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:
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.
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.
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'!
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?
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.
Possibility to use a potentiometer?
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.
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.
Attachments
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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.
I'm alive!
Kind of. So, time has passed and I did gave it some thought. Lets focus on the line amplifier/volume control. I'm thinking how to do it in a best way possible. I got inspired by hifisonix.com Ovation amplifier:
Ovation Symphony Line Preamplifier
It uses opamps with additional class A high current buffers to achieve low distortion and higher drive ability. Since I can't design anythind discrete I'd like to try this as it is a form of composite amplifier that has best of both worlds.
I want to use 3 stages for this part:
The whole design will be balanced in dual mono config, so folks can use it as a balanced, or unbalanced preamp depending on their needs. The whole circuit will be symmetrical and will use dc-servo instead of coupling capacitors.
Input stage needs top provide at least 60dB of CMRR. That requires the use of precision resistors. INA1620 is a wonderfull audio opamp with integrated, thin film 0,04% 1 k resistors already in the package. It solves the problem completely, but creates another one. It's in WQFN package, that I can't solder. It also consists of RFI protection. It's either hot air station, or 0,1% resistors and bigger layout.
Volume control is MUSES72320 with external opamps. It gives me the most flexibility as it is just a resistor ladder.
Output buffer will consist of a high performance opamp with buffers and an unbalancer circuit. It will have two XLR outputs, two RCA, and two XLR subwoofer outputs.
So that is for now. It is chaotic, but so is my mind now. Any input is highly appreciated.
Kind of. So, time has passed and I did gave it some thought. Lets focus on the line amplifier/volume control. I'm thinking how to do it in a best way possible. I got inspired by hifisonix.com Ovation amplifier:
Ovation Symphony Line Preamplifier
It uses opamps with additional class A high current buffers to achieve low distortion and higher drive ability. Since I can't design anythind discrete I'd like to try this as it is a form of composite amplifier that has best of both worlds.
I want to use 3 stages for this part:
- Input buffer/balancing circuit/RF filter
- Volume control
- Output buffer/unbalancer
The whole design will be balanced in dual mono config, so folks can use it as a balanced, or unbalanced preamp depending on their needs. The whole circuit will be symmetrical and will use dc-servo instead of coupling capacitors.
Input stage needs top provide at least 60dB of CMRR. That requires the use of precision resistors. INA1620 is a wonderfull audio opamp with integrated, thin film 0,04% 1 k resistors already in the package. It solves the problem completely, but creates another one. It's in WQFN package, that I can't solder. It also consists of RFI protection. It's either hot air station, or 0,1% resistors and bigger layout.
Volume control is MUSES72320 with external opamps. It gives me the most flexibility as it is just a resistor ladder.
Output buffer will consist of a high performance opamp with buffers and an unbalancer circuit. It will have two XLR outputs, two RCA, and two XLR subwoofer outputs.
So that is for now. It is chaotic, but so is my mind now. Any input is highly appreciated.
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