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My first DIY amplifier 20 years a go
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Old 19th June 2013, 01:26 AM   #361
Bigun is offline Bigun  Canada
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My first DIY amplifier 20 years a go
Ah - understand what you meant better now !
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Old 19th June 2013, 11:04 AM   #362
wahab is offline wahab  Algeria
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Quote:
Originally Posted by gaborbela View Post

Wahab I didn't tested yet the mosfet amplifier, I really feel bad about that.
Just need those diodes ad trimmers to test that amp.
I was busy with some amplifier enclosures and other work at my free time but still I supposed to test that amp way back.
For the darlington which was modded by you only I made the PC boards yet.
I will test thoroughly that soon, for test I buy regular resisters at first.
I want to test if the stability of the amp get improved. If yes and the sound remain the same I do build that later with exotic parts.
Also I'm planing to test the mosfet version but not now.
First I must test of the Hitachi mosfet amplifier.. Only need to spend on that 10-15 bucks.
Probably next week I buy those diode and I put together the amp at least on a piece of plywood.
Greetings Gabor
Hi Gabor ,

To take time for a project has some advantages as often
we think about a few things quite lately when building a project ,
so stretching the things can only be profitable implementation wise.

About the project in this thread i would point a few things
that have been already said but are scatered in a lot of pages.

As you pointed it , the basic CCS allow far better DC stability
than the original version , rendering the input stage insensitive
to DC supply variations that otherwise would influence greatly
the quiescent current value.

Sanken darlingtons should provide not only better distorsion
figures but also higher power supply noise rejection due to
the absence of base-emitter resistors for the drivers ,
wich are implemented in Banat s replacements with a classic
double EF , those resistors are to be removed , as well as the
input stage dedicated VRs that not only are dangeourous if
trimmed to low values but have also the same drawback as in
the original schematic , that is highly variable input stage
current with all the nefarious consequences mentionned above.

On the use of laterals , Hitachi/Renesas are very good
but as you can see i did put a pair as it allow more
conductance and should largely compensate for the
lower current capability of thoses devices in respect of BJTs.

Lazycat claim that the fets he used for this design
sound better than the Hitachis is quite dubious and has
more to do with marketing behaviour than actual differences.
Exicon basicaly makes copies of the Renesas but with generaly
higher input capacitance and gate voltage thresholds , overall
they have not better specs at all , quite the contrary.

Overall , i find this design more balanced and reliable as well
as better compensated , the vssa has overshoots in the frequency
response at very high frequencies , at lest in the first versions ,
dont know how this was dealt with on following iterations.

On quiescent current stability experimented by Ashok ,
it appear that in the original design a PNP VBE multiplier
was used because it has lower junction voltage and as such
it seems the Iq is slightly more stable than with a NPN ,
i ll check again and post the results later.

Looking further the results of your experimentations
and how i could help if necessary , although it seems
to me that you have both all knowledge needed
to make the thing working reliably , neverless ,
i ll give a try to Bigun s proposition of using diodes
instead , a solution that i frequently used and wich
has worked very well.
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Old 19th June 2013, 01:53 PM   #363
Bigun is offline Bigun  Canada
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My first DIY amplifier 20 years a go
Quote:
Originally Posted by wahab View Post
Sanken darlingtons should provide not only better distorsion figures but also higher power supply noise rejection
This is the type that I have, they look very nicely made. It would be handy to have spice models for these but alas they are not to be found.
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"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.

Last edited by Bigun; 19th June 2013 at 01:55 PM.
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Old 19th June 2013, 02:48 PM   #364
ashok is offline ashok
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Quote:
Originally Posted by wahab View Post

.........it appear that in the original design a PNP VBE multiplier
was used because it has lower junction voltage and as such
it seems the Iq is slightly more stable than with a NPN .......
It did occur to me that the original circuit used the PNP for better stability though I was not sure about it. However I did think of replacing the NPN that I used ( I have an excess of them ! ) with a PNP which entails some track cutting etc. Or maybe just do it point to point off the board.
After that I'll try the LatFet's that are just waiting to be tested. Assuming that all else works well the LatFET looks most interesting because it will be stable with regard to dc bias. I've been playing the existing circuit with reduced bias ( about 50 mA when idling) and find it works very well . It sounds very nice too !

