Hi Mike,
Hmmmm, watching the watchers!
Cool. Where do you get the time one wonders?
As for the wall speaker application, single amp chassis with a local volume control. One supply for both channels (standard stereo application). We have wall speakers in the kitchen and master bath. See what happens when the builder lets you in? There is a local stereo set in each location with free standing speakers and volume control is an issue. I can also roll off the bass and maintain full damping on the speaker. Spoiled rotten my wife is!
Yes, fets have a low drain source voltage. I still think I'll create a "flying mess" to lower the collector / drain voltage. This should make the diff pair more linear. We shall see if this helps or hinders. It may not make any audible difference at all. Either way, your amp is a great test bed for this kind of experiment. For caps, I'm trying to find poly props for most of them. I don't like ceramics except across DC supplies.
I do all tests by hand now. I also ran into ground loop issues with my test setup using a sound card. I'll have to ask Pavel exactly what he uses.
-Chris
Hmmmm, watching the watchers!
Cool. Where do you get the time one wonders? As for the wall speaker application, single amp chassis with a local volume control. One supply for both channels (standard stereo application). We have wall speakers in the kitchen and master bath. See what happens when the builder lets you in? There is a local stereo set in each location with free standing speakers and volume control is an issue. I can also roll off the bass and maintain full damping on the speaker. Spoiled rotten my wife is!
Yes, fets have a low drain source voltage. I still think I'll create a "flying mess" to lower the collector / drain voltage. This should make the diff pair more linear. We shall see if this helps or hinders. It may not make any audible difference at all. Either way, your amp is a great test bed for this kind of experiment. For caps, I'm trying to find poly props for most of them. I don't like ceramics except across DC supplies.
I do all tests by hand now. I also ran into ground loop issues with my test setup using a sound card. I'll have to ask Pavel exactly what he uses.
-Chris
MikeB:
I uses a M-Audio 192 balanced sound card without any problem. I just used the + and ground and ignored the -. Combined with a SCSI Plexor 12Plex CDROM (Tosigba 4101 under the cover), using reclocking of the sound card then feed it digitally to a California Audio Gamma DAC, provided me a very good CD source. I have tried a few of other CDROMs which all gave inferior results. The DAC and audio part of the sound card was just not a match of the external DAC. I did have to swap out some capacitors and replace the OPAMP with a OPA627 running in class A for the Gamma DAC to make it sound good though. Maybe if I do the same mods with the M-Audio sound card, it may sound OK. Unfortunately the modern card are so miniturized with SMDs, it is very hard to make any mod.
BTW, after my last post, I found and read the NP's post on rectifiers and he seems to like Schottky diodes better the regular bridge. I have ordered some Schottkys to be used in my SYMASYM, just in case it make any difference.
I uses a M-Audio 192 balanced sound card without any problem. I just used the + and ground and ignored the -. Combined with a SCSI Plexor 12Plex CDROM (Tosigba 4101 under the cover), using reclocking of the sound card then feed it digitally to a California Audio Gamma DAC, provided me a very good CD source. I have tried a few of other CDROMs which all gave inferior results. The DAC and audio part of the sound card was just not a match of the external DAC. I did have to swap out some capacitors and replace the OPAMP with a OPA627 running in class A for the Gamma DAC to make it sound good though. Maybe if I do the same mods with the M-Audio sound card, it may sound OK. Unfortunately the modern card are so miniturized with SMDs, it is very hard to make any mod.
BTW, after my last post, I found and read the NP's post on rectifiers and he seems to like Schottky diodes better the regular bridge. I have ordered some Schottkys to be used in my SYMASYM, just in case it make any difference.
PROTOS FINISH
HI MIKE,
Thank you for your design and the time that you give in this thread .
I' spend a long time to read it and i'have not finish yet !!
I' finish this week the proto of symasym 5.3 according your web site .
It works great !
Offset 2 mv !
As i' want to use it in a active system (5 sections) i' will built 10 pcs.
I would like to implement some" gadjet" or modification.
First one control polarisation by external switch and relay .( low level when not listeniing seriously and more high when listening 100% ) for saving power!
Second one: can I' use inverter input for inputing the modulation ? Normaly it's better for the linearity.Is it possible ?
Witch modification i' have to do?
The amplifier power supply is a tree phases ( star / delta coupling ) 24v transformer and 2*47000 µf by rail.
Now i will order some better component to finish this project capacitors....output devices ?
Thanks ...
JC BALTHAZARD
HI MIKE,
Thank you for your design and the time that you give in this thread .
I' spend a long time to read it and i'have not finish yet !!
I' finish this week the proto of symasym 5.3 according your web site .
It works great !
Offset 2 mv !
As i' want to use it in a active system (5 sections) i' will built 10 pcs.
I would like to implement some" gadjet" or modification.
First one control polarisation by external switch and relay .( low level when not listeniing seriously and more high when listening 100% ) for saving power!
Second one: can I' use inverter input for inputing the modulation ? Normaly it's better for the linearity.Is it possible ?
Witch modification i' have to do?
The amplifier power supply is a tree phases ( star / delta coupling ) 24v transformer and 2*47000 µf by rail.
Now i will order some better component to finish this project capacitors....output devices ?
Thanks ...
JC BALTHAZARD
Attachments
Hi balthazard !
