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PostPosted: 02 Sep 2010, 12:27 
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Location: Winnipeg, CANADA
A 10k pot is pretty common. Try Radio Shack or a guitar store. 20k, 25k and 50k are also common and can be used. Let us know how you make out.
Cheers

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PostPosted: 03 Sep 2010, 21:57 
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Joined: 21 Jul 2010, 22:04
Posts: 7
Location: Toronto - ON
Hi guys,

I've built one of these Rogers Gomez's HeadAamp and It works like a charm.

First I made a prototype, using a 4k7 fixed resistor, but the voltage between Source and ground was above 10V.

Through an oscilloscope I could notice that the positive half waves were clipped and obviously sounded really distorted. So I made a second PCB, using two multiturn trimmers, and I was able to set Vcc/2 as bias voltage (6.3V at 12.6V). The whole thing draws in 410mA.

Now I can listen to my music at high volume and the sound is always undistorted and clear.

I'd like to show you some pictures. I put the PCB in a little (110mm x 65mm) plywood box. Something really cheap, from a dollarstore. I just painted the box to make it a little better and nicer to look at.

Thanks a lot to the DIYAP community, this thread was very helpful. This is my first project with a tube.

Piero

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PostPosted: 06 Sep 2010, 20:08 
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Awesome! Glad to hear you are enjoying the head amp! ;)
Cheers

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PostPosted: 10 Sep 2010, 16:28 
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Joined: 17 Apr 2010, 16:07
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Location: Huddersfield ,West Yorkshire,UK
Hey guys

Just catching up on the thread and there are some great builds in here i really need to start my own nearly gathered all the parts inbetween other stuff .

trying to get to grips with eaglecad at the mo to try and integrate a 555 timer into the circuit for delayed on .

nice to see Rogers is giving his continued great support to the thread.
Rupert

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 Post subject: convert it to preamp
PostPosted: 13 Sep 2010, 11:49 
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I'm new here and I see I posted my question on the 'wrong' thread, so here it comes again.

I like the simplicity of this hybrid tube-CCS amp for headphones. I wonder whether it can be turned into a very good hifi-preamp with moderate gain (12-15 dB) and low output impedance.

For a start I want a BJT like a BD139 at the output. I think for a linestage preamp the idle current of 125mA is too much. I would go for around 30mA.

So I simulated the circuit, changed the LM317 10ohm resistor into 39ohm, put the BD139 in. To get around half of V+ at the output I had to use 8k2 into the anode of the ECC82.

I estimate a gain with this preamp of around 6-7 db (again in the simulation). I see no simple way of increasing the gain:

- Using higher V+ of around 50V increases the gain to around 15dB. But too much wasted heat and demands a new power supply for the heater. Not an option.
- Using another tube like ECC81?
- Change the tube for a small bjt-stage? Not hybrid anymore and will make it more complicated.

Anybody ideas here?


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 Post subject: Re: convert it to preamp
PostPosted: 13 Sep 2010, 18:39 
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Location: Huddersfield ,West Yorkshire,UK
rmgvs wrote:
I like the simplicity of this hybrid tube-CCS amp for headphones. I wonder whether it can be turned into a very good hifi-preamp with moderate gain (12-15 dB) and low output impedance.

For a start I want a BJT like a BD139 at the output. I think for a linestage preamp the idle current of 125mA is too much. I would go for around 30mA.

So I simulated the circuit, changed the LM317 10ohm resistor into 39ohm, put the BD139 in. To get around half of V+ at the output I had to use 8k2 into the anode of the ECC82.

I estimate a gain with this preamp of around 6-7 db (again in the simulation). I see no simple way of increasing the gain:

- Using higher V+ of around 50V increases the gain to around 15dB. But too much wasted heat and demands a new power supply for the heater. Not an option.
- Using another tube like ECC81?
- Change the tube for a small bjt-stage? Not hybrid anymore and will make it more complicated.

I was also thinking the same thing but my knowledge of tubes is non existent thus im starting this build as soon as i get round to getting some more board

Maybe Rogers can throw us a bone :P

k00g

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PostPosted: 18 Sep 2010, 13:43 
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Joined: 18 Sep 2010, 12:48
Posts: 81
does anyone knows that any changes to capacitors, resistors that would make the sound bassier, brighter, more headstage, transparent etc? What I am trying to say is that any tweaks that could make on this circuit?


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PostPosted: 19 Sep 2010, 04:47 
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Joined: 18 Sep 2010, 12:48
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keechoon wrote:
Rebuilt and shrank mine into a 7 x 9 cm protoboard :mrgreen:

Image

Image



you built in on a stripboard/veroboard or prefboard?

mind to share the layout?


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PostPosted: 19 Sep 2010, 22:15 
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Joined: 19 Sep 2010, 22:09
Posts: 4
Bah, I've got the Amp built, however I am having strange issues.

The output is really low, if I turn the source up too much the volume gets better however it starts to distort.

Heaters are on and glowing red.

I think there's a problem with the IRF510 or the LM317... adjusting the 10k pots gives me the exact same voltage output on the LM317's (1.27v)

I do notice changes in volume while making the adjustments however... ideas?

FYI... I am using replacement parts which might be causing the issue:

IRF510 -- NTE2382
LM317 -- NTE956

I have some *real* LM317's coming... It might be the NTE956 however that are giving me the problems... thoughts?


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PostPosted: 21 Sep 2010, 22:41 
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Location: Winnipeg, CANADA
santik wrote:
does anyone knows that any changes to capacitors, resistors that would make the sound bassier, brighter, more headstage, transparent etc? What I am trying to say is that any tweaks that could make on this circuit?

C1 and C3 can have a big effect on the "sound". Use your favorite type of capacitor for C1 (2.2uF). Likely best to experiment with C3 (470uF). Try different types and brands of electrolytic caps with and without film bypass caps.

Other ideas that will have less effect - low ESR for C2, adding bypass and decoupling caps.

Are you using a battery supply?

Cheers

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