Hello,

2A3 will have problem driving cans without transformers. Besides, it is not cost-efficient. Good 2A3 are hard to come by and cost a lot. DHT are not really the BEST solutions. I know an ultra-crazy audiophile DIYers in Japan use only DHT. But he told me one day that the reason why he use DHT is that he can't see the pins!

Your amp should not cost too much. I do not believe many people are willing to invest so much money of headphone amp. Some people do spend over 2000 USD on amps but that is rare and not common occurence. So that excludes almost all the DHT power tubes. (6C33 is NOT DHT, but it is way too hard to deal with.) I think you should find power driver tubes.

Actually, there is a few power DHT which probably can power high impedance headphones. AVVT makes some 2A3/300B like DHT triodes with higher power dissipation. ... But then again these go for 150 a pop. 300 a pair.

Power driver tubes are like 5687 or E182CC. ... might not have enough gain ...


TOmo

Quote:



Joseph,

Things like p2p wiring and SET based designs are unrealistic wants for a < $700US amp. So I have some real questions, comments, and suggestions after giving it some real thought. But let me just say up front that what you are talking about sounds very exciting!!

Why use a tubed regulator? How about using a good solid state regulator instead? It can just be servo feedback looped using op amp's floating - one with output imp of a couple milliohms and regulation within .001% and noise and ripple in the 10 vu range, and then you don't need the choke either and will have a lower output imp, right? Also, it would be nice to have DC filaments too. And how about going to polyprop caps - no electrolytic caps in the power supply - maybe Solen brand since you only need, what, 20 or 30 uf for something like this? And how about using high speed soft recovery diodes - maybe Motorola's hyper soft recovery. And as for tubes, 6DJ8s sound "glassy" and have a shrill upper mid. Maybe you could ship with 7308s? I think they sound much better but I don't know the cost difference. I would want to make the switch as an end user for sure. But if cost goes up too much, ship with dj8's and I'll roll. Also, for a headphone OTL, I wonder if you have considered 6SA7 - a multisection low output impedence triode? Perfect for OTL and inexpensive!! Just wondering...

OK, that's all for now. Back to work. Thanks for listening!

Quote:



Motorola, my mom's employer, make the BEST soft recovery diodes.

Quote:



Float the DC. Use a 10 ohm variable resistor across the filament leads center to ground. Make sure the resistor can handle the power dissipation.

Hey, I happen to like the 6BQ5. It is a great sounding little tube that trades the "romantic" sound of the 2A3 /45 etc triodes for a little bit of punch. (my opinion). (lets not turn this into a tube debate, start a new thread to beat me up in.)

Oh, and Joseph, while I'm thinking of it - one more thing... How about considering 6GU7 instead of the DJ8's ? In fact, you can use all 6GU7s even for OTL. I think not many people know about 6GU7 but they are more linear than 6SN7 even (MicroZOTL's OTL choice).

Have you looked at 6gu7s?

Thanks.

Brian. (This is fun )

I never used it before ! It is hard to consider use a strange tube in products. We are difficult to get quanity tube Difficult to sure it can found in future ! (We want to sure can supply service parts for at least 5 years).
I will try to found the information. is it inter changeble with other tube ?
I just start to made a chassis for this new Prototype. I may be will use ECC99 x 2 as Output tube. 6DJ8 as driver. It seem so good ! even can drive down to 16 Ohm. It have a seperated power supply. Wow ! It is a Heavy duty power supply. It can supply up to 280V DC 250ma. (I had not test it soon. I think it is no problem). Have Power supply. So You may be can buy other modual like , other design headphone , Phono amps , Line amps , Oh ! May be even can supply to samll power amps ! or use it in your DIY project !
Also I had finished a Line/Headphone amps with remote control in Low cost. I had test a Prototype. It sound so good. It is so simple. Power section : Solid state rectifier by FR1007 , Regulated by a 6BM8 , 6DJ8 in SRPP + 2 Matching transformer for headphone. It cost may be just around US$400 only.
I had not test it with low ohm Headphone now. I will try to test it on a 32 Ohm Headphone. WIll keep watching on this Link. Bye !

Joseph, yeah, unfortunately the 6GU7 isn't being produced anymore. All tubes except the few being made like 6550 el34 12ax7 6dj8 300b etc aren't being produced anymore. Sorry, I wasn't thinking of it in terms of mass production. It is so unfortunate because the tubes being made today either don't last or don't sound as good as those of yesteryears...

Hey Joseph,

I was just wondering out of all our suggestions... Which ones did you choose?

Thanks again!

