Doug Self Preamp from Linear Audio #5

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PJN

Member
Joined 2004
Hi Carl,

I'm listening to my copy of this preamp daily and love it. One some of the most useful parts that I really like are the balance and tone controls, and of course the nifty source selection. That said have you ever given thought to modularizing the balance/tone/vol section to stand alone so that it could be used with other preamp designs. It would be great to be able to upgrade other preamps in the stable with these useful features.

Paul
 
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Carl_Huff

Member
Joined 2004
kadproducts.com
PJN said:
Hi Carl,

I'm listening to my copy of this preamp daily and love it. One some of the most useful parts that I really like are the balance and tone controls, and of course the nifty source selection. That said have you ever given thought to modularizing the balance/tone/vol section to stand alone so that it could be used with other preamp designs. It would be great to be able to upgrade other preamps in the stable with these useful features.

Paul
Click to expand...

Sorry about the PICs not being visible to all. Here is a link to the album. Carl Huff projects - Google Photos

Paul,

For the most part I have already done the very thing that you have asked for but haven't mentioned it here. I have a version of this project that breaks everything into modules including the tone controls. Source selection is also a module. I have a Source selection module version similar to what is in this project as well as another that includes a vinyl preamp and another that adds a color OLED display driven by an Arduino NANO that supports remote control. Perhaps I should start a thread. Do you think there would be much interest?
 
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PJN

Member
Joined 2004
Hi Carl,

I can only speak for myself but I would certainly be interested in several boards for a tone control and another few for source selection. I have several decent DIY preamps that I would like to upgrade. One of the biggest issues with a lot of my DIY preamps is that even though they may sound great they are bare bones. The Doug self pre is full service and has spoiled me. I'm guessing that others might feel the same.

Paul

Carl_Huff said:
Sorry about the PICs not being visible to all. Here is a link to the album. Carl Huff projects - Google Photos

Paul,

For the most part I have already done the very thing that you have asked for but haven't mentioned it here. I have a version of this project that breaks everything into modules including the tone controls. Source selection is also a module. I have a Source selection module version similar to what is in this project as well as another that includes a vinyl preamp and another that adds a color OLED display driven by an Arduino NANO that supports remote control. Perhaps I should start a thread. Do you think there would be much interest?
Click to expand...
 
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tER299

Member
Joined 2012
Carl_Huff said:
Actually there is a thread of sanity to the BOM madness ...

The BOM (as well as the schematic) describes the passive parts required for a single channel. The preamp is two channels, thus the need to double the passive parts called out in the BOM.

The op amps are active parts and are listed in the BOM as the number required to complete the project. This may sound crazy to some but it is a practice that I established a long time ago when a single quad op amp might service up to four channels and projects might have 'n' channels.

Please write your confusion off to my old habits. Ha, ha ...

If you are truly interested I invite you to adjust the BOM to your satisfaction, forward it to me and I will make it available to all that want it.
Click to expand...

I found some other errors in the BOM (incorrect amount/missing C47 values, among other missing items), but after some strolling through the thread, I found this: DSelf Preamp - Google Drive (courtesy of HaroldHill). This seems to contain the right amount of everything, so it might be beneficial to use this (just ask HaroldHill, I haven't asked for permission myself).

There is one more thing to note for other buyers:

My PCB is version 1.2 (no c,d or anything), and the C8 and C5 capacitors that are mentioned in all official versions of the BOM don't fit. I bent some leads, and made it work. I had to bend the C42, C43 capacitors too, as they didn't fit either, and I'll have to re-order some C44 caps (numbers didn't add up). It might be useful for other owners of the 1.2 to replace the C8 and C5 caps with smaller ones (10mm and 6.3mm respectively), and use regular ceramics for the C42-44 instead of polypropylene ones. As mentioned in this thread, the errors are not crucial, but having to order components for the 4th time is getting a bit expensive.

Nonetheless, it's a great project and design, and I'm really looking forward to seeing any other of your modules (especially any headphone/phono designs). :D
 
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orreborre

Member
Joined 2014
I have finally finished the project but have encountered a problem with the balance of the pre amp.

If I start with the the volume pot at the lowest volume there is a slight whisper in both speakers, equally "quiet". If I increase the volume pot the left speaker starts sounding louder than the right speaker. So at moderate listening levels the balance is far to left speaker. If I further increase the volume the balance starts to correct itself more to the center. At louder listening levels (measured to around 0.1V) the balance in spot on centered again. Other than this issue the pre amp sounds great

Any ideas of where to start to look?

Thanks
/Oskar
 
diyralf

diyralf

Member
Joined 2016
As far as I remember, Douglas Self is preferring low impedance designs in Active Volume Controls. This is a problem in volume controls. The resistance is very very small. Somewhere I have read that the gain error should be less than 1.5 dB. They would hardly be heard. Your circuit seems to have more.
 
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orreborre

Member
Joined 2014
I tried scottjoplins method to lower the input signal to the preamp, and compensate by increasing the volume pot. This solves the problem with the gain imbalance. The problem seems to only appear when the pot is in its minimum range, regardless of what the output voltage of the pre amp is. Guess the questions comes down to if to switch the pot, lower the gain of the pre amp or lower the gain of the amp itself (honey badger)
 
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ammel68

Banned
Joined 2009
scottjoplin said:
A number of people (me included) had a similar problem. The circuit is sensitive to slight imbalances in the volume pot at the start of the track. See post 722 and onwards for advice
Click to expand...

Regular volume pots that use carbon impregnated plastic(or polymers) are a waste of time and money if one is looking for reduced channel imbalance issues at lower(volume) levels.
That's why there are stepped attenuators and LDR attenuators.
Problem solved!

By the way Scott, I like your avatar of Boy George.
Sure brings back memories of those good ole' Culture Club songs from the 1980s.:p
 
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AndrewT

R.I.P.
Joined 2004
dual gang log vol pots always have some imbalance in resistances.
Anything you can do to swamp these imbalances will reduce the range of volume available from the vol pot.
The only solutions are switched, or digital controls.
LED/LDR does not offer a solution to channel imbalances..
 
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georgebrooke

Member
Joined 2006
oaklodgeconsulting.co.uk
Hi Carl,
I love the idea of the tone control section being used as an upgrade to the many bare-bones "audiophile" preamps that are out there. The preamp design has brought me to a stop.....I can't see spending more money & time on more builds. But modules...now there is an idea I could go with...as long as the modules can share PS, etc. Sounds a great idea

George
 
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