I'm planning a spud headphone amp build. Started my tube DIY addiction with a Van Waarde OTL and now looking to try OPTs.
Perusing schematics from Bartola, Ciuffioli, ECP Audio and the like I went back and forth between basic single ended and Parafeed topology several times. Finally settled on Parafeed to hopefully keep things easier on the wallet.
Specifically I've been inspired WTFamps Papa Rusa (russian spud). The deciding factor for me to follow this design was the excellent design guide for the Papa Rusa that was extremely educational. With the low/high impedance switch this seems to be a good choice. My HP collection is currently Grado SR80 (32ohm), Massdrop AKG K7xx (62ohm) and Sennheiser 6xx (300ohm).
I'm thinking of building the stock Papa Rusa and upgrading as budget allows.
Upgrades I have planned:
Updates as design & build progress.
Perusing schematics from Bartola, Ciuffioli, ECP Audio and the like I went back and forth between basic single ended and Parafeed topology several times. Finally settled on Parafeed to hopefully keep things easier on the wallet.
Specifically I've been inspired WTFamps Papa Rusa (russian spud). The deciding factor for me to follow this design was the excellent design guide for the Papa Rusa that was extremely educational. With the low/high impedance switch this seems to be a good choice. My HP collection is currently Grado SR80 (32ohm), Massdrop AKG K7xx (62ohm) and Sennheiser 6xx (300ohm).
I'm thinking of building the stock Papa Rusa and upgrading as budget allows.
Upgrades I have planned:
OPT: Upgrade stock Edcor OPTs with sowter 8665 or Lundhal LL2765
CCS: Walter Jung's LM317 + DN2540 Cascode, or Bartola's Gyrator
B+ regulator: Salas Shunt High Voltage Regulator (SSHV2)
Filament regulator: Salas Shunt Low Voltage Regulator SSLV
Updates as design & build progress.
I was about to post a similar thread when I just saw this. I hope you don't mind if I add my thoughts here. I'm in the middle of a spud headphone amp build for my AKG K701s. I made and auditioned a 6N30 stage with LL1660 in 4.5:1. Damping was poor into 62R cans though it would have worked into 300R cans. So clearly I need a bigger step-down OPT for the K701s, which I don't have with a gap for 15mA or so. Plus the 1K or so Ra of the 6N30 is unlikely to be bettered with a decently high mu. So a parafeed design seems inevitable.
Choice 1 - Plate choke
I have some plate chokes, so this will be tried. For the 62R of the K701 I'm thinking about a 10:1 step-down. I do have a pair of LL1689/PP which can do this but then I remembered threads about using a mains toroid as the OPT in parafeed. For 10:1 this looks like a 230:12+12 giving 230v into 24v. This should be in the ballpark if my calculations are correct.
Choice 2 - Ale's Gyrator
Ale Moglia is a good friend and as we all know an incredibly helpful source of tube knowledge and parts, and I have a few of his gyrators. He has a couple of headphone designs on his Bartola Valves site and he's a fan of pentodes in triode, especially the Russian ones. Since the gyrator lowers the output impedance, we're then back to something like 4.5:1 OPT. This assumes a low Ra tube like around 2K. For a toroid that would be 230v into 24+24 = 48v. Much less common than 12+12v. Raise the Ra with something like a 6N1P and then maybe we'd go back to 230:24.
With both of these alternatives I'd be trying out SIC diode bias, which is a trick I learned from Ale, and his headphone designs use this. Sounds good. For tubes I used and sold 12b4 and 6AH4. Good but there's probably better. 6N30 may work. Otherwise higher mu pentode/triodes like E282F, E810F, E180F, 6J49, 6J11, 6J9, 6e6, 6e5, 6P15P (EL83)
Anyway, I have time on my hands since it's stay-at-home conditions ATM. So will hopefully be able to construct both alternatives from existing parts and report back. I'll start with the 6N30 but may go over to a pair of pentodes in triode. Clearly it's all about impedance matching, and since I'm shooting for a 62R headphone there are plenty of options for using similar headphones within this impedance range.
It looks like we're thinking on similar lines here, so hopefully we can share experiences and others can come in with their own experiences, designs and builds. Good time to build a headphone amp.
