I checked on my other 2 meters. Original one currently reading 252v, second one reads 252v also, third one (a clamp one with probes) reads 249-250v. Are we getting too much juice 😱 😀
The Symasym boards are currently getting 37.8V from thier buzzy transformer if that helps 🙂
The Symasym boards are currently getting 37.8V from thier buzzy transformer if that helps 🙂
ask your supply company to check your voltage and reset if necessary.
@252Vac you have +-44Vac with quiescent current.
@254Vac this will rise to <44.5Vdc and probably less than 47Vdc if the fuses blow.
This is safe for use with 50V caps.
Bensen's spreadsheet model predicts 68W into 8ohm and below the 100mS temp de-rated SOAR for 60degree phase angle @ Tc<=70degC.
I used 6% regulation for the transformer and +-9400uF for smoothing.
It will just drive a 4r0 resistive load to 107W if you can keep Tc below 70degC.
This implies a fairly big heatsink and Ts<=60degC for all operating conditions. Probably best with a 60degC cutoff switch for the mains and aim for sink <50degC in worst conditions.
I tried adjusting the smoothing, for power output to match Cordell's criteria (+80% into half load resistance) for good power delivery, you need +-40mF and 5% regulation. To satisfy my criteria of three times power from 16r to 4r0 requires +-15mF. For good bass into 8ohm I recommend +-20mF.
The PCB does not have sufficient space to reach these levels of smoothing capacitance.
@252Vac you have +-44Vac with quiescent current.
@254Vac this will rise to <44.5Vdc and probably less than 47Vdc if the fuses blow.
This is safe for use with 50V caps.
Bensen's spreadsheet model predicts 68W into 8ohm and below the 100mS temp de-rated SOAR for 60degree phase angle @ Tc<=70degC.
I used 6% regulation for the transformer and +-9400uF for smoothing.
It will just drive a 4r0 resistive load to 107W if you can keep Tc below 70degC.
This implies a fairly big heatsink and Ts<=60degC for all operating conditions. Probably best with a 60degC cutoff switch for the mains and aim for sink <50degC in worst conditions.
I tried adjusting the smoothing, for power output to match Cordell's criteria (+80% into half load resistance) for good power delivery, you need +-40mF and 5% regulation. To satisfy my criteria of three times power from 16r to 4r0 requires +-15mF. For good bass into 8ohm I recommend +-20mF.
The PCB does not have sufficient space to reach these levels of smoothing capacitance.
I probably should have mentioned this is the midrange amp of a 3 way tri-amped setup, it will drive a Dayton RS52 (probably...). It is extremely unlikely to need more than about 20W in normal use, it's quite efficient and is crossed above 800hz 24db.
Power supply is +/- 14100uf (plus 1000uf on the symasym board). Objectively the heatsink looks very overspecified at 300mm x 100mm x 40mm, it is rated at 0.4c/w. I can't imagine it overheating in this application (driving 4ohm bass speakers I would be concerned though). The Dayton dome is around 6ohms really in the range I want to use it.
I used all the reccomended small signal devices from the parts list so providing these are suitably rated voltage wise I should be good to go? On board capacitor ratings are a little close but should be safe (they are high temp good quality anyhow if thats relevant!).
Amp currently using the +/-30v transfomer will be getting a +/-40v one; being 750VA it'll need softstart though. Thanks for your advice!
Power supply is +/- 14100uf (plus 1000uf on the symasym board). Objectively the heatsink looks very overspecified at 300mm x 100mm x 40mm, it is rated at 0.4c/w. I can't imagine it overheating in this application (driving 4ohm bass speakers I would be concerned though). The Dayton dome is around 6ohms really in the range I want to use it.
I used all the reccomended small signal devices from the parts list so providing these are suitably rated voltage wise I should be good to go? On board capacitor ratings are a little close but should be safe (they are high temp good quality anyhow if thats relevant!).
Amp currently using the +/-30v transfomer will be getting a +/-40v one; being 750VA it'll need softstart though. Thanks for your advice!
i am having problem in setting the bias ,i have checked the schematic & PCB with utmost care but could not find the prob.Otherwise the amp is running OK.when measuring the voltage across the .22E resistors it is zero with no voltage applied,when input is touched the voltage rises to130ma pls help.
setting up bias and offset
short the input of the RCA socket to the ground of the RCA socket.
Then measure the output offset and measure the Vre (voltage across the emitter resistor)
short the input of the RCA socket to the ground of the RCA socket.
Then measure the output offset and measure the Vre (voltage across the emitter resistor)
Hi bitravi,
Are your heat sinks grounded? This is important. Also, make sure your other ground paths are complete. There is a signal ground to system ground resistor. Make sure it's not open or too high a value.
Now, when you are measuring DC offset and bias current, your inputs should be shorted as Andrew has mentioned. Also, you should have no load on the amplifier. That means no speakers or dummy loads.
-Chris
Are your heat sinks grounded? This is important. Also, make sure your other ground paths are complete. There is a signal ground to system ground resistor. Make sure it's not open or too high a value.
Now, when you are measuring DC offset and bias current, your inputs should be shorted as Andrew has mentioned. Also, you should have no load on the amplifier. That means no speakers or dummy loads.
-Chris
What does grounding of heat sink play the role in bias adjustment?I have already isolated the heat sink & transistors with mica washers.Only difference in component is that i have used 2.2k instead of 2k & 500 ohm instead of 499 ohm & .25 ohm at emitter of 5200 & 1943 else every thing i have rechecked thoroughly.
I usually power the amp first with less voltage,now its +-26.Should i increase it to+-36?
