It's time to make some conclusions based on the information you have given.
Let's assume the average output level of the Modi is -6 dB below the maximum i.e. 0.75 Vrms.
The maximum gain of Magni is 5 (14 dB). So with max. volume setting the output level would be 5 x 0,75 V = 3.75 V.
You told that you most often use 1/5 of max volume setting.
In case of logarithmic potentiometer 1/5 represents not more than 5 % of the whole resistance.
Then we can see that the typical signal level to your earphones is 0.05 x 3.75 V = ~0.19 V.
At 600 ohms this voltage generates power of 60 µW (P = U²/R).
The sensitivity of T-1 headphones is 100 dB/mW, so the approximate sound level you use is:
100 dB - 10 log (60 µW/1 mW) = 100 dB - 12 dB = 88 dB.
So, the typical power level you use with your T-1 headphones is only 60 µW.
Could we therefore say that just 1 mW is sufficient power level for an headphone amplifier ?
This is 12 dB higher power you typically use.
Or should we add an other 10 dB ? Then the design target power level would be 10 mW and some 22 dB above the typical listening level.
Let's assume the average output level of the Modi is -6 dB below the maximum i.e. 0.75 Vrms.
The maximum gain of Magni is 5 (14 dB). So with max. volume setting the output level would be 5 x 0,75 V = 3.75 V.
You told that you most often use 1/5 of max volume setting.
In case of logarithmic potentiometer 1/5 represents not more than 5 % of the whole resistance.
Then we can see that the typical signal level to your earphones is 0.05 x 3.75 V = ~0.19 V.
At 600 ohms this voltage generates power of 60 µW (P = U²/R).
The sensitivity of T-1 headphones is 100 dB/mW, so the approximate sound level you use is:
100 dB - 10 log (60 µW/1 mW) = 100 dB - 12 dB = 88 dB.
So, the typical power level you use with your T-1 headphones is only 60 µW.
Could we therefore say that just 1 mW is sufficient power level for an headphone amplifier ?
This is 12 dB higher power you typically use.
Or should we add an other 10 dB ? Then the design target power level would be 10 mW and some 22 dB above the typical listening level.
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I decided i will use a 8/4 ohm output transformer. and a 9 ohm resistor, the secondary impedance with a 10K transformer that is connected to a 600ohm headphone would be about 11K, is that too much? If so i will recalculate for lower resistance. Do you have any recommendations for small output transformers from Hammond?
Also what would i need to change in the SE OT schematic in the link i posted earlier?
i would also use a 11 ohm resistor as a low impedance headphone resistor.
I intend to use this amp for a while, and i am looking to buy a Hifiman HE560 headphone in 1 1/2 years. And i would like the amp to be able to handle that as well as my T1.
Also what would i need to change in the SE OT schematic in the link i posted earlier?
i would also use a 11 ohm resistor as a low impedance headphone resistor.
I intend to use this amp for a while, and i am looking to buy a Hifiman HE560 headphone in 1 1/2 years. And i would like the amp to be able to handle that as well as my T1.
Checking the datasheet:
http://frank.pocnet.net/sheets/010/p/PCL86.pdf
Shows recommended load impedance of 5.1-5.6K depending on bias conditions (sh-4).
That schematic is not a good place to start, Start with a fresh schematic of a PCL86 SE output amp, like the one on this page:
PCL86 Piccolo Triode Amplifier
Or this one, which is a bit simpler:
diyAudio
http://frank.pocnet.net/sheets/010/p/PCL86.pdf
Shows recommended load impedance of 5.1-5.6K depending on bias conditions (sh-4).
That schematic is not a good place to start, Start with a fresh schematic of a PCL86 SE output amp, like the one on this page:
PCL86 Piccolo Triode Amplifier
Or this one, which is a bit simpler:
diyAudio
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I was actually referring to the Piccolo Amplifier schematic. not the YouTube one. Also i am currently trying to decide if i should go with Edcor or with Hammond for the output transformers. Or maybe i could go strait to Lundahl (although that seams overkill for this project).
So you are suggesting i use a 5K 8ohm transformer then. Also would the power transformer and choke mentioned in the schematic and the webpage be any good?
So you are suggesting i use a 5K 8ohm transformer then. Also would the power transformer and choke mentioned in the schematic and the webpage be any good?
seeing as i have already designed the basic look of the amp, id say id spend up to 500$ (that makes the Lundahl Transformers a non option) at max. Id prefer it to be less expensive. The level i would want is, to beat my Schiit Magni by a fair bit.
