 and BC550/560 ?

I didn't worried much of the 16,2 circa output I had, but I have time now to focus on it. Imo there is a problem with the resistor values around the BC transistors. I have 36V, two x 18Vac secondaries in serie for the center tap, so enough voltage DC at the output of the smoothing caps (32 Vdc exactly as I have a R-Core which multiplication factor is more near x 1.25 than the usual 1.41. I have already changed the diodes which the reverse voltage was too much weak because of the secondaries in serie, but would like to solve the output DC.

I have 16V and 16.2V rigth/left mismatch. My basic understanding is the offset is not a problem really but the Douglas pre will be better drived at 17Vdc as designed.

Resitors are 15K between reg output and BC transistors and 1k between resistors and the central zeroV ref rail. I beleive there was a problem maybe on the edition of Douglas Self book where the PS shematic was took, or ?

help appreciated please

PS: I re read the thread, has someone noticed a sonic enhancement if tried several different PS or the rejection of the oaps are sufisant on their own not for noticing any audible change ?

Thanks
 
qubeaudio72

qubeaudio72

Member
Joined 2021
diyaudio.com/forums/newreply.php?do=newreply&noquote=1&p=6499857
itsikhefez said:
I've been spending some time with this preamp and have a few interesting learnings.
Firstly, I would like to thank again Carl and everyone else's in this thread for the bits of information, this preamp really is special.

* Subjectively, it "sounds" amazing paired with the Benchmark AHB2 amp on low gain. The high voltage output drives the AHB2 perfectly.
I've played around with EQ with some records and the result is very satisfying.

* I received the rear panel based off of the scaled PCB in post #1953 and it is a perfect fit. I will upload all of my files when I am finished with the project (updated BOM, front and rear panels). The 230mm depth Slimline 1U is a perfect fit.

* Grounding -- I had initially connected the IEC socket to chassis, in addition the PSU 0V through a ground-loop breaker. With that setup, I had a buzz once the volume pot was at a moderate listening level. I had assumed that XLR Pin 1 is connected to signal ground based off of post #928, but it seems like on the latest IO board Pin 1's are not tied to ground.
Shorting the Pin 1 pad on the PCB to the chassis took care of the buzz and the preamp is dead silent even at max volume.

* Balance and channel matching -- I used Bourns center detent pots (PDB182-K220K-502B) in all positions except volume. At the center detent, the channel matching is off by 0.5dB (at Unity gain). As such, I figured its better to use the Alpha pots without the detent and screw center the knob where the channel matching is optimal. At unity gain (and less even), channel matching is better than 0.1dB. (graph attached)

* EQ measurements -- I measured the EQ with gain set to max (-/+ ~9dB), and the frequency at the pot extremes and center detent (80hz, 200hz, 680hz).
With the knob at the center (200hz), 9dB gain occurs up to around 50Hz, whereas there is ~3dB at 200hz.
At the 680hz mark, 9dB gain is up to around 200hz, whereas again it is around +3dB at 680hz.

Given that, I could use some assistance in understanding whether this is expected, or the front panel markers should be updated to more accurately represent where the EQ is happening
Click to expand...
Please upload design file and Gerber files
 
diyiggy

diyiggy

Disabled Account
Joined 2019
Ah thanks, so my understanding was wrong as I believed it was meant to work at 17 Vdc as a design target. So I will change nothing if it is idem.
Btw a picture:
 

Attachments

  • 20220413_185107.jpg
    20220413_185107.jpg
    271.3 KB · Views: 146
tomlang

tomlang

Member
Joined 2009
I've received these wonderful boards and am ordering parts. As a real old school guy I've never worked with euro connectors before. The BOM calls for 4 of Amp #103308-5. These solder to the boards.

What part do I use to capture the ribbon cable that plugs into these connectors?

Do I have to order the connectors that plug-in and ribbon cable and a tool to install so I make up my own cables?

Or can I order premade ribbon cables to length?
 
C

Carl_Huff

Member
Joined 2004
kadproducts.com
The EURO Connectors are for +/-17 volt wire connections. Those are easy and obvious to use.

The other connectors are stock 2mm Pitch, 2 x 10 Pin, 20 IDC ribbon cables and connectors. They come in most any length. The length that you need is determined by the enclosure that you choose. You could build your own but I never do. Digikey, Mouser and EBay are good sources to buy from.

Here is an example from EBay https://www.ebay.com/itm/170644288774

The part numbers for the board cable sockets is listed in the BOM.

I hope that I gave you good answers. Let me know if I can be of further help

​

 
You must log in or register to reply here.
Top Bottom