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gaborbela 15th November 2008 01:47 AM

My first DIY amplifier 20 years a go
 
2 Attachment(s)
Hello
These was my first DIY amplifier , I built about 20 years a go .
Now I think to rebuild it . From beter quality parts .
Any comment welcome .
When firs I built it I used one pair power transistors but after I added one more pair which brought a lot of improvement in the sound .
More dynamic , more bass , I used +/-56V power supply with two pair 50 000uF Mepco capacitors .
I post the schematic you can take a look . No need for preamplifier , just a 10K pot. . On the input is better to use a bit higher value capacitor .
One more time any comment ,advise welcome
Greetings

lineup 15th November 2008 02:04 AM

looks like what I call emitter feedback (curr-fb )
but I have never seen this very type before
something new to me = more interesting

practically all transistors can be upgraded, improved
personally I should start with +-30 Volt
and try to make it work/sound perfectly with one output pair

another thing
these type often benefit much with separate power supply for output stage
and the input/driver part a well regulated own supply

gaborbela 15th November 2008 03:30 AM

Hello lineup
Thanks for your advise , the separate power supply I think probably is a great idea .
We did tried with lower power supply voltage and after adjust the bias but the amp lost a lot from the dynamic from the bass and from the control over the speakers .In a simple sentence the sound get somehow thin and weak .
We even tried to adjust the resistors, using lower value, calculated after the lower voltage but it didn't help at all.
So that was the reason we doubled the power transistors .
Another reason at +-56V those Darlingtons produced a lot of heat , to solve the problem we decided the best would be 2 pair output transistor . To spread the heat better .
Clearly I remember that gave to the amp more dynamic and better bass more authority ower the speakers.
By the way it sounded really sweet and nice , a bit warm like (I could com pair the sound of the amp to the Hiraga Class A , or like Naim like , somehow a bit warm sound ) so that is the reason I think after 20 years I would give another try again .
But now I try to improve the passive components , better quality resistors , and capacitors . like Dale resistors and Cerafine or BG capacitors at least to the low voltage type . Some silver mica capacitors instead the cheap ceramic caps .
For power transistors we have not to many option here .
We tried Motorola MJ11015/16 Darlington but get worst . There is not to many Darlington on the market . Very few amp was built from Darlington transistors .I know Hiraga Class A etc used the Darlington circuit but not the transistor it self . And we tried to use TIP142 /147 but BDW83C under the name of Morocco , or Texas Ins. was the best .
Philips had some good Darlingtons but today discontinued parts very hard to find and even they ask $30 for a piece .
We built the Darlington schematic out of Toshiba transistors but somehow it get the amp much slower .
BF transistors are high voltage type so for the 56V power supp we needed that . But today we can find from ON Semi maybe better driver transistors with high voltage .
One of my friend after 20 years still use these amp and very happy with .
I gave him a Symasym kit with good parts but after he built it He told me "thanks but I stick with my old amp."
Thanks one more time for your advise .
Greetings

anatech 15th November 2008 04:07 AM

Hi gaborbela,
Nice amp. Interesting.

It looks almost like a unity diamond buffer, but you are modulating a "current sources" for gain. Interesting.

From my work with similar circuits, the doubled outputs will give better damping and life to the music. It probably sounds slightly compressed at higher levels, but with good detail. Can you stabilize the bias with lower value emitter resistors? Say 0.22 R? Even 0.33R would be an improvement. Adding more outputs will improve the sound also, not for heat spreading but to lower the range of current each output gets.

Coupling the bias transistor thermally to the drivers should help to control the bias current a little better than if they were on the heat sink. All you can do is try this. You will want to keep the input pair as cool as you can. Getting the bias to stay right is a balancing act sometimes.

Running the voltage amp stages (from the fuses back) off regulated supplies might help with any interference from the outputs, but your diodes will at least decouple from sudden drops in the unregulated voltages. You were thinking of this I bet.

Do you have a picture of the completed amplifier? An inside shot might be nice.

-Chris

lineup 15th November 2008 04:12 AM

Quote:

Originally posted by gaborbela
One of my friend after 20 years still use these amp and very happy with.
I gave him a Symasym kit with good parts but after he built it He told me "thanks but I stick with my old amp."

:) would tell us something about the potential of this amp
because not many dare to call SymaSym is a bad amplifier - because it is not

MJL21193 15th November 2008 04:26 AM

Hi Gabor,
Funny question, but did I buy a transformer from you on Ebay about 2 years ago? A 39-0-39 750VA?
This being a small world and all...

lineup 15th November 2008 04:50 AM

If you want to stay Darlington in one package,
Sanken has got some really Fast!!! MONSTER 200 Watt darlingtons
npn, 2SD2561 ... fT typ 70 MHz, Cob 120 pF
pnp, 2SB1648 ... fT typ 45 MHz, Cob 320 pF


Sanken Datasheets
http://www.allegromicro.com/en/Produ...n/Transistors/
from
www.AllegroMicro.com with many resellers

gaborbela 15th November 2008 05:05 AM

HI
First I want to say all my respect to Mike B and his Symasym amplifier ,is really nice amp !!!
My friend told that thanks but he does not want from sound of the Symasym .
When I ordered from China the Symasym PC boards the min. order was 5pc. So I ordered 6PC and I sent a full kit to my friend to Budapest .
Yes the amplifier is very stable firs we used .33R emitter resistors but after we doubled the output the amplifier designer advised to us to increase a bit those resistors .
Of course the BD136 must be on the main heat sink .
It need a bit larger heat sink than the usual classic Class A/B amplifier , somehow the Darlington tend to run hot .
Right now I don't have the amp , only my fried still has it after 20 years .
When I built first these amp I had a pair Revox vintage tube mono block amplifier upgraded by a tube amp designer but after I start listening to these amp I sold those .
I like power amplifiers with big VU meters so from the ad I look up a Sansui power amp about 45lb but when the owner brought to my home to test it we com pared with these amp and He didn't believe to his ear . He started to look to the speaker cables if these amp runing or something else.
Of course it sounded much better than his Sansui power amp .So he took his amp home .
Another guy try to sell me a Tehcnics power amp (the old type) but with the same result. (Today I have a large Akai PS-200M power amp with big blue VU meters but need to be rebuild both side are dead about 70lb . )
The amplifier was design by a Hungarian electrician engineer .
20 year before I was totally a greenhorn in DIY . I did try to improve the sound buy testing all kind of transistors , capacitors until I destroyed the PC board . Of course with out any success only improved from the double power transistors and higher voltage . The designer advise was that to.
One day I played with the amp and I burnt one of my woofer so I took the amp into parts and I trow the PC board to the garbage .
Now I did share the schematic with another(DIY-er) fried Tymo and he wrote he will design me a new PC board when he will has time for .
So I hope soon can rebuild it again .
Thanks for your advise .
Greetings

gaborbela 15th November 2008 05:06 AM

Hello
Thank you lineup.
Greetings

gaborbela 15th November 2008 05:25 AM

Hello

Here is the data of the BDW83C Darlington transistor .
http://www.st.com/stonline/products/...re/ds/4265.pdf
I'm still learning about the semiconductors so I'm not sure I can replace these with those Sanken type .

Greetings


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