I am using BC550 at input (matched),i am confused what should i do?
I have checked with input shorted to GND offset is zero.
I usually power the amp first with less voltage,now its +-26.Should i increase it to+-36?
I am using BC550 at input (matched),i am confused what should i do?
I have checked with input shorted to GND offset is zero.
anatech said:
Hi Chris,
I hope you mean grounded at AC, not DC 😉
2...4uF VIMA MKS between stargroung and heat sink will suffice
Cheers,
M
My fault
hi everyone,it was my fault i had used one 750E resistor instead of 150E.
I am a happy man now.This amp is really very nice no need to add tone control ,every thing is very smooth clean & detailed.
Thanks to Mike B.
hi everyone,it was my fault i had used one 750E resistor instead of 150E.
I am a happy man now.This amp is really very nice no need to add tone control ,every thing is very smooth clean & detailed.
Thanks to Mike B.
Hi roender,
Hi bitravi,
If your heat sink is left to float, it's not uncommon to couple different points of your circuit together at high frequencies. That's because your outputs and everything else on that heat sink are capacitively coupled. The heat sink also makes for a dandy antenna to transmit any HF into any high gain stages laying around unprotected.
So now you know.
-Chris
Doesn't matter either way. It would be grounded to the chassis ground rather than the signal ground. Don't want any loops forming. A heat sink is normally grounded to the chassis when you assemble an amplifier, but when it's out on the bench, people forget to do that.
Hi bitravi,
A great deal if it's oscillating. The inability to be able to adjust bias current down to it's proper value is one indicator that your amplifier is oscillating. 😉
If your heat sink is left to float, it's not uncommon to couple different points of your circuit together at high frequencies. That's because your outputs and everything else on that heat sink are capacitively coupled. The heat sink also makes for a dandy antenna to transmit any HF into any high gain stages laying around unprotected.
So now you know.
Just an error. Everyone has done something similar. I'm glad you found it.
-Chris
mje340/350
Hi,
I`m really interesting to build this amp, however currently refer to the schematics i dont have mje340/350 transistor, can i replace it with tip41c/42c? I have all other components except mje`s, i have bd139/140 and all others.
Regards.
Hi,
I`m really interesting to build this amp, however currently refer to the schematics i dont have mje340/350 transistor, can i replace it with tip41c/42c? I have all other components except mje`s, i have bd139/140 and all others.
Regards.
Hi norazmi,
The TIP41C and TIP42C are both lower in voltage and slower devices. The cases are also larger than the MJE cases.
-Chris
You will not be disappointed.
Can you please give a link to which version you are building? The normal amplifiers do not use MJE340 or MJE350 transistors.
The TIP41C and TIP42C are both lower in voltage and slower devices. The cases are also larger than the MJE cases.
-Chris
Hi Chris,
Thanks for the fast reply, its mistake about mje340/350 and it was mje15030/31. I`m refering to the sym5.2 schematic, but from your info details about tip41/42 i think its not good and i need to find mje15030/31 for better performance.
Thanks alot Chris,
Regards.
Thanks for the fast reply, its mistake about mje340/350 and it was mje15030/31. I`m refering to the sym5.2 schematic, but from your info details about tip41/42 i think its not good and i need to find mje15030/31 for better performance.
Thanks alot Chris,
Regards.
Would anyone be so kind to advise me what are the best sounding transistors for the latest version of SymAsym? There are so many, I'm confused.
Thanks and regards.
Andriy.
Thanks and regards.
Andriy.
currentflow said:
Thanks for your reply.
So, I can choose any for 36VDC version of SymAsym depending on my taste and availability?
Thx.
AndriyOL said:
There should be no problem selecting from those mentioned in the links, as long as the minimum loudspeaker impedance is observed and that you don't attempt to bridge two such amplifiers into a 4 ohm load.
It might be worth reading a few threads on the many SymAsym variants which now exist for further selection ideas.
Good luck with your build!
Regards,
Steve
My Symasym v5.3 finally finished
Hi dear, i finally finished my symasym 5.3v and i loved, great sound,
thank you Mikeb for this great amp.
I am using MPSA18, now i am planning to use 2sk170bl. My psu gives 37,5 vdc, what i have to do to use these jfets ? I think it´s not safety to use them under this voltage.
best regards
steppen
Hi dear, i finally finished my symasym 5.3v and i loved, great sound,
thank you Mikeb for this great amp.
I am using MPSA18, now i am planning to use 2sk170bl. My psu gives 37,5 vdc, what i have to do to use these jfets ? I think it´s not safety to use them under this voltage.
best regards
steppen
I apologise for not going through all this thread, there isn't any chance that I will have the time to read all 146 pages very soon. So, as I am preparing to populate two SymAsym 5_3 boards there are a few questions arising.
First, I don't have any MJL transistors but I have a few pairs of NJW3281/1302. Can I use them instead?
Second one - how should R22 (the bias setting pot) be turned at first power up in order not to blow the output transistors? Minimum or maximum resistance?
And the final one (for now)... Can I use one 26-0-26 Vac / 120VA transformer for each channel, or would the amplifier be underpowered? I plan on using 30,000uF filtering capacitance per rail on each channel.
First, I don't have any MJL transistors but I have a few pairs of NJW3281/1302. Can I use them instead?
Second one - how should R22 (the bias setting pot) be turned at first power up in order not to blow the output transistors? Minimum or maximum resistance?
And the final one (for now)... Can I use one 26-0-26 Vac / 120VA transformer for each channel, or would the amplifier be underpowered? I plan on using 30,000uF filtering capacitance per rail on each channel.