Cheap Single Ended Quality

[tubehunter]

Hi all


I've just finished this project and thought I might share it.
I wanted a cheap amp for upstairs in the computer room, I have some 95db speakers in there so didn't require much power.
I've always built push pull amps in the past and had good results, but this build has surprised me.

Totally liquid sound can't stop listening to it.

Total cost around £250 as I had the poly caps for the power supply already.

I sprayed the Alu chassis using paint which gives that stone look with matt black transformer covers.
I used Kiwame resistors through out as I like their sound and find that they have very good spec. All power supply capacitors are polypropylene from Clarity Cap and Obbligato (thanks Marco). Star ground so the amp is very very quite.
The el84 grid 2 is connected to the driver supply as feeding the screen a clean DC voltage greatly reduces the noise through the pentode.

I would recommend this as a first build for anyone looking for an excellent sound for little outlay.
You will need over 90db sensitive speakers to enjoy this fully, but it will drive lower.

Duncan


http://i514.photobucket.com/albums/t350/halx00/Duncans%20EL84%20se/duncansel84se_zpsfea05e74.jpg

http://i514.photobucket.com/albums/t350/halx00/Duncans%20EL84%20se/el84se_zpsd1459c9b.jpg

http://i514.photobucket.com/albums/t350/halx00/Duncans%20EL84%20se/IMG_6535_zps084c2ba6.jpg
http://i514.photobucket.com/albums/t350/halx00/Duncans%20EL84%20se/IMG_6534_zps46f79620.jpg
http://i514.photobucket.com/albums/t350/halx00/Duncans%20EL84%20se/IMG_6533_zps713290c1.jpg
http://i514.photobucket.com/albums/t350/halx00/Duncans%20EL84%20se/IMG_6532_zpsffd105bc.jpg
http://i514.photobucket.com/albums/t350/halx00/Duncans%20EL84%20se/IMG_6529_zpsdac1e987.jpg
http://i514.photobucket.com/albums/t350/halx00/Duncans%20EL84%20se/IMG_6523_zps9dfd8194.jpg
http://i514.photobucket.com/albums/t350/halx00/Duncans%20EL84%20se/IMG_6522_zps094bc84a.jpg
http://i514.photobucket.com/albums/t350/halx00/Duncans%20EL84%20se/IMG_6521_zps74e14d95.jpg
http://i514.photobucket.com/albums/t350/halx00/Duncans%20EL84%20se/IMG_6512_zps98c1af51.jpg

[freefallrob]

That looks really nice!

I'm looking around myself at the moment for valves as I have the itch again after years of solid state, this looks just the thing i'm looking for.

Is this a kit you can buy?

How many watt roughly it 6/8 ohms?

I would like to run an EAR834P phonostage and CD player into it.

Cheers,

Rob.

[tubehunter]

Hi Rob

No, not a kit but you can buy the transformers from VVT Transformers based on the IofW.
Mains is VTH12219-1300
Outputs are VTS12198-1300

The Hammond Choke 193H and Hammond Chassis 1444-28 can be purchased from Bluebell Audio as can the tagboards, valve sockets etc....

The polypropylene capacitors are expensive but worth it I think. They can be bought from the likes of HIFICollective.

I have just one input but it would be easy to add more with a suitable switch.

As for how many watts, around 4 or 5.
It can upset the neighbours if pushed with high sensitive loudspeakers.


Duncan

[hoopsontoast]

Looks like a great little project :popcorn:

Is it your own design?

Just embarking on a Decware Zen build myself :)

[tubehunter]

Yes it is my own design.
I used PS Designer 2 for the power supply section and Multisim 9 by Electronics Workbench for the circuit.
It really sounds great.

I looked at the Decware Zen and even built a prototype, but I couldn't live with the lower power and zero feedback even though it sounds good.

[hoopsontoast]

Cool, looks like a nice simple circuit. :)

What speakers are you using it with?

Big fan of EL84 amps, had the Decwcare (SV83/EL84) before, along with a Puresound A10 and loved the Audio Note Oto (PP version IIRC) whenever I have heard it.

[Dingdong]

Cool, looks like a nice simple circuit. :)

What speakers are you using it with?

Big fan of EL84 amps, had the Decwcare (SV83/EL84) before, along with a Puresound A10 and loved the Audio Note Oto (PP version IIRC) whenever I have heard it.

