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One of the Top Solid-State CFA amp design
One of the Top Solid-State CFA amp design
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Old 20th June 2018, 09:57 AM   #721
mjona is offline mjona  New Zealand
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Quote:
Originally Posted by AndriyOL View Post
Not exactly. If you mean I mentioned some 1k resistors from post 709, this is stand alone testing of frontend psu without amp with help of 1k resistors. However R10, R11 on the pcb are the same. Zeners on the amp drop voltages, for example, from initial 49V input at 5V zeners to 44 Volts, which appears to be at bases of Q16, Q17, and to 15 Volts at 15V zeners. All these can be checked in the sim.
Light bulb has nothing to do with the sag (which is also present with frontend psu connected directly to mains) which is constant not only in charge time.
R10, R11 values are just right. If you check the sim I can raise them to 1.1k only to maintain 15V at D1, D2. With 2.2K there won't be 15V potential, only just 7-10V.
As I mentioned in previous post, more likely psu sag appears from not proper input voltage setting to shunt psu which my frontend is. Output voltage of shunt psu cannot be the same as it's input voltage.
Judging by the size of the front end toroid this should be able to supply your needs even with shunt load resistors. What are the specifications for this - winding voltages and the regulation%.

If the winding voltage is low and regulation is not tight you might achieve above the voltage nominal figure with no load and have that reduced when the load is applied.

If there is a problem with rating or regulation of your transformer you should connect the primary to the mains to avoid any compromise in that respect.

There is a further need to identify the load where the current is being drawn to - I mentioned some resistor numbers where to measure voltage drops and calculate currents in my last post.

How hard is that to do.
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Old 20th June 2018, 01:10 PM   #722
R Dijk is offline R Dijk  Norway
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Originally Posted by dadod View Post
Say that to Lazy Cat. Simple Symetrical Amplifier
Sorry to see that the ballanced potential is not beeing used.
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Old 20th June 2018, 07:11 PM   #723
AndriyOL is offline AndriyOL  Ukraine
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Originally Posted by R Dijk View Post
Shunt psu, now you may have an high output resistance....
In witch post is your correct circuit with correct values ?
This Lazy cat circ do have the same issues whatever input trannies you are using. Yes i understand its not yours its your friends circ. The same you tried to fault trace for ore than a year without results?

Sorry to see somone using this topology. the input circuit is a bad topology.
In post One of the Top Solid-State CFA amp design there is psu schematic. I used 50V zeners instead.
How these issues influence or appear in operation of the amp, what are the negative effects? Yes, before I tried flawed balanced input topology.

Quote:
Originally Posted by mjona View Post
Judging by the size of the front end toroid this should be able to supply your needs even with shunt load resistors. What are the specifications for this - winding voltages and the regulation%.
How hard is that to do.
The toroid has 37VAC secondary without load, maybe 30-40W, I was usung it for two PSUs for both channels with 3mA bias current without issues. I don't know what % regulation it has.
You didn't asked me to measure. The Voltage drop at R10, R11 is 17.5-18V, 17.15-17.6V and keep rising a bit. At R14, R15 is 173.2mV for both. Front end voltage now is 37.5V, rectified voltage is 46V (psu input voltage after rectification). When I connect low wattage bulb 40W, Psu voltage at out is 36V and 36V rectified voltage. In this case the bulb is limiting the current.
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Last edited by AndriyOL; 20th June 2018 at 07:40 PM.
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Old 20th June 2018, 07:47 PM   #724
AndriyOL is offline AndriyOL  Ukraine
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With refference to gnd the measurements are: R11 - 15V\32.9V, R10 - 14.95V\32.6V, R15 - 37.80V\38V, R14 - 37.44V\37.60V
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Old 20th June 2018, 08:01 PM   #725
R Dijk is offline R Dijk  Norway
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Originally Posted by AndriyOL View Post
In post One of the Top Solid-State CFA amp design there is psu schematic. I used 50V zeners instead.
How these issues influence or appear in operation of the amp, what are the negative effects? Yes, before I tried flawed balanced input topology.
tnx. shunt front end psu.