Ok Tube Headphone Amp at less than $1,000 Well Topology interest me more than anythihg elce. what i would like is Direct Coupeling evean on the Output Possibly Cascoded gain and output Stage, The Ability to Drive down to 16 Ohms good also. Then All Satin Silver Case Nice just my 2c worth.

I will use following Idea in my new Headphone amplifier :

1.Possible to upgrade from Basic version to premium -
It will break in to separated power supply section and main amplifiers section.
a.a basic power supply
b.a Basic OTL amp – ½ 6DJ8 drive to cathode follower. Can drive high impedance Headphone only.
c.a high grade OTL amplifiers section – ECC99 or 6C19PI x 8 connect in cathode follower and drive by 6DJ8.
d.Point c. + 4 Input selection and 2 Line Output , ¼” Jack for HeadPhone , May be consider Neutrik as option Jack.
e.A top grade power supply with tube rectifiers , tube regulated , DC filament , 2 Power output.
2.Point to point wiring - It will be in amplifiers section only not for power supply. (not for basic model).
3.Gold RCA input - All our products use Gold RCA already.
4.Can drive Low impedance output – down to 16 Ohm (no output) - It can do it on high grade version. Basic can additional a Headphone converter (Our new products) to made it can drive low impedance. See our web site.
5.Filament regulated – all model.
6.Leave space for Stepped attenuator – It will no problem on high grade version. It will have a Remote V.R. You can change it to stepped attenuator if you don’t want remote. It is no fo basic model.
7.Dual Headphone Jack – For all model.
8.Line Filter – Consider to use if it cost not much. (Not for Basic model).
9.Xfeed – Will study it soon.
10.Pre-amps – Ability – It will be for high grade model.
11.IEC sockets – all our products already have.
12.Silver Finished – It is depend on our Distributors need. We can supply any finished like Aluminum , steel in Chrome color , Iron with powder…… May be will use Aluminum in silver color for top model.

I think the first point will made this series of Headphone amps so interesting due to it upgradable. You can buy a Basic model first + a Basic simple power supply. You can upgrade the power supply to top grade later and here after can upgrade it to top model amplifers section or our later version of Headphone amplifiers. The top model power supply even can use on small power amplifiers like 2A3 , 5BQ5 , 6V6….

Hello,

Paralleling so many tubes achieve OTL is not a very good idea. This requires precisely matched tubes to avoid it from oscillating due to mismatch. Also, break down of tubes in the output stage will be very annoying to fix since you never know which one.

Thus, I think paralleling benefit will go to limit pretty quickly and cost-effectiveness fall. I understand 2 para or 3 para but not 8. That will not only be costly but dangerous and so prone to failure. Your company may end up not making money off of amp but making money from fixing them.

I would do 2 para 6C19, 6H30, or ECC99 in SRPP or Mu-stage. Personally I think I can do with one stage SRPP/Mu-Stage, but if you feel necessary you can try suitable driver. This will be cheapest to do with massive returns. (But load impedance effect performance.)

Or, PPL's suggestion about using push-pull output stage is pretty good idea. It will be more easier to handle and perhaps cheap as well. But DC-Coupling the output will be a mistake since current discharge during the "accident" will not only fry your cans but your ears too. Nonetheless, this will be more resistant to changes in load impedance and thus a better alternative dispite the fact that cost will perhaps nearly double. (cost-effectiveness might sour)

If headphones were widely sold with balanced inputs, there are half dozen more nice things you can do with awesome cost-effecitiveness but hey life have got to suck right?

Only one another alternative possible. Pick modern high performance tubes. Since many people's eyes are now going toward tube state amps, there are some people who has began designing and building new tubes. AVVT is a good example. If you have seen the specs for their driver tubes, you will see that these can drive moderately low impedance headphones (120~300 ohms) with only 1 tube. Each tube cost about 100~200 but since it require very small number of parts, the total cost will be well below 1000 USD. Also, I know few other high tech modern tube. One of them called TST-W11. This is crazy power triode. You can build 8~16W amp with 3~5 other parts. The other is called VT25920. It is driver triode with smaller power but more awesome characteristics. Good things about these are that you can run these at low voltage like 20~40V. This should allow PPL's dream to come true without cooking PPL in the process. (Fried PPL sound bad ...)

Tomo

Hey Joseph,

Just some ideas:

1. I've read quite a few times and even streophile recommends that tube cages (if you're going to include them) shouldn't be made in silver/gold. This reflects heat and according to Cary Audio shortens the life of tubes. Cary has now opted to make all tube cages black.

