Evens C-500 amplifier ....opinions? - Page 3 - diyAudio
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Old 17th March 2010, 07:48 PM   #21
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Ok..measured with a thermometer I get about same reading 27.3 and ~28 degrees so it can't be anything wrong with them. Was just my imagination .
Homemodder can you please tell me the role of Q10 and Q5....I'm thinking to replace them with something a bit more powerful like mje340/350 or bf469/470. What do you suggest?
I like amplifiers that when they blow up... only the output transistors burn before the fuses.
Checking all the small transistors on the board is a pain .
Also I want to mention that I used normal cheap carbon resistors 5% tolerance (when measured are more like 10% tolerance to me ). The designer mentioned on the website to use 1% metal film resistors for improved performances. Matching the transistors like Homemodder suggested sounds like a very good idea. The amplifier sounds pretty good with cheap resistors and unmatched transistors, low noise, no hum just a bit of hiss on high SPL speaker.
I cranked up the volume but I didnt manage to burn anything with 2n355/mje2955 as outputs.
Also I want to mention that the output only has the coil connected....the output resistor does not exist on the original design...the latest review has holes on the PCB for a resistor.
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Old 17th March 2010, 08:32 PM   #22
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Ok where to start you asking many questions.

Glad you got the biasing sorted, either the 2sd tranny is faulty or then just connected incorrectly, the pins are not the same for the bd and the 2sd pats. I would stick to using the bd part as good performance is obtained with this part in many amps and better can only be obtained using high beta parts such as those I mentioned before. The 2sd2012 if you look at datasheets is actually inferior to the bd139.

There should be a resistor connected in paralel with the output coil, around 2.2 ohms is good.

The designer of the amp obviously knows what he is doing and thats why he changed the input cap to 470pf too. I havent done the maths on that low pass filter, for more info you can read about low pass filters on wakipedia and how to calculate their response.

Q10 together with Q12 form a complementary feedback pair as does Q5 and Q13 and these drive the output transistors. Theirs not much current going through these I think depending on the design but if they are only at 28 degrees its just fine. Dont use mje340, performance will degrade substantually, bf470 is ok. A complementary feedback pair was used because it is more linear and provides high input impedance to the vas and is a higher performing stage than the usual emiter follower used here.

Like I said this design looks very good and only minimal improvements can be made, its more like little corrections such as the resistor and the input cap. It should sound very good indeed, when you change the outputs to sankens or toshibas the sound will improve another couple of notches too, 2n3055 are dinosuars and will cause high frequency distortion. Using quality parts such as metalfilms will improve the sound as well offcourse and using 5 percent carbon is also a reason for your DC offset, youll find it difficult to match currents in your differential.

Matching the transistors will improve things further.
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Old 18th March 2010, 01:57 AM   #23
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Thanks for reply
The bd139 has reversed pins . I always check transistors data-sheet before i use them.
The 2sd is not faulty...checked...probably not sensitive enough as you said.
I hope I can build second prototype.....with better components and matched transistors. It should sound at least 20% better I think.
2n3055 are dinosaurs indeed but for testing are just great CHEAP AND RELIABLE . One Toshiba costs 5X the price of 2n3055.
Any good alternative to BF422/423? I think the bf423 i bought are fake or really low quality. They look a bit weird.
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Old 18th March 2010, 02:23 AM   #24
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Those BFs are very good transistors for the purpose, actually excellent, you could try
2sa1208 and complement from profusion which are also excellent for this role, another is 2sa1360 but this comes in different casing, 2sa1145 is about the best you can get. When it comes to the driver transistors I wouldnt recommend changing the ones Ive mentioned except for 2sa1360 and 2sa1208 because of safe operating power.
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Old 18th March 2010, 05:53 AM   #25
jaycee is offline jaycee  United Kingdom
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BF422/423 have been discontinued by Philips/NXP but OnSemi still make them. Simply make sure you get OnSemi branded ones.

MPSA42/92 also seem suitable here.
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Old 18th March 2010, 07:58 AM   #26
evens is offline evens  Thailand
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Hello all....
I am Evens from Thailand.
Problems of this project by selecting the output transistor of 2N3055 and MJ2955 is not appropriate to the voltage conditioning. + /-40VCC should move to MJ15003/15004. Or other Vce can tolerate more than 80V of power supply.