It is however a busy week and I have to get some serious matters completed before the weekend. After that I'd be much more relaxed.

IF all goes well I'll be implementing a stereo board with 4 Power devices to each channel on a much larger heatsink. I still feel that I need to hear the amp in stereo to compare it properly against others.
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Last edited by ashok; 19th June 2013 at 03:00 PM.
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Old 19th June 2013, 05:08 PM   #365
ashok is offline ashok
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As expected the data sheets do not show any difference between the PNP and NPN at a specific temperature. I would think that mounting the bias spreader on the power transistor might be the best bet. But just to complete the picture I will in any case try the PNP device also. It will delay my test with the LatFET's !

I think the approximate border at 100mA could just be due to reaction time of the bias spreader. Heat dissipation of the sink might be poorer at higher temperature and with the time delay associated with the bias spreader it causes the system to slowly approach a runaway condition. Maybe !

Another thing that might be a problem. The bias spreader when mounted on the power transistor will 'see' the power device through some thickness of plastic and that isn't a very good heat conductor. It might be better to place the BD139 upside down with the metal tab side facing up. Then place a small metal plate with mica insulation on it and then bolt it to the power transistor. Now the heat will flow up the screw into the metal plate and on to the metal tab of the bias spreader. This will reduce the temp differential between the two devices. Reaction time should be very low. Any thoughts ?
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Last edited by ashok; 19th June 2013 at 05:14 PM.
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Old 19th June 2013, 05:24 PM   #366
Bigun is offline Bigun  Canada
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I don't think NPN or PNP is going to be a significant change wrt stability - I think the other approaches will be far more effective (i.e. degeneration, Hagerman bias spreader, NTC )

Edit - ignore that, I'm one post behind...



The bias spreader also has a sensitivity, not just how fast, but how much it changes the bias voltage for a specific change in temperature. I believe you can adjust it by changing the resistors around it - to change how much VAS current flows through the Vbe transistor and how much VAS current flows through the Vbe transistor bias string. You may need to make it more sensitive by increasing the impedance of the Vbe bas bias string (with same ratios).
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Last edited by Bigun; 19th June 2013 at 05:31 PM.
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Old 19th June 2013, 06:23 PM   #367
banat is offline banat  Serbia
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Few pictures

Set`s of 2sa1095 & 2sc2565 from that black discarded PA Amp , and some NOS Hitachi Laterals which was bought long time ago but I never use them .

Regards !
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Old 19th June 2013, 06:31 PM   #368
AndrewT is offline AndrewT  Scotland
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Some folk will pay you a relative fortune for those genuine NOS Hitachi Lateral mosFETs.
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Old 20th June 2013, 03:08 AM   #369
gaborbela is offline gaborbela  Canada
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wahab
Thank you for your help I got to these project and to the mosfet amplifier also.
I'm at the door step to test that, also I'll go ahead to test the modded verison of these Darlington circuit.
About the Exicon LatFet
I tested the Hitachi vs. Exicon in my DIY ProFet amplifier.
I do preffer the Exicon in that circuit.
But again that a Class A amplifier similar to the N Pass F5 with LatFet.
I do have no interest to promote the Exicon in any way!
I'm happy you still follow these thread, we need your help, advise here.
Bigun
I hope you"r serious to test those Sanken Darlingtons soon.
I invested so much to these project over the years I do not want to keep spending just to get more experince..
If I know those or other Sanken I can use sucsessfully at these project (even if I get just a little improvement, stability) definately I would invest, but again....

banat
Those Toshiba devices one of my favorite power transistors.
It is a same no longer avaleble, just some China made Ebay stuff.

Greetings G

Last edited by gaborbela; 20th June 2013 at 03:10 AM.
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Old 20th June 2013, 05:21 AM   #370
bluevas is offline bluevas  Indonesia
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Hi G,

I look upon the schematic on post 336 with japanese transistor...what is the bias for this amp? i have all the transistors...did it sound horible if using original transistor?

greetings,

Josh
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