Yamaha A-S500 Amplifier DC protection

[Audiorepair]

Hmm,

as I understand it, the OP has established the amp shuts down due to DC on the speaker output on one channel when moving the volume pot. 
He has observed this happening.

There are many of these 10uF caps between IC401 and the power amp, including C103 and C104 on the power amp itself, so I don't get why you seem to think a faulty IC401 could possibly inject DC into the power amp input circuit.

But maybe you are correct.

Personally, I would be looking at the caps as the culprit, this is cheap and easy to do and a very common problem in all sorts of units.

And if that doesn't work, then the amp is toast anyway.

[elecdonia]

There are many of these 10uF caps between IC401 and the power amp, including C103 and C104 on the power amp itself, so I don't get why you seem to think a faulty IC401 could possibly inject DC into the power amp input.

IC401 operates on balanced +/-7V supply rails. But an internal fault might cause a full -7V to +7V step function at its analog output pin when the volume control gets rotated. This is large enough to be seen by the DC voltage detector at the power amplifier output, even after passing through several 10uF coupling capacitors.

See my previous post for a description of the (really strange) way the volume control section works in this unit.

[Audiorepair]

Logic in fault finding often leads to trying to find the component that has failed.

Real world experience fault finding teaches you that sometimes many, most or ALL of these 10uF capacitors may have failed.

The cumulative result of all these failures being DC is able to get through to the Power Amp.

[Martin72]

I wish I had the amp here and could do some scope measurings.

[David_AVD]

Another thought - I had a weird fault with a Denon amplifier a while back where one of the voltage rails to the selector / volume chip was missing and from memory it caused distortion.

The actual +/- rails were ok from the regulators, but there was a corroded trace near the chip so it wasn't until I checked the voltages right at the chip that I found the issue.

So I would carefully check that the +/- 7V rails are really on the chip itself before replacing the chip.

[elecdonia]

So I would carefully check that the +/- 7V rails are really on the chip itself before replacing the chip.

It is a good idea to check the +/-7V power supply voltages on IC401. However, because one channel has no DC offset but the other channel does, this leads me to suspect a fault inside IC401.

I’m thinking that a power supply fault would cause both the left and right channels to have DC offset.

Or, more correctly, a huge DC “step function” which occurs when the volume control is rotated.

[tiggerlator]

Thanks for all the input guys.

I repeat, there is no DC voltage on the L speaker output.

If i cannot get the faulty IC repaired, could i use it as a power amp, by using an input into CB101?

I will see if i can check the 10uf caps, and the voltages to ic104

[elecdonia]

Actually I think it can be rewired to bypass the faulty IC401.
One pair of line-level analog inputs could be re-routed to go through the "conventional" bank of 4 knobs in the middle of the panel: These controls are bass, treble, balance, and "loudness."  None of this circuitry requires IC401.
The loudness circuit can easily be revised to become a simple "volume" control circuit without the low-frequency boost at low volumes

However the "Volume" control with the large knob and the selector switch with the large knob aren't usable without a functional IC401.

[Martin72]

could i use it as a power amp, by using an input into CB101?

Should be no problem.

I will see if i can check the 10uf caps, and the voltages to ic104

Do this, but I´m afraid elecdonia are right.
Between the volume out from the IC401 and the input of the power amp are three bypass caps(including the one in the power amp input), if I count it right.
Chances are very low that all caps are defective (shorted) so dc components could disturb the power amp.
Normally bypass caps are used to block dc components of the signal.
For a very short time they let them through because of charging.
It must be a kind of repitive signal which can pass the caps, this could be only coming from the IC401.
Two "last chances":
-Observe the solderings on the pcbs for faulty areas.
-Check the transistor Q802 in the mute circuit.

[elecdonia]

This “signal” isn’t a steady unchanging DC offset. Rather, when the “volume” control is rotated, sharp pulses of several volts + or - pass through the cascade of 10uF capacitors and may still be large enough to produce pulses of perhaps + or - 30V at the speaker terminals.

Consider what the OP observed: “Rotating the volume control makes loud pops on the right channel and then triggers the protection mode.”

To simulate: Make this testing device: 1.5V battery, a series resistor between 1k and 10k ohms, and a momentary pushbutton switch. Connect it to an audio cable with a male RCA plug on the far end. Plug this cable into any line input of an integrated amplifier or receiver. Starting with amplifier’s volume control fully counterclockwise, gradually increase the volume while pushing and releasing the button. Slowly raise the volume. Try to avoid damaging your speakers or use a disposable junk speaker. How loud does it get? How high did you raise the volume before you decided it was unsafe to make it any louder?
To push things harder put a 100 ohm 5W resistor in series with the test speaker. This will act a an attenuator to prevent speaker damage. Then you can continue raising the volume until the pop (or bang) from pushing the button triggers the DC protection circuit in the amplifier.

Now, consider that the pulses generated by a malfunctioning digitally controlled attenuator inside the IC401 might produce a pulse (step function actually) as large as 1/2 of 7V. That’s 3.5V. Twice what the 1.5V test rig generates. How loud would that be? Would it trigger most DC protection circuits?

[tiggerlator]

This “signal” isn’t a steady unchanging DC offset. Rather, when the “volume” control is rotated, sharp pulses of several volts + or - pass through the cascade of 10uF capacitors and may still be large enough to produce pulses of perhaps + or - 30V at the speaker terminals.

Consider what the OP observed: “Rotating the volume control makes loud pops on the right channel and then triggers the protection mode.”