Choice 1 - Plate choke
I have some plate chokes, so this will be tried. For the 62R of the K701 I'm thinking about a 10:1 step-down. I do have a pair of LL1689/PP which can do this but then I remembered threads about using a mains toroid as the OPT in parafeed. For 10:1 this looks like a 230:12+12 giving 230v into 24v. This should be in the ballpark if my calculations are correct.
Choice 2 - Ale's Gyrator
Ale Moglia is a good friend and as we all know an incredibly helpful source of tube knowledge and parts, and I have a few of his gyrators. He has a couple of headphone designs on his Bartola Valves site and he's a fan of pentodes in triode, especially the Russian ones. Since the gyrator lowers the output impedance, we're then back to something like 4.5:1 OPT. This assumes a low Ra tube like around 2K. For a toroid that would be 230v into 24+24 = 48v. Much less common than 12+12v. Raise the Ra with something like a 6N1P and then maybe we'd go back to 230:24.
With both of these alternatives I'd be trying out SIC diode bias, which is a trick I learned from Ale, and his headphone designs use this. Sounds good. For tubes I used and sold 12b4 and 6AH4. Good but there's probably better. 6N30 may work. Otherwise higher mu pentode/triodes like E282F, E810F, E180F, 6J49, 6J11, 6J9, 6e6, 6e5, 6P15P (EL83)
Anyway, I have time on my hands since it's stay-at-home conditions ATM. So will hopefully be able to construct both alternatives from existing parts and report back. I'll start with the 6N30 but may go over to a pair of pentodes in triode. Clearly it's all about impedance matching, and since I'm shooting for a 62R headphone there are plenty of options for using similar headphones within this impedance range.
It looks like we're thinking on similar lines here, so hopefully we can share experiences and others can come in with their own experiences, designs and builds. Good time to build a headphone amp.
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How's the build coming on, Neodystopia? Great name.
Update: I finished off a basic parafeed circuit, using toroidal transformers as the OPTs. Very cheap option and I'm very impressed indeed with the sound. I used a Lundahl LL1660/18mA just the primary as a plate choke because I had a pair available. A cheap option would be Hammond 157G like Hagerman uses in the Tuba. I have a pair of Hammond 126B doing nothing, and I could use the primaries of that, which would allow up to 30mA.
Sound is wonderful - everything I hoped for. So a generic parafeed circuit like this, which is very similar to the Hagerman Tuba for example, or most other simple parafeed designs, can really make your cans come alive. I've attached the circuit I used for reference. One thing to watch out for is high frequency oscillations in tubes like this. Not what you want in headphones. I didn't use ferrite beads in this case, but I probably should have and may retro-fit them. Power supply is in a separate box, and I stole it from one of my preamp builds.
Update: I finished off a basic parafeed circuit, using toroidal transformers as the OPTs. Very cheap option and I'm very impressed indeed with the sound. I used a Lundahl LL1660/18mA just the primary as a plate choke because I had a pair available. A cheap option would be Hammond 157G like Hagerman uses in the Tuba. I have a pair of Hammond 126B doing nothing, and I could use the primaries of that, which would allow up to 30mA.
Sound is wonderful - everything I hoped for. So a generic parafeed circuit like this, which is very similar to the Hagerman Tuba for example, or most other simple parafeed designs, can really make your cans come alive. I've attached the circuit I used for reference. One thing to watch out for is high frequency oscillations in tubes like this. Not what you want in headphones. I didn't use ferrite beads in this case, but I probably should have and may retro-fit them. Power supply is in a separate box, and I stole it from one of my preamp builds.
Attachments
Hey Andy, you're more than welcome to join in! It does seem like we've got a very similar strategy. Following your design process is very instructive. I'm very interested in how you are impedance matching the headphones to the tubes via the transformers. I definitely need more practice at this. I'll work through what you posted and see if I can follow Ong with the math.
Great progress you've made so far! My progress will be much slower as I have very little on hand. My first tube project was the OTL I mentioned before, and I've just completed it after about 6mo! I already placed an order for Edcor power trafo choke and OPTs. Now just need to wait 4-5 wks and collect the other parts.
I like your initial design with the parafeed choke and the toroidal power trafos. I've never seen power trafos used as OPTs. Very interesting idea! How does the sound compare to other OPTs in your opinion.
Seeing your semiconductor free prototype makes me want to try it out first and gradually try out CCS and Powe supply regulation later. I've got a 115+115 : 18 + 18 that might work. Just need chokes. I'll check the Hammond you suggested.