Twas an Otto Se. I have one of the ones you heard here for repair after Chris 'modified' it.

[hoopsontoast]

Twas an Otto Se. I have one of the ones you heard here for repair after Chris 'modified' it.

Ah right :) Good to know

[walpurgis]

I like that. Very neat and the 'stone' finish is attractive.

Any photos of the back and the innards?

[Alex_UK]

Very neat. I'd call the look "Industrial Chic."

[tubehunter]

Thanks

Yes there is something right about the EL84 imho.

I'm using an old pair of large 3 way Wharfedales.

A couple of pictures showing the back and with her bottom exposed.:)

http://i514.photobucket.com/albums/t350/halx00/Duncans%20EL84%20se/IMG_6553_zps2dec6667.jpg
http://i514.photobucket.com/albums/t350/halx00/Duncans%20EL84%20se/IMG_6551_zpsfc108a0e.jpg
http://i514.photobucket.com/albums/t350/halx00/Duncans%20EL84%20se/IMG_6549_zpse82b242b.jpg

[freefallrob]

Nice!

Though very scary for an electrical numpty like me:)

[Jonboy]

there is something right about the EL84 imho.



Very Nice Duncan, i must agree with the above statement

[hoopsontoast]

Looks lovely, nice and neat.
Whats the big ClarityCap for?

[tubehunter]

That is the first capacitor after the valve rectifier (33uf 630v).
It draws a large current pulse from the rectifier and power transformer, so good quality here is important.

The GZ34 rectifier tube has a limit of 60uf.

[istari_knight]

It does look nice, good job :thumbsup:

One question: Could you add a headphone socket straight off the outputs via a pair of resistors like you can with a transistor amp ? Or is that a no no with valve amps ?

[tubehunter]

I'm thinking....


http://i514.photobucket.com/albums/t350/halx00/Duncans%20EL84%20se/HeadphoneJack_zps07f642c3.jpg

If that's too loud you could replace the 10 ohm resistor with a pair and form a potential divider.
eg.
Two 5 ohm 10 watt resistors and connect the 120 ohm at their junction. This would half the volume and reduce noise.

Should work ok, I've never needed to try this as I don't use headphones.

Duncan

[awkwardbydesign]

I would try to use a switched jack socket, and do away with the switch.

[istari_knight]

I'm thinking....


If that's too loud you could replace the 10 ohm resistor with a pair and form a potential divider.
eg.
Two 5 ohm 10 watt resistors and connect the 120 ohm at their junction. This would half the volume and reduce noise.

Should work ok, I've never needed to try this as I don't use headphones.

Duncan

Looks simple enough, thanks for that :)

Will have to add this to my list of projects I never get 'round to!

[tubehunter]

I'm going to have to retract my earlier statement about the Decware Zen and negative feedback and low power.

Just reconfigured the circuit and bloody hell someone just nicked my stereo and plonked a bunch of musicians in my lounge.:eek:
Massive improvement. This might stay downstairs.


Revised circuit, spot the difference:-

http://i514.photobucket.com/albums/t350/halx00/Duncans%20EL84%20se/duncansel84setriode_zps97ce9dc7.jpg

[Firebottle]

Mmmm, triode mode, lovely.

Is there really that much difference? The amps I have built have all been triode mode so have never tried to spot the difference.

:cool:Alan

[hoopsontoast]

I'm going to have to retract my earlier statement about the Decware Zen and negative feedback and low power.

Just reconfigured the circuit and bloody hell someone just nicked my stereo and plonked a bunch of musicians in my lounge.:eek:
Massive improvement. This might stay downstairs.


Revised circuit, spot the difference:-


I can see the difference but I don't know what it means.... :scratch: :D

Switched from SE'P' Pentode to SE'T' Triode?

[Firebottle]

Look at the middle grid on the pentode (screen grid), it is now connected via a resistor to the anode of the pentode.
The valve now acts like a triode, simples;)

:cool:Alan

[hoopsontoast]

Look at the middle grid on the pentode (screen grid), it is now connected via a resistor to the anode of the pentode.
The valve now acts like a triode, simples;)

:cool:Alan

Yeah, what he said ;)

All I know is that the EL84 is a Pentode and its wired as a Tripode in the Zen design so I had a guess....