ECC88 OTL heaphone amp

[merlin el mago]

Looking for a tube headphone amp for my Sennheiser HD600 I saw this OTL with ECC88, it seem simple design & easy to make, advice & ideas will welcome.

PSU

OTL headphone amp

PCB

Picture

Also exist other version without integrated PSU.

 

[Stixx]

Hi Merlin,

this schematic is loosely based on the better known Morgan Jones ECC88 OTL headphone amp which is an improved version of the famous Earmax amp.
Check out the info on
HeadWize - Project: The Morgan Jones Mini Tube Headphone Amplifier by Chu Moy since the original Headwize site is down.
I have built the Morgan Jones myself with LED bias for the first stage and a better psu (but now I would definitely use the Salas shunt for B+). When you are interested in a schematic I can mail it to you... it is easily built P2P on perf board. It is a nice sounding amplifier although there are better ones (non-OTL comes to mind).
When you are interested I can give the details for a very good sounding amp based on the C3G wired as triode, Salas shunt for HV and output transformers...

Cheers

 

[merlin el mago]

Hello Stixx,

I'm looking for a tube headphone amp capable to drive my Sennheisser HD600 not necessary must be OTL, I'm interested on the C3G amp please send me details (I have Salas shunt HV for B+)

Greetings

Felipe

 

[Stixx]

See schematic attached... it doesn't get much simpler than that.

http://s7.directupload.net/images/user/110817/fg3o8znu.jpg

You have the choice of output transformers... I am using headphone opt's from Reinhoefer in Germany that sound very good at about 55€ a piece. But you can try anything that has about 7.5k:300 for your Sennheiser phones ( I am using Sennheiser's). Lundahl and Sowther have very good OPT's as well. Or have them custom wound at AE Europe in the Netherlands.

My amp is still on the breadboard
--> http://s3.directupload.net/images/user/101118/rap477if.jpg
but will eventually look like this -->
http://s1.directupload.net/images/user/110114/wzrdgt9j.jpg

Just my two cents in headphone amplifiers...but I have tried quite a few schematics and am currently building the eighth one

 

[Stixx]

Forgot to mention that I am running the C3g at around 150V and 15mA now...but with the Salas shunt it is easy to try different voltages until you find your "sweetspot". The rectifiers provide a slow ramp up of the HV after about 20 sec.
Cheers!

 

[merlin el mago]

Thanks for schematics & pics, where can buy the matched C3G tubes with a reasonable price with good quality?

 

[Stixx]

check german Ebay...

here for instance
2 PIECES OF C3g-C3 g-SIEMENS-NOS-NEW-OWN BOX | eBay

Good seller, although prices have gone up over the last years. But a good ECC88 is not cheap either...

 

[merlin el mago]

I have a couple of these E88CC Russian military stock bought to Erno Borbely (sounds amazing), could I use them?

 

[Stixx]

No, ECC88 cannot be used in a single stage amp, it is best for preamp duty.

 

[merlin el mago]

OK thank you.

 

[merlin el mago]

Sorry my ignorance, wich kind of sockets uses C3g?

 

[Cassiel]

but will eventually look like this -->
http://s1.directupload.net/images/us...4/wzrdgt9j.jpg

If it ends up looking like that I want to see it when it's finished.

 

[Stixx]

Sorry my ignorance, wich kind of sockets uses C3g?

It uses loctal sockets... also occasionally offered on Ebay (or the better tube vendors).

If it ends up looking like that I want to see it when it's finished.

I will not disappoint you... the chassis is currently in the works at my carpenter
Regulators and the OPT's will be hidden underneath.

 

[ruffrecords]

Looking for a tube headphone amp for my Sennheiser HD600 I saw this OTL with ECC88, it seem simple design & easy to make, advice & ideas will welcome..

A lot depends on your headphones. Yours are 300 ohm impedance and quoted as 97dB/mW. To ensure you have enough headroom for transients you need to be able to drive them 10dB harder than this i.e 10mW. For 10mW into 300 ohms you need an rms current of just over 18mA or a peak swing of 26mA. This means the standing current in the ECC88s needs to be at least 26mA and that is way too high for that type of tube.

Cheers

Ian

 

[merlin el mago]

@Ian
Thanks for the input.

@Stixx
I'd like to see pics of your finished headphone amp.

 

[ingenieur24]

Merlin,

Very interesting project. I just sent you a PM. Please check. Thank you.

 

[merlin el mago]

Merlin,

Very interesting project. I just sent you a PM. Please check. Thank you.

YHPM

 

[stajo]

Lundahl and Sowther have very good OPT's as well.

Which ones in Lundahls sortiment are you refering to Stixx?

best
Staffan

 

[Stixx]

Hi Staffan,

I was referring to output transformers for headphone amplifiers in general.
Sowther has several dedicated opt's for either SE or Parafeed operation.
For my latest amp (C3G-SE) I am using Lundahl LL1689 at 9:1. I like it very much. Also suitable might be LL1630...

 

[stajo]

Thanks. I was just looking at it. I guess its SE-gapped for 18 mA?. It can do 18:1 also for even lower Z out.

How would C3G do in pentode mode in this application? Jacmusic has plenty of info on C3G/N C3g-C3m-info and states "They show their extreme low distortion only as pentodes. They can be used triode connected, but then gain comes down a lot, and the distortion increases to a level just below triodes like 6SN7."

Staffan