what could be the reasons for High freq roll off after 14khz

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Jump to Latest
R

rhythmsandy

Member
Joined 2012
can I know why hiraga super class A 30w doesnt have this RL.

http://diyaudioprojects.com/Solid/J...-Hiraga-Super-Class-A-Amplifier-Schematic.png

Can I know how its not oscillating.

Another question is that there are no Emitter resistors which is still good for higher fidelity as there are no passive components in the path.

can we use such resistor less pushpull config? I do understand the importance of it so how come the hirga amp doesnt have it...

I know a friend of mine built hiraga and also F5 says hiraga is way too ahead of F5 even though Nelsons designs are very famous. What could be the reasons...

I have even seen Nelsons schematics no amp has got a RL they might have RC shunted but not RL...

Im a bit confused..

ill get the measurements soon..
 
JMFahey

JMFahey

Member
Joined 2009
It's impossible that the few uHy typical "stability inductor", normally consisting of less than 20 turns of enamelled wire around a 1W resistor, cut output above mere 14 KHz.
I think you used a "bought" inductor and misread or mis ordered its value.
Go for the simple DIY solution and remeasure.
Or your problem lies somewhere else.
 
R

rhythmsandy

Member
Joined 2012
absolutely there is something wrong...
I have simulated the circuit with TinaTI with all the same values used in the schematic and im getting a very bad response
Imageshack - respu.jpg
please have a look..

I think somebody said in the previous posts that the prob with NFB it seems right...

what I need to do is to rework on the NFB can anybody recommend me the values?
 
Last edited:
R

rhythmsandy

Member
Joined 2012
yeah i do agree but I see that the response is good enough is there anything wrong why it could be behaving like that?
just that one capacitor is changing everything...
what could be the problem.... I couldnt get it since the gain setting is made properly so even the input rc constant is not a problem as 2.2uf and 2.2k is still decent

I could see only that one value... but the strange thing is that in the RTA it was showing rolloff after 14Khz and in the amp sim its showing before that... howz that possible?
 
Ian Finch

Ian Finch

Member
Joined 2010
Paid Member
If your Zobel network and the output coil network both cause such heavy HF attenuation of the amplifier response, the error is in the amplifier circuit, preamp and/or simulation. We have been over this several time already and if you won't look at other designs to realize that virtually all class AB amps use these standard values, give or take, then you will get nowhere just trying crazy different parts like this in all the wrong places.

The amplifier shown, is designed and specified for a flat response within its bandwidth. If it doesn't do that with standard components as supplied, return it for a refund. If you actually want boosted treble response, the place to do that is in the preamplifier (assuming you are using an appropriate preamplifier and not feeding something poorly matched), never by surgery on the amplifier.

As advised earlier, you play with fire if you reduce the effectiveness of the zobel network by raising the pole into the RF bands. The result will be dangerous instability, as could well be the result of cutting the output coil back to a pointless value that will be less significant than even the speaker cable. It may be fine with trivial loads and short leads, but if you don't mind smoke and fireworks, try it again at full power in a real venue.

This is just being silly, whatever the apparent improvements. Why not tell us what sound card is being used or is specified for an on-board type. RTA is only as good as the card and wiring.
 
Last edited:
R

rhythmsandy

Member
Joined 2012
yeah do agree we need a proper test equip but im looking from the simulation point of view that if something is wrong at design phase we can correct it but lets get the test equp this time...

there is one more thing i wanted to tell that for the 1st order crossover for the tweeter ive used .47uf caps x 28 to get the total cap of 13.4uf for the tweeter..

i suspect that the freq rolloff is happening with the inductance caused by these huge number of capacitors at high frequencies but they are still in parallel would that be causing the rolloff? lets see..
 
JMFahey

JMFahey

Member
Joined 2009
Something that is "brickwall" bandwidth limited at, say, 22 or 24 KHz, can't be trusted above half that, simply because the system runs out of samples to depict *any* waveform.
So that's not so unexpected.
What *is* strange is that even in the pure, ideal world of Simulation, response falls off in such a way, without nothing warranting it.
And the resonant peak is even worse.
Searching for posible culprits: where/how did you get the equivalent model of your driving IC?
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Top Bottom