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Old 21st July 2011, 01:18 PM   #1
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Default DX Precision I Simplified, Help

I have modified the DX Precision I to simplify the circuit so it will fit in a smaller chassis. can someone please check over my circuit to make sure the it won't blow up my speakers or something. I have changed some transistors because those are the ones that I have. Will those transistors work as good as the original's ?

Replaced Transistors:
2N5401 = BC556B
2N5551 = BC546B
BD140 (VAS) = KSA1381
2SC4793 (VAS) = KSC3503
2SC4793 (Driver) = KSC2690A
2SC1837 (Driver) = KSA1220A
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Last edited by benproiii; 21st July 2011 at 01:20 PM.
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Old 21st July 2011, 01:33 PM   #2
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Do NOT modify a tested and proven circuit!!!!!

Your mods will most likely cause the amp to blow up the second you turn it on.

If the board for this amp is too big, choose an amp with a smaller board!
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Old 21st July 2011, 01:45 PM   #3
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At least if you have no background knowledge. With so many changes to the original circuit that will be a completely new amplifier.
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Old 21st July 2011, 02:33 PM   #4
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Default It may work fine Benproiii..... transistors you're using are

good substitutes...nice equivalents that may not produce tragedies.

If you are only substituting transistors.... i think it is all right.

Q3 will change the trimpot position...the preset adjustment... resistance adjusted will be different because different transistor gain..original was gain 100 measured in these standard multimeters (digital and yellow).

You have reduced the output pairs i think.... so, your amplifier will be reliable with 8 ohms loads...maybe will survive to 4 ohms.... will be less strong.... you may have to increase R26...that damn thing is useful in these cases..when people use less power transistor than they should..... you know...one error to fix another.... i do not like this resistance...in my home amplifier i do not use the transistor associated..but you may need... because changes you have made.

Amplifier are a system...balanced system..when we change something we must compensate in another place... changing you may have to recalculate other things, to reduce VAS current, to change bias point, to replace power emitter resistances by larger ones... the better idea is always to search for something that matches your need in the place to modify something was tested.

That resistance should be increased in order to protect your poor 2 pairs...sound will be worse because of that...but may help your output to survive.

If you face problems..well... do not publish that Precision 1 has not worked..that has problems or anything alike...please...because i do not want to take responsability by a modified design and also will not be happy with this nice unit exposed to a shame.

I am not angry....just worried.

Good luck.

regards,

Carlos
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Last edited by destroyer X; 21st July 2011 at 02:47 PM.
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Old 21st July 2011, 03:38 PM   #5
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Will this improve stability?

Im going to power it with +/- 50V not 63V so should that make it more stable into 4ohm loads.
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Last edited by benproiii; 21st July 2011 at 03:42 PM.
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Old 21st July 2011, 03:48 PM   #6
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Default No dear Benproiii, it will not turn the amplifier more stable

It will just control the power...will compress your audio in a such level your power transistors will not be destroyed.

I cannot say the correct value...because i would have to assemble it once again and i have no one assembled at my home..simulators may help, but usually they show wrong values...the real world test is the best solution.

So, install a 100 ohms, or 50 ohms trimpot in the place of that resistance, and then put your unit to play over 4 ohms speaker... go increasing volume till your amplifier starts to clip..then go increasing the trimpot that must start in zero, or 1 ohm resistance..go increasing till you perceive distortion reduces... this is the point you must use.

I do not know... 47 can be too much and may limit your power....this must be done testing.

I do not like this circuit... it looks to me a very poor solution... a pig (dirty) solution, as we destroy audio dinamics in order to protect power transistors...and we go protecting power transistors because they are not the quantity of transistors the power amplifier should need to face low impedance or difficult loads...so...we start making foolishes and the foolish we have made forces us to make another foolish, and this compresses audio because the hell limiter circuit, when you increase volume...go compressing audio... high levels stays fixed in volume (bass) and treble go increasing while you increase volume...awfull effect... sounds alike junk amplifiers..that BC547 and the 22, or 47ohms resistance is the circuit i am talking about.

So..it is a bad thing to fix another bad thing and will result in a huge awfull thing.

I have installed because pressure...people bothering and saying this was needed...and people was believing (that time) that this was needed...then i had to introduce the subcircuit to shut the bad guy's mouth....but i have suggested folks not to install the transistor.... or to listen with and without to see the awful thing this transistor makes with sonics.

Now i am angry...not with you, because of you or against you..but remembering that bad guy disturbing... supporting bad ideas... and bad ideas are the ones disturbs sonics..electrically can be a nice thing...as will allow factories to produce cheap produces... reducing power transistors and increasing their profit...but for us, audiophiles, this kind of mind is a tragedy.

regards,

Carlos
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Last edited by destroyer X; 21st July 2011 at 04:02 PM.
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Old 21st July 2011, 09:59 PM   #7
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OK, I think I will use the 3 output pairs to improve the sonics.
Are my transistor choices as good as the originals.
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