Symasym - the sequel

[Dr_EM]

I have still 2 of mikes 5.3 PCBs and might make another stereo amp (once the first is done!) with them. It'd be for use with tweeters so I was thinking about using regulated supplies and biasing to give a few watts of class A power. Any thoughts on this? Is it likely to be successful/beneficial? The tweeter is planar so a nice easy load and the heatsinks are 0.4c/w per amp.

 

[Carl_Huff]

Is there a PCB layout someplace on this board for roender's version with ThermalTrak output devices? I've got some ThermalTrak devices that I'd like to try.

 

[TedS]

Not to speak out of turn, but roender ceased development of that design and created this one:

http://www.diyaudio.com/forums/showthread.php?s=&threadid=111756

It uses the Thermaltrak components and seems to be very promising, but it hasn't generated much of a following yet. I'm hoping to see a groupbuy for it organized.

 

[currentflow]

Question for Al (AAK) if you're around please. For your “50V” version of the Symasym – what would be the maximum supply voltage acceptable for use with 6 ohm speakers? I am interested in building a version similar to that shown in post #53: http://www.diyaudio.com/forums/showthread.php?postid=1021217#post1021217

Also, can MJE15030/1 be used for the drivers without too much degradation? These are lower hFE (40 min) and fT 30MHz.

Thanks in advance,

Steve

 

[AndrewT]

1pair of 1943 can drive a 12ohm load to 75W from +-50.2Vdc.
It is on the 25degC SOAR for 100ms when the load is 60degree phase angle.

I would not try to use this on an 8ohm speaker.

The 1943 have abysmal SOAR at higher voltages.

 

[AAK]

Hi currenflow,

MikeB designed Symasym to drive a 4ohm load at I believe +/-36V rails, that makes for about a 25VAC transformer. My version is no different, it can easily drive a 6ohm load. I would stick with 36V rails for the minimum voltage, 50V for the maximum for my version. You could go lower but that will require some resistor value changes to set the correct bias current. The use of MJE15030/1 for drivers should work fine.

Regards,

Al

 

[currentflow]

I appreciate your reply, Andrew.

So you wouldn't recommend AAK's design, although he appears to be driving into 8 ohms with a +/- 50V supply:

Re: post #266: http://www.diyaudio.com/forums/showthread.php?postid=1135684#post1135684

I'm hoping to drive some Q-Acoustics 1050i speakers (6 ohms) from a single pair of 1943/5200 devices, but would like to squeeze the maximum peak power available while still maintaining some margin of safety. With the standard +/- 36V, I should obtain around 75W into this load. If I can increase the supply to +/- 42-43V, (using a 30V-0-30V tfmr) without exceeding the SOAs, I would be more than happy.

Thank you,

Steve

 

[AAK]

The 1943 output works great in this design. And BTW it's used in many popular designs including Hugh Dhein's AKSA.

 

[currentflow]

Hi Al,

Thank you for your comments. So my configuration intentions shown in post #447 should be fine, without risk of exceeding the output pair SOAs as far as you are aware?

Just to confirm, do I understand correctly that you're saying any rail voltage between 36V and 50V will be satisfactory for loads between 4 and 8 ohms?

If so, I will probably order a 300VA 30-0-30 transformer unless you recommend otherwise (for stereo).

The 1943 output works great in this design. And BTW it's used in many popular designs including Hugh Dhein's AKSA.

Well I was suitably impressed by PMA's (Pavel Macura) Symasym review (and many others) using these devices and they are readily available here in the UK.

Steve

 

[chalkandtalk]

I have made two of these amps - for a two way active system. In one I have used a 25V transformer and a 30V transformer in the other. Both run well and comfortably drive my Living Voice Avatar speakers (not sure of their impedance). Both amps use the 5200 and 1943 as on AAK's BOM.

Thanks for a geat amp AAK. But I have a question for you:

I have just built a Buffalo DAC which has a balanced output. Is the any way of making a balanced amp from two Symasyms?

 

[AndrewT]

Hi,
these 1943/5200 amplifiers are great using +-30Vdc to +-40Vdc as supplies.

One pair on +-50Vdc asks too much when driving reactive speakers.

The 1943 SOAR is poor at higher voltages.
It is down to a single shot 100ms pulse of ~4.2Apk @ 50Vce and falls to just 0.38A @ 100Vce. Yes, only 38W and still to be temperature de-rated.
Compare to the 150W 2n3773 that is guaranteed 1.5A @ 100Vce. About 4times more current at the same voltage

The 1943 suits lower supply voltages.

 

[AndrewT]

you're saying any rail voltage between 36V and 50V will be satisfactory for loads between 4 and 8 ohms?

did you understand post 445?

 

[currentflow]

Andrew,

Sorry, I read your reply 445 too quickly. What I originally wished to know was the maximum safe rail voltage for a 6 ohm load (my post 444).

Al - Please ignore my second paragraph question in post 449. I know, this makes no sense!

Regards,

Steve

 

[AndrewT]

Hi,
1pair of 1943 can drive a 6ohm load to 85W from +-39Vdc.
It is on the 63degC SOAR for 100ms when the load is 60degree phase angle.

Keeping Tc<=43degC would fit my reliability criteria.
This is roughly equivalent to a maximum heatsink temperature of 35degC.

You can test to maximum power (with a cold heatsink) into a 3r0 load.

 

[currentflow]

Thanks for the calculations Andrew.

39V rails will be tricky for transformer selection (I'd rather go higher than lower), so perhaps on reflection, I should be looking at the MJL3281/1302, in which case I can safely look at 30-0-30V giving 43-44V.

Regards,

Steve

 

[lgreen]

Boards needed

Does anyone have boards and a current BOM for this amp?

I am wanting to make one!

 

[Rick NL]

Board

Hi Igreen,
I am building an AAK inspired board that I designed for use with 2SC2922 2SA1216 O/P pair. One R Core 2x25V 160 VA trannie and 6 x 6800 uF, 50V per Amp.
Testing to be done next week. When OK I could sell you the two spare boards.
Rick

 

[ostripper]

I can not deny the quality of the original symasym , but it was a tad small for my tastes. For rear channels , I might make a pair but with NJW0281/0302's.

If anyone is inclined to do the toner transfer , the 225W version's
artwork will soon be done. Schema is finalized and the first pair is driving paralleled 8 ohm loads with the greatest of ease. These beasts are running cool off of a 50-0-50 /1500VA trafo w/120k uF.
Same killer HF performance as the original , but better bass and
a lot more headroom.
OS

 

[lgreen]

Re: Board

Hi Igreen,
I am building an AAK inspired board that I designed for use with 2SC2922 2SA1216 O/P pair. One R Core 2x25V 160 VA trannie and 6 x 6800 uF, 50V per Amp.
Testing to be done next week. When OK I could sell you the two spare boards.
Rick

OK sounds good. What is your rough timeframe (weeks/ months?)

I can not deny the quality of the original symasym , but it was a tad small for my tastes. For rear channels , I might make a pair but with NJW0281/0302's.

If anyone is inclined to do the toner transfer , the 225W version's
artwork will soon be done. Schema is finalized and the first pair is driving paralleled 8 ohm loads with the greatest of ease. These beasts are running cool off of a 50-0-50 /1500VA trafo w/120k uF.
Same killer HF performance as the original , but better bass and
a lot more headroom.
OS

Also interested in this but it does not appear to be avail in boards yet and I cannot do toner artwork.

 

[Rick NL]

Will test my amps next week, when ok I can put them in a bubble envelope immediatly, so all within 2 weeks.
Rick