Great progress you've made so far! My progress will be much slower as I have very little on hand. My first tube project was the OTL I mentioned before, and I've just completed it after about 6mo! I already placed an order for Edcor power trafo choke and OPTs. Now just need to wait 4-5 wks and collect the other parts.
I like your initial design with the parafeed choke and the toroidal power trafos. I've never seen power trafos used as OPTs. Very interesting idea! How does the sound compare to other OPTs in your opinion.
Seeing your semiconductor free prototype makes me want to try it out first and gradually try out CCS and Powe supply regulation later. I've got a 115+115 : 18 + 18 that might work. Just need chokes. I'll check the Hammond you suggested.
I think I have a better understanding of why your initial 4.5:1 LL1660s were not working well with your 62ohm headphones. I calculated a Damping Factor of 2. That's no bueno! But as you mentioned with 300ohm cans you would have been OK at damping factor of 7. Your 10:1 power transformers in the parafeed design you tried also give you a DF of 7. I've got a pair of 115+115:9+9 2A toroids from an aborted solid state project so I'm tempted to try them. In 115:18 configuration the voltage ratio would be about 6.4:1. With the 6c45p and my Sennheiser 6xx, I calculated a DF of 11. Might be worth a shot.
I purchased a power transformer 250-0-250 60mA, as suggested in the Papa Rusa guide and immediately regretted not getting a higher current rating. I won't be able to use dual mono Salas Shut regulators for the B+ as I hoped because it needs 20mA headroom over the 30mA 6c45p bias the Papa Rusa uses. However I've seen several people suggest running the 6c45p at a lower bias current so maybe I can try that with my 60mA B+ transformer.
Still trying to source Salas Shunt High Voltage regulator PCBs. Looks like I just missed the group buy.
I purchased a power transformer 250-0-250 60mA, as suggested in the Papa Rusa guide and immediately regretted not getting a higher current rating. I won't be able to use dual mono Salas Shut regulators for the B+ as I hoped because it needs 20mA headroom over the 30mA 6c45p bias the Papa Rusa uses. However I've seen several people suggest running the 6c45p at a lower bias current so maybe I can try that with my 60mA B+ transformer.
Still trying to source Salas Shunt High Voltage regulator PCBs. Looks like I just missed the group buy.
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Was able to snag a pair of Salas SSHV2 PCBs and transistor/resistor kits from the Group Buy. Thanks Teabag! Also picked up a HV rectifier board and a filament DC regulator board from Pete Millett.
I've decided I'll try to use modular PCBs as much as possible on this build. This will facilitate prototyping to make sure I've got everything dialed in before moving to a chassis. Also my experience with my first tube amp verified my suspicion that I don't have a natural aptitude for point to point soldering
The CSS I've decided on is Walter Jung's DN2450 & LM317 cascode.
/https://audioxpress.com/assets/upload/files/Sources_101_P2.pdf
Currently waiting for Digikey, Parts Connexion and Edcor orders to come in.
I've decided I'll try to use modular PCBs as much as possible on this build. This will facilitate prototyping to make sure I've got everything dialed in before moving to a chassis. Also my experience with my first tube amp verified my suspicion that I don't have a natural aptitude for point to point soldering
The CSS I've decided on is Walter Jung's DN2450 & LM317 cascode.
/https://audioxpress.com/assets/upload/files/Sources_101_P2.pdf
Currently waiting for Digikey, Parts Connexion and Edcor orders to come in.
My update is that I abandoned the mains toroids - I was getting some kind of ringing somewhere in the system and I couldn't measure it.
