dBs
100+ Head-Fier
- Joined
- Jan 6, 2009
- Posts
- 471
- Likes
- 12
If you'll allow, I will do a brief history. If you don't want to read any of this, feel free to skip right to the part that says PLANS.
HISTORY
I just graduated this last year with a bachelors in EE. Unfortunately, my senior project was less than successful. I will fail, but that doesn't mean that I have to like it. I wont let it dissuade me from pushing through, learning, and progressing. I decided that I wanted to design, from the ground up, a DIY open-source project amp as a way to "give back" to the audio community. I had asked for help in form of a mentor on here and received no reply. Being of thick head, I wasn't going to let that stop me, it simply meant that I would have to teach myself. Unfortunately, tubes are a technology of yesteryear and college looks at them as outdated (which they are for most purposes, lets be honest) so I learned nothing of them in college.
I bought some books, attempted some light reading but found the turmoil of setting up my new "working world" life more time consuming than I anticipated. Now life has slowed down enough to allow me to do the research I wanted to do. I have researched relentlessly the last three weeks. I think I am ready to start.
PLANS
There are already a million different amps out there already for the open-source DIY community, even in the tube genre. Being the kind of person who doesn't like to tackle a challenge the same way as those before me, I would like to take a slightly different approach and no idea is really too out there.
I am looking to keep the parts list no higher than the $300 parts range so it can be afforded by anyone. At this point I would like it to be a single ended push-pull (SEPP) topology. I will be attempting to avoid output transformers (OTL) for their cost and potential influence on the sound. This will likely limit my output impedance (Zo) for lower impedance headphones, but the P-P should help with that a bit. I would like the output tubes to be triodes. I will be driving them as linearly as possible while keeping the bias current as low as possible. I don't want there to be a chance of them going into class AB operation.
The input stage I am still debating on and will think about a bit more this week. I am considering pulling one of the P-P tubes grids from the plate of the input tube and the other from the cathode of the input tube. I would prefer a triode in this stage. I am hoping to avoid the added cost and complexity of a differential pair.
I am leaning toward chokes instead of cathode resistors (Rk) if I can find them cheaply enough. I am debating bypass capacitors but I wont know if I will use them or not until I've started building (I will design for both possibilities).
I am looking to avoid negative feedback (NFB) if I can help it, which I believe I will be able to do. I like how it lowers the harmonic distortion level but I don't like how it mirrors it to higher orders.
I am probably half way through my research of power supplies. I like the idea of using a tube rectifier but I am not sure how that will affect cost and complexity. I suspect I will be forced into solid state. Chokes in the Pi filters would be nice but I think would prove too expensive.
As this project progresses, I will be keeping this up to date with schematics, math, thoughts, questions, etc. until a final project is realized. At this point we will see what happens regarding the possibility of a kit or group buy for parts if anyone is actually still interested at that point. Even if this never garners any other attention, at least I would have vindicated myself from my senior project, hahaha.
YOUR HELP
Where I would like the communities help is while college taught me the theory, they didn't teach me real world implementation. I could spend at least a month intently researching the various tube types and the trade offs associated with them but seeing as this is intended as a "giving back" and I want there to be interest in the project as well as the result, I think asking you all is the perfect solution to this.
What tube/s would you like to see used? Are there any that are horribly under appreciated and deserve their spot in the limelight? Tube rolling is always nice but what tubes offer the best flexibility? What about rectifier tubes? What type of tube offers the best sonic flexibility? Etc.
Also, I haven't researched yet the different capacitor types and brands. The same applies to chokes, resistors, transformers, etc. I was planning on doing this anyway, but if time can be saved by tapping into the cumulative knowledge of this highly educated community I certainly wouldn't turn it down.
So, thoughts?
UPDATES
I forgot to mention the most basic parts! I plan this amp to be for headphones. The Zo is naturally the lower the better, but until the output tube/s have been decided upon and whether or not there will be output capacitors or bypass capacitors, it cannot be determined yet. A basic potentiometer based volume control that will be put to ground in parallel with another resistor to keep the pot itself out of the signal path. Only one headphone output at this point to keep costs down. A basic 2 input (+), 1 output headphone amp.
It is a bit of an "out of thin air" number, but I will be trying for a Zo of around 50 Ohms. I believe that could be a realistic value. Output power I am not as certain on. My aim is quality to that end I need to run my tubes as linearly as possible so less than 1 watt but more than 400 mWatts. I want to be able to drive Hd650's without difficulty and with enough confidence to run 600 Ohm DT880/990s. P-P running in lower power operation should hopefully enable running lower impedance headphones like the K701s. I think I would find it difficult to run Denons or Grados but I will try my best.
