# Creating DIY Open-Source Tube Amp Project - Input Requested



## dBs

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 Unfortunately, tubes are a technology of yesteryear and college looks at them as outdated (which they are for most purposes, lets be honest) so I learned nothing of them in college.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.


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## pabbi1

If you have not already, I would read Pete Millett's DIY Audio pages - it is full of real world implementation, as well as discussions on tubes.

 To keep glass costs down, I would suggest Russian tubes - 6n1p, 6n6p and 6h23, all plentiful and cheap.

 Otherwise, best of luck.


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## Leny

Hello dBs, I admire your enthusiasm. However before progressing you need to take a step back and decide exactly what you are going to design. For example…

 Is it going to be for dynamic headphones, electrostatic headphones, etc.?
 If dynamic, what impedances must it drive, and to what level?
 Is it to have a volume control or reply upon a volume control built into the source?
 How many inputs?
 Etc,. etc., etc..

 So, my recommendation is to write a short statement defining exactly what it is to be. Then write an objective list of target performance, features and facilities.

 Only then can you start assessing alternative ways to achieve your objectives. Likewise remember that cost is closely associated with technical feasibility, so you may need to vary your budget a bit.

 Good luck.


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## dBs

Quote:


  Originally Posted by *pabbi1* /img/forum/go_quote.gif 
_If you have not already, I would read Pete Millett's DIY Audio pages - it is full of real world implementation, as well as discussions on tubes.

 To keep glass costs down, I would suggest Russian tubes - 6n1p, 6n6p and 6h23, all plentiful and cheap.

 Otherwise, best of luck._

 

Thanks, I will look into those tubes. The site I'm sure will also prove useful, thank you.

  Quote:


  Originally Posted by *Leny* /img/forum/go_quote.gif 
_Hello dBs, I admire your enthusiasm. However before progressing you need to take a step back and decide exactly what you are going to design. For example…

 Is it going to be for dynamic headphones, electrostatic headphones, etc.?
 If dynamic, what impedances must it drive, and to what level?
 Is it to have a volume control or reply upon a volume control built into the source?
 How many inputs?
 Etc,. etc., etc..

 So, my recommendation is to write a short statement defining exactly what it is to be. Then write an objective list of target performance, features and facilities.

 Only then can you start assessing alternative ways to achieve your objectives. Likewise remember that cost is closely associated with technical feasibility, so you may need to vary your budget a bit.

 Good luck._

 

I have it up there but I suppose I didn't state it explicitly but this would be for headphones. I haven't thought about preamp capabilities or anything yet but at this point I would probably not involve any as it would up the complexity and cost.

 As far as the number and types of inputs, there isn't much to that. I don't plan to incorporate any DAC functionality, so I could leave it at RCA type plugs. As far as Zo, I haven't decided on that yet as that will be determined in part by the type of tubes I go with and whether or not I end up incorporating any bypass capacitors or output capacitors. Naturally the lower the better, but until I have a set of tubes decided upon, there wont be much of a way to determine what Zo I will be aiming towards.

 I do plan on incorporating a simple POT (probably use a paralleled variation implementation to remove the pot itself from the signal path. I haven't researched any sort of delay circuit yet but that is up for consideration.

 Cost is a factor but I suppose not entirely set in stone. If some leeway is needed than that is fine as ultimately the DIY'er can go with a cheaper capacitor or resistors if they felt the cost prohibitive in default configuration. I definitely understand that my developmental costs will go above the amps cost, that is to be expected. I don't even own an oscilloscope or frequency generator yet XD. This will be a piece by piece endeavor, as it will be personally funded.

 Features are basic, no real frills: I will at least create it with two inputs in mind simply so a person could very easily add in parallel any additional inputs they may desire, basic potentiometer volume control, one headphone port. Basic 2 in, 1 out =).


 Someone PMed me saying that there is an over-saturation of this style of amp already and that I should think about creating a DIY DHT SET amp that doesn't hum. Any thoughts on this idea? It's early so P-P can be "voted" out.


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## nikongod

Quote:


  Originally Posted by *dBs* /img/forum/go_quote.gif 
_Someone PMed me saying that there is an over-saturation of this style of amp already and that I should think about creating a DIY DHT SET amp that doesn't hum. Any thoughts on this idea?_

 

There is not an oversaturation of what you described, indeed it is quite unusual. Unfortunately it is already the basis of a DIY project (Cavalli Bijou). The idea to run a SEPP stage off of a long tail pair is neat and I can tell you it sounds awesome with 6sn7.

 On the topic of the individual who PM'd you: Have you researched this individuals recent threads and general opinions? Would you follow this person into a project based on their previous track record. If the individual has more than about 200 posts the find started threads button should be quite helpful. fewer than 150, read everything they have to say before you believe a word of it.
  Quote:


 It's early so P-P can be "voted" out. 
 

Why should push-pull be voted out? There are plenty of reasons to say that its a great topology to look at if you have a budget. Here are a few of the better ones:
The amp has better PSR. A simpler PS can be used, saving money.

Cheap PP transformers generally have better bandwidth than cheap SE transformers.

With the goal of creating something new, there is not much to say for SE. There are tons of neat things to try with PP that have not been used in ages.
Technically the last one is not really new but nobody has seen it in long enough that you can take credit.

 I should add that a parafeed SE amp offers many advantages to a budget minded amp as well. Another great topology to look into.


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## Leny

Quote:


  Originally Posted by *dBs* /img/forum/go_quote.gif 
_As far as Zo, I haven't decided on that yet as that will be determined in part by the type of tubes I go with… _

 

Yes and no; there is a better way...

 First decide what you are trying to achieve, then look for alternative ways to get there.

 So first research the Zo you need, and document it. THEN look for ways to achieve it.

 It may be that as the project evolves you find that it is difficult to achieve your target, and you may have to accept a ‘deviation’ from specification. However in order to increase your chances of success you should always start with a specified target, not with a decision on the ingredients. 

 So what output impedance would you like as a target? 
 Must this be the same for all impedances of headphones?


  Quote:


  Originally Posted by *nikongod* /img/forum/go_quote.gif 
_I should add that a parafeed SE amp offers many advantages to a budget minded amp as well. Another great topology to look into._

 

Seconded.


 Keep it up,
 L.


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## dBs

Quote:


  Originally Posted by *nikongod* /img/forum/go_quote.gif 
_There is not an oversaturation of what you described, indeed it is quite unusual. Unfortunately it is already the basis of a DIY project (Cavalli Bijou). The idea to run a SEPP stage off of a long tail pair is neat and I can tell you it sounds awesome with 6sn7._

 

I was hoping to avoid a differential pair if I could help it to keep costs down. I suppose it could be done without significant increased cost if the tube was a twin triode, maybe.

  Quote:


  Originally Posted by *nikongod* /img/forum/go_quote.gif 
_On the topic of the individual who PM'd you: Have you researched this individuals recent threads and general opinions? Would you follow this person into a project based on their previous track record. If the individual has more than about 200 posts the find started threads button should be quite helpful. fewer than 150, read everything they have to say before you believe a word of it._

 

I trust this individual. Ultimately, while this project is for myself, it is also for everyone else as well. I want people to be interested in this project as well. I want people to actually want to build this thing so catering to the tastes of people here is important to that end =)

 I've done my research pretty well on P-P and basic SET. I know the trade offs and advantages well =) I'm hoping to do something a bit unique though, and I haven't seen a lot of SEPP in the cheaper DIY genre.

 I did consider "bringing back the retro" with a circlotron but to implement them correctly you really need to bring in an output transformer and that would cripple the cost.

  Quote:


  Originally Posted by *nikongod* /img/forum/go_quote.gif 
_I should add that a parafeed SE amp offers many advantages to a budget minded amp as well. Another great topology to look into._

 

I have not researched these very extensively yet as I was concerned with the OPT cost. I thought I would incorporate more complex and expensive options in later designs (I don't intend this to be the only thing I design =)). If this is what the customer wants though, I haven't steadfastly written anything off.

  Quote:


  Originally Posted by *Leny* /img/forum/go_quote.gif 
_First decide what you are trying to achieve, then look for alternative ways to get there._

 

I'm just concerned of painting myself into a corner. If someone comes up with a really intriguing idea--to me and any community members who take interest in this idea--but I can't give it a shot because I set up prerequisites, then I'm not doing this project any favors. I kind of like the idea of experimenting along the way =D

 You are right though, I should have set something up a bit more definitive. I will include some more specific thoughts into the *UPDATE* on the OP.

  Quote:


  Originally Posted by *Leny* /img/forum/go_quote.gif 
_Must this [Zo] be the same for all impedances of headphones?_

 

I didn't entirely understand what you asked here, could you rephrase it?


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## Leny

Quote:


  Originally Posted by *dBs* /img/forum/go_quote.gif 
_I didn't entirely understand what you asked here, could you rephrase it?_

 

Sorry for not being clear. 

 Transformer coupled amps with switchable taps (for matching to different impedance headphones) change their output impedance from tap to tap according to the reflected impedance of the tube. 

 For example it might be 10 Ohms on the low impedance setting and 30 ohms on the high impedance setting. Their designers believe this to be fine, and I wondered if this is something that you had considered, and whether you believed it important or not. 

 However, I have now re-read your posts and see that you would prefer no output transformer, so my question does not apply anyway!!!


 But then again, if you do decide to consider an output transformer, take a look at the Hammond 119DA which is about US $25 at Antique Electronic Supply. It's performance seems good for the price. It is used in the Hagtech Castanet and the M.A.D. amps.


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## dBs

Quote:


  Originally Posted by *Leny* /img/forum/go_quote.gif 
_But then again, if you do decide to consider an output transformer, take a look at the Hammond 119DA which is about US $25 at Antique Electronic Supply. It's performance seems good for the price. It is used in the Hagtech Castanet and the M.A.D. amps._

 

That is a good piece of information and far cheaper than I have seen unto this point. That will be worth looking into.

 If I was going to do an OPT design, I would have done tapped, absolutely =)


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## regal

Quote:


  Originally Posted by *dBs* /img/forum/go_quote.gif 
_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. ._

 

How do you plan on Zo=50ohms with a P-P OTL and little NFB? You're looking at a lot of output tubes and a huge power supply. Unless you are talking about a Futterman type design? An OPT is much less costly.

 I'm personally not inerested another OTL when they are all over eBay and from China for cheaper (just one example for $213 http://www.head-fi.org/forums/f5/ell...lifier-420767/than one can build and as mentioned for DIY the Bijou is tough competetion. The problem with OTL is the big cap at the output makes them all sound like that big cap to a certain degree. But I applaud you for making a group project, great DIY spirit.

 As far as parafeed, looks at dsavitsk's page, he has done a lot of good work with parafeed spud amps.


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## burgunder

I think it would be great if you and the community would design an OPT amp, but I will suggest another desing than parafeed as it seems there might be a kit avaiable with the L'espressivo design at least the amp has had it's own section at DIYforums for some time. But this is only speculation, so a parafeed could still be OK.


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## nikongod

Quote:


  Originally Posted by *dBs* /img/forum/go_quote.gif 
_I've done my research pretty well on P-P and basic SET. I know the trade offs and advantages well =) I'm hoping to do something a bit unique though, and I haven't seen a lot of SEPP in the cheaper DIY genre._

 

Despite the fact that people know no limits on how much to spend on parts for it a bijou can be built fairly inexpensively. 

  Quote:


 I did consider "bringing back the retro" with a circlotron but to implement them correctly you really need to bring in an output transformer and that would cripple the cost. 
 

Edcor makes push pull output transformers for as little as $18. The bandwidth is kind of poopy, but the ones for $25 look much nicer.
  Quote:


  Originally Posted by *regal* /img/forum/go_quote.gif 
_How do you plan on Zo=50ohms with a P-P OTL and little NFB? You're looking at a lot of output tubes and a huge power supply. Unless you are talking about a Futterman type design? An OPT is much less costly._

 

 Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_the Zo of the Bijou is about 55R with no NFB._

 

I dont understand what makes the futerman circuit anything more than a white cathode follower with a bias scheme that circumvents older patents.


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## dBs

Ok, I like what I'm seeing, a good exchange of interest now!

 I will look into parafeed and see what the good/bad/trade-offs/major considerations are.

 Keep it up!

 Don't forget to give me ideas on tubes. That's one area I could spend months learning about and only be scratching the surface. Any tubes that you find are unappreciated, over hyped, just plain bad, or exceptional?


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## nikongod

Quote:


  Originally Posted by *nikongod* /img/forum/go_quote.gif 
_I dont understand what makes the futerman circuit anything more than a white cathode follower with a bias scheme that circumvents older patents._

 

I just goggled exactly what a futerman circuit means, thinking forever that it meant the output stage of the Bijou. A futerman circuit is an OTL amplifier with a positive feedback loop nested in a global negative feeback loop.


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## TimJo

Quote:


  Originally Posted by *nikongod* /img/forum/go_quote.gif 
_I just goggled exactly what a futerman circuit means, thinking forever that it meant the output stage of the Bijou. A futerman circuit is an OTL amplifier with a positive feedback loop nested in a global negative feeback loop._

 

So the positive feedback is coming from the cathode current of the phase splitter in that design, correct?


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## nikongod

Quote:


  Originally Posted by *TimJo* /img/forum/go_quote.gif 
_So the positive feedback is coming from the cathode current of the phase splitter in that design, correct?_

 

I had never looked at it that way. Thats too cool.


