Transnova Circuit

i ve seen this circuit thanks to our friend....here is a linkhttp://www.audio-circuit.dk/Schematics/USA1310.pdf
ok its a transnova i wonder if a design like that ( looks so simple ) worth making in a smaller scale .....

it seems that this schematic is designed to produce loads about power ...but what about quality ????? and if quality is ok then does it worth to built this for 100 w version ????

also thinking that designs like that originate from hafler so it should sound right ....

i also noticed that looks like djk's favourite design

coments are very welcome

thank you
 

wg_ski

Member
2007-10-10 5:21 pm
Don't let the apparent simplicity fool you. It requires *completely* isolated power supplies for each channel. Which is ok if you were planning for that in the first place. But may not be the least expensive option in onsey twosey quantities.

In my personal opinion, the SQ is limited by the output stage running out of oomph. Make it into a triple (as in the low side of a Crown grounded bridge) and it will be much better. But at only 100 watts, 2 stages of current gain is often enough.
 
thanks andy

for point this link to me ....actually didnt know that i was looking at a qsc amp any way ....

i thought that this was a copy of qsc since called USA 1310....

looking at this schematic made me even more close to construct this since you can almost use the same pcb for versions from 50 to 500w....

on the other hand i like very much the simplicity and the balance of the circuit symetry was always my thing i like square things ....

but still i get no comments of the expected quality .......

also another question most of this big comercial amps come with this network of transitors arround the drivers or the output transistors in the base area for protection IE monitoring current flow of the output and limiting the drive when amplifier is overdriven or shortcircuited ....

why in such an amplifier is not there ??????? not needed and why ?????
 
but still i get no comments of the expected quality .......

I'd ask DJK.

i thought that this was a copy of qsc since called USA 1310....

USA1310s are made by QSC Corporation.

On the margin I'd change the thread's title 'cause discussion is not running about Transnova circuit here.

And Sakis, I know you're from Greece and the english is not your mother language. There is no problem with your english.
But your sentences are disorganised! They haven't got any front or any end. And that many periods...
Then it's really hard to understand your post.
I'm in the same position 'cause since english is not my native language, but hey I proud the forum members, I making an effort to write undersandable sentences.
 
my english .....

you are probably right since its too many things that i want to ask and too many in my mind.

Girlfriend of mine said that i have a 'popcorn brain " too many things jumping .....

english should be less of the problem though..... amplifiers is the interest .

please advice me how to call this post cause now i am confused and i have to detail look about trans nova.....

finally all my above questions remain unanswered .....

1)what makes this amp so powerfull and yet so simple
2) why the absense of all the ccs, vas, and protection circuits
 
Re: my english .....

1)what makes this amp so powerfull and yet so simple
2) why the absense of all the ccs, vas, and protection circuits

1., A good design idea and the proper realization.
2., Weird question (too). There are protection circuits - see schematic! The topology don't need any CCS - then why use CCS?
It's not a conventional design. Do not search for conventional VAS/CCS/protection circuits on the schematic.
 

wg_ski

Member
2007-10-10 5:21 pm
The output stage of the old QSC circuit *is* the VAS. It's common emitter, with the collector output coupled through the power supply. It's an exercise in getting the most output for the least number of stages.

Current limit is buried in the circuit. Short term is limited by limiting the peak output from the 5532 with zener diodes. Long(er) term is limited by how much charge the 100 uF bypass caps that filter the 5532 power supply can hold. The +/-15 is boot strapped by the caps during output excursions above +/-15V. When the caps run dry it limits. The op amp must supply base current to the OPS, and the more you draw the quicker it limits. If the 100 uF caps dry out or fail, the amp's output is limited to +/-15V (ask me how I know this).
 
wg_ski said:
(ask me how I know this).

How do you know this? :D

Kidding aside, you gave a very nicely summarised description of the circuit wg_ski. I must say that the protection circuit looks so simple that it's easy to ignore it completely. Anyway, QSC calls it “Output Averaging Short Circuit Protection” and it is patented technology (although the patent may have expired by now). One can find more details from U.S. Patent 4,321,554 "Time-delayed variable output current limiting means for power amplifiers", Mar. 23 1982. Inventor: Patrick H. Quilter Assignee: QSC Audio Products
 

wg_ski

Member
2007-10-10 5:21 pm
Re: thanks

sakis said:
for the reply ....

could you be kind enough tell us more about the sound ....and/or problems ????



The USA1310 is a PA amplifier. It's not particularly bad, or particularly good in terms of SQ. There were compromises in the design to make it simple and cheap. It was however, reliable - with twice the output transistor complement of its modern cousins. That was because the old MJ15024's beta drooped at high currents and two stages of current gain is barely adequate to drive 4 ohms bridged. Heat sinking was marginal for that kind of abuse and I used to shut them down occasionally. But it never blew one out, either. The only problem I had was the 100 uf caps in the op-amp power supply getting leaky from all the heat and then the amp would quit working right, but never catastrophically.

The same general design could be made to sound a lot better - a better op-amp, another current gain stage, and bigger supply reservoir caps would help.
 
True ....

and very correct BUT!!! i wasnt talking about this protection .....i belive that a methode as used in the out put is the best ....

i was actually refering to the overall design .....like for example any amplifier you have in this forum except very simple amplifiers like rods p3a ...all of them have a CCS on the LTP stage .....