I ended up with a 4P1L and Lundahl LL1689/PP in 9:1. By far the best sound. I was using a very nice amorphous core plate choke. I'll use this setup as the first stage in my 4P1L PSE amp and put a switch to switch between headphones and speakers. The NP plate choke and Lundahl OPT are overkill really. I'm wondering about some smaller OPTs. I have a pair of small Lundahl microphone transformers, LL1515. Can anyone tell from the data whether they would overload into a headphone? The current model is the LL1530
I have some LL1515. What is it and how can I use it? ⋆ Lundahl Transformers
https://www.lundahltransformers.com/wp-content/uploads/datasheets/1530.pdf
I ended up with a 4P1L and Lundahl LL1689/PP in 9:1. By far the best sound. I was using a very nice amorphous core plate choke. I'll use this setup as the first stage in my 4P1L PSE amp and put a switch to switch between headphones and speakers. The NP plate choke and Lundahl OPT are overkill really. I'm wondering about some smaller OPTs. I have a pair of small Lundahl microphone transformers, LL1515. Can anyone tell from the data whether they would overload into a headphone? The current model is the LL1530
I have some LL1515. What is it and how can I use it? ⋆ Lundahl Transformers
https://www.lundahltransformers.com/wp-content/uploads/datasheets/1530.pdf
I’ve have many serial and parallel feed headphone amps with 600 ohm OPTs as I use them to drive Beyerdynamic 600 ohm headphones and drive long interconnects to my amp/speaker setup in another room.
All amps connect with umbilicals to a variety of power suppliers I use, 60V, 120V, 150V and 200V, or an adjustable bench supply. I also have an LCLC adjustable filament supply on a variac that handles DHT heading. I use stacks of lead-acid batteries for B+ as well as filament duties.
If you buy two extra Edcor XSMs you can use them as plate chokes if you want to try an all iron parallel feed version. Hook the primary and secondary in series for more H if you need it, or leave unused secondary open.
Edcor used to make GXSE5-600-5k (5k/600) and GXSE5-600-15K (15K/600). Both were series feed 5W rated outputs so good for almost any tube you wanted to try. Seems like they were around $20US. I don’t know why they are not currently listed but as they made them not too long ago I’m sure they can still wind them up. I mostly used the 5K version and usually with the trioded 6P30B-R. I cannot think of a better series feed output for the price.
A parallel feed headphone amp uses Quad Eight QEE 3436 outputs (20K/600ohm) and Electraprint AC9037 chokes (100H/10mA) with 1.5 Solen tin blocking cap. It was originally designed for 26, 01a and 801a, but I mostly use GS24B ceramic tubes in it. I know its not the tube for this but it sounds super.
A few months ago to use some un-gapped Carnhill VTB2291 (9.6K/600ohm) I had I added a plate choke (Hammond 156C) and squeezed it all into a 4.5 x 7.25 x 2.25 Hammond tin box.
I would save on B+ regulator boards and invest in output iron. I expect a Bartola's Gyrator provides all the plate voltage stability you need. My better headphone amps have Magnequest B7 and TL-404 output iron with Russian KBG-MN 2 to 4uf blocking caps and Magnequest chokes and they sound quite a bit better than the above.
Matt
All amps connect with umbilicals to a variety of power suppliers I use, 60V, 120V, 150V and 200V, or an adjustable bench supply. I also have an LCLC adjustable filament supply on a variac that handles DHT heading. I use stacks of lead-acid batteries for B+ as well as filament duties.
If you buy two extra Edcor XSMs you can use them as plate chokes if you want to try an all iron parallel feed version. Hook the primary and secondary in series for more H if you need it, or leave unused secondary open.
Edcor used to make GXSE5-600-5k (5k/600) and GXSE5-600-15K (15K/600). Both were series feed 5W rated outputs so good for almost any tube you wanted to try. Seems like they were around $20US. I don’t know why they are not currently listed but as they made them not too long ago I’m sure they can still wind them up. I mostly used the 5K version and usually with the trioded 6P30B-R. I cannot think of a better series feed output for the price.
A parallel feed headphone amp uses Quad Eight QEE 3436 outputs (20K/600ohm) and Electraprint AC9037 chokes (100H/10mA) with 1.5 Solen tin blocking cap. It was originally designed for 26, 01a and 801a, but I mostly use GS24B ceramic tubes in it. I know its not the tube for this but it sounds super.
A few months ago to use some un-gapped Carnhill VTB2291 (9.6K/600ohm) I had I added a plate choke (Hammond 156C) and squeezed it all into a 4.5 x 7.25 x 2.25 Hammond tin box.
I would save on B+ regulator boards and invest in output iron. I expect a Bartola's Gyrator provides all the plate voltage stability you need. My better headphone amps have Magnequest B7 and TL-404 output iron with Russian KBG-MN 2 to 4uf blocking caps and Magnequest chokes and they sound quite a bit better than the above.
Matt
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Mwiebe, thanks for your input on plate chokes and all iron parafeed. I guess I gravitated towards SS B+ regulation and Mosfet CCS as I'm in more familiar territory having built SS in the past. Also I love soldering PCBs!