Works like a capasitor bank then a current sorce then a shunt.

I dont know hov mutch power the shunt is capable of (Q6 and 7).

To increase current from current sorce reduse R3 and R4

Typical 1.8V across LED , 0.6V base emitter T1 and T2.
Max current out is then (1.8V-0.6V) / R3 .

To find value for 100mA it becoms 1.2V /0.1 = 12 Ohm
for 50ma it is 1.2/0.05 =24 Ohm.

Without load the shunt transistor Q6 and Q7 shoul bee able to take (Zener voltage + 1.8V ) multiplyed by current sorce.
(50Volt zener+1.8v) multiply by current sorce with 12 Ohm (100mA)
51.8 * 0.1 is 5.18 Watt.

Front end needs approxymately 40Ma steady state + and minus voltage amp range wich is approxymately 10mA-20 mA dependent on input bias.
That means your powersupply should bee able to deliver minimum 60 mA.

Setting it to deliver 70 mA should give a bit margin.
resistor R3 and R4 to approx 1.2/0.07 = near 17 Ohm
Bleed transistor max power 51.5*0.07 =

I would give that a god start. This is just using Ohms law if i remember right after to long time at school.

Too doo this make shore your transformer has windings to do so. If not use volage doubling for front end.

Last edited by R Dijk; 20th June 2018 at 08:14 PM. Reason: info
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Old 20th June 2018, 09:43 PM   #726
AndriyOL is offline AndriyOL  Ukraine
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Originally Posted by R Dijk View Post
I dont know hov mutch power the shunt is capable of (Q6 and 7).
To increase current from current sorce reduse R3 and R4
Too doo this make shore your transformer has windings to do so. If not use volage doubling for front end.
Q6, Q7 are MJE15035\34, with 4A Collector Current Continuous, 50W Pd.
I'll use 12-17 Ohm for R3, R4, whatever closer value I find to 70mA. There are prety big heatsinks, which are totaly cold now with current stock values. They only become little warm when PSU On witout load and the LEDs aren't working without load. This is frontend PSU from Roender's FC100 amp.
Perhaps I need to increase secondary windings to 47VAC without load, now it's 37VAC to have 50V out. Maybe it will be enough just only 45V for front end if the main amp PSU will be 40V, for example?
Thanks.
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Last edited by AndriyOL; 20th June 2018 at 09:54 PM.
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Old 20th June 2018, 09:55 PM   #727
mjona is offline mjona  New Zealand
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Originally Posted by AndriyOL View Post
With refference to gnd the measurements are: R11 - 15V\32.9V, R10 - 14.95V\32.6V, R15 - 37.80V\38V, R14 - 37.44V\37.60V
You have roughly 18 ma consumption through the zeners and virtually nil through R14 and R15 which supply the output section.

The current from the output feeds the rest of front end via R19 and R20 - what are the voltage drops across these.
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Old 20th June 2018, 10:25 PM   #728
AndriyOL is offline AndriyOL  Ukraine
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Originally Posted by mjona View Post
You have roughly 18 ma consumption through the zeners and virtually nil through R14 and R15 which supply the output section.

The current from the output feeds the rest of front end via R19 and R20 - what are the voltage drops across these.
R14, R15 set the VAS bias should be around 15-25mA.
R19, R20 has 0.600V, 0.627V across them.
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Old 20th June 2018, 11:33 PM   #729
mjona is offline mjona  New Zealand
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Originally Posted by AndriyOL View Post
R14, R15 set the VAS bias should be around 15-25mA.
R19, R20 has 0.600V, 0.627V across them.
Divided by 1500 each that is about 400uA which is about right under static conditions.

I think you made mention of owning a variac which is what a service man would use for setting up an amplifier test? If so why would you not be using that instead of a light globe in the mains connection?
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Old 21st June 2018, 05:54 AM   #730
AndriyOL is offline AndriyOL  Ukraine
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Because light bulb is more informative, can limit the current if something goes wrong.
Regarding voltage sag of frontend psu, as R Dijk stated and according to sim the IPS of the amp requires at least 50-60mA with 4mA bias. My psu with current setting capable of 36mA only.
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