HISTORY
I just graduated this last year with a bachelors in EE. Unfortunately, my senior project was less than successful. I will fail, but that doesn't mean that I have to like it. I wont let it dissuade me from pushing through, learning, and progressing. I decided that I wanted to design, from the ground up, a DIY open-source project amp as a way to "give back" to the audio community. I had asked for help in form of a mentor on here and received no reply. Being of thick head, I wasn't going to let that stop me, it simply meant that I would have to teach myself. Unfortunately, tubes are a technology of yesteryear and college looks at them as outdated (which they are for most purposes, lets be honest) so I learned nothing of them in college.
I bought some books, attempted some light reading but found the turmoil of setting up my new "working world" life more time consuming than I anticipated. Now life has slowed down enough to allow me to do the research I wanted to do. I have researched relentlessly the last three weeks. I think I am ready to start.
PLANS
There are already a million different amps out there already for the open-source DIY community, even in the tube genre. Being the kind of person who doesn't like to tackle a challenge the same way as those before me, I would like to take a slightly different approach and no idea is really too out there.
I am looking to keep the parts list no higher than the $300 parts range so it can be afforded by anyone. At this point I would like it to be a single ended push-pull (SEPP) topology. I will be attempting to avoid output transformers (OTL) for their cost and potential influence on the sound. This will likely limit my output impedance (Zo) for lower impedance headphones, but the P-P should help with that a bit. I would like the output tubes to be triodes. I will be driving them as linearly as possible while keeping the bias current as low as possible. I don't want there to be a chance of them going into class AB operation.
The input stage I am still debating on and will think about a bit more this week. I am considering pulling one of the P-P tubes grids from the plate of the input tube and the other from the cathode of the input tube. I would prefer a triode in this stage. I am hoping to avoid the added cost and complexity of a differential pair.
I am leaning toward chokes instead of cathode resistors (Rk) if I can find them cheaply enough. I am debating bypass capacitors but I wont know if I will use them or not until I've started building (I will design for both possibilities).
I am looking to avoid negative feedback (NFB) if I can help it, which I believe I will be able to do. I like how it lowers the harmonic distortion level but I don't like how it mirrors it to higher orders.
I am probably half way through my research of power supplies. I like the idea of using a tube rectifier but I am not sure how that will affect cost and complexity. I suspect I will be forced into solid state. Chokes in the Pi filters would be nice but I think would prove too expensive.
As this project progresses, I will be keeping this up to date with schematics, math, thoughts, questions, etc. until a final project is realized. At this point we will see what happens regarding the possibility of a kit or group buy for parts if anyone is actually still interested at that point. Even if this never garners any other attention, at least I would have vindicated myself from my senior project, hahaha.
YOUR HELP
Where I would like the communities help is while college taught me the theory, they didn't teach me real world implementation. I could spend at least a month intently researching the various tube types and the trade offs associated with them but seeing as this is intended as a "giving back" and I want there to be interest in the project as well as the result, I think asking you all is the perfect solution to this.
What tube/s would you like to see used? Are there any that are horribly under appreciated and deserve their spot in the limelight? Tube rolling is always nice but what tubes offer the best flexibility? What about rectifier tubes? What type of tube offers the best sonic flexibility? Etc.
Also, I haven't researched yet the different capacitor types and brands. The same applies to chokes, resistors, transformers, etc. I was planning on doing this anyway, but if time can be saved by tapping into the cumulative knowledge of this highly educated community I certainly wouldn't turn it down.
So, thoughts?
UPDATES
I forgot to mention the most basic parts! I plan this amp to be for headphones. The Zo is naturally the lower the better, but until the output tube/s have been decided upon and whether or not there will be output capacitors or bypass capacitors, it cannot be determined yet. A basic potentiometer based volume control that will be put to ground in parallel with another resistor to keep the pot itself out of the signal path. Only one headphone output at this point to keep costs down. A basic 2 input (+), 1 output headphone amp.
It is a bit of an "out of thin air" number, but I will be trying for a Zo of around 50 Ohms. I believe that could be a realistic value. Output power I am not as certain on. My aim is quality to that end I need to run my tubes as linearly as possible so less than 1 watt but more than 400 mWatts. I want to be able to drive Hd650's without difficulty and with enough confidence to run 600 Ohm DT880/990s. P-P running in lower power operation should hopefully enable running lower impedance headphones like the K701s. I think I would find it difficult to run Denons or Grados but I will try my best.