As I collect more iron I'll probably experiment with other topologies like series feed and choke loaded parafeed. I never considered using one side of an OPT as a plate choke? How can I find the inductance of a cheap-ish OPT like an edcor?
Is this cap the type you describe?
As I collect more iron I'll probably experiment with other topologies like series feed and choke loaded parafeed. I never considered using one side of an OPT as a plate choke? How can I find the inductance of a cheap-ish OPT like an edcor?
Is this cap the type you describe?
Some PCBs came in:
Salas Shunt Regulator High Voltage v2 SSHV2
Pete Millet Rectifier board and Filament Regulator
Thinking about the kind of case I'll eventually use. My previous OTL project was a aluminum plate on top of a walunt box. Nice for point to point but might be nice to have something with heatsinks on the sides for the SS components.
Salas Shunt Regulator High Voltage v2 SSHV2
Pete Millet Rectifier board and Filament Regulator
Thinking about the kind of case I'll eventually use. My previous OTL project was a aluminum plate on top of a walunt box. Nice for point to point but might be nice to have something with heatsinks on the sides for the SS components.
Neodystopia
Measuring inductance is not simple. A small LCR meter does not measure inductance at the current of interest. You need a signal generator, a 'scope and a little math to get close. It's easier to try and see.
4P1L is a directly heated pentode and it is a nice sounding tube. Headphone listening is sensitive to hum but it is not hard to tame. Search for "Coleman filament" on this forum and you will find plenty to read. I use a LCLC filament supply and Colemans. Both work fine for headphones.
Matt
Measuring inductance is not simple. A small LCR meter does not measure inductance at the current of interest. You need a signal generator, a 'scope and a little math to get close. It's easier to try and see.
4P1L is a directly heated pentode and it is a nice sounding tube. Headphone listening is sensitive to hum but it is not hard to tame. Search for "Coleman filament" on this forum and you will find plenty to read. I use a LCLC filament supply and Colemans. Both work fine for headphones.
Matt
Finally got an update to share! I've received most of my parts from Edcor, Digikey and Parts Connexion. Unfortunately Parts Connexion was out of the new Sovtek 6C45P tubes so I ordered a Reflektor NOS matched pair from Ebay. Fortunate to get a matched pair but unfortunate that shipping from their motherland will take some time...
I built up the Millet Rectifier PCB, the SSHV2, and bread-boarded the Jung LM317/DN2450 Cascode CCS. Testing these together to deliver B+ to dummy load in place of the tube went really well. Was able to supply a steady 275V B+ with a constant 18mA current.
The Millet rectifier board had more options than I needed, it had a secondary screen output and it also was designed for a full wave bridge rectifier but after studying the schematic I was able to stuff it to support my single B+, full wave rectifier design.
The SSHV2 went together easily, I've got its CCS biased for 20mV. The heatsink is temporary and definitely not up to the task. It exceeded the suggested 60degC limit after a few minutes. I'll probably heatsink to my chassis. I noticed the B+ takes quite a long time to stabilize, perhaps due to my inadequate heatsink, and the trimpot adjustment is extremely sensitive.
Edcor XFMR and choke
Millet rectifier and CLC PCB
SSHV2
Millet Filament Regulator
Jung LM317/DN2450 Cascode CSS
I built up the Millet Rectifier PCB, the SSHV2, and bread-boarded the Jung LM317/DN2450 Cascode CCS. Testing these together to deliver B+ to dummy load in place of the tube went really well. Was able to supply a steady 275V B+ with a constant 18mA current.
The Millet rectifier board had more options than I needed, it had a secondary screen output and it also was designed for a full wave bridge rectifier but after studying the schematic I was able to stuff it to support my single B+, full wave rectifier design.
The SSHV2 went together easily, I've got its CCS biased for 20mV. The heatsink is temporary and definitely not up to the task. It exceeded the suggested 60degC limit after a few minutes. I'll probably heatsink to my chassis. I noticed the B+ takes quite a long time to stabilize, perhaps due to my inadequate heatsink, and the trimpot adjustment is extremely sensitive.
Edcor XFMR and choke
Millet rectifier and CLC PCB
SSHV2
Millet Filament Regulator
Jung LM317/DN2450 Cascode CSS
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