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## ericj

Last few years, the problem with this kind of collaborative effort is that when you reach the proof of concept stage, digi01 starts selling boards and you get bogged down supporting builders of an unfinished project.


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## tomb

Quote:


  Originally Posted by *burgunder* /img/forum/go_quote.gif 
_I think it would be great if you and the community would design an OPT amp, but I will suggest another desing than parafeed as it seems there might be a kit avaiable with the L'espressivo design at least the amp has had it's own section at DIYforums for some time. But this is only speculation, so a parafeed could still be OK._

 

It's not speculation. There are two prototypes operating as we speak and another 6 on the way. Things are progressing nicely, but I'll defer to Dsavitsk for any other details, if he wishes.


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## Leny

Quote:


  Originally Posted by *dBs* /img/forum/go_quote.gif 
_At this point I would like it to be a single ended push-pull (SEPP) topology._

 

Just a quick thought; there has been some confusion in the past about what SEPP means. Most understand it to mean one triode on top of another, however some have bundled the mu-follower under the SEPP banner. You might already have considered the mu-follower, but if not then consider adding it to your list of possibilities.

 Mu follower
 6SN7
 About 10 or 12mA
 Parallel-feed
 Hammond 119DA
 No 'driver' required for an overall gain about 1.5-ish
 Plenty for modern high-efficiency 'phones when input is from a normal digital (2V) source

 Just a thought!


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## n_maher

Quote:


  Originally Posted by *ericj* /img/forum/go_quote.gif 
_Last few years, the problem with this kind of collaborative effort is that when you reach the proof of concept stage, digi01 starts selling boards and you get bogged down supporting builders of an unfinished project._

 

When is the last time this actually happened? I thought things with Digi had been dealt with to a certain extent? Feel free to PM me with details but if any member is abusing the DIY forum to the detriment of the general membership I'd like to hear about it. It's not something I'm interested in tolerating.


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## dsavitsk

Quote:


  Originally Posted by *tomb* /img/forum/go_quote.gif 
_It's not speculation. There are two prototypes operating as we speak and another 6 on the way. Things are progressing nicely, but I'll defer to Dsavitsk for any other details, if he wishes.
	

	
	
		
		

		
		
	


	


_

 

For now, beyond the fact that it is a low cost, high performance, tube parafeed amp, details are under wraps -- but we are working hard to get this done sooner than later.


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## dBs

Well, I did some research today into parafeed (//feed) OPT design and I like the idea a lot. A very elegant solution to what seems to have been a long plaguing problem. It seems like a reasonable prospect to me since the series cap can be of a very small value which means either high quality or cost compensation for the OPT and choke. The OPT could be cheaper as well since it doesn't need to be as big and doesn't require an air gap.

 I really like the //feed idea. It seems that that so far is favored over the P-P design. I certainly think it would be an easier topology to design, especially for the PSU.

 I like this, I feel like we're starting to get somewhere now =D I would hate to bite on dsavitsk's feet though =X


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## regal

Quote:


  Originally Posted by *dBs* /img/forum/go_quote.gif 
_I like this, I feel like we're starting to get somewhere now =D I would hate to bite on dsavitsk's feet though =X_

 


 You can take a different approach, his design is a single gain stage. Look at the 6EW7 datasheet, it would be ideal as one section is a gain stage and the second a drive. So with 2 tubes stereo you get higher gain for high imp phones and lower output impedance for low impedance phones. Bottlehead's amp is similiar but he uses a slightly different tube(same family) which presents some compromises for headphones.


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## dBs

I will look into that combination, thank you for the suggestion.

 You guys are getting me all excited to start XD But there's a lot to do yet; math, CAD, buying an oscilloscope and signal generator (not looking forward to that =P).


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## dBs

Researched Mu Followers a bit today. They sound like their advantages are great and one of the few disadvantages they have would be alleviated by the inclusion of a //feed.

 I am going to do a bit more research on the mu though as most of what I found today was mathematical design principles and less of the subjective information (I view both as important as I do believe that the ear cannot be summarized by an oscilloscope).

 I am attracted to the fact that a twin triode could be utilized as well to make the design a bit simpler (but only a bit since the part count for a Mu goes up significantly).

 Something I have been wondering about and have tried to research but found no information on is if twin triodes that are not strapped have the potential to cross talk between each half? That would be an unwelcome occurrence.

 I think Leny might be on to a good combination here.


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## regal

Quote:


  Originally Posted by *dBs* /img/forum/go_quote.gif 
_Researched Mu Followers a bit today. They sound like their advantages are great and one of the few disadvantages they have would be alleviated by the inclusion of a //feed.

 I am going to do a bit more research on the mu though as most of what I found today was mathematical design principles and less of the subjective information (I view both as important as I do believe that the ear cannot be summarized by an oscilloscope).

 I am attracted to the fact that a twin triode could be utilized as well to make the design a bit simpler (but only a bit since the part count for a Mu goes up significantly).

 Something I have been wondering about and have tried to research but found no information on is if twin triodes that are not strapped have the potential to cross talk between each half? That would be an unwelcome occurrence.

 I think Leny might be on to a good combination here._

 

Read Broskies, SRPP Deconstructed article. They are very load dependant as the load is in the circuit, I've never had much luck with them. Most folks have switched to CCDA is which is also on Broskies site.


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## dBs

Quote:


  Originally Posted by *regal* /img/forum/go_quote.gif 
_Read Broskies, SRPP Deconstructed article. They are very load dependant as the load is in the circuit, I've never had much luck with them. Most folks have switched to CCDA is which is also on Broskies site._

 

Yea, I did read that they were load dependent. If you drop the load too much you enter distortion. They also are very prone to quick cut off distortion that escalates very quickly. With a transformer though, I think there is more control over the load. If there are concerns that the load may drop too low, then I can try to design it with a different turns ratio or a tapped transformer.

 It seems like the kind of challenge I am drawn to though XD If you tell me something isn't possible or is very difficult, I am more apt to try, lol.

 Ultimately, it is a current source strapped to a basic class A triode if I'm understanding it right. If the source of the problem you describe is the fact that it's active load due to the current source aspect then wouldn't you find the same problem if you did a PRIMM based current source? I haven't heard of this problem very much when those are implemented.


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## Leny

Quote:


  Originally Posted by *dBs* /img/forum/go_quote.gif 
_I am going to do a bit more research on the mu though as most of what I found today was mathematical design principles and less of the subjective information (I view both as important as I do believe that the ear cannot be summarized by an oscilloscope)._

 

Yup, that age old problem… the ear is not an oscilloscope, and at least 50% of subjective opinion is based on false deduction (eg. “I heard a system containing a 12AX7 and the sound was lush. Therefore all 12AX7s sound lush. Get a 12AX7 because they are a lush sounding tube”).


  Quote:


  Originally Posted by *dBs* /img/forum/go_quote.gif 
_Something I have been wondering about and have tried to research but found no information on is if twin triodes that are not strapped have the potential to cross talk between each half? That would be an unwelcome occurrence._

 

I think it would be difficult for an electron from the cathode of triode A to meander over to the anode of triode B. Having said that it seems some triodes did introduce a central shield, so maybe there were some issues? Maybe capacitive coupling at radio frequency (just guessing)? The later version of the 6SN7 was the 9-pin miniature 6CG7, and that certainly had an internal shield connected to pin 9. 


  Quote:


  Originally Posted by *dBs* /img/forum/go_quote.gif 
_ I am going to do a bit more research…_

 

Just for info: with the mu-follower the upper tube’s cathode is at a high voltage and that might exceed the heater-cathode voltage rating of the tube. In which case designers add a positive off-set to the heater voltage to reduce the difference. That seems to suggest that the lower triodes share one bottle while the upper triodes are in the second bottle.


 As you seem set to spend a few $, consider spending a few more on TubeCAD from Glass-Ware (John Broskie).

 Cheers for now,
 L.


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## regal

Quote:


  Originally Posted by *dBs* /img/forum/go_quote.gif 
_
 Ultimately, it is a current source strapped to a basic class A triode if I'm understanding it right. If the source of the problem you describe is the fact that it's active load due to the current source aspect then wouldn't you find the same problem if you did a PRIMM based current source? I haven't heard of this problem very much when those are implemented._

 

No it isn't analogous to a CCS loaded anode follower, the SRPP is a push-pull design where the load (transformer/headphone/top tube) is seen by the bottom triode. Read the Broskie article it is very enlightening, he explains it much better than I can. You are correct that the best way to deal with SRPP is with an ouput transformer so the ideal load is the same / somewhat independant of the headphone impedance. This has rarely been done because you need a gain stage in front of it, most designs just throw a cap on the end and make it an OTL. When I had an SRPP DAC I did a lot of experiementing and I saw a huge reduction in distortion when I lowered my amp's input impedance to the ideal load, however it still didn't sound as good as a SE stage.


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## dBs

Quote:


  Originally Posted by *Leny* /img/forum/go_quote.gif 
_As you seem set to spend a few $, consider spending a few more on TubeCAD from Glass-Ware (John Broskie)._

 

Right now I am holding off on making any considerations for the order or priority of any expenses. I will definitely have to look into these considerations and being as I am funding it all myself and I'm only just graduated, it may be a slow process XD I have Electronics Workbench software already for the and I will see how good the functionality is for tubes in there. I suspect it wont be very good though, at which point, depending on cost, it would make sense to look into TubeCAD.

  Quote:


  Originally Posted by *regal* /img/forum/go_quote.gif 
_No it isn't analogous to a CCS loaded anode follower, the SRPP is a push-pull design where the load (transformer/headphone/top tube) is seen by the bottom triode. Read the Broskie article it is very enlightening, he explains it much better than I can. You are correct that the best way to deal with SRPP is with an ouput transformer so the ideal load is the same / somewhat independant of the headphone impedance. This has rarely been done because you need a gain stage in front of it, most designs just throw a cap on the end and make it an OTL. When I had an SRPP DAC I did a lot of experiementing and I saw a huge reduction in distortion when I lowered my amp's input impedance to the ideal load, however it still didn't sound as good as a SE stage._

 

I read the TubeCAD information on the Mu Follower today. The source I looked at yesterday was Morgan Jones's Valve Amplifier book. It looks like he came to the current source conclusion as he neglected to account for the loads influence on the circuit.

 Unfortunately, there isn't anything new in the world of tube design but I am hoping to avoid the standard SET but just about everything you read now sources you to the sink known as SET XD.

 Ultimately, while TubeCAD did show that the Mu is merely a smidgen variation of the SRPP. He didn't really hit on too many major issues with it though beyond the strict shared resistor value. That being the case, I still feel it's worth considering. //feed would be a fitting complement since each of their respective weaknesses are addressed by the other without undue complexity. At the very least the PSRR would be very low, lol.


----------



## dBs

Quote:


  Originally Posted by *regal* /img/forum/go_quote.gif 
_You can take a different approach, his design is a single gain stage. Look at the 6EW7 datasheet, it would be ideal as one section is a gain stage and the second a drive. So with 2 tubes stereo you get higher gain for high imp phones and lower output impedance for low impedance phones. Bottlehead's amp is similiar but he uses a slightly different tube(same family) which presents some compromises for headphones._

 

I'm rereading the thread to see if I missed any juicy nuggets. I assume you mean in this as 2 separate class A stages where the second gate is fed from the plate output of the first? I just want to make sure I am understanding you completely =)


----------



## regal

Quote:


  Originally Posted by *dBs* /img/forum/go_quote.gif 
_I'm rereading the thread to see if I missed any juicy nuggets. I assume you mean in this as 2 separate class A stages where the second gate is fed from the plate output of the first? I just want to make sure I am understanding you completely =)_

 

Yes but the single tube contains the tube very different stages. I have a schematic at work I can foward you, it is for s ingle-feed but parafeed probably makes more sense because you can CCS feed the output stage and it doesn't reuire such a demanding powersupply.

 Right now I am building a SE OPT 5842 amp with Salas HV shunt PS, pratcically no caps in the audio cicuit.


----------



## nikongod

You should look into the PSR of Mu followers. I la-la-love to hear that Im wrong about these thigns, but PSR on a Mu follower is no where near as good as CCS loaded plate output.

 Assuming Im actually right about that:
 You may be better off finding the path to lower output impedance elsewhere with better PSR. What does another active stage cost to add to the circuit with a different turns ratio on the OPT? What does the PS quiet enough to meet your standards of a quiet output with a mu-follower cost? compare them.


----------



## regal

This basically takes the best features of the Bottlehead S.E.X amp and the Woo6 and combines them for an amp with good gain for headphones, good PSRR, relaticely inexpensive. I decided to go the single 5842 route instead because I want to avoid caps altogether, but this option I considered is much more versatile ( the 5842 amp I'm building is a Grado only thing.)

 This is just a rough scetch of what I was trying to describe in words to give you some thing to think about. I know you seem to be leaning against SET amps but they are the way to go, being an EE if you could really crack the code on a quiet background DHT SET you would have the low distortion you seem to be after and an amp that would be up there with the most expensive options. How hard can it be to make a quiet musical .25A 5V filament supply for a recent EE grad who hasn't forgot all the book stuff? 
	

