I recently got a Rane 6 channel amp. Testing it after unboxing, it seemed a little lifeless on the high end. So I did a quick FR measure (each channel measures identical) and it's down 3.5db at 20kHz, starting at about 6k. Spec is 20-20k with no db part mentioned. I verified my test setup using another SS amp which goes right out to 20k flat, then falls off.
I simplified the schematic to make it less of an eye candy. The input op-amp has a bandwidth limiting cap, but its spec says that rolls off starting at 50kHz...
It's understandable why they designed it that way, as it has to drive whatever a system installer can throw on its output. I promise to be more gentle with loading. Thank-you for any insight toward modification to change this aspect!
I simplified the schematic to make it less of an eye candy. The input op-amp has a bandwidth limiting cap, but its spec says that rolls off starting at 50kHz...
It's understandable why they designed it that way, as it has to drive whatever a system installer can throw on its output. I promise to be more gentle with loading. Thank-you for any insight toward modification to change this aspect!
Hi. R13 R14 C31 and part of volume potentiometers resistance ,depending on position , forms input filter . Try to verify frequency response in simulation ,to ensure that only these components are related. So for calculation we can use 15k (if volume pot in middle position - worst case) and 270pf ,36k as load. But those components also relates to what amplifier is capable for, pulse response especially, so need to ensure proper waveform if change values. If you want flat response , input filter should be about 1k and 1000 pf roughly , you have here 15k , so capacitor should be reduced to 68pf maybe.
No. C11 is 0.1uF and it is in parallel with 22uF, which dominates easily, and which are both shunting away NFB, not signal. I see now that these two caps and R24 are a DC servo. They only affect the LF response, not HF.
Sure, I did not really spend the time required to analyse this circuit....They are actually ensuring there's very little gain at close to DC frequencies.
I wouldn't touch anything... except C31... Maybe L3... definitely not C16/17 and C10. If playing with L3, I'd check for oscillations... depending on the load used at the output, and speaker cable specifications.
I wouldn't touch anything... except C31... Maybe L3... definitely not C16/17 and C10. If playing with L3, I'd check for oscillations... depending on the load used at the output, and speaker cable specifications.
Yes, the C10 equivalent is connected right across R24 in the older MA6B design. Someone at Rane must've gone "circuit bending" this round.
C16/C17 - I've just seen equivalents in Planet10 dave's LXI amplifier schematic; I bet it goes rail flat to 20k no problem. C14's role is why I'm asking for help to understand what to do! I certainly cant tell what it does by looking at the circuit arrangement.
I did measure with an 8 Ohm resistive load. Since I have two elements for that "both channels driven", I can easily connect them in series and see.
L3 appears to be a 2" long maybe 3/8" diamater aircore part. They dont provide a parts list in the service manual, so I have no idea what 150-004 means. Just shipped out my Genrad RLC bridge today...
I could make an adventure to have a look across R15 with the SA. The boards are stacked vertically, so you have to take the amp enclosure apart to get at one of the PCB surfaces, in order to probe.
Copy that.
I've also been looking at https://www.diyaudio.com/community/threads/rane-ma6s-upgrade-or-replace.258168/, wherein it is written; "Note that removing any of the amplifier cards requires removing the output transistors from the heatsink, and replacement of the insulator pads may be needed upon reinstallation. Read disassembly instructions carefully."
Thanks for the assistance, perhaps even changing C31; even as a snip out, might be more than I'm willing to do. I bought an amplifier unheard, assumed it'd be OK.
Last edited:
Are we sure the C19/20 are drawn correctly? They are decoupling the positive rail to a speaker output... speaker output is a virtual ground from a DC point of view... but can we confirm this was drawn correctly??
I have used a version of this since 1986.
Mine uses irf530 and irf9530.
LF353 instead of 5534.
Frequency response greater then 300khz.
The 33pf cap may be reduced to 22pf.
The comp cap C8 on the 5534 may be lowered or removed. Be careful here as it may oscillate.
Mine uses irf530 and irf9530.
LF353 instead of 5534.
Frequency response greater then 300khz.
The 33pf cap may be reduced to 22pf.
The comp cap C8 on the 5534 may be lowered or removed. Be careful here as it may oscillate.
C19 and C20 and the two resistors R41 and R42 form a bootstrapping circuit. It behaves a bit similar to a big inductor with a resistor in series and allows the base of Q13 to swing above the positive supply.
Measuring the response before L3 could provide a clue. If its value is ~71.2uH it provides ~3.5 dB loss at 20 KHz and ~0.47 dB at 6 KHz, just as the plot shows.
To cover 20 Hz - 20k sure, and the inductor always is in parallel with a small resistor, 1 - 5 ohm. Or the circuit diagram isn't complete.
Inductor at output is placed to prevent oscillation with capacitive load , not to filter output by audible frequency range.
Very much doubt what you call "lifelessness" and that tiny drop at 20kHz are related.
Very much doubt your own response at 20kHz isn´t down ,say, 10 dB or even 20dB or anywhere in between at such frequency.
You perceive it as "lifeless"?
Fine with me, it´s an opinion/taste and everybody has his own.
Then you went out chasing goblins, found this and think it´s the "cause".
But you are not listening to the amp alone, but through a speaker system ... how does IT measure at 20 kHz?
Where are you listening?
Unless 1 meter in front, in an anechoic chamber, response will vary more than 3.5dB at various frequencies (not only 20 kHz) ,if you are in any kind of normal room.
You might try to correct that 3.5dB drop, why not?
But doubt that solves anything.
Easy peasy test: insert an equalizer and rise response at 20kHz by 3.5dB, so combined response is now flatb to 20kHz .... is it now day and night?
Lifelessness now became vibrant live reproduction? Not so sure about that.
Of course it might.
Please do the test to clear your doubt, in my book testing beats guessing 1000:1
I agree. 'Lifeless' does not correlate to -3dB at 20KHz, which most of us would barely detect, if at all. Your plot looks like it was taken in a room with a microphone, not at the output point of the amplifier.
The problem with frequency rolloff does exist, have myself proved that , if that rolloff begins to early , starts at just few kHz . Sound is not clear as it can be , in hf range ,and reducing input filter capacitance while listening proves that. Offcourse depending on music material and source .
But there is no evidence here that the amplifer is at fault. Certainly this is a room response, not a plot taken at the output terminals.