JFET input, MOSFET VAS, VERTICAL output - diyAudio
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Old 7th August 2011, 12:28 PM   #1
kees52 is offline kees52  Netherlands
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Default JFET input, MOSFET VAS, VERTICAL output

promised I put here the version of thread JFET input, MOSFET VAS, LATERAL output = Perfect! here.

I have make some changes in the jfet input and the vas, the vas has higher id of 20 mA maybe it has even higher like 30 or even 50mA to prevent distortion in the drivers in relation with mosfet capacity, vbe multiplier is not simulate properly and has to be made in real, carefull!..

I will post sometimes progres and tests, but only simulation, people here can test it in real, I do that also but I have only scoop not THD meter.

We try to make it as simple as possible, less parts better sound, oneven harmonics weh have to fight even harmonic is of less problematic because it give music sometimes a nice body.
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File Type: pdf forumtest.ms11.pdf (21.9 KB, 284 views)
File Type: pdf Instruments.pdf (120.3 KB, 108 views)
File Type: pdf AC analyses.pdf (17.7 KB, 72 views)

Last edited by kees52; 7th August 2011 at 12:30 PM.
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Old 7th August 2011, 12:37 PM   #2
AKSA is offline AKSA  Australia
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Kees,

Nice circuit, but symmetrical.

This tends to give odds higher than evens, and this is the reason the single ended approach was taken in the other thread.

Can you comment on your reasons for selecting this 'balanced' approach?

Cheers,

Hugh
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Old 7th August 2011, 01:27 PM   #3
juma is offline juma  Germany
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hi kees52, what do you mean by "vertical output" in the thread's title - your schematic shows k1058/j162 which are not vertical but lateral MOSFETs ?

Also, the way you did cascoding of the input stage is suboptimal - Q1 and Q4 have too small Vds (0.2-0.3 V) to work properly. You should choose cascoding devices (Q5/Q6) with higher Vgs(off) like k246/j103 or you can raise gate potential of Q5/Q6 with voltage divider.

Not to forget, Vds(max) for 2sj108 is 25V and Q6 in your schematic works with Vds of about 35V - a risky strategy...

Last edited by juma; 7th August 2011 at 01:31 PM.
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Old 7th August 2011, 05:40 PM   #4
fojica is offline fojica  Romania
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Hi, kees52

I think that R18 should be lower than R17, since P-ch has bigger Cgs capacitance - the idea being that you want to obtain an equal rolloff on N-ch and P-ch.

regards,
Tibi
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Old 7th August 2011, 11:02 PM   #5
kees52 is offline kees52  Netherlands
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Quote:
Originally Posted by juma View Post
hi kees52, what do you mean by "vertical output" in the thread's title - your schematic shows k1058/j162 which are not vertical but lateral MOSFETs ?

Also, the way you did cascoding of the input stage is suboptimal - Q1 and Q4 have too small Vds (0.2-0.3 V) to work properly. You should choose cascoding devices (Q5/Q6) with higher Vgs(off) like k246/j103 or you can raise gate potential of Q5/Q6 with voltage divider.

Not to forget, Vds(max) for 2sj108 is 25V and Q6 in your schematic works with Vds of about 35V - a risky strategy...
Hi all

I have post the wrong schematic, and I now that the resistors are differend for both fets, but this has to try en measured in real time.

The cascode of j fets has advantages lower miller and more voltage, until now we have to keep voltage low, but I think we have to make the design more complicated, and put some fets in work, mirrors, ccs?

The j fets I have in schematic is because i have not much choice in multisim, the higher vgs jfets are not there, I will put them in and try the simulation again, and post itm or use enhanced mosfets with deviders as replacement..

Hmm be aware, I am not a scientist, but hobbyist like the most here, praktice do it not the school calculations is my experience..

First helping my friend, who has proberly cancer in his lungs, smoking habbits.
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Last edited by kees52; 7th August 2011 at 11:14 PM.
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Old 8th August 2011, 04:17 PM   #6
kees52 is offline kees52  Netherlands
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Hi her a new version who has not the mentioned disadvances, the j fets get now a lower voltage and are cascoded with higher voltage mosfets, we call it version 2, it is nice playing with it, but make a amp very simpel with low distortion is not easy, maybe not possible.
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Old 17th August 2011, 05:51 PM   #7
kees52 is offline kees52  Netherlands
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Quote:
Originally Posted by AKSA View Post
Kees,

Nice circuit, but symmetrical.

This tends to give odds higher than evens, and this is the reason the single ended approach was taken in the other thread.

Can you comment on your reasons for selecting this 'balanced' approach?

Cheers,

Hugh
There are fine amps with symetrical design, it cancels out the evens that is right, and let the odd intact, so you have to make a real symetrical amp by use components who have to be paired, that is however difficult with mosfets, the other tread use also symetrical output mosfets, and here it wil distroy the asymetrical approach, only the ZEN way works with a high current CCS, it is I think not always bad to get symetrical it is a lot used in practice, a clever approach is needed and I do combine already invented ideas, I am not so clever with the cosmetic words;-).

I will build this amp some day and look what it does with sound.

I have read something about od and even harmonics, but the science around it have some bottlenecks, a musician kan explaine that better then I can, music is a mix, the amp has only as task amplify it without put his own character in it.

Thanks for your attention.

Last edited by kees52; 17th August 2011 at 06:07 PM.
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Old 14th November 2011, 12:34 PM   #8
kees52 is offline kees52  Netherlands
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The final one to try, I have a lateral and vertical version, lateral schematic is on lateral perfect discussion.

Here is only the vertical version, I do make this one,s pcb if I have time and that is almost there.
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Old 4th March 2012, 07:20 PM   #9
kees52 is offline kees52  Netherlands
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Hmm old topic, but oke, blow some live in it.

The symetric solution has as al the balanced amps that give more odds harmonics, but I think that this is not the real problem with of a amp sound right or not, my opinion is still, high bandwith, only current feedback and much casode soultions, because compression and the voltage feedback give mucho problemens, we need to give amps air.

I like cascode tubes but the problem with them is S a lot are to weak, and so I use then penthodes in triode with high gm, the sound is then (dutch) luchtig.

Oke, I have did some experiments with the pc, and maybe you laugh all her, it healthy I now.

but see and let me now your thoughts about it, maybe it is already here somewhere, this idea is also candidate for hybride. canceling capacitance reduce distortion considerably.

There a two schematics, one with 4 ohm load and one with 8 ohm load, the 4 ohm 194 watts, (watch distortion), but in real don,t try that, mosfets get stressed.
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Last edited by kees52; 4th March 2012 at 07:28 PM.
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Old 5th March 2012, 12:57 AM   #10
AKSA is offline AKSA  Australia
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Kees,

This is a fully symmetrical, fully cascoded PP AB power amp, using fets, mosfets and latfets throughout, but aside from competent design, high loop gain and low THD I can't see that it would sound much different to lots of other designs built with similar components. I'm also fairly sure it would have no image depth because of mosfet VAS and global feedback.

I guess these are obvious comments, but given your interest in tubes, why not stick to your original idea of a hybrid, and try to reduce the active component count?

I believe that the more complicated you make a circuit, the less DIYers build it. It reminds me of the inaccessible oil filter in a crowded automobile engine bay; it doesn't get changed enough, too expensive and difficult. A beautiful engine then gets a bad reputation for durability! Use NP's approach, keep it really simple, and put your effort into correct component choice and very precise dimensioning.

Sorry about the long post, didn't have time to write a short one!

Cheers,

Hugh
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