	
	
		
		

		
			










 Edit: Mistake 2nd tube after CCS should be 150V at the plate, negative bias at the grid should read 17V. Sorry but I will fix the schematic when I get a chance.


----------



## Leny

Quote:


  Originally Posted by *nikongod* /img/forum/go_quote.gif 
_You should look into the PSR of Mu followers. I la-la-love to hear that Im wrong about these thigns, but PSR on a Mu follower is no where near as good as CCS loaded plate output._

 

I think you are spot on, Mr. nikongod. 

 The mu follower does have less power supply ripple rejection, yet allows the current in the lower tube to stay more-or-less constant. Meanwhile the CCS as an anode load has very large power supply rejection, yet allows the current in the lower tube to vary as current is transferred to the load.

 So it's a case of weighing up the theoretical pros and cons: mu-follower has lowest distortion owing to near-horizontal load line yet requires more intensive power supply treatment, while CCS anode load requires less power supply investment yet has higher distortion owing to non-horizontal load line.

 That's something for dBs to consider.



  Quote:


  Originally Posted by *nikongod* /img/forum/go_quote.gif 
_Assuming Im actually right about that:

 You may be better off finding the path to lower output impedance elsewhere with better PSR. What does another active stage cost to add to the circuit with a different turns ratio on the OPT? What does the PS quiet enough to meet your standards of a quiet output with a mu-follower cost? compare them._

 

You are right about that. However the psu for the mu-follower could be a TL783 for each channel (plus a few resistors and caps). Not sooo expensive, but certainly more complicated to build.

 Horses for courses. As you say... "compare them".


 Have a nice day, one and all.


----------



## dBs

Everyone is bringing good ideas to the table.

 Naturally I don't have the wealth of experience that you all seem to have, so it would be wise of me to ask if traditionally the PSU or the amp itself is the more difficult element to design and balance (balance the trade-offs)? I imagine that the answer will be "it depends on if you try to design it without ______ or with ______". If I were to go for a mu follower and have to consider a more perfected--complex?--PSU, would that difficulty only be marginally more so than the one demanded by a CCS? Conversely, if the CCS is a more difficult amp to design, is that a marginal increase in complexity versus the mu follower? Which increase in difficulty/complexity the bigger hurtle, PSU or amp?

 If that didn't make sense, a distinct possibility, than I can clarify.

 I like the ideas floating around now though. There's still a fair bit of time yet before I have the means to begin purchasing parts.


----------



## Leny

Well, there be more than one way to skin a cat, especially in DIY land. In my day job (electrical engineer, not electronics engineer) I recommend that folk fully document the specification then start the system design by considering the end and then work their way back. (Obviously it takes some wiggle and adjustment along the way, and it’s not an entirely linear process). 

 Anyway, that would translate in your task here as: choose an output transformer, design the output stage to drive it, (then if you are going to have one) design the input stage to drive the output stage, then design whatever supply was needed by the stages in order to achieve their objectives.

 Or something like that.


----------



## Leny

dBs, I don't know if you have seen this, but it might be adaptable to your needs: http://www.forsselltech.com/download...VT%20Opamp.PDF


----------



## dBs

Thank you for sharing that. Actually, that confirms pretty well what I had been thinking along the lines of. I have a biiig white board (best things on Earth) where I put up ideas, sketches, quick notes, etc. and my sketch looks pretty similar to that. I haven't involved any differential pair and there are a few things I'm not entirely certain as to the reason for (though I'm sure there are good reasons), but I do like that there are more similarities than differences =D

 I'm starting my research a bit now into the power supply end of things. I understand this area better than I do amp design since my classes were more relevant in this arena. I do have some general questions though; mostly with grounding. Grounding is one area that can cause major problems with ground loops, improper grounding, chassis vs earth, isolated grounds, etc.. This is one area where I think colleges really need to almost dedicate a class on as it is pertinent to almost all areas of electrical engineering.

 I am also curious as to the advantages of dual power supplies as is used in my 337. I would see that as a risk for ground loop problems, PSU and part variability, and susceptibilities. It isn't something I plan on putting into this particular design for obvious reasons, but I am still curious.

  Quote:


  Originally Posted by *regal* /img/forum/go_quote.gif 
_This basically takes the best features of the Bottlehead S.E.X amp and the Woo6 and combines them for an amp with good gain for headphones, good PSRR, relaticely inexpensive. I decided to go the single 5842 route instead because I want to avoid caps altogether, but this option I considered is much more versatile ( the 5842 amp I'm building is a Grado only thing.)

 This is just a rough scetch of what I was trying to describe in words to give you some thing to think about. I know you seem to be leaning against SET amps but they are the way to go, being an EE if you could really crack the code on a quiet background DHT SET you would have the low distortion you seem to be after and an amp that would be up there with the most expensive options. How hard can it be to make a quiet musical .25A 5V filament supply for a recent EE grad who hasn't forgot all the book stuff? 
	

	
	
		
		

		
		
	


	


_

 

Your design definitely looks unique. I wont take it just by virtue of the fact that it wouldn't be mine and I don't to steal your idea. You did remind me of the possibility of using diodes off of the cathode though. I read very briefly about that a while ago and was curious, but have forgotten to investigate further. I only ran across it that one time so it is a seldom used technique.

 Were you planning on using some kind of PRIMM or SS designed current source?

 As far as being able to crack DHT hum problems, the easiest thing that comes to mind is using a separate power supply for the heating. I would be surprised if that hasn't been done before though so I suspect there are significant drawbacks to that method. Even though I have a piece of paper on my wall, I put more value in the experienced knowledge of people like yourself and other longtime (aged? XD) DIY designers. I only know theory. The real world is a different place, and while my ego would want me to claim I could crack that code, my sensibilities suspect that if others haven't cracked that code yet the odds aren't in my favor...yet. A few years of real world experience and I may be ready for that challenge. I will look into it despite though, it is best to know ones enemy after all!


----------



## FrankCooter

Quote:


  Originally Posted by *regal* /img/forum/go_quote.gif 
_ How hard can it be to make a quiet musical .25A 5V filament supply for a recent EE grad who hasn't forgot all the book stuff? 
	

	
	
		
		

		
		
	


	







_

 

This would be really useful and really helpful to anyone that works with DHT's. Don't mean to insult you, but it would also be something specific and concrete you could really sink your teeth into, rather than flopping around and trying to "reinvent the wheel" with vague "blue sky" amp ruminations.

 All DHT's require seperate filament supplies. In most cases, DC is reuired. All the usual methods (battery, brute force, volt. reg., current reg., etc.) have their own problems. Probably the best, but the least used, is ultrasonic AC. Something like a Colpitts oscillator running at 50khz into a small broadband amp might be a possibility. You could probably even make money selling it in board or kit form. I'd buy it!


----------



## regal

Quote:


  Originally Posted by *FrankCooter* /img/forum/go_quote.gif 
_This would be really useful and really helpful to anyone that works with DHT's. Don't mean to insult you, but it would also be something specific and concrete you could really sink your teeth into, rather than flopping around and trying to "reinvent the wheel" with vague "blue sky" amp ruminations.

 All DHT's require seperate filament supplies. In most cases, DC is reuired. All the usual methods (battery, brute force, volt. reg., current reg., etc.) have their own problems. Probably the best, but the least used, is ultrasonic AC. Something like a Colpitts oscillator running at 50khz into a small broadband amp might be a possibility. You could probably even make money selling it in board or kit form. I'd buy it!_

 

10-4, to me this is the biggest missing link for the DIY tube headphone amp builder. DHTs practically took over the speaker amp world with their linearity and wonderful sound, yet they have barely made an impact on headphone amps because of this issue. 

 Pmillet has an incomplete ultra-sonic oscillator schematic for DHT filament supplies on his web page that you may be able to use as a starting point.


----------



## Leny

Just seen the 6EW7 datasheet from RCA, and it looks like a nice tube for the job:
http://www.scottbecker.net/tube/sheets/049/6/6EW7.pdf

 dBs there is another example here: 6EW7 Se amplifier

 Regal, you might want to reconsider your ouput tube operating point!


----------



## regal

Quote:


  Originally Posted by *Leny* /img/forum/go_quote.gif 
_
 Regal, you might want to reconsider your ouput tube operating point!_

 

Its OK, max disspapation for section 2 is 10W if I posted the right schematic should be 150V*.045A= 6.75W (note the negative grid bias used to avoid the cathode cap). You want to run this thing hot to get the lowest Rp (see the last page of the datasheet).


----------



## Leny

I meant the way it's drawn shows 265V anode to cathode (i.e. supply) and -117V grid to cathode (i.e. bias), which is not feasible.

  Quote:


  Originally Posted by *regal* /img/forum/go_quote.gif 
_... if I posted the right schematic should be 150V*.045A= 6.75W _

 

Yup, 150V and 45 mA sounds / looks good.

 : )


----------



## regal

Quote:


  Originally Posted by *Leny* /img/forum/go_quote.gif 
_I meant the way it's drawn shows 265V anode to cathode (i.e. supply) and -117V grid to cathode (i.e. bias), which is not feasible.



 Yup, 150V and 45 mA sounds / looks good.

 : )_

 

Yea I need to clean that up should be 150V on the plate after the CCS and -17 on the grid, originally it was DC coupled. But with the parafeed it makes more sense to try and eliminate as many big caps as possible.


----------



## regal

dB,

 Here is a link to P Milltets ultrasonic oscillator DHT filament supply. The parts list is so vague it would take a damn electrical engineer to figure it out
	

	
	
		
		

		
			





 Note that he says he encourages someone to polish up the design and use it for DIY.

HF filament supply


----------



## nikongod

Quote:


  Originally Posted by *FrankCooter* /img/forum/go_quote.gif 
_All DHT's require seperate filament supplies. In most cases, DC is reuired. All the usual methods (battery, brute force, volt. reg., current reg., etc.) have their own problems. Probably the best, but the least used, is ultrasonic AC. Something like a Colpitts oscillator running at 50khz into a small broadband amp might be a possibility. You could probably even make money selling it in board or kit form. I'd buy it!_

 

Indeed.
 Since no actual tube amp design has come from this thread perhaps the goal could shift to constructing a PCB and running a group buy for an HFAC filament supply.
 Someone should ask any of the people who have posted their designes for this for permission to run the boards in limited QTY's and get the ball rolling!


----------



## dBs

Well there certainly seems to be enough interest here to warrant a further look. I'll see if I can decipher this high frequency oscillator and do further research into DHT (I did a bit already but I will do more). As the 300B is a biiit out of the price bracket I was aiming for I will have to find some common DHT heater specs so I could tailor it to that/those tubes.


----------



## dBs

Researched AC heaters the last couple days (been a busy couple of days). There is a bit more that I would like to look into though. I will be trying to look at DC heaters the next couple of days. At this point I would be more inclined to go with a DC though what I have read about them usually indicates that they result in underwhelming performance. Surely there must be a good way to make one =D I have definitely found some good links though regarding AC heaters.


----------



## regal

Quote:


  Originally Posted by *dBs* /img/forum/go_quote.gif 
_Researched AC heaters the last couple days (been a busy couple of days). There is a bit more that I would like to look into though. I will be trying to look at DC heaters the next couple of days. At this point I would be more inclined to go with a DC though what I have read about them usually indicates that they result in underwhelming performance. Surely there must be a good way to make one =D I have definitely found some good links though regarding AC heaters._

 

The only way to make a good DC heater for DHT is for it to have a high impedance to AC (audio signal) that way it doesn't pickup noise, there are still drawbacks. See Rod Coleman's design on DIYAudio.


----------



## dBs

I've been really busy but researching the vagaries of the DHT PSU. At this point, I am getting the suspicion that taking on something like this might be a bit more than I could chew as a first project. The complexity significantly goes up not just in the amp in general but also in just that PSU set of components. While I am an ambitious fellow, I suspect this might be a bit outside my abilities at this point.

 I am still strongly leaning to the Mu follower with //feed. I have some ideas in mind on how to make it happen already and will be looking to start breaking out the math maybe this weekend if an LA trip isn't on tap.


----------



## dBs

I'm starting to hone in on the tubes I am thinking of using. Right now I am steering for dual triodes and pentodes to keep costs down. I can share tubes for each channel or...

 I found a gem piece of tube advice on TubeCad where a person pointed out a nice cheap tube that seems to have gone mostly unnoticed; the 6GU7. Aikido All-in-One HPA/LSA & The 6GU7

 Looks nicely linear, middle of the road mu, VERY cheap. With a tube that cheap I could make each channels tube unique and just strap the two triode halves together to boost the gain while hopefully not unsettling performance too much.

 I am debating a pentode in the upper position of the Mu Follower for the high mu value. The question will be if the added noise is a worthy trade off for the increased performance...as is usually the debate.

 I am having a heck of a time trying to find choke components in Electronics Workbench (using version 10). Nothing comes up on index searches. The tube selection is really limited as well. I haven't looked yet, but I suspect that I can find parts that I can add to the programs database or modify the parameters to reflect my tube choice.

 I'm sure that I'm the last one to the party on this site but if anyone hasn't found it yet, a great visual "calculator" for tube parameters based on resistor values, capacitors, B+, etc.: Cathode Bypass Capacitor Calculator


----------



## fishski13

i've been looking for a fun tweaker headphone project, 2A3 or 300B. from what i've researched, DC with CCS seems to be the easiest compromise for the filaments. i think head-fier dsavitsk has built a quiet DHT headphone amp with a simple LM317 configured as a CCS, but his website has been down for the last few days. 

 would a toroid be better than an EI?

 as far as schematics go, i've really only put some time in looking at the many Loftin-White 2A3 variants.