( to my understanding keeping the ltp curent flow stable is a form of protection ...in a way .... ( except sound performance )otherwise if you just use a simple resistor then with the smalest change presuming your rails are quiet high or you get any other stability issue temperature depeding or so ..... then you get a big baaaam)

wg-ski's explanation about all this was a very good info so far but since my theory is not enough i need to study more about this circuit to understand better how is working ....

still i wait to listen about performance and sound chracteristics ..... i thing i am going to make a search about this generally .....


for sure there must be a qsc users forum or something

thanks guys

in some time ( no longer than a month i will construct a protoype just to listen to) the plan is to use the same topology ...exactly .... but use lower rails and more simple outputs something like 2sd1894 and 2sb1254...since i have plenty of them and they are panasonic made

of course i dont expect 1KW per chanel but i will be very happy for 200-250W @8R with 6 sets of outs per amp ....

lets see !!!!
 
It is possible to make a very simple version of this topology using a single power supply and a pair of lateral MOSFETs, directly driven by an OP-amp capable of 300 ohm drive (like the venerable NE5534, it is even possible to use the dual NE5532 with a bit of attention to the power supply). The neat thing about lateral MOSFETs is that their source terminals are on the package tab, so they can be bolted directly to a heatsink, and the heatsink tied to ground. This is actually the power ground of the circuit, which also makes wiring easyer.
 
Here it is, but remember it's just a circuit idea and not tested, so some things are not shown, like gate stopper resistors for the MOSFETs, any protections, the compensation caps have no values and the power supply is shown as a battery.
In the real transnova the output and filter caps are one and the same, to be honest I'd rather have an extra smoothing cap after the rectifier (across the full power supply) and connect that to the schematic as shown via a fuse and a small value resistor in series, just to lessen the burden on the OP-amp front end.
A dual OPamp can be used for stereo if the extra output channel is connected to the power supply for theOPamp as shown in the picture. The second channel power supply of course has to be fully independent and floating.
 

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ilimzn Transnova circuit idea

ilimzn;

I like your idea - I have been trying to figure out how to design a discrete 25-50W guitar amplifier using a QSC style circuit (power transistors bolted directly to chassis) by using a simple Lin topology circuit with the outputs configured as Sziklai (CFP). I am worried about the stability, especially near clipping, and originally tried to use base-emitter protection diodes (like Quad 303) to provide temporary short-circuit protection. Is it possible to use the IRF530/630 and your suggested P-channel equivalents to develop a QSC style design ? Or would I be better off sticking to my original design using MJ2955/2N3055 ?
 
ilimzn said:
Here it is, but remember it's just a circuit idea and not tested, so some things are not shown, like gate stopper resistors for the MOSFETs, any protections, the compensation caps have no values and the power supply is shown as a battery.
In the real transnova the output and filter caps are one and the same, to be honest I'd rather have an extra smoothing cap after the rectifier (across the full power supply) and connect that to the schematic as shown via a fuse and a small value resistor in series, just to lessen the burden on the OP-amp front end.
A dual OPamp can be used for stereo if the extra output channel is connected to the power supply for theOPamp as shown in the picture. The second channel power supply of course has to be fully independent and floating.
Will that output stage run as a follower (sans op-amp) ?
 

rtarbell

Member
2005-09-16 2:39 am
I certainly don't mean to thread jack, but while we're on the topic of the Transnova concept:

How would you calculate the values for the triangle feedback network?

Why is this "triangle" topology needed? What if the feedback was taken only from the output (strictly global feedback)?
 
Re: ilimzn Transnova circuit idea

balaboo said:
ilimzn;
I like your idea... Is it possible to use the IRF530/630 and your suggested P-channel equivalents to develop a QSC style design?

You could use the same topology as above, with, say, IRF640/IRF9540, but you need to replace the simple trimmer with a Vgs multiplier, of course, you can't bolt the MOSFETs directly to the chasis because standard VMOS and HEXFETs have their drain terminal on the case. Alternatively, you need a CFP configuration. If you go this way, stability issues are simpler with BJTs as outputs.

hitsware said:
Will that output stage run as a follower (sans op-amp)?

No, the way the concept works is that it makes the stage wotk in common source, i.e. it has gain, this is why it's sources are grounded and the power supply is floating.

rtarbell said:
I certainly don't mean to thread jack, but while we're on the topic of the Transnova concept:
How would you calculate the values for the triangle feedback network?
Why is this "triangle" topology needed? What if the feedback was taken only from the output (strictly global feedback)?

I am assuming that you are asking about the low ohm divider in parallel with the load, to which the 33k feedback resistor is connected (the whole thing is global feedback). This is because you want reasonably high input impedance, in this case 33k. In order to get the required gain, a straight feedback from the output would be about 30x larger, so about 1M ohm. If you do this, you have two problems:
1) Using a bipolar input OPamp would cause a huge offset due to the input bias current making a voltage drop over the 1 meg feedback resistor. In order to get it somewhat balanced, you would need the same resistor on the - input of the OPamp, plus balance trim - or a FET input OPamp.
2) The above is quite irelevant once you consider the input and stray capacitances of the wiring around the OPamp inputs. What you get is a huge peak in the transfer curve at high frequency, because the feedback is actually attenuated at high freqecies by the RC combo made out of the 1 meg feedback resistor and the input capacitance of the OPamp.
So, on both accounts, you need a much lower impedance for the feedback network. In order to do this, you pre-divide the output by a low impedance divider, by your intended amplification factor, and then feed that into a regular higher impedance (33k in this case) 1:1 feedback network.

The extra trick here is that the low ohm divider is actually composed of 4 resistors. The two 22k resistors that come from the ends of the power supply, are there to insure that the single power supply is properly centered around the ground point. This scheme will work for many OPamps, but it has the drawback that it is sensitive to power supply ripple. An alternative is to place balancing resistors across the 4700uF caps, but still, excess offset can result because the OPamp offset is amplified by the total gain. All of this is needed because the output is actually AC coupled, so without it, there is nothing to set the DC level of the power supply with respect to GND (remember that the power supply is floating).