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"Daddy" preamplifier - complete DIY project
"Daddy" preamplifier - complete DIY project
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Old 8th August 2018, 07:40 PM   #1
SomekPoland is offline SomekPoland  Poland
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Join Date: Mar 2011
Default "Daddy" preamplifier - complete DIY project

Hi Greedy Boyz,

Inspired by the magnificent Bruno Putzeys and his article: "The G-word: how to get your audio off the ground" I've built the preamplifier from that paper. It sounds really good, though it is a very simple project. What I've found lacking is a DIY project that "has it all". By all I mean:
  • Phono preamplifier
    XLR and RCA inputs
    Tone control
    Volume control
    Balanced and unbalanced buffers
    Sounds really good

Based on my experience with mentioned preamp I decided to use the metodology from the article and build upon it. Input is selected by relays, then goes straight to THAT1203 reciever. Then single ended signal is treated as it was balanced, as in "The G-word". Tone control I have chosen for now is this:
Audio Designs With Opamps -2 fig. 12

Regarding volume control I'm split between MUSES72320 IC and relay based ladder as in "RelaiXed" project.

Phono preamp I'm open for hints as I'm not really into LPs.

The purpose of this thread is to come up with a finished project, that will be avaiable to anybody wishing to do it.
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Old 8th August 2018, 09:40 PM   #2
Mixi is offline Mixi  Europe
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Join Date: Mar 2017
Location: Vienna
sounds like a great project. regarding phono stages i can recommend the hagerman bugle 2 circuit or the muffsy phono pre circuit. i've built both and both are great. one runs off 24vdc, the other needs 15vdc.

i'll soon build a circuit by doug self to compate with the ones mentioned above - i'll report my findings if you want.

i really like the idea of a pre that 'has it all'!
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Old 9th August 2018, 10:12 PM   #3
SomekPoland is offline SomekPoland  Poland
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Join Date: Mar 2011
Quote:
Originally Posted by Mixi View Post
sounds like a great project. regarding phono stages i can recommend the hagerman bugle 2 circuit or the muffsy phono pre circuit. i've built both and both are great. one runs off 24vdc, the other needs 15vdc.

i'll soon build a circuit by doug self to compate with the ones mentioned above - i'll report my findings if you want.

i really like the idea of a pre that 'has it all'!
Thanks for the input, I'll take a look at them.

For volume control I'm thinking more and more about MUSES72320. It has advantages over relay based attenuator.

First of all: no precise resistors buying/matching. You can either buy very precise resistors, or you can get a lot of 1% and match them by hand. Both not very comfortable.

Second problem is relays themself: they are big, they draw a lot of current (compared to integrated circuit). They are big and they are expensive. Considering one relay costing around 4$ and having 6 of them + resistors...

MUSES doesn't seem to be to expensive anymore, does it?
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Old 9th August 2018, 10:39 PM   #4
Carl_Huff is offline Carl_Huff  United States
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Join Date: Dec 2004
Location: Bakersfield, CA
Quote:
Originally Posted by SomekPoland View Post
... MUSES doesn't seem to be to expensive anymore, does it?
The MUSES 72320 part is priced at $25 each at Mousers.

Add to that the MCU to control it and other required parts and you are quickly at $50.
__________________
Best Regards,
Carl Huff
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Old 15th August 2018, 03:10 PM   #5
SomekPoland is offline SomekPoland  Poland
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Join Date: Mar 2011
Default Possibility to use a potentiometer?

Quote:
Originally Posted by Carl_Huff View Post
The MUSES 72320 part is priced at $25 each at Mousers.

Add to that the MCU to control it and other required parts and you are quickly at $50.
W need MCU anyway to controll the inputs. Of course one can use a switch for that, but it still leaves us with a need to control the volume somehow. I can leave pads for potentiometer, no problem.

Yesterday I decided to use opamp input stage as in the article. Why, you might ask? If anybody is on a tight budget, they can go with NE5532, or some of those nice, cheap JRC opamps and still get a very good sound at much less cost.

Posting screens of what I did today, don't mind the mess in part names, I'll clean that in the end.
Attached Images
File Type: png Input.png (18.4 KB, 215 views)

Last edited by SomekPoland; 15th August 2018 at 03:19 PM.
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Old 15th August 2018, 04:51 PM   #6
kstylianos is offline kstylianos  United States
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Join Date: Jan 2006
Location: Washington, DC
How about LDR for attenuation prior to buffer/gain section...you know, if you're going all out

I can attest to the Hagerman phono sections...very nice!
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Old 15th August 2018, 08:05 PM   #7
SomekPoland is offline SomekPoland  Poland
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Join Date: Mar 2011
Quote:
Originally Posted by kstylianos View Post
How about LDR for attenuation prior to buffer/gain section...you know, if you're going all out
Not really convinced: signal is directly modulated from power supply. Also potentiometer works with DC current which is also not too good. One needs to match LDRs which I don't find to nice either. Again, if you wish, you can make it and plug it in the pot socket.
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