----------



## dsavitsk

Quote:


  Originally Posted by *fishski13* /img/forum/go_quote.gif 
_from what i've researched, DC with CCS seems to be the easiest compromise for the filaments. i think head-fier dsavitsk has built a quiet DHT headphone amp with a simple LM317 configured as a CCS, but his website has been down for the last few days._

 

Website should be back up soon ... I hope. 

 I use a LM317 regulator followed by a CCS and it is very very quiet. I tried LM317 based CCSes, but found that they never sounded quite right and were likely oscillating. I switched to a basic mosfet + BJT and it works great. This works fine for low current tubes, but once you are doing high current it is a little more work.

  Quote:


  Originally Posted by *fishski13* /img/forum/go_quote.gif 
_would a toroid be better than an EI?_

 

An EI is generally better for power supply duty as EI power transformers don't pass high frequencies and toroids do. Toroids are used because they are more efficient, lighter, and cheaper and they don't radiate as much meaning they can be closer to other stuff. But, if you have the space, and EI is generally preferable.


----------



## dsavitsk

Quote:


  Originally Posted by *dBs* /img/forum/go_quote.gif 
_I found a gem piece of tube advice on TubeCad where a person pointed out a nice cheap tube that seems to have gone mostly unnoticed; the 6GU7._

 

Worth playing with, perhaps, but the curves I found don't inspire confidence.


----------



## dBs

Ewww, yea that certainly isn't the curves that were shown over at TubeCAD, which looked much more promising. Hmmm. I can't read the values too well in the graph you posted so I can't tell if your graph represents the same ranges as the one on TubeCAD.

 I would imagine that such plate characteristic graph inconsistencies aren't uncommon in the world of tubes given their construction and manufacturing processes of the time.


----------



## dsavitsk

Quote:


  Originally Posted by *dBs* /img/forum/go_quote.gif 
_I would imagine that such plate characteristic graph inconsistencies aren't uncommon in the world of tubes given their construction and manufacturing processes of the time._

 

More relevant probably is that the curves were drawn by hand.

 The ones I posted are from the RCA datasheet. The ones on Tubecad are from the GE sheet. 

TDSL Tube data [6GU7]

 But, even looking at those closely, I still don't think they look great. Certainly not as good as a 6SN7. If you want an oddball with similar mu and Gm but with fantastic linearity, look at the 2c22.

TDSL Tube data [2C22]


----------



## fishski13

dsavitsk,
 thanks. this will be my first "design". i'll no doubt have more questions over the next few months for you and others much more knowledgeable than me.

 i have TurboCAD, but what electronics schematic software would people recommend?


----------



## dBs

Quote:


  Originally Posted by *dsavitsk* /img/forum/go_quote.gif 
_More relevant probably is that the curves were drawn by hand.

 The ones I posted are from the RCA datasheet. The ones on Tubecad are from the GE sheet. 

TDSL Tube data [6GU7]

 But, even looking at those closely, I still don't think they look great. Certainly not as good as a 6SN7. If you want an oddball with similar mu and Gm but with fantastic linearity, look at the 2c22.

TDSL Tube data [2C22]_

 

Wow, good call on the 2C22. Did some brief research today and couldn't find anyone who didn't like it. The price is certainly right with them as well. I definitely think you found a winner there, thank you =D


----------



## dBs

At this point I am thinking of implementing the //feed using a constant current source instead of a choke. This makes me wonder if the mu follower is pointless, or rather the upper tube is pointless. The idea is that the mu follower replicates (while not perfectly) a ccs. This isn't entirely true when a load is connected, never the less, I suspect that the ccs would make the upper tube portion of the mu follower pointless.

 I am also concerned that if the headphones/load is removed, then the top tube is acting as a ccs, but in series with an actual ccs. I know that that is generally a no-no in design to put two current sources in series with one another. I haven't found any mu followers with a ccs after B+ and I suspect that these are the reasons. 

 I suspect that another reason a mu follower is rarely mixed with a //feed is because the //feed capacitor would have to be a fairly large value due to the low output impedance of the mu follower architecture. I am wondering if my thinking is correct on these points, or if I am thinking about it all wrong.

 Otherwise, I found a bit of time today to look at the 2C22 curves and throw some numbers together. I like the values that I am getting. It feels good to be doing math again, lol. My native language.


----------



## Leny

Hello dBs,

 Yup, you have confused yourself a tad there. It will be either CCS on top of a amplifier tube, or mu-follower whereby the upper tube (or FET) approximates a CCS. Never a CCS on top of a mu-follower for the reason that you noted.

 If you choose the CCS on top of an amplifier tube then the PSRR is very high. The current from the CCS is divided between load and tube, hence the current through the tube is not constant. The output impedance is dictated by Rp (the internal anode resistance of the tube).

 If you choose mu-follower then the PSRR is less high, and the performance of the PSU is more important. The mu-follower diverts PSU current to the load while maintaining almost constant current through the lower tube. The output impedance is dictated by the follower section, which if done right is going to be significantly smaller than the internal anode resistance of the amplifying tube.

 Both CCS loaded amp tube and mu-follower are fine for parallel-feed configuration. Surely the output cap value is determined by the inductance of the output transformer primary? 

 Cheers for now,
 L.


----------



## dBs

I have been looking hard for a couple of days for what I could expect to be the average input voltage for my amp from your average DAC. I would like to think that something like this would be relatively standard, but more than likely the answer is "it depends". I have found no specifications from DAC models (Audio GD, Zero, etc.) on what their output voltages are. It's a little tough planning your input stage without knowing what input grid voltage you're going to be running.

 At this point I might have to start over on the output stage as I suspect that my selected grid voltage there is too high for any DAC (if I made it only one stage), or too low for any tube input/gain stage. Basically, I have painted myself into a corner unless the output voltages of your average DAC are low enough.


----------



## jcx

desktop digital source consumer audio devices usually put out 2 Vrms full scale

 older "standards" include 0 dBv and 0 dBu; 1 and ~.7 Vrms


----------



## dBs

Quote:


  Originally Posted by *jcx* /img/forum/go_quote.gif 
_desktop digital source consumer audio devices usually put out 2 Vrms full scale

 older "standards" include 0 dBv and 0 dBu; 1 and ~.7 Vrms_

 

Ahh, thank you. I've gone crazy looking for that information. As I suspected, it is a bit too low for my grid to go one stage. I will have to do some redesign. No biggie


----------



## nikongod

What output voltage swing are you looking for?


----------



## Leny

...and you only need to set your input grid voltage to just above your expected max input peak. So if you use 2V rms as a working assumption for input then peak will be about 2.8V, so a bias point of 3V should be fine. 

 Obviously you can raise that if you want to get into a particular part of the anode characteristic curves for whatever reason, ... or if you happen to choose a tube that turns out to draw significant grid current when approaching 0V!

 (3V bias will actually be -3V, but I am sure you know that already).


----------



## regal

Quote:


  Originally Posted by *Leny* /img/forum/go_quote.gif 
_...and you only need to set your input grid voltage to just above your expected max input peak. So if you use 2V rms as a working assumption for input then peak will be about 2.8V, so a bias point of 3V should be fine. 

 Obviously you can raise that if you want to get into a particular part of the anode characteristic curves for whatever reason, ... or if you happen to choose a tube that turns out to draw significant grid current when approaching 0V!

 (3V bias will actually be -3V, but I am sure you know that already)._

 


 Don't forget there will be a volume pot, many good headphone amps have enough gain that a 1V bias works fine. I always target 2V bias, makes using an LED on the cathode easy which to my ears always sounds better than an electrolytic capacitor.


----------



## dBs

Wow, a lot of insight in just a few short posts. You guys are great =D Confirming the conclusions I have been slowly coming to in some cases. I don't mind [too much] banging my head against a wall if it means I'm not going to forget.


----------



## dBs

Quote: 





nikongod said:


> What output voltage swing are you looking for?


 

  Well I was looking at using the 2C22 tube at Ip=9mA with Vg=-5V so my Vp=176V and my Vp-p would have been ~100V. This was before the knowledge that I would be receiving roughly 3V in from the DAC. If I am willing to go single stage at Vg=-3V then I get a Vp-p of roughly 130V at the same quiescent. The mu of the 2C22 is 20 so with this topology I expect to get most of that gain.
   
  Just finding it difficult to find a input/gain tube that can take ~-3 in and amplify it only like 10-15 to fit the usual low-mu tubes for the driver stage. If I go the multistage route, I am tentatively looking at the 6AS7 and equivalents.


----------



## nikongod

Quote: 





dbs said:


> Well I was looking at using the 2C22 tube at Ip=9mA with Vg=-5V so my Vp=176V and my Vp-p would have been ~275 to ~75. This was before the knowledge that I would be receiving roughly 3V in from the DAC. If I am willing to go single stage at Vg=-3V then I get a Vp-p of roughly 130V at the same quiescent. The mu of the 2C22 is 20 so with this topology I expect to get most of that gain.
> Just finding it difficult to find a input/gain tube that can take ~-3 in and amplify it only like 10-15 to fit the usual low-mu tubes for the driver stage. If I go the multistage route, I am tentatively looking at the 6AS7 and equivalents.


 
  First off this new forum software is very confusing. I would like to break this quote up into smaller sections, but I cant. This makes me sad. Updated: firefox automatic spell check does not work in this f|_|c!<1|\|g text window. ****ity **** **** ****. now the world will know how I really spell. What a bandolier of carrots we have been sold into.
   
  to put this into perspective without line by lining like I would have on the old site:
  You are adding another whole tube for less than 6db of gain.
   
  You wanted 275 to 75V (200vp-p) but only get 130vp-p. You lost less than 6db, not even a factor of 2!
   
  Get creative, and come up with another way. 1:2 input transformers may yield better results than a smatering of another tube and the rest spent on wasteful attenuation.
   
  This of couse feeds back to my question of how much output voltage swing do you need? YOU are the designer, you tell us.


----------



## regal

From past experience with a source of 2V P-P,   a gain of 7 wasn't quite enough for 600 ohm phones but a gain 10 works just about right.   These were Sextetts,  I believe one of the worst case for voltage swing needs (maybe AKG340 even worse).   Hope this helps


----------



## dBs

Quote: 





nikongod said:


> to put this into perspective without line by lining like I would have on the old site:  You are adding another whole tube for less than 6db of gain.
> 
> You wanted 275 to 75V (200vp-p) but only get 130vp-p. You lost less than 6db, not even a factor of 2!
> 
> ...


 
  Hahaha, yea, I noticed the spell check right away. That will be tough. As I've said before, math is my native language, not English XD
   
  Unfortunately, I don't know what kind of voltage swing to aim for. College made the main attention the gain, not the swing (unless of course you wanted the max swing). I did note that most headphones tend around the 90-105dB/V but that somehow seems wrong to me as that would mean (105x50)dB for 100V swing. That seems way too large, so I am either missing some key piece of information or I am not understanding something simple (I tend to make the simple things harder than they are).
   
  I am aiming less for quantity and more for quality. Not looking to push K1000s or anything. The output transformer should help with the low impedance headphones. I think I am starting to give up on the notion of a cheaper amp, I am probably just taking the easier road in that decision, hahaha.
   
  At this point I am leaning toward a single stage. From the few instances of Vp-p for speakers that I have read about (haven't found any information on what is recommended usually for headphones), 130V would be sufficient and the current source portion of the mu follower should give enough current as well.
   
  ...uh oh. Don't resize the reply box, BTW. I just tried that and I can't scroll to the side to see/edit what I typed on the right side.
   
  I think I gave enough of an impression here though. Sorry if it seems like you guys are holding my hands or something. I can be a bit slow in the beginning, but my grasping pace will pick up, I promise, hahaha.
  
  Quote:
 Originally Posted by regal View Post
  From past experience with a source of 2V P-P, a gain of 7 wasn't quite enough for 600 ohm phones but a gain 10 works just about right. These were Sextetts, I believe one of the worst case for voltage swing needs (maybe AKG340 even worse). Hope this helps
   
  That helps a LOT, thank you. Yea, you make me think that the single stage 2C22 will be sufficient. Think I will find a higher mu tube for the top tube in the mu follower though to up that performance a little. I will be avoiding pentodes though, quality>quantity!


----------



## dsavitsk

Firefox spell check may not work, but SeaMonkey spell check works fine.
   
  You can design 100 amps on paper and never get it right, or you can build one, get it mostly wrong, but get a very good idea of how this all works.  I suggest you put down the calculator and get out the soldering iron.  And, don't worry about making a project for everyone else. Make one for yourself first.
   
  Most phones are spec'd at ~98dB per _*mW*_ which is the key bit of information you were missing. 
   
