Building the Preamp ...
For those of you building this project you will need to buy these two items (or their equivalent) not listed in the BOM:
5K dual linear potentiometers. You will need 6 of these.
Tayda Electronics is a good source of these. 5K OHM Linear Dual Taper Potentiometer
Lorlin brand 12 position, 1 pole shorting switch. You will need one of these.
You can get it from Mousers. CK1059 Lorlin | Mouser
For those of you building this project you will need to buy these two items (or their equivalent) not listed in the BOM:
5K dual linear potentiometers. You will need 6 of these.
Tayda Electronics is a good source of these. 5K OHM Linear Dual Taper Potentiometer
Lorlin brand 12 position, 1 pole shorting switch. You will need one of these.
You can get it from Mousers. CK1059 Lorlin | Mouser
Switching good quality relays so doesn't matter in this instance. I'd be more concerned by those pots
Carl, thank you for keeping the project alive. I have a few questions regarding the latest round.
1. What are the PCB dimensions (main PCB, PS, and IO)? Trying to figure out what chassis to use...
2. Is the Power Supply one from Doug Self 'Small Signal Audio Design' book as you referred to earlier?
3. How are mounting holes spaced? DIY Audio Store switched to using 10mm x spaced mounts which makes things so much easier when using their chassis with base plates...
Thanks!
1. What are the PCB dimensions (main PCB, PS, and IO)? Trying to figure out what chassis to use...
2. Is the Power Supply one from Doug Self 'Small Signal Audio Design' book as you referred to earlier?
3. How are mounting holes spaced? DIY Audio Store switched to using 10mm x spaced mounts which makes things so much easier when using their chassis with base plates...
Thanks!
The MAIN PCB measures 255mm wide x 155mm deep and ...
the IO PCB is 235mm wide 69mm deep.
I can supply multiple power PCBs. The original power supply that I shipped was the one described in Doug's 'Small Signal Design' book. That one measures 159mm x 64mm in size.
However some builders were unhappy that the plus & minus rails could not be made to exactly track one another. As result I began shipping a version that includes a pair of pots that making the rails adjustable. This one measures 155mm x 64mm.
I also have a third 'old school' power supply that I can supply either in built or PCB form shown here ...
Low Noise Power Supply – KAD Products
The old school power supply PCB measures 174mm x 64mm in size.
If you have a preference let me know when you order. The three variations of power supply PCBs are priced the same.
As to chassis I have been using the DIYAudio Stores SLIMLINE 1U boxes. I prefer to drill my own holes using the PCBs as a template. The chassis that I buy have all been 280mm deep. That depth affords plenty of room and ventilation.
Lowering Gain to Unity
I saw the question and response in posts 558 & 559 for lowering the gain.
Is this suggestion to use a 1.5 kOhm and 3.3 kOhm resistors in parallel for a equivalent single resistor of 1 kOhm? In other words, if I haven't populated the board yet, I could replace R42 and R45 with 1 kOhm resistors instead of the 3.3 kOhm resistor called for in the BOM to lower the gain from 3.3 to 1. Is that correct?
Or use some other value to achieve the overall gain I need?
I saw the question and response in posts 558 & 559 for lowering the gain.
Is this suggestion to use a 1.5 kOhm and 3.3 kOhm resistors in parallel for a equivalent single resistor of 1 kOhm? In other words, if I haven't populated the board yet, I could replace R42 and R45 with 1 kOhm resistors instead of the 3.3 kOhm resistor called for in the BOM to lower the gain from 3.3 to 1. Is that correct?
Or use some other value to achieve the overall gain I need?
Exactly so. Replacing R42 and R45 with 1Kohm resistors will give gain of 1.
This part of the overall design is same as in the original Elektor 2012 one. I did this same adjustment to my 2012 build to reduce the gain and enable volume control to sit a little further off the bottom end stop ( and help the balance between left / right).
Rick, very nice looking case! I love those knobs! Judging by the look they are probably by Kilo International... What color/style are they? Is volume 23.5mm or 19.05mm diameter? What abut the rest? I am planning my own build and would appreciate the details.
Yeah, they look great! I have exactly the same case, black slimline 1U from diystore. I am split between black gloss and clear gloss knobs. The sizes look right though so I think I am going to use the same diameters.
Do you have by any chance design files left for Front Panel Express?
reedcat,
I do have the files, but my main computer is in the shop. will be at least a week to 10 days before i get it back. If your willing to wait, i can send them when i get it back.
You should try out the free software as it is Very Easy to use, & kind of fun once you get the hang of it.
Rick
I do have the files, but my main computer is in the shop. will be at least a week to 10 days before i get it back. If your willing to wait, i can send them when i get it back.
You should try out the free software as it is Very Easy to use, & kind of fun once you get the hang of it.
Rick
Thanks, Rick. The labeling stage is at least a couple weeks away for me, so I am definitely willing to wait.
I already downloaded the software and am playing around with it however getting those levels lined up the right way turns out to be a challenge.
How long does it take for FrontDesign to turn around your order? I would like to have my complete preamp done by Christmas.
The original article at Elektor Magazine doesn't specify type for bypass caps (while mentioning it in other instances), however looking at the picture of the completed PCB those caps don't look like ceramics.
The new article at Linear Audio doesn't mention bypass caps at all and doesn't have them in the schematics. Carl's BOM asks for Polypropylene. I would be curious to hear the designer's opinion on this matter.
By the way, if you want to save on these cap a bit, here is the Mouser part that costs almost 4 times less: 505-MKP2D031001F00KI
It is $0.201 vs $0.719 for the part in the original BOM. The only difference is tolerance (10% vs 5%). Everything else (manufacturer, type, size, lead spacing, etc) is the same.
Considering you need 30 of these this is significant savings
It is $0.201 vs $0.719 for the part in the original BOM. The only difference is tolerance (10% vs 5%). Everything else (manufacturer, type, size, lead spacing, etc) is the same.
Considering you need 30 of these this is significant savings
Me as well. I have existing stock of .01uF WIMAs that I always use around my op amp circuits for bypass.