Well done !
On your photo i miss the biasing pot ? Maybe an older photo...
About your modifications,i am not sure if i understood them. Do you want to apply an external switch lowering the supply voltage ? Normally i would say that symasym is cold enough to not need it, but with ten of them the idle dissipation becomes evident. I see no problems in doing so, symasym was designed to work within a wide range of supply voltages. Or do you want to change the biasing ?
About using the -input for feeding the signal, i can't really recommend it. Symasym was not designed to be used like that and will need a reworked feedback network. I doubt you will benefit from that in this case, symasym has already a reasonably good behaviour in the input stage.
A better idea might be adding a unitygain buffer with low output impedance to feed all 5 amps at once ?
Mike
Well done !
On your photo i miss the biasing pot ? Maybe an older photo...
About your modifications,i am not sure if i understood them. Do you want to apply an external switch lowering the supply voltage ? Normally i would say that symasym is cold enough to not need it, but with ten of them the idle dissipation becomes evident. I see no problems in doing so, symasym was designed to work within a wide range of supply voltages. Or do you want to change the biasing ?
About using the -input for feeding the signal, i can't really recommend it. Symasym was not designed to be used like that and will need a reworked feedback network. I doubt you will benefit from that in this case, symasym has already a reasonably good behaviour in the input stage.
A better idea might be adding a unitygain buffer with low output impedance to feed all 5 amps at once ?
Mike
Hi MIKE,
Thanks to reply.
Sorry do not be so clear !
I' put a fixed resistor for the bias .
It is this resistor that i' want to switch the value for changing the bias via relay.( 20ma - 500ma )
I' keep power supply at 36 V by rail.
I' need 10 pcs for active systeme (Crossover is 2 *dcx 2496)
After dcx output there is 10 Koms stepper attenuator.
My idee (i'saw it in instrumental amplifier like B&K ,,Tecktronix they use inverter input) is to use also inverter input .
I' will make some test on big power speaker.
Here under the transformers for 5 sets.
JC BALTHAZARD
Thanks to reply.
Sorry do not be so clear !
I' put a fixed resistor for the bias .
It is this resistor that i' want to switch the value for changing the bias via relay.( 20ma - 500ma )
I' keep power supply at 36 V by rail.
I' need 10 pcs for active systeme (Crossover is 2 *dcx 2496)
After dcx output there is 10 Koms stepper attenuator.
My idee (i'saw it in instrumental amplifier like B&K ,,Tecktronix they use inverter input) is to use also inverter input .
I' will make some test on big power speaker.
Here under the transformers for 5 sets.
JC BALTHAZARD
Attachments
Hi balthazard, i understand ! Will the relay be directly on the pcb using only short cables ?
20ma might be very low bias, this will be easily audible, you shouldn't go far below 50ma.
About using the inverted input, i am not sure if it is a good idea. In theory it should not really improve linearity for symasym, because of the high gain the current swing in input diffamp is already very low.
But, i have not really experience with this kind of input.
Mike
20ma might be very low bias, this will be easily audible, you shouldn't go far below 50ma.
About using the inverted input, i am not sure if it is a good idea. In theory it should not really improve linearity for symasym, because of the high gain the current swing in input diffamp is already very low.
But, i have not really experience with this kind of input.
Mike
Hi Mike,
I am looking forward to finishing them. However, I will take my time and get the parts I know work well. I want to hear these stock, the best they can be before playing with them.
I am not ordering really expensive parts, just parts from good "families" . I don't want to see any ceramics on these boards at all. I am looking for non-inductive emitter resistors (plate style) as well. 10 years ago this would have been very easy, not now until I re-source my fav. parts. It doesn't help that I have to rebuild my parts supplies after selling my shop either. 
-Chris
I am looking forward to finishing them. However, I will take my time and get the parts I know work well. I want to hear these stock, the best they can be before playing with them.
I am not ordering really expensive parts, just parts from good "families"
. I don't want to see any ceramics on these boards at all. I am looking for non-inductive emitter resistors (plate style) as well. 10 years ago this would have been very easy, not now until I re-source my fav. parts. It doesn't help that I have to rebuild my parts supplies after selling my shop either. -Chris
Hi Chris, no need for a hurry, i was just curious... Maybe you should have sold your shop with the lifetime right to get everything you need ?
You're right about the ceramics, replacing mine with a mica had an immediate improvement on sound...
Sheldon, wow, that's gonna be some PSU !
10.000uF each cap or even more ?
What are these brown battery-like things in the top corners ?
"One of two", are you building two stereos ?
Mike
You're right about the ceramics, replacing mine with a mica had an immediate improvement on sound...
Sheldon, wow, that's gonna be some PSU !
10.000uF each cap or even more ?What are these brown battery-like things in the top corners ?
"One of two", are you building two stereos ?
Mike
Hey Mike,
I was just happy to get out. Consumer service was being to tank big time when that happened. I miss the industry, but the industry is dead now.
Instead of ceramic, I was thinking polyprop or styrene. That's what I am looking for. I have to get used to what is available now.
-Chris
I was just happy to get out. Consumer service was being to tank big time when that happened. I miss the industry, but the industry is dead now.
Instead of ceramic, I was thinking polyprop or styrene. That's what I am looking for. I have to get used to what is available now.
-Chris