  Anyhow, a 2c22 has an rp of ~6600. You want your transformer's primary to be at least 3x that.  Really, you want it a lot more, but a transformer with a primary much higher than 15K is really pushing things. Let's say you are happy with a 20K primary.  2VRMS, or 125mW, into grados will make your ears bleed, so let's make 2x that power the target to allow for sufficient headroom.  Ignoring copper losses, that is a 70VRMS swing into the 20K primary.  mu is 20, so you will need a 3.5VRMS signal to get that.  Practically speaking, due to copper and core losses, etc, figure to add at least 20% to that.  Basically, the rp is too high, and the mu is too low to use the 2c22 (or the 6SN7, 12AU7, etc.) in this arrangement.  It will drive headphones just fine, but it won't be the ultimate tube amp you are probably looking for as there are too many compromises.  Find something with a similar mu but a lower rp (5687, 6n6p, 6H30), or a higher mu (6DJ8, D3a, 5842, 6688, C3m, etc.)
   
  Edit: And, don't dismiss pentodes because the audio boards told you they were bad.  One of my all time favorite amps I have built is a simple transconductance amp using a high Gm pentode transformer coupled to a set of Grados. Works awful with other phones, but great with Grados. I think 99% of the reason many people dismiss pentodes is because they are a little harder to use.


----------



## cobaltmute

Quote: 





nikongod said:


> First off this new forum software is very confusing. I would like to break this quote up into smaller sections, but I cant.


   
  Sort of like this?  You can do it, but you have to goto source, which is not great unless you can read HTML.
   


> This makes me sad. Updated: firefox automatic spell check does not work in this f|_|c!<1|\|g text window. ****ity **** **** ****. now the world will know how I really spell. What a bandolier of carrots we have been sold into.


 
  Click on source and then do your correcting and then click on source again.


----------



## dBs

Quote: 





dsavitsk said:


> Firefox spell check may not work, but SeaMonkey spell check works fine.
> 
> You can design 100 amps on paper and never get it right, or you can build one, get it mostly wrong, but get a very good idea of how this all works.  I suggest you put down the calculator and get out the soldering iron.  And, don't worry about making a project for everyone else. Make one for yourself first.
> 
> ...


 
  Unfortunately, right now all I can do is calculator math gymnastics. I don't have the money yet for parts or testing equipment (I plan to get a cheap oscilloscope and signal generator even though I know that they TECHNICALLY aren't essential pieces of equipment) yet. It wont be until mid next month that I will have the money to start going in at this. So in the mean time it's calculate away while trying to grasp better the nuance of tube amp design. At this point, my weakest areas of knowledge are at the "ends", meaning input and output considerations and calculations, and tube selection itself. I found a GREAT resource on //feed but how that interrelates with the design of the tube stage and accompanying passive elements I have seen little. When it comes to tube selection, I just don't know that many yet. There are soooo many so having an idea of what tubes offer the gain I am looking for along with the Vg I am looking for, along with the Iq I am looking for, and the grid/V swing I am looking for (if I go pentode top) is more just google searches for "low-mu medium grid" and/or luck of the draw. Not the most expedient of means to find such things but also pretty interesting in its own right.
   
  When it comes to using a pentode as the top tube, there are 2 things: finding a tube that has the same Iq as the lower triode (haven't looked too far into this so this may prove to be a non issue), and my 337 already has a pentode in it so I was hoping to go all triode and see how different it would sound =D
   
  I probably sound like I am making a lot of excuses, and maybe I am. Just a very large subject that I am throwing myself into headlong, as is my nature. As such there are a lot of gaps of knowledge to fill. Besides, we all know that college really doesn't "prepare you for the real world", hahaha.


----------



## nikongod

cobaltmute:
  Thanks for telling me how to do that: Its been ages since I have read HTML code, but I guess its time to relearn that.
  
  Quote: 





dbs said:


> Unfortunately, right now all I can do is calculator math gymnastics. I don't have the money yet for parts or testing equipment (I plan to get a cheap oscilloscope and signal generator even though I know that they TECHNICALLY aren't essential pieces of equipment) yet. It wont be until mid next month that I will have the money to start going in at this. So in the mean time it's calculate away while trying to grasp better the nuance of tube amp design. At this point, my weakest areas of knowledge are at the "ends", meaning input and output considerations and calculations, and tube selection itself.


 
  This last bit is the problem.
   
  Dont worry about the tubes. What you need to worry about to design a (at least half) decent amp of ANY kind is exactly what you dont know, thats OK, admitting you dont know it is how you go out and learn it.
   
  Before you think about more schematics & topologies and whatnot you need to go out and figure out what it is you are trying to accomplish. That is the key. Are you trying to put 100v into a 300ohm load? Are you trying to put 2a into 32ohms? Do you want an output impedance less than 0.0001ohms? what *EXACTLY* are you trying to do? For sure you could design an amp that would accomplish these feats, but do you have any real need for that beyond mental masturbation and bragging rights?
   
  The really good news is you probably have most of what you need to figure this out. the DV337 should be able to drive a sennheiser to dumb volumes. Measure the ac voltage that it takes (its much much better if your meter will accurately display less than 2vac). If your meter has AC current, do that to or just crunch the numbers. Test it out on a grado too. learn for yourself exactly what it takes to drive these headphones. people love to spout rules about how to drive a senn, How many people are just parrots repeating unconditional rules they dont understand?
   
  Perhaps even more telling, and where many people stray (IMO) is what it takes to drive these headphones to your own listening levels (for this you will almost certainly need a meter that displays less than 2vac with good precision). Does it matter that someone else's amp can put 20v into 300ohms when you only use 0.25v? I would say hardly so, what matters is that YOUR amp sounds nice at realistic volumes. does this necessarily mean that an amp that only puts out 2.5v (0.25v+20db headroom) WILL sound better? not at all, but the odds are stacked in your favor.
   
  Now would be as good of a time as any to figure out what output impedance you need. Guess what, its not going to be zero with tube output stages. If you need that (and maybe you do, although I have not found that to be the case) have fun with SS stuff & hybrids. Again figure out what you NEED. The DV amps have kind of high output impedances for testing, so build a cmoy with a 500ohm pot on the output to adjust output impedance. Try a bunch of things out with a bunch of headphones.
  
  So far you have spent the cost of building a cmoy plus a cheap 500ohm pot (and a meter that can display less than 2vac, if you dont have that) and learned a bunch.
   
  Quote: 





dbs said:


> I found a GREAT resource on //feed but how that interrelates with the design of the tube stage and accompanying passive elements I have seen little. When it comes to tube selection, I just don't know that many yet. There are soooo many so having an idea of what tubes offer the gain I am looking for along with the Vg I am looking for, along with the Iq I am looking for, and the grid/V swing I am looking for (if I go pentode top) is more just google searches for "low-mu medium grid" and/or luck of the draw. Not the most expedient of means to find such things but also pretty interesting in its own right.


 
  Dont worry about the tubes. Worry about what you need out of the amp. 
   
  After you have figured out what you need out of the amp you can work the rest backwards from the output. You will probably be surprised how well things fall into place.
  
  Quote: 





dbs said:


> When it comes to using a pentode as the top tube, there are 2 things: finding a tube that has the same Iq as the lower triode (haven't looked too far into this so this may prove to be a non issue), and my 337 already has a pentode in it so I was hoping to go all triode and see how different it would sound =D


 
  The amps are totally different, even with the same tubes the amps would sound and work differently. By not using a cathode follower (unless you really want to use a Mu follower, in which case you owe it to yourself to listen to a few mu follower amps to help you change your mind) you have already changed the sound of the amp a great deal. Pentodes make great CCS's, why not use one? There are a couple disadvantages in a parafeed amp: you need higher voltage rails than with a SS CCS and you need a second heater supply.


----------



## burgunder

Hey it's your project so you are the one who's in charge of how fast it's progessing, so just keep it up the work and I'm sure you will succeed


----------



## regal

NikonGod gave good advice.    My design that I am working on now was zero and I mean zero caps in the signal path all the way back to the powersupply,  so I worked from there.  It reminds me of my bosses always saying start with a vision statement and work from there.  Yes I think it is possible,  hope to know shortly.  I came to this after learning that capacitors highly influence the sound to my ears just by switching brands.
   
  With a parafeed design you may also want to look at the newer gyrator circuits in place of a ccs,  reports are that they keep the tube more linear?  I haven't tried them but heard good reports and they are cheap to try.  Sorry if this has already been mentioned as the new site is very slow for me to navigate page to page.


----------



## dBs

Quote: 





regal said:


> NikonGod gave good advice.    My design that I am working on now was zero and I mean zero caps in the signal path all the way back to the powersupply,  so I worked from there.  It reminds me of my bosses always saying start with a vision statement and work from there.  Yes I think it is possible,  hope to know shortly.  I came to this after learning that capacitors highly influence the sound to my ears just by switching brands.
> 
> With a parafeed design you may also want to look at the newer gyrator circuits in place of a ccs,  reports are that they keep the tube more linear?  I haven't tried them but heard good reports and they are cheap to try.  Sorry if this has already been mentioned as the new site is very slow for me to navigate page to page.


 

 Tried a different browser to see if it's browser specific? I used to freelance web design in high school for spare cash (back when HTML was cutting edge) and back then I made use of iFrames and image maps for my personal sites and they weren't supported by all browsers so wonky things would happen in those instances.
   
  (back to amp design) Thus far I have taken the tactic of designing around the amp itself with the goal of balancing the many various trade-offs, steering to the lowest noise and most linear possible, without resorting to really complex topologies. The idea is that, as far as the output was concerned, I would tailor the transformer to the output impedance, voltage, current that I wanted to fit the headphones I am looking to interface with. The method would be to take the output impedance, voltage, and current of my amp, find the best corresponding primary value, and decide on the best turns ratio to achieve the Z, V, and I that I wanted for my headphones. Thus, I haven't strongly concerned myself as much with those factors as I have seen them easily flexible given that relationship. I could be thinking about this in too much of an idealized "perfect" world though, and in real world amp design this tactic may not be affective. Is this a correct assessment?
   
  Unfortunately, it was my lack of foresight that resulted in the input V/I/P problem. In all the things I've read, no one has mentioned anything about that consideration (probably assuming that it was implied, lol). The same has been the case for the output properties to aim for (in a generalized sense). Everyone is so focused on the sexy amp topologies and misc. tweaks that they overlook the input and output properties that matter in the design and end result. I'm not trying to make excuses, but I am honestly surprised that these problems were able to "sneak up" on me without my reading about the ranges (in the real world) that tend to be acceptable. Kind of thought these would be advertised specs on my amp or other market amps where I could find a generalized range to base from. Well, lesson learned. Hopefully this thread will help those who follow behind me. That is my biggest goal here and why I plan to have everything be known and open for all to see from the math to the design and the build, I want another beginner like me to be able to know every step in the process.
   
  Yea, I honestly jumped the gun a bit. It has taken me a bit longer to pay off (long story XD) a rather large sum of debt I had accumulated due to my job. I will be at zero debt mid next month though (minus student loan and car), so I will be able to start buying equipment and parts. I am just determined to be paid off before I do anything else, I just didn't think it would take this bloody long XD


----------



## dsavitsk

It's a bit of  messy subject. Actual necessary gain and output power for headphone amps is really quite modest. IMO, gain for low Z phones probably should be unity or lower, and for high Z, more like 3 to 4. People will tell you higher, but then, those people rarely turn the volume knob past 10:00 -- it seems to give people a sense of "power" if the output ramps up quickly rather than over the whole range of the pot.  Moreover, output power likely doesn't need to be over 250mW with perhaps 400mW a reasonable headroom target.  And even that is high -- the 1st mW is what counts.  Indeed, amps using things like 300B's are necessarilly compromised -- one noted transformer manufacturer pointed out that a single feed 45 needs a core that that can normally handle 70W ungapped to handle the gap and DC necessary for that tube to produce under 2W.  All that does is throw away low level detail and render the tube very ordinary.  A 300B is worse.  Big power tubes sell amps, but they don't work better.
   
  Not all phones are happy with that, but the bulk are, and trying to make an amp that pleases everyone will no doubt end up pleasing no one. For the esoteric phones, it is better to design something esoteric.


----------



## FrankCooter

As usual, I agree with about 99% of what Doug says. But in the case of his comment about big power tubes,  I'd like to point out that the Japanese DIY community, which historically has been the forefront of the DHT revival, has been running large transmitting tubes at low levels for years. However much this violates generally accepted engineering principals, the results can be surprizingly, even stunningly, good. Sorry to drift off point.
   
  dBs, it's definitely time to end the "math gymnastics" and break out the soldering iron.Your making this a lot more complicated than it really is. Most of your problems will be in implementation rather than design.dsavitsk, nikongod, and regal, have given you more than enough good and useful information to actually get started.
  .


----------



## dBs

Quote: 





frankcooter said:


> As usual, I agree with about 99% of what Doug says. But in the case of his comment about big power tubes,  I'd like to point out that the Japanese DIY community, which historically has been the forefront of the DHT revival, has been running large transmitting tubes at low levels for years. However much this violates generally accepted engineering principals, the results can be surprizingly, even stunningly, good. Sorry to drift off point.
> 
> dBs, it's definitely time to end the "math gymnastics" and break out the soldering iron.Your making this a lot more complicated than it really is. Most of your problems will be in implementation rather than design.dsavitsk, nikongod, and regal, have given you more than enough good and useful information to actually get started.
> .


 
  Yes, but until I have the funds to do that, I may as well learn as much as I can. There is always more to learn!


----------



## regal

Quote: 





dsavitsk said:


> It's a bit of  messy subject. Actual necessary gain and output power for headphone amps is really quite modest. IMO, gain for low Z phones probably should be unity or lower, and for high Z, more like 3 to 4.


