Inverting GC variant

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#3
I think I get most of this(the easy part).
U1a is unity gain buffer no phase shift.
U1b (unity gain) and u2 provide 360deg of shift.
Active volume in the feedback loop of U1b.

Questions
What is the purpose of the loop from o/p to +i/p of u1b with the clipping cct(4148)?
Does C2 form an i/p lowpass filter?
Does the Lin pot give a fake log taper in conjuntion with the feedback res of u1b?

Interesting cct.
Thanks for sharing
Hugh
 
#10
Generally, are able use on U1 all the OPamp compensated to works at unit gain. Nearly all the duals OPamp used in audio have this characteristic, but be necessary see the datasheet case by chance. The circuit is calibrated for a direct coupling among U1a-U1b and U2. If U1 has diverged input corrent , this don't come compensated by the R5-C4 net, then be necessary change the R5 value among 15K min and 47K max. If uses the pot. with other chips it may compensate adding in parallel R4 a capacitor from 10pF to 100pF depending on the circumstances.

Mauro
 
#11
Please excuse my simple question, but I am still new. I see you use two sybols on the schematic for ground, one which is labeled "gnd" and the other "0V". Looking at the schematic it seems the one labeled "0V" are signal ground and that "gnd" is power ground. Please help me understand if they should be trtead differently, or if I should look at them as all terminating at a star ground point.

Thank You,

Russ
 
#13
Wow, you answered my next question before I could even ask it! 🙂 I was going to ask about the diode bridge. Are the diode part numbers critical? I have some 100V 3A fast recovery diodes. Will they be OK?

[edit] I re-read your previous post. It seems you meant the diode bridge at the power supply. I was referring to the two diodes D1 and D2 near C4.
 
#14
The matter of the PSW is a lot of controversial in this forum, and I hope to not creating problems exposing my point of view. In my circuits I uses from a great deal of time a integrated diode bridge , with tides >10A and >100Vac, and 2 El. Cap. from 10.000µF. in the circuit " My amply " I have make a diode bridge DIL from 5A suns without never corresponding any breakdown, but it be worthwhile always abound with the current margin.
Generally, all the variations of PSW that have seen in this forum even is proper to my ideas. I suggestion to use un integrated Diode bridge, much near to the El cap, and inserts always a MKT capacitor from about 100nF among the 2 points of Vac1 and Vac2 ( as from MY ampli ") and weaves the wires of the transformer. The seas to discrete diodes is a generators of high frequency spike, and the nets of capacitor about doesn't always succeed to resolve the problems ( perhaps for this the snubber net are do profits...) I prefer eliminate the problem to the base. Other fundamental thing is that the PSW is more possible near to LM3886, because the connection wire create a lot of problems.

Mauro
 
#18
If it's of interest,I publish the complete "kit" of this circuit, for the beginners that have not the halves to draw the PCB. The circuit is done with traditional components, on 100*160 single layer board and is complete of loudspeakers protection and power supply( misses only the transformer ). This circuit is a synthesis of my vision on: GC, Power supply (for GC) and ground loop. Naturally it may it serve as base of evaluation for other configurations.
To build the circuit it may use the draw (bottom copper, top view) on transparent paper and behaviour the photo-impression ( or furnish the draw to firms specialized in PCB).

Ciao

Mauro
 

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