I do intend to build something better in the future, but that will have to wait till after my Graduation from University. I have access to CNC tools so making the Case will be easy for me.
I do intend to build something better in the future, but that will have to wait till after my Graduation from University. I have access to CNC tools so making the Case will be easy for me.
Vacuum tube rectifier may look cool, but does not improve the "sound" (=performance) compared to much cheaper solid state rectification.
Personal opinion follows:
Start with that schematic and add a 1MEG grid to ground resistor on the first stage in case the pot wiper opens.
Add a blocking cap on the input unless you are sure your source will not have a DC offset on the output.
Add a 10K series grid-stop resistor to the grid of the triode.
Replace the 1K triode cathode resistor with a cheap red LED.
Add a 4.7K Grid Stop resistor to the output tube.
Increase the output tube cathode bypass cap from 100uF to 470uF.
Do not ground one side of the heater supply . place two 220R resistors in series across the heater supply. Connect the center point to a .022uF cap to ground, or better yet to a resistor divider from B+ with a tap at about 65V.
That transformer puts out the wrong voltage for PCL86, 12.6 vs 13.3V
GXSE10-16-5K or GSXE15-16-5KWith a 50 Ohm resistor across the output for minimum load. Leave this in and don't switch it when you plug your headphones in.
The input triode has so much gain, you may find wit the 50 Ohm headphones that you can drive the output tube directly.
Simulations look good with both 50 Ohm headphones and 600Ohm headphones.
Start with that schematic and add a 1MEG grid to ground resistor on the first stage in case the pot wiper opens.
Add a blocking cap on the input unless you are sure your source will not have a DC offset on the output.
Add a 10K series grid-stop resistor to the grid of the triode.
Replace the 1K triode cathode resistor with a cheap red LED.
Add a 4.7K Grid Stop resistor to the output tube.
Increase the output tube cathode bypass cap from 100uF to 470uF.
Do not ground one side of the heater supply . place two 220R resistors in series across the heater supply. Connect the center point to a .022uF cap to ground, or better yet to a resistor divider from B+ with a tap at about 65V.
That transformer puts out the wrong voltage for PCL86, 12.6 vs 13.3V
GXSE10-16-5K or GSXE15-16-5KWith a 50 Ohm resistor across the output for minimum load. Leave this in and don't switch it when you plug your headphones in.
The input triode has so much gain, you may find wit the 50 Ohm headphones that you can drive the output tube directly.
Simulations look good with both 50 Ohm headphones and 600Ohm headphones.
Reach for the ....
You have a set of these
! 
.And a budget of $500.Here's my fancy.PS-6 & Aikido Split-Load Phase Splitter.
The PS-6 you can buy from tubecad $49.What?!! Yes $49 including all parts.
Two sets of 6082 tubes will set you back $26 from Surplus Sales Nebraska.
Substitute the 6sn7 for a 12sn7-same valve different heater.Surplus Sales are asking for your 6.50 to 8 dollars.Have you seen the price of 6snsevens lately! Ouch! I have a pain in my wallet just thinking about it.
As you've been to Edcors already I'm sure you can locate a suitable power supply transformer there too.
Surely that's way under budget.
PS have a read of broskies blog0268 on tube math.
You have a set of these
.And a budget of $500.Here's my fancy.PS-6 & Aikido Split-Load Phase Splitter.The PS-6 you can buy from tubecad $49.What?!! Yes $49 including all parts.
Two sets of 6082 tubes will set you back $26 from Surplus Sales Nebraska.
Substitute the 6sn7 for a 12sn7-same valve different heater.Surplus Sales are asking for your 6.50 to 8 dollars.Have you seen the price of 6snsevens lately! Ouch! I have a pain in my wallet just thinking about it.
As you've been to Edcors already I'm sure you can locate a suitable power supply transformer there too.
Surely that's way under budget.
PS have a read of broskies blog0268 on tube math.
Well one thing needs correcting, my budget is actually 500 Euros, not 500$ (although the way things are going in the world, that might soon be the same). And yes i spent a ridicules amount on my headphones. The reason i have that budget is to see if i can build an amp using the PCL86 / ECL86 Tube. I was also considering a 300B Amp project. The Schiit Magni / Modi are a relic from my old headphones. And since they work reasonably well i didn't want to buy a better amp right away. If i can i will try using Lundahl Transformers, if all the parts don't go over 800 euros (the 500 euros are a target for the PCL86 amp) Also seeing as the projected may take me some time to complete (due to university) money is not the biggest problem, time is.