 


 I think I posted my gain suggestion but it may have been lost with the transistion.   I had a DAC with a ~2V p-p output (very low but concieveably encountable) with 600 ohm Sextetts an amp with a gain of 7.5x was loud enough with the volume pot all the way maxed when playing 24 bit padded 20 bit HDCD decoded well mastered music(about the worse case scenario.).  Now I have an amp with 10x gain and it is just right for both 32 ohm and the 600 ohm phones.   The newer HDCD software decoders may not have this issue but anyway I think it explains the descrepency between our target design gains.  Also take into account a lot of folks listen to bootleg music (raw soundboards or audience recordings)  where the levels are very low.  The old tapers did this to absolutely avoid clipping when they are recording live music on the fly.   So it can be a messy subject,  I'm probably a worst case scenario with the low source output and the low level bootlegs (believe it are not many of these are better than what the studios put out.)


----------



## dBs

Good advice so far, helped give a sense of scope.
   
  EDIT: Ha! Well that's ironic. I found the tube I talk about bellow on a site listing different medium-mu tubes. Low and behold I see it was a tube *dsavitsk *had pointed out. I looked through the ones you pointed, but maybe I accidentally missed/skipped that particular one. Well, you were absolutely right! Good call =D
   
  I found a tube that may be more fitting. Of course, my version of "found" at this point may just mean stumbling across one of the most popular tubes, hahaha. In any case its the 5687 dual triode. It seems fairly common, fairly inexpensive, nice and linear from the couple of data sheets I've looked at, has a nice low Rp value between 1650 Ohms @-2Vg and 3000 @-12.5Vg. A mu of 17, same as the 2C22, but because it is a dual triode, I can parallel the two sides together to up the output power so without having to resort to anything exotic, and should allow me to make it a one stage job. Only concern with that tactic is finding an upper tube that can handle the added current that will be needed to run the combined Iq. If need be I can go with a paralleled upper tube as well, but that gets a bit close to http://gilmore2.chem.northwestern.edu/projects/showfile.php?file=barbour_prj.htm and I don't want to bite someone else's design if I can help it.
   
  I have to do some number crunching, but at this point, I like what I am seeing in the 5687 tube.


----------



## FrankCooter

If you're looking for a beefier 5687, consider the octal 6bl7.The 6bx7 is even better.
   
  The "Brute Force in a Line Stage"  is an exellent first tube DIY project. I've built 4 or 5 different versions. Even one with a DHT (112A) on the bottom.. Worked surprizingly well. This is definitely a good place to start.


----------



## Leny

Quote: 





dbs said:


> If need be I can go with a paralleled upper tube as well, but that gets a bit close to http://gilmore2.chem.northwestern.edu/projects/showfile.php?file=barbour_prj.htm and I don't want to bite someone else's design if I can help it.


 


 Or just copy it and add a Hammond 119DA or (if you are feeling rich) a Sowter 8665 on the output. It would make a good learning project, it would work, and you could progress from there into your first home-grown design!


----------



## dBs

Naaaah, that's one of the reasons I am designing it from the ground up. I want that added challenge, level of customization, and the other flurry of benefits that go along with that method.


----------



## dBs

Ok, I feel confident in my tube choices now.
   
  I have the dsavitsk 5687 dual triode lower tube (connected in // for 2 tubes total), and a 12HL7 upper single pentode for the top (for 2 tubes total).
   
  The major considerations for the pentode came with the // triode which meant that I needed the pentode to be able to handle the 40mA that I plan to run them at (20mA each since they are in //). I didn't want to have to have a really power PSU so I tried to find a pentode with lower Ec2 and Vp operating points. The pentode also had to be able to accept the voltage swing that the lower 5687 tubes would be using. The 12HL7 on the surface appears to fit the bill nicely.
   
  At this point this is how I am looking to operate the 5687:
   
  Vg=-3V
  Ip=20mA (each)
  Vp=107V
  Mu=~17
  Rp=~1.6-1.7k
   
  which yields a Vp-p of 110V
   
  I have to crunch some numbers for the pentode which I hope to do tonight, but from what I see, it should work well. I haven't found much on it, but I suspect that the way you set the operating point is as if it was a pentode running in cathode bias cathode follower configuration with the traditional RL in series with Rk. I don't see the lower triodes acting as a CVS so I'm expecting to plan for this using the traditional load line method.


----------



## dBs

Ok, long weekend, hopefully I'll find some time to get this blasted math done. Bit stuck right now finding an RL value. I'll get it, but it has proven less than cooperative, lol.
   
  Otherwise, I had a REALLY out there idea to maybe tackle that DHT problem that was mentioned a long time ago in this thread. I think I might have found a way to heat a 300B (for example) without using a transformer of any kind, or a battery of any kind. What about stringing together a series of diodes? Your average solid state diode has a knee voltage of .6-.7V. The 300B has a filament voltage of 5V, that is only 8-9 diodes in series. Now, this will drop your signal by that 5V and that number of diodes in series might produce enough noise to make more of a problem than it solves, but I haven't seen anyone propose that idea before. There may be a reason for that, but I figure I'd propose it =D


----------



## nikongod

What does RL mean?
   
  My guess is "load resistance" (Resistance of the Load) as in the headphone, or the reflected load on the primary of the transformer which is not a constant. If I guessed right you are trying to hit a moving target with a stationary gun. In the dark.


----------



## dBs

Nah, like the RL from here: http://www.freewebs.com/valvewizard1/mufollower.html
   
  They use lower case L so it looks like a 1 kinda. Basically top tubes CCS load resistor.
   
  EDIT: Ok, never mind! I just read that and saw it, lol. I google for a simple example picture and I find a good explanation. It's ok, I've made a fool of myself before and I am sure I will again, lol.


----------



## dBs

Ok, I'm going to have to explicitly ask for help this time. I have been toiling over this for the past month or so I would say. There is a constant struggle between finding a pentode for the CCS that can yield a good rp (not Rp), but also not exceed the screen dissipation. I found what I thought was a good combination but that screen dissipation keeps killing me. Both find mutual benefit (good rp and lower screen dissipation) when Ip is low. There is a bit of a trade off between lowering the Ip and consequently increasing the Rk+RL, but the Pg2=Ip^2*Rg2, so it makes more sense to favor lowering Ip than Rk+RL, especially when increasing Rk+RL benefits rp.
   
  Now I am reading that all this struggle may have been for no reason. I have been toiling under the idea that keeping in the linear region of operation is as important for a pentode CCS as it is for the triode that it supplies. I ran across some information that I should have looked at before that made it sound like a constant current SINK (not source) doesn't need to be run in the linear region like a the triode would. In fact, it goes so far as to say that you should operate the pentode in a sink with significantly less Ip than where you would normally run it. I do not know if this applies to CC sources as well as sinks, and my gut tells me that it does not, but I very much hope so. If I can feel sonically safe running the pentode CC source in a much less linear, lower Ip area of the curves, then it would REALLY save me from bashing my head more than I already have.
   
  I will finally have the money to order parts this Friday, but until I can get this blasted step figured out, I will be going nowhere. I can clarify if anything I said above doesn't make sense. I can also supply some visuals if that would help clarify things. I'm a very visual person so I've been using Photoshop to handle all my load lines and such.
   
  Hahaha, I've run through the equations so many times that I finally just made an Excel spread sheet so I can just throw in my load line numbers and have instant answers. This is actually working REALLY well and I think I will be continuing to do this for all future designs. Essentially making a quick look up table to determine what tubes and operating conditions will and wont work with one another with almost no effort. I could then even put them online for other people who may not want to break out the really difficult math but still want to get a bit more involved than just doing a Lego set amp...Lego SET amp, interesting idea XD
   
  I am also going to eventually throw together (probably as I go along AFTER this amp is done) an Excel sheet of as many tubes as I can with all their most important ranges and values stored so that they can be organized and browsed as quickly as possible to locate alternatives.
   
  So, if there was a time I needed some insight, it would be now XD I am at your gentle mercies.


----------



## Leny

I can't help with pentodes 'cos I've only played with triodes.
   
  However if you find yourself fully stuck then consider using a solid state upper element.
  Nip over to DiyAudio.com, go to the Articles section, then to 'His Masters Noise' phono amp, then Page 10, then Figure 5, then steal the cascode of FETs !!!
  Tweak the current set resistor to your liking, then take your signal from the source pin of the lower FET, and it's 'Job done'.
   
  Just a thought.
  Good luck.


----------



## nikongod

RJM twilight FTW!!!111


----------



## dBs

It looks like I didn't make much sense, so I will try to clarify. The design I would like is your basic mu follower with two triodse in parallel in the lower section and single pentode up top. That is starting to become rather difficult so a basic mu follower with a pentode top is probably what will really result.
   

   
  Take the example I THOUGHT was going to be a real winner:

  The blue line is where the load line for the lower triode would be if I can find a way to parallel two of them together in the lower stage. The red load lines are where I would like to operate if I am forced into a single lower triode. The currents are 7.5mA and 11mA respectively. The swing is 130V in both cases. Amplification factor is 20, and rp is the usual 6600 and 7700 Ohms.
   
  Now the upper pentode:

   
  This is the 6JC6A pentode. The lines correspond as before, mostly. The red/pink lines in this case, however, are lower than they should be, I started going lower to see if I might get it to work at a lower current. Neither way worked. The voltage swing of the blue line gets a bit closer to 130V than I would like, but I was willing to take the risk. Also note that the 400V on the pentode would not be possible, that was more for an experiments sake that I will explain bellow.
   
  Now the problem arises in the combination of factors that are joined at the hip, as it usually the case, they conflict with one another. I have been laboring under the possibly false idea that pentodes acting as CCS's still need their linearity considered in order for them to sound their best. I have been trying to find pentodes that were the most linear in the current ranges I have been hoping to operate under, like the one above. The problem is that CCS's benefit from having the flattest load line possible as that will increase the cathode and load resistors (Rk2+RL) which will in turn increase the rp seen by the lower triode/s. rp=(Rk2+RL)/(1-Av'), where Av' is the cathode follower gain of Av/(Av+1). So, I have been working to find a tube that would allow me to have as flat of a load line as possible while offering the current range linearity I also wanted. When I speak of acceptable rp values, I am hoping for at least a megaohm, which is achievable, buuuuut...
   
  Additionally, the screen power dissipation Pg2 benefits from having a low current. Pg2=Ig2^2*Rg2, where Ig2 is the screen current and Rg2 is the screen resistor. Now, lowering the current, would mean a flatter load line, which would increase Rg2, BUT also decrease Ig2 and because Ig2 is squared in that equation, that is the better trade off. The greatest struggle has been keeping this Pg2 down to the .7W that is specified by the pentode shown above. I could accomplish it, but the currents were so low as to make the triode very nonlinear, as well as the pentode itself. The voltage of the pentode could be increased to have the same effect, unfortunately, all pentodes seem to be basically voltage bound at or bellow 300V in these current ranges.
   
  The idea then was to find a pentode with higher current capabilities, this got me researching again. I found a section in the Morgan Jones book talking about constant current SINKS (not source like I am trying to develop here). In the book he talks about using pentodes at unusually low currents when trying to use them as sinks. Well that would solve my problem perfectly! The question though is if linearity is a problem? It would appear that it is not much of a problem in sinks as he recommends it and even offers up pentode options that work well for specific current ranges. Now that has me wondering if the same is true for sources. I have looked far and wide for that information but I cannot find it. That probably means the answer is so obvious that I have overlooked it. From the schematic for a pentode sink given in the book, I would not think that the two are the same, so what may work for the sink may not for the source. This also has me wondering if maybe it would be possible to make a mu follower using a sink instead of a source. I do realize that I would lose the PSRR in that case so it may not be a true mu follower, but maybe a more simple topography to implement, while offering most of the same benefits. As I was planning to go parafeed anyway, the PSRR should be pretty good so this makes this option even more intriguing.
   

           Vp 1     Vp 2  Vp max     Vg1   Ip:Ig2 ratio 7 125 300 2.75 3.81           Vg1-1     Vg1-2  Ip max    Ivg1   0 2.75 0.0176 0.0104              Av1                           42.91          Av1'                              0.98          Rk1+RL                   17,045.45          rL2                 748,450.41          Rk1                         264.42          RL                   16,781.03          Rg2                   63,935.73          Ig2                              0.00          Pg2                              1.36        
  (Rg2 in the table is the screen resistor, not the grid to cathode resistor like in the image above)
   
  Hopefully that clears things up a bit.
   
  Now I MIGHT have found a pentode (Z759) that would work. It gives me an rp of 748kOhms with a Pg2 low enough to pass. It even seemed relatively linear, not as good as I would like, but better than I could with any other tube I could find. The values for this tube can be seen above. While the tube isn't terribly expensive, it is really difficult to find. It's the best option I have found so far though, unless I find out that I should be running a pentode source like a pentode sink.


----------



## dsavitsk

Leaving aside the mu follower stuff for now, a pentode as a CCS late load is going to work just like a depletion mode mosfet. You put a resistor under the cathode, and tie the grid (through a stopper) to the base of the resistor. It will self bias and act as a constant current source, or sink (only with BJTs does this distinction matter).  With a pendode, what you are looking for is flat curves -- MJ mentions a few. There are any number of ways to bias the screen grid, but a resistor from b+ and a cap from the SG to the cathode fine.
   