However, I think the aluminium chassis is a great idea. It would allow the unit to act as one giant heatsink.

Rega:
http://www.rega.co.uk
Utilizes aluminium on all their designs and it really looks attractive. They offer black finishes and polished finishes!

2. Also I've read quite a few times about a standby mode for tubes. Would it be possible to integrate this into your amplifier design? It entails leaving on the heaters and supplying reduced voltages to the tubes.

This in turn extends tube life without the problems of excess power consumption or the effects of heat stress. This is great if for example you have to leave for around two-three hours but don't feel like turning off your equipmnet.

Maybe the unit can go into standby itself after an hour of inactivity. You could also look into a triple coloured LED for the front panel:

Red - Is when the unit is first on
Yellow - Indicates tubes are warming up
Green - Indicates amplifier is ready or at optimal performance.

I'm not an expert on amplifier design. It seems that Tomo knows a lot more than me but what do you all thing?

Take care...

[It only Use ECC99 x 2 /Channel not 8 Pcs/Channel. ECC99 is a Dual Triode. I parellel total 4 Section to archive low output impedance. Not 8 tube.
]Originally posted by Tomo
Hello,

Paralleling so many tubes achieve OTL is not a very good idea. This requires precisely matched tubes to avoid it from oscillating due to mismatch. Also, break down of tubes in the output stage will be very annoying to fix since you never know which one.

Thus, I think paralleling benefit will go to limit pretty quickly and cost-effectiveness fall. I understand 2 para or 3 para but not 8. That will not only be costly but dangerous and so prone to failure. Your company may end up not making money off of amp but making money from fixing them.

I would do 2 para 6C19, 6H30, or ECC99 in SRPP or Mu-stage. Personally I think I can do with one stage SRPP/Mu-Stage, but if you feel necessary you can try suitable driver. This will be cheapest to do with massive returns. (But load impedance effect performance.)

Or, PPL's suggestion about using push-pull output stage is pretty good idea. It will be more easier to handle and perhaps cheap as well. But DC-Coupling the output will be a mistake since current discharge during the "accident" will not only fry your cans but your ears too. Nonetheless, this will be more resistant to changes in load impedance and thus a better alternative dispite the fact that cost will perhaps nearly double. (cost-effectiveness might sour)

If headphones were widely sold with balanced inputs, there are half dozen more nice things you can do with awesome cost-effecitiveness but hey life have got to suck right?

Only one another alternative possible. Pick modern high performance tubes. Since many people's eyes are now going toward tube state amps, there are some people who has began designing and building new tubes. AVVT is a good example. If you have seen the specs for their driver tubes, you will see that these can drive moderately low impedance headphones (120~300 ohms) with only 1 tube. Each tube cost about 100~200 but since it require very small number of parts, the total cost will be well below 1000 USD. Also, I know few other high tech modern tube. One of them called TST-W11. This is crazy power triode. You can build 8~16W amp with 3~5 other parts. The other is called VT25920. It is driver triode with smaller power but more awesome characteristics. Good things about these are that you can run these at low voltage like 20~40V. This should allow PPL's dream to come true without cooking PPL in the process. (Fried PPL sound bad ...)

Tomo [/QUOTE]

[Stand By Mode is possible , just additional a Switch to switch off the High Voltage
Cage in Black - Yes ! We will supply Cage in black but also a See through Acrylic Plate on the front side.]
Originally posted by evilcthul
Hey Joseph,

Just some ideas:

1. I've read quite a few times and even streophile recommends that tube cages (if you're going to include them) shouldn't be made in silver/gold. This reflects heat and according to Cary Audio shortens the life of tubes. Cary has now opted to make all tube cages black.

However, I think the aluminium chassis is a great idea. It would allow the unit to act as one giant heatsink.

Rega:
http://www.rega.co.uk
Utilizes aluminium on all their designs and it really looks attractive. They offer black finishes and polished finishes!

2. Also I've read quite a few times about a standby mode for tubes. Would it be possible to integrate this into your amplifier design? It entails leaving on the heaters and supplying reduced voltages to the tubes.

This in turn extends tube life without the problems of excess power consumption or the effects of heat stress. This is great if for example you have to leave for around two-three hours but don't feel like turning off your equipmnet.

Maybe the unit can go into standby itself after an hour of inactivity. You could also look into a triple coloured LED for the front panel:

Red - Is when the unit is first on
Yellow - Indicates tubes are warming up
Green - Indicates amplifier is ready or at optimal performance.

I'm not an expert on amplifier design. It seems that Tomo knows a lot more than me but what do you all thing?

Take care... [/QUOTE]