I'm also designing the amp for a friend as well as myself. He he uses a 250 ohm DT880.
Also its primarily a, first tube amp project, to "wet my feat" in tube amp design.
I'm also designing the amp for a friend as well as myself. He he uses a 250 ohm DT880.
Also its primarily a, first tube amp project, to "wet my feat" in tube amp design.
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Sorry for the bit of a Rant in the previous post. I had a bad day.
So to the subject of the amp its self: I have descided to go with the Lundahl LL1623 Transformer, primaray is 5.5K and the Secondary would be 16ohm Single ended configuration. Based on the post by TheGimp, this should be fine. I also had the idea of rectifighing the 13.5 V coming from the power transformer and then putting it into a 12V voltage regulator. That should get the voltage i need. Although tell me if this is, again, a stupid idea.
Alternatively i could use the ECL86 tube instead, as that one has a 6.3V heater voltage.
now the only problem i see, is getting those massive Lundahl transformers into, or rather onto the case of the headphone amp.
Also i have a question, dose the quality of the power transformer and filtering choke influence sound quality? And if so, how much?
So to the subject of the amp its self: I have descided to go with the Lundahl LL1623 Transformer, primaray is 5.5K and the Secondary would be 16ohm Single ended configuration. Based on the post by TheGimp, this should be fine. I also had the idea of rectifighing the 13.5 V coming from the power transformer and then putting it into a 12V voltage regulator. That should get the voltage i need. Although tell me if this is, again, a stupid idea.
Alternatively i could use the ECL86 tube instead, as that one has a 6.3V heater voltage.
now the only problem i see, is getting those massive Lundahl transformers into, or rather onto the case of the headphone amp.
Also i have a question, dose the quality of the power transformer and filtering choke influence sound quality? And if so, how much?
Why not opt for an OTL? The idea had been floated before it dissolved into the background noise, but it looks quite an attractive option: the P/ECL86 can easily manage this kind of task and it eliminates the bulk and degradation associated with a transformer (I do not even mention the price).
In addition, a transformerless amp can more easily accept NFB, also beneficial to the performance.
As for the choke, apart from residual hum, it has no direct influence on the quality: it just needs to be large enough.
The PT simply needs to be capable of providing the current. It should also have reasonable magnetic leaks, otherwise it may also cause hum.
Some example of OTL's found on the net:
http://jarrod.elektroda.eu/uploads/images/wzmacn1.gif
http://www.jogis-roehrenbude.de/Verstaerker/ECL86-VV1.jpg
They are pretty basic, and it would be possible to come up with something more sophisticated, including FB for example
The thing is, i'm not sure that a OTL design can boath drive a 600ohm headphone (Beyerdynamic T1) as well as a low impedance headphone like the Fostex F900 (25 ohm) or Hifiman HE560 (50 ohm). I do not mind building a very large and heavy Amp. Based on my current design (Case / chassis) the amp would weigh between 8 and 10 Kg (depending on some design choices and calculating error).
I will be sharing my "Lundahl" version of my amp in the form of a 3D render soon (well as soon as i finalize the design, and have time to finish the 3D model).
If the OTL design can drive everything from 25 to 600 ohms then i might consider it, but based on what i have learned about OTL, that probably will not work.
I have also decided to add a B+ Delay circuit to prevent Cathode damage from the B+ Voltage being applied during warm up. I had the idea after damaging a Transmitting tube this way. It might have been coincidence, but better safe then sorry. Id use a delay of 20 sec (a little more then the warm up time of the ECL86, according to the datasheet.
I will be sharing my "Lundahl" version of my amp in the form of a 3D render soon (well as soon as i finalize the design, and have time to finish the 3D model).
If the OTL design can drive everything from 25 to 600 ohms then i might consider it, but based on what i have learned about OTL, that probably will not work.
I have also decided to add a B+ Delay circuit to prevent Cathode damage from the B+ Voltage being applied during warm up. I had the idea after damaging a Transmitting tube this way. It might have been coincidence, but better safe then sorry. Id use a delay of 20 sec (a little more then the warm up time of the ECL86, according to the datasheet.
The OTL would probably have an output impedance of a little under 100 ohm (raw, before any FB is applied), which makes it unsuitable for driving impedances below that level at the max power level, in the watt region. But for headphones, you don't need watts unless you want to lose your hearing in a matter of minutes, and for milliwatt level, you could go down under 1Ω, if that makes any sense.
The upper impedance limit is approximately ∞, give or take one or two ohm...
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