  But, the important point is that, like any other CCS, the pentode will drop whatever voltage it needs to, and this will be controlled by the triode.  The pentode's linearity does not enter into it.  Does this change taking the output from the pentode's cathode instead of the triode's plate? Maybe, but I'd wager not very much. The pentode is running under 100% local negative feedback that should linearize it. That would be my guess anyway.
   
  So, I don't see any inherent difficulty in running parallel triodes, other than the bigger power supply -- thought I am not sure I see much of a point in it, either. As for the pentode, if you need a ton of current use an EL34. That should handle it.   Seriously, you just need to find a pentode that can handle heat dissipation and current, and that has reasonably flat curves.


----------



## JB197

dBs,
  There is a pentode mu-follower in post #5 here: http://www.diyaudio.com/forums/parts/79300-lundhal-line-input-transformer-question.html .
  It shows a 6AC7... I have no idea if this will help you, but surely worth a peek...


----------



## dBs

Quote: 





dsavitsk said:


> Leaving aside the mu follower stuff for now, a pentode as a CCS late load is going to work just like a depletion mode mosfet. You put a resistor under the cathode, and tie the grid (through a stopper) to the base of the resistor. It will self bias and act as a constant current source, or sink (only with BJTs does this distinction matter).  With a pendode, what you are looking for is flat curves -- MJ mentions a few. There are any number of ways to bias the screen grid, but a resistor from b+ and a cap from the SG to the cathode fine.
> 
> But, the important point is that, like any other CCS, the pentode will drop whatever voltage it needs to, and this will be controlled by the triode.  The pentode's linearity does not enter into it.  Does this change taking the output from the pentode's cathode instead of the triode's plate? Maybe, but I'd wager not very much. The pentode is running under 100% local negative feedback that should linearize it. That would be my guess anyway.
> 
> So, I don't see any inherent difficulty in running parallel triodes, other than the bigger power supply -- thought I am not sure I see much of a point in it, either. As for the pentode, if you need a ton of current use an EL34. That should handle it.   Seriously, you just need to find a pentode that can handle heat dissipation and current, and that has reasonably flat curves.


 
  See, all this great new stuff I'm learning is why I wanted to do this from scratch rather than following some recipe =).
   
  At 2am on Saturday night, I realized just how stupid I have been all this time. I realized why I've had half of the problems I've had. I'm guessing this is a problem that most either see as too obvious, or maybe it's just such a rare issue that it is overlooked. It is best shown by illustration:
   

   
  I forget how I found this beauty of a tube but she is gorgeous! She solves the other half of the problem I've been having; screen dissipation. I've run the numbers and with paralleled triodes or single triode, I can operate well under. The revelation of my stupidity can be seen in the lines though. This whole time, whenever I have been calculating my rL2, I have been basing my Av1, Av1',... values from the intersection of the load line with the quiescent current and the intersection of the load line with Ec1=0V. Essentially the maximum swing possible. On a triode this makes perfect sense to do this. On a pentode, however, it makes no sense because the change in Ec1 is VERY fast near Ec1=0V, deceptively fast (at least deceptive mathematically). You only gain a couple of plate volts for LARGE changes in Ec1. This gives your voltage gains Av1, Av1',... values deceptively bad results. When you make the calculations from a more reasonable value Ec1>0V, then the real numbers become clear. I can't believe I didn't see this before. The same affect happens on a triode if you try to max its Ec value, but most people don't run them that way so this problem isn't often encountered.
  
  Either way, this tube solves both the problem I just described, and my plate dissipation. So I can FINALLY move on to the other aspects of the amp that should HOPEFULLY prove easier.
   
  As far as why I want to go parallel on the triodes, I would like the increased gain, especially since it will be mostly current gain so as to work better with low impedance headphones. Also, it will halve the rp value and output impedance which should mean a smaller output transformer is needed as well as improving the performance with lower impedance headphones.


----------



## dBs

Long break as I had family visiting for basically the past 3 weeks. In the last few days, I have made a lot of progress. All my math and component values are pretty much determined for the amp itself. The last part I'm on is the OPT. Transformers, despite their simple basic concepts (not the more involved emag concept), and simple math, they have always been an Achilles heal of mine. It seems as though the number of turns is of little consequence so long as the input impedance is correctly chosen to match well with the plate choke and para capacitor and the turns RATIO is sufficient for the desired Zo and plate resistance. I'm guessing that as far as turns ratio is concerned, I will probably be forced to compromise as having one custom made will not be cheap. I am reading that standard toroidal PSU transformers can work and work well so I am also investigating that path.
   
  After this it's just the PSU and I am confident that that should not prove to be as time consuming as the amp itself has been, lol.
   
  I just figured that I would give a quick update and that things do seem to be going well =D


----------



## regal

Electra-Print is the go to DIY budget custom headphone amp OPT supplier.  His transformers are very good but not real expensive.  If you want expensive transformers no holds barr transformers use O-netics (contact Bud at DIYaudio).


----------



## dBs

Quote: 





regal said:


> Electra-Print is the go to DIY budget custom headphone amp OPT supplier.  His transformers are very good but not real expensive.  If you want expensive transformers no holds barr transformers use O-netics (contact Bud at DIYaudio).


 

 Great info. I will absolutely look into both of them. Thank you.


----------



## natrix

dBs,
   
  I've finished reading most of this thread - there is a lot of really good information here.
   
  I plan on creating my own amplifier, although I am going the solid state route, with a +/- 15 volt supply (I currently am using the AMB sigma22 until I figure out a design of my own) which seems a whole lot easier than dealing with tubes. I've already purchased some decent opamps and some output buffers for prototyping - the LME49600 are about $10 a piece! However, they look great on paper, at 0.00003% THD+N with a 2000V/uS slew rate capable of delivering 250mW to each channel. I intend on driving HD650's in an unbalanced fashion, I will probably be using a Cirrus Logic DAC as a source with some kind of switch for bypassing the DAC/active filter and going right to the gain/buffer stage from an analog "line level" input.
   
  I have already designed and tested an active lowpass filter with a gain of 1 and a cutoff frequency of 25kHz. It works great! Using an HP 8903B I measured the distortion at 0.003% at full scale output at 10kHz.
   
  By the way, a great piece of equipment for testing audio hardware is the HP 8903B. It isn't cheap, but you can find them used for well under $1000. It's great for measuring distortion and gain.
   
  Maybe once my solid state amplifier becomes a product I can actually sell, I will dive in to the tube stuff.


----------



## regal

Quote: 





natrix said:


> Maybe once my solid state amplifier becomes a product I can actually sell, I will dive in to the tube stuff.


 


 Not a good way to make a first impression on a DIY forum.


----------



## dBs

Quote: 





natrix said:


> dBs,
> 
> I've finished reading most of this thread - there is a lot of really good information here.
> 
> ...


 
   
  Personally, I think SS amps are more schematically complex and that's one of the reasons I'm going the tube route. I also REALLY like the tube sound from my very limited experiences with it. I've always been a fan of simplicity of design (though I like to be adventurous in the more complex realms on occasion), and that is definitely tube design.
   
  Glad you are finding this thread informative. Beyond my degree, I know nothing of tubes or their amp design. I figured, I would be willing to sacrifice my dignity for a completely open air thought/design process from a beginner so that others can learn from my mistakes and find answers to questions that might be overlooked in other sources.
   
  Quote: 





			
				regal said:
			
		

> Electra-Print is the go to DIY budget custom headphone amp OPT supplier.  His transformers are very good but not real expensive.  If you want expensive transformers no holds barr transformers use O-netics (contact Bud at DIYaudio).


 
   
  Good call on Electra-Print. They seem very well priced and very flexible with their designs. I am trying to tailor my parafeed configuration to the well documented experimentation done at http://www.siteswithstyle.com/VoltSecond/Parafeed_fun/Parafeed_fun.html I requested info for the likely primary inductance on an output transformer with the following specs:
   
  8k primary inductance
  30mA
  3W
  flexible output impedance (they go from 4-32 and any of those is fine for full sized headphones)
   
  In that article they specify that anything of >~40H per kOhm of reflected load.
   
  I also asked if it would be possible, and how expensive, for them to whip up a couple 150H 30mA plate chokes.
   
  It's nice that they are located in Las Vegas, only a few hours from me.
   
  ::UPDATE::
  I got a reply back and it was pretty curt, lol. I wrote almost verbatim what was above and it seemed like he thought I was insulting his intelligence with a nerdy prank email or something. He recommended specifications of his own, so the question then arises do I trust the site with the quantified test results, or the gentleman from Electra-Print. I favor Electra-Print since I'm sure they've significantly more experience than a single test barrage.
   
  The gentleman from Electra-Print indicated that the only specs that mattered for the OPT is the primary impedance, secondary impedance, and output power. He also recommended that the plate choke be around 50H.


----------



## Leny

Hello dBs, I've not read all of the VoltSecond information, but what I did read seems generally fine, so you may have possibly misinterpreted some stuff?
   
  Maybe I misunderstand but it seems that in your request to Electra-Print you asked for a transformer capable of handling DC (i.e. 30 mA), however a parallel feed is always going to be capacitor coupled hence free of DC current in the primary. It may be that which confused the E - P guy. It is the DC or no DC situation which defines transformer design parameters in addition to the 'primary impedance, secondary impedance, and output power' as noted by E - P.
   
  Having a transformer designed for no DC will result in proportionally higher inductance, all else being equal. So specify no DC, the turns ratio (primary impedance, secondary impedance) and the ouput power required, and then the inductance turns out to be whatever it turns out to be. Then choose your output coupling cap according to the inductance that you have ended up with. 
   
  The (no DC) Sowter 8665 is noted as having a resulting primary inductance of 137 H (http://www.sowter.co.uk/headphone-transformer.php) and multiple taps (12, 6, 4 : 1). I doubt that you will find better. Expensive, but worthy of consideration because it does the right job right!


----------



## regal

I would just trust Jack, read his webpage he is very specific on what info he needs to build a transformer,  get it working and as I said before when you want to get specific with exotics and the like, Bud from Onetics is the go to guy.   Just for reference a popular $5000 tube amp here uses standard Electra-print transformers. With any new design its smart to start with a mid-level transformer until you perfect everything,  then when everything is working as you want on the bench and 100% complete buy the expensive transformers. You can't do it all from textbooks,  too many variables.    JMHO


----------



## dBs

Sorry for the delayed responses. I found out Monday last week at lunch time that I would be working 6pm-6am out in the testing areas for the entire week. Needless to say, the only thing I wanted to do was sleep, lol.
  
  Quote: 





leny said:


> Hello dBs, I've not read all of the VoltSecond information, but what I did read seems generally fine, so you may have possibly misinterpreted some stuff?
> 
> Maybe I misunderstand but it seems that in your request to Electra-Print you asked for a transformer capable of handling DC (i.e. 30 mA), however a parallel feed is always going to be capacitor coupled hence free of DC current in the primary. It may be that which confused the E - P guy. It is the DC or no DC situation which defines transformer design parameters in addition to the 'primary impedance, secondary impedance, and output power' as noted by E - P.
> 
> ...


 
  If you look at their site, they lump SE with DC and parafeed under the same category (though they and I both realize that they are not the same and also the reasons they are not the same). Apparently his frustrations were more at finding another site that spreads false information and that such a site is merely simulation and preposterous.
   
  I will look into that transformer you recommend there. While most parts I can buy cheaper equivalents early on to keep costs down during prototyping and troubleshooting, transformers is not one of those elements. Transformers are potentially the most important element effecting the sound, so I am willing to put the lions share into those.

  
  Quote: 





regal said:


> I would just trust Jack, read his webpage he is very specific on what info he needs to build a transformer,  get it working and as I said before when you want to get specific with exotics and the like, Bud from Onetics is the go to guy.   Just for reference a popular $5000 tube amp here uses standard Electra-print transformers. With any new design its smart to start with a mid-level transformer until you perfect everything,  then when everything is working as you want on the bench and 100% complete buy the expensive transformers. You can't do it all from textbooks,  too many variables.    JMHO


 
  Oh I trust him, absolutely. His experience is likely more than that of the web site I linked, furthermore, his experience is in the real world. I definitely trust him. You're absolutely right regarding the parts. I am planning to get cheaper stuff for prototype and troubleshoot. After everything seems optimal at those given parts, then I will start buying the quality stuff.
   
  I am onto the power supply design now. I have a lot going on right now so it might be slow going, but I'll get there, I always do =D
   
  My question now is how to go about prototyping these things, hahaha. I suspect your average bread board wouldn't handle it well.


----------



## dBs

Ugh, I see why most people are content to buy amps instead of make them...even if they have the knowledge to make them! I go to calculate the needed HT or B+ conditions from the power supply...800V. Yea...that is just way too much. Back to the drawing board. Thankfully that upper pentode should work for most any lower triode tube I could want to use so I just will pick a triode with lower current. To that end I will also probably be forced to scrap the idea of the triodes being paralleled. Looking at the oft used 6SN7 and single triode equivalent. Thankfully, with this lovely Excel sheet I've constructed, I only have to pick my desired operating conditions and everything is calculated for me.
   
  Very frustrating none the less. Find a solution, walk the path, hit a brick wall. Find a different solution, walk the path, another brick wall...somewhere else this time. Find a different solution, walk the path, brick wall, so close that time too! Lol, very frustrating.


