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Old 23rd May 2005, 04:03 PM   #61
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Default Excellent!

Thank you very much Mauro!

ciao
Russ
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Old 24th May 2005, 02:08 AM   #62
Mark Kravchenko --- www.kravchenko-audio.com
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Default Thankyou Mauro!

LÓ Ŕ la gioia pi¨ grande che ingiving che nel recieving

Hope that the translation is not to bad!

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Old 31st May 2005, 10:57 PM   #63
Floric is offline Floric  Europe
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Hi Mauro,

thank you very much for your schematics.

I only have some questions cencerning the setup you recommend for your approach:

Are you using your approach with a preamp? If yes which preamp? Is it advisable to use your approach with a potentiometer as a integrated amplifier?

Thanks

Floric
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Old 1st June 2005, 02:29 PM   #64
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I use this amplifier with launch preamplifiers, because me understanded of often change my setup. Sincerely, am appraising the idea to build from it a High- end and per hour from it uses a provisional based on LM318 modified ( low open loop gain & large BW ).
The imput impedance of this amplifier is 100Kohm and the gain is 30 dB, for which not there are particular problems of interface with a log pot.. Suggestion to use a value not superior to 22Kohm, to avoid that the serious resistance creates an excessive high frequency cut off.

Ciao

Mauro
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Old 8th June 2005, 01:42 PM   #65
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Any technical precise statements:

In the circuit I have not specified the method of protection for the
breakdowns. How to have noticed, am not add Fuse there on +-35V. To protect from possible breakdowns, have anticipateded to use a delayed fuse of the same value of the current max. of the transformer ( es. 300VA at230V=1.3A or 300VA at 120V = 2.5A )

A detail that I have not explained is that have chosen deliberately to not using the fuses on the card, because they increase the Zout of the PSU and overall much times are source of not linearity in the peak current, on account of the contacts with the socket and of the termal cicles (D. Self have investigate this problem on power output, but it's teorical analog on PSU).
If is wants insert the fuses are able insert to mountain of the diode bridge or of the electrolytic capacitors ( holding account of their current charge peak ).
In any case LM3886 and the bridge that I have make a will am practically indestructible, and the loudspeakers are well protected.

LM318N has to be of National Semicnoductor production. Other manufactures have not was characteristic( believe for tolerances of testing or little differences in the net of compensation ) and have not same audio quality. If you wants fun with the theories of OPamp linearizing, you are able put a resistance from 470Kohm among the pin 6 and 8. This modifies reduce the opened loop gain to about 65dB, and widens the BW to over 20Khz. This modifies me like much in my preamplifier. To try...

Ciao

Mauro
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Old 8th June 2005, 02:08 PM   #66
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Mauro, have you got any confirmation that your design has any possibility to work in real life? If I'm not mistaken a LM3886 must have gain of at least 10 to work. I admit though that I haven't tested where the actual limit is. Feedback-wise I think your design looks a bit dangerous.
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Old 8th June 2005, 02:40 PM   #67
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Quote:
Originally posted by peranders
Mauro, have you got any confirmation that your design has any possibility to work in real life? If I'm not mistaken a LM3886 must have gain of at least 10 to work. I admit though that I haven't tested where the actual limit is. Feedback-wise I think your design looks a bit dangerous.
I think post #14 answers your question.
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Old 8th June 2005, 03:24 PM   #68
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Have not well understanded to do it reports you. From your allusion to the LM3886, believe that you has of the doubts on the operation of the varying the latests that have proposeded.
I don't know as I am accustomed to working other participants of this forum, but of some I make a will always in the every reality circuit that develop. Not only, but I propose the layout PCB that I have used to avoid problems in this sense (oscillations,etc...).
Naturally the configuration to bridge of LM3886 makes it intrinsec more unstable, but the only limit of this topology (in my app.) is a clipping more "nervous". Defines the "dangerous" thing for this seem me exaggerator.
Is not the first that is set the problem of "establishes" if this circuit works or no. This circuit is not a variation of datasheet, is not a GC or a his variation, is not a casual nest of 2 OPamp. What likes or no, it is a my personal interpretation about how improving the "musical" performances of an amplifier, without using expensive or time-wasting technology. All have the legal right to appraise the validity of my proposal, and to decide if try it or no. Different is to questions my technical ability ( I with the electronic planning work, not fun).

Ciao

Mauro
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Old 29th June 2005, 09:58 AM   #69
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I have seen that some members is building this circuit. In this post I reassume the My_REf evolution, and the possible variations.
In this circuit I have sought-aftered nearly exclusively any "sonic" characteristics that like it. In particular, I am not worried me to improve the behaviour to the clipping and the "extreme" stabilities ( es: pure capacitive load ), because my is an applicatory example, not a commercial circuit to all the effects.
Naturally this circuit is perfectly working in all the his variations, and I have make a will to found all the conditions. Base on the tastes of every DIY, is possible to modify the encircled for changes the "sonic" imprint.
Every change described in this post does reference to the final scheme of My_ref understanded in the kit complete of PCB Layout.

- Basic version = My_ref BOM; "Old style" sound. Good for ZLoad>=8ohm or "fizzy" speakers.

- Variant 1 = replace C10(100p) & C25(100p) to 47pF(MKT or C0G); like basic version but for load< 8ohm

- Variant 2 = add net C30+R37 & C31+R38, add C32 & C33, change C10 &C25 value. see schematic... ; improved stability, reduce load dependent, ecc... This is a best (actual) tech/sound compromise. try it you...

- Variant 3 = Bridge value = old My_amp (first schematic). It is sufficient replace R5-6-8-9 & R28-28-31-32 to 10K 0.1% and R3-26 to 0.01 2W. It is a "ibrid" solutions among variant 1 and variant 2.

- for all variant: Add R39(470K) & R40(470k) for improved input stage linearity (OL BW=20Khz & OL gain=65dB). Not in all the conditions it improves the final sound, try it you...

My actualy circuit on evaluations is variant 2, but I elaborate ( and make a will ) a variation per week....

Ciao

Mauro
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Old 29th June 2005, 12:16 PM   #70
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Thanks Mauro!

A few questions:

1) I notice that in this new schematic you have a 470K resistor(R39/R40) from U1 out(pin 6) to U1 comp -2(pin 8) Is this resistor critical? Can it be ommited? Since there are no pads for R39/R40 on the rev. 1 boards, I suppose one could simply solder a small (1/8 - 1/4W) resistor directly to the op amp, or on the bottom of the board.

2) I think I found an error on the silk screen/serigraphy on your first revision. R9 does not match the schematic, and R50 is missing altogether. I am referring to REV E. (17/12/2003). Is there a more up to date schmatic? I just want to be sure the schematic I have matches the boards I just had made.

3) Also, where would one put C30/31 and R37/38 on the Rev. 1 boards.

Thanks,
Russ
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