C10 If the cost will range 33pF sensitive to high frequency noise from switching power supply, so we changed to 470pF, which makes up better.

Response frequency of the C-500 frequencies lower deep as 10Hz ever to reduce input capacitor into could help filter frequency Sub Sonic can do.
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Old 18th March 2010, 10:48 AM   #27
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Quote:
Originally Posted by evens View Post
Hello all....
I am Evens from Thailand.
Problems of this project by selecting the output transistor of 2N3055 and MJ2955 is not appropriate to the voltage conditioning. + /-40VCC should move to MJ15003/15004. Or other Vce can tolerate more than 80V of power supply.

C10 If the cost will range 33pF sensitive to high frequency noise from switching power supply, so we changed to 470pF, which makes up better.

Response frequency of the C-500 frequencies lower deep as 10Hz ever to reduce input capacitor into could help filter frequency Sub Sonic can do.
Hi Evens

Good you are a member here.

This is a very nice design you have here, I have something very similar I use as car amplifiers but with a triple loncanti mosfet output, during prototyping I did indeed try this outputstage whith very good results. The amp not only measures good but sounds excellent when well built.

I can recommend anyone to try it, pity I dont see more members here showing any interest as the design provides excellent sound.

I only have two suggestions and that is the layout of PCB and the value of the feedback resistor. You shouldnt place the output coil so close to the driver heatsinks and the output transistors should rather be part of the heatsink instead of transistors being connected with wires which could lead to oscilation problems. The feedback resistor could have a smaller value like 22K and with the corrosponding modifications made to the gain network to reduce noise. If I can remember correctly when I was prototyping my design the lowering of the feedback resistor also gave improved THD20 figures.

We dont know yet what voltages butch_vlad will be using as final design as it will impact the choice of transistors but I think he will settle later for the toshibas as you have recommended, I think he is only using the 2n3055 for testing and they certainly arent good for this amp and the mj15003 are also dinosaurs.
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Old 18th March 2010, 01:23 PM   #28
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Hi Evens, thanks for your support!

Really nice design, sounds good even with cheap components.
The amplifier noise is really low and using metal film resistors and matching transistors will improve performances a lot.

For PA use I recommend that C7(input cap) should be reduced to sub 4,7 mfd to avoid subsonic frequencies that could destroy speakers and the amplifier at loud volumes. For home hi-fi use C7 can remain 10 mfd as long as the amplifier is not pushed to hard for extended periods of time.

For C10 I used 470 pf ...the value should be increased to 1n for high power (over 200w)...usually for PA use this capacitor is increased to maintain amplifier stability, from what I've researched in the past few days. I studied about 30 amplifier schematics to better understand how they work and how to make better design. ESP website is very helpful with lots of information. Rod Elliott explains his designs and the choices he made in a manner that every diy person can understand.

Homemodder please can you tell me which one is the feedback resistor.
Didn't have any problems with amplifier gain...seems just fine using PC soundcard.
For the final design I will use 70 v rails and 4 or 5 pairs of toshiba 2sc5200/2sa1943.
I was also considering MJL21193/21194, sanken 2sa1494/2sc3858 and sanken 2sa1295/2sc3264 .

For Evens
Do you consider making a new review of the current PCB design and schematic?
There are 2-3 small modifications you could make, like changing the components for BIAS adjustment, placing a trimpot to fix the DC offset.
These are just small modifications that don't require to much time and will not modify the sound of the amplifier, it will just make is easier to build.
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Old 18th March 2010, 02:03 PM   #29
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Can someone post a power supply schematic and pcb please.
I am looking for something like this:
PSC-Audio | PsC-Audio | KIT125B_1 - Redresare+filtrare, 2x25A, 6x10.000uF/50V SAMWHA
The PSU-Three Power Supply Module
I know how to build psu's but I don't have any nice PCB layout. Usually I make a hand drawn design and most of the time is UGLY .
I want something fused onboard, with bleeders and snubbers.
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Old 19th March 2010, 04:29 PM   #30
evens is offline evens  Thailand
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Hello you two.
C-500, this project I created from Crown Amplifier XLS Series.
Circuit characteristics of a C-500 is found more often considered a form of expanding the range of quality sound pretty good.
Now I produce C-500 sold in Thailand and try to develop better again.
Thanks for your feedback.

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Last edited by evens; 19th March 2010 at 04:48 PM.
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