----------



## dsavitsk

You are making this a lot harder than it is.  800v? For headphones?


----------



## dBs

Hahaha, yea exactly. I didn't think these were adding up as much as I thought. Most of the voltages were ok, the problem came when I calculated the drop of the pentodes cathode resistor and the pentodes load resistor. Those dropped a LOT more voltage than I had expected. When you added that voltage into the power supply, it just became the unreasonable 800V. I'm retooling now, we will see what happens.
   
  I'm starting to think that it isn't a matter of me making things too difficult now, just that this topology when done all in tubes is genuinely difficult with all the different aspects that are interlinked with one another and have to be within pretty small ranges. It isn't as bad if you design it with a triode as the current source since you don't have the screen to contend with. That screen has caused a lot of the problems I have had unto this point. I wanted a challenge, well I am certainly getting it...even if for any average DIY tube designer this is probably really simple, lol.
   
  UPDATE:
  Ok, I have a configuration that should work now (as if I haven't said this before, lol). Single 6J5 lower triode operating at 8mA. The pentode operating...bah, I'll just show the pictures. The table on the right is the one I would be enacting. The one on the left is a comparison of what I had before.


----------



## dsavitsk

Quote: 





> Originally Posted by *dBs* /img/forum/go_quote.gif
> the pentodes cathode resistor and the pentodes load resistor.


 
   
  Can you post a schematic? That doesn't make sense ...


----------



## dBs

Like this but with a pentode up top. The resistor that looks like Rl is the RL pentode load resistor. Rk2 is the pentodes cathode resistor. Not my schematic so some things are slightly different, but the important parts are the same.


----------



## nikongod

Stop. Put your pen down. Take 10 deep breaths.
   
  Build something. Go out into the world, find something that appeals to you, and build it. Its simple. It could be an OTL, a parafeed amp, a series-feed, or something else. There are tons of PROVEN designs out there, but the important thing is actually building something. Its not as rewarding as designing and building your own thing, but you will gain XP this way.


----------



## dBs

That is exactly what I am doing. Honestly, this is going to happen. When someone tells me I can't do something, that makes me want to do it all the more. It's the CHALLENGE that drives me. If I wanted to do something easy, I would and would be done with it already. If I'm not challenged, I'm bored and my interest wont stick.
   
  This is going to happen, even if from this moment onward no one lays another finger to help.
   
  Right now, I can't order parts until I actually KNOW what rough values to buy, even a ballpark.
   
  There's a bit of experience to be gained building a Lego set amp, namely how to soldier and practice safe high voltage building. Both are very good things, but A) I know how to soldier already, and B) high voltage is high voltage when you usually talk about headphone amps. You might be "lucky" enough to run into a problem in which case you can try to problem solve the solution, but that's mighty tough when the design and the reason for specific parts of the design are a mystery.
   
  I thank you for your advice, but I will be moving forward. I'm getting close to doing exactly what you say anyway. The last part the needs to be designed is the PSU. With that completed, it'll time to order anyway.


----------



## dBs

Only a little bit of an update because I've had so much going on. All that is [still] left is the PSU filter. Keep in mind that there are some parts of this that have been glossed over.


----------



## regal

You can't design a  DC Heater for DHT's  that that doesn't hum with on Grados yet sounds like AC, to share with our DIY community cause you're a green wet under the ears EE.
   
  Motivated now?
	

	
	
		
		

		
			




   
  Seriously your amp is nice not really a new design but has some nice twists.  Have you made sure that the load is proper for balanced  SRPP per Broskies formula in "SRPP Deconstructed" ?
   
   
  Quote: 





dbs said:


> That is exactly what I am doing. Honestly, this is going to happen. When someone tells me I can't do something, that makes me want to do it all the more. It's the CHALLENGE that drives me.


----------



## FrankCooter

First thing you need to do is correct the connections on the rectifier bridge, Second is take the switch out of the power transformer secondary and move it to the primary where it belongs. Add a fuse and a safety ground while you're at it. The power supply you've drawn is not only wrong, it's dangerous.
   
  I guess the audio circuit would sort of work, but it's very awkward. Nothing wrong with a 6j5 to start, but you've got a redundant jumble of various output and loading schemes. Back to the drawing board, Think simple, direct, conceptional. And please, keep your computer turned off!


----------



## dBs

Quote: 





regal said:


> You can't design a  DC Heater for DHT's  that that doesn't hum with on Grados yet sounds like AC, to share with our DIY community cause you're a green wet under the ears EE.
> 
> Motivated now?
> 
> ...


 
  Hehehe, I was waiting for someone to do that XD Right now, I don't feel that I (or anyone else based on what I've seen) is exactly sure what the specific problem is associated with the DHT issue. That will take more time than I will be able to muster currently. You've already seen how long this thing has dragged out, lol.
   
  I don't recall seeing any actual formulas in the Broskie article. I've read it over a few times, but it was a while ago. I will take another look.


  
  Quote: 





frankcooter said:


> First thing you need to do is correct the connections on the rectifier bridge, Second is take the switch out of the power transformer secondary and move it to the primary where it belongs. Add a fuse and a safety ground while you're at it. The power supply you've drawn is not only wrong, it's dangerous.
> 
> I guess the audio circuit would sort of work, but it's very awkward. Nothing wrong with a 6j5 to start, but you've got a redundant jumble of various output and loading schemes. Back to the drawing board, Think simple, direct, conceptional. And please, keep your computer turned off!


 
  The topology is actually very common from what I have seen. Basically any tube amp schematic for a mu-follower looks almost exactly how mine looks. I had hoped that wouldn't be the case, but the combination of factors that I was facing to keep most of the unique elements I had wanted was too great, I had to scrap most of them. If that is too "redundantly jumbled", then so is every other mu-follower created =P At this point, the ONLY thing that is truly unique about this mu-follower versus the dozens of others with almost identical topologies is that I am also incorporating parafeed. You might be able to make the case that the pentode upper tube is adding the complexity that looks odd, but that is still VERY textbook.
   
  You are definitely correct, I accidentally swapped the rectifier diode outputs...plus it looked messy that way XD I fixed it and cleaned it up.
   
  As far as the elements missing. I had said that some things were omitted on purpose for the sake of ease; essentially they were implied. I figured that having the switch on the secondary would allow the heaters to stay on even with the unit off and thus stave off some of the problems associated with a cold start and solid state PSU. After thinking about it though, you are right, it should be on the primary so the transformer doesn't run the risk of seeing an infinite load or too much energy suddenly getting shoved into the heaters. I have put up a revised version that makes it, hopefully, seem less dangerous.
   
  As far as the computer thing; yea, yea, yea, real world > theory, blah, blah, blah. Sorry if I'm frustrated but I've been hearing that since college and over and over in this thread. Consider the dead horse beat please and let us move on. I will get there when I get there, I am not going to rush into the real world until I am ready. Heck, based upon your seeing that my design wasn't safe, you would think that you would be HAPPY that I wasn't rushing headlong into real world, lest I burn my house down =P


----------



## beachgeek

Looking good, I'm re-learning a lot.
   
  Thanks for the wonderful experience!


----------



## dBs

Well, thank everyone else. They are the ones imparting the knowledge. I'm merely taking the ego blows so you can take the knowledge XD


----------



## beachgeek

Well you got the ball rolling & everyone talking.  Sounds like you either need to learn how to solder or don't want to get your hands dirty.  Whatever, can't be a good engineer without real hands-on down in the mud, burning stuff up once in a while.


----------



## dBs

I have no problem soldering. The issue is, until I know the value of parts that I need, by doing the computer/book/paper/theory work, I can't exactly BUY anything to BUILD anything. Unless I buy all pots and variable capacitors for every component and just start turning knobs, I'm not going to be able to magically know what value part to get for element. In college, I had access to a storehouse of parts and testing equipment. Now that I'm out of college, I don't have that luxury. All I have now, is an iron, and a DMM. I don't cache of parts that I can just grab and throw together to test my ideas.
   
  What people are wanting me to do is build someone else's proven design (which is basically has been reduced to anyway). What I have, exhaustively, stated, is that I'm ready for that next step. I can build a Lego set, been there done that. At what point does a person become magically deemed to be "ready" to make it to the harrowed halls of designing from scratch?
   
  I would love to be able to start throwing things together now and trying stuff out. I would have long ago if I actually had a mass of parts cached up like most of the people here do. I wouldn't have had the patience NOT to, but since I don't have parts laying around at my disposal of all different sizes and values, I have to be patient and buy stuff that I think will work.
   
  I went ambitious with this project, more than some would have liked me to go. That's fine, I have no problem with that. It is what it is and I am VERY close to being ready to actually making the jump of prep work into hands on. I do find it ironic that in the beginning, most of what I heard was that I should be building a plan to work from, now all I hear is to forget the plan and DO something. All in due time.
   
  If it makes everyone feel better to think that I'm just some hard-headed youth that isn't willing to listen to the wisdom of his elders, then that's fine. At this point, I just wish the topic would actually move to something with more substance to it. The sooner I figure out those last unknown values, the sooner I get to fulfilling everyone's shared dream for me, hehehe.


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## regal

What you are missing is its all been done before,  sure you might come across some combo of tubes in a topology that hasn't been done before but so what.
   
  The only thing left for DIY headphone tube research is DHT's and Hybrids.   Make one of those work and then you can "say" you designed from scratch if that is your goal.


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## dBs

You're absolutely right about that. But there is something to be said about doing it from the ground up. I like that =D


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## FrankCooter

Quote: 





dbs said:


> Basically any tube amp schematic for a mu-follower looks almost exactly how mine looks.


 

 No, they don't look like yours, but it won't do you any good if we fix it. For a start though, what's your output transformer doing hanging off the cathode follower of the upper pentode rather than coming off the plate of the lower triode.?  What function is the choke above the pentode serving? Is a single 6J5 suitable for transformer loading? You're mixing up OTL and para-feed topologies. Pick one and stick with it.
   
  I see you live in Ridgecrest. Some Saturday, drive down to LA (San Fernando) and visit an electronics suplus/junk store called Apex. It's huge and dirt cheap. Buy yourself a variety of passive components, connectors, wire, breadboard materials etc. Pick up a few junk tubes and transformers off Ebay. Experiment. Play around with your ideas. When you get something roughly working, then refine it by modeling. Keep it simple at first.
   
  Regal's suggestion of doing something with a small DHT is a good one. It's one of the few incompletely explored areas left in tube headphone design. It's a big interest of mine as well. How about a mu follower with a DHT on the bottom? A 26 or a 112A is pretty much a DHT  6J5. You get everything else together and I'll contribute a couple of 26's.


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## Uncle Erik

Quote: 





frankcooter said:


> I see you live in Ridgecrest. Some Saturday, drive down to LA (San Fernando) and visit an electronics suplus/junk store called Apex. It's huge and dirt cheap. Buy yourself a variety of passive components, connectors, wire, breadboard materials etc. Pick up a few junk tubes and transformers off Ebay. Experiment. Play around with your ideas. When you get something roughly working, then refine it by modeling. Keep it simple at first.


 

 dBs, just wanted to encourage you to visit Apex.  Be sure to give yourself at least 5-6 hours.  There are lots and lots of boxes that need looking through.


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## beachgeek

Shopping through old electronics stuff is better than shopping for clothes, although not by much.
	

	
	
		
		

		
			




   
  P.S. Shopping is a sport!


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## dBs

Quote: 





beachgeek said:


> Shopping through old electronics stuff is better than shopping for clothes, although not by much.
> 
> 
> 
> ...


 
  Indeed it is a sport!

   
  I have been looking for an excuse to go to LA and test out Verizon vs AT&T (running both right now for a personal test, lol). I will maybe see about whipping up some super quick and easy schematics so that I have SOME kind of direction when I'm down there, otherwise I may come back with a ton of stuff...none of it useful =P
   
  I will still continue with this current design so far as well. I still fail to see any problems that I wasn't already aware MAY be a problem (the parafeed in conjunction with pentode current source-the choke above the plate). The output from the cathode of the current source IS the recommended output location. I can link you to any number of places that confirm that as well as quote Jones' Valve Amplifiers book, so I know I am right there. Otherwise, it's just a pieced together standard pentode current source above a standard mu-follower topology. There might be a part or two that could be omitted where the two different topologies merge, but I can't find anything that wouldn't detract from the intended performance. The screen resistor and capacitor are required for the pentode current source operation for the 100% feedback. The network of resistors and single capacitor between the pentode and triode are staples in any mu-follower topology. The capacitor before the output transformer is part of the parafeed. I've admitted from the beginning that the pentode current source in series with the choke portion of the parafeed may be problematic. Usually the choke acts as a semi-current source when in a parafeed configuration, and two current sources in series is a no-no. I figured this was something I had never seen before and thus I am willing to take the gamble to find out. If a 6sn7 can push an output transformer, a 6j5 should be able to.
   
  At the very least, even if this particular design is destined for failure (I don't expect a symphony without some tweaking, but I am confident in the design), it gives me a direction for parts to buy. Unless there is a 1ohm-10Mohm assortment pack I can buy, I have to have some kind of a direction, and I would like if it was the one I have been working off and on with for this long.


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## J-Pak

dBs just curious did this project come to fruition?


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