To simulate: Make this testing device: 1.5V battery, a series resistor between 1k and 10k ohms, and a momentary pushbutton switch. Connect it to an audio cable with a male RCA plug on the far end. Plug this cable into any line input of an integrated amplifier or receiver. Starting with amplifier’s volume control fully counterclockwise, gradually increase the volume while pushing and releasing the button. Slowly raise the volume. Try to avoid damaging your speakers or use a disposable junk speaker. How loud does it get? How high did you raise the volume before you decided it was unsafe to make it any louder?
To push things harder put a 100 ohm 5W resistor in series with the test speaker. This will act a an attenuator to prevent speaker damage. Then you can continue raising the volume until the pop (or bang) from pushing the button triggers the DC protection circuit in the amplifier.

Now, consider that the pulses generated by a malfunctioning digitally controlled attenuator inside the IC401 might produce a pulse (step function actually) as large as 1/2 of 7V. That’s 3.5V. Twice what the 1.5V test rig generates. How loud would that be? Would it trigger most DC protection circuits?

Iirc, the voltage on the right speaker was as high as -12v.

Shame about the fault, i only paid £25 for it, assuming it would likeley jusy be a popped main tranny. As it is, the repair is probably beyond my skills, so i will either take it to a proper repair shop, or try and use it as a power amp only with a pre amp for input to it some how, as it is a 85wpc amp.

I will see if i can see any problems on any on the input PCB's, but there is a shed load of 10uf caps all over the input section, so "if" that is the fault, finding which one/s that are faulty will be a pita.

Shame i do not live close to one of you pros.

Thanks anyway, and i am kinda glad i gave you guys something to think about.

[elecdonia]

I will see if i can see any problems on any on the input PCB's, but there is a shed load of 10uf caps all over the input section, so "if" that is the fault, finding which one/s that are faulty will be a pita

While it’s true that these small electrolytic capacitors sometimes fail, I sincerely doubt they are an issue in this amplifier.

A couple of posts back I suggested the input(2) PCB could be modified to provide one set of line-level audio inputs along with the 4 controls in the middle of the front panel remaining functional (balance, bass, treble, loudness). This wouldn’t be a difficult job. It requires only a little bit of desoldering/soldering. The faulty IC401 can be left in place. IC401 doesn’t need to be removed in order to make this modification. If you are interested I will provide instructions for doing it.

I searched ebay and saw listings for several A-S500 and similar models. Some were offered “for parts only” at reasonable prices ( < $50 USD ). My approach to repairing audio gear is to get at least two similar units. This makes “board swapping” possible.

[elecdonia]

I disconnected the R channel input from the CB101 connector and amp works just from left channel.

May I ask you to check some more things related to the left channel?

1) With R disconnected from CB101, then connect a line level audio signal to only the left channel RCA input jacks one at a time. Do not connect anything to right channel RCA jacks. Connect speaker to the left channel only. Nothing connected to R speaker outputs.
2) “Pure Direct” button must be released(off). Then switch on the power button.
3) Are you able to hear the audio source for each of the following inputs: CD, line 1, 2, 3, and Tuner? ( note that you must rotate the “source select” knob to match the input jack you are applying the audio signal to)
4) Does the large “Volume” knob work to control the left channel volume?
5) Does rotating the large Volume knob cause any loud pops from the left speaker?
6) Does the sound you hear from the left speaker seem “normal?” (Not distorted or noisy, the volume seems correct for the position of volume control knob, the source selector knob works properly for each line-level input)
7) With the large Volume knob at a middle setting, then rotate the “Loudness” knob counterclockwise. Is the “Loudness” knob able to control the volume? Does it make the volume go all the way to zero when fully counterclockwise? The goal of this test is to see if the “Loudness” control will work OK as a substitute for the large “Volume” control.
8 ) Did the “protection” activate at any time while doing these tests?

Please post the results of this test.

[tiggerlator]

I disconnected the R channel input from the CB101 connector and amp works just from left channel.

May I ask you to check some more things related to the left channel?

1) With R disconnected from CB101, then connect a line level audio signal to only the left channel RCA input jacks one at a time. Do not connect anything to right channel RCA jacks. Connect speaker to the left channel only. Nothing connected to R speaker outputs.
2) “Pure Direct” button must be released(off). Then switch on the power button.
3) Are you able to hear the audio source for each of the following inputs: CD, line 1, 2, 3, and Tuner? ( note that you must rotate the “source select” knob to match the input jack you are applying the audio signal to)
4) Does the large “Volume” knob work to control the left channel volume?
5) Does rotating the large Volume knob cause any loud pops from the left speaker?
6) Does the sound you hear from the left speaker seem “normal?” (Not distorted or noisy, the volume seems correct for the position of volume control knob, the source selector knob works properly for each line-level input)
7) With the large Volume knob at a middle setting, then rotate the “Loudness” knob counterclockwise. Is the “Loudness” knob able to control the volume? Does it make the volume go all the way to zero when fully counterclockwise? The goal of this test is to see if the “Loudness” control will work OK as a substitute for the large “Volume” control.
8 ) Did the “protection” activate at any time while doing these tests?

Please post the results of this test.

3- Are you able to hear the audio source for each of the following inputs: CD, line 1, 2, 3, and Tuner? ( note that you must rotate the “source select” knob to match the input jack you are applying the audio signal to) YES. Could hear music on all of these inputs L channel
4) Does the large “Volume” knob work to control the left channel volume? Yes, perfectly.
5) Does rotating the large Volume knob cause any loud pops from the left speaker? No, no pops, clicks or anything else, sound is crisp and clear, see 6
7) With the large Volume knob at a middle setting, then rotate the “Loudness” knob counterclockwise. Is the “Loudness” knob able to control the volume? Does it make the volume go all the way to zero when fully counterclockwise? The goal of this test is to see if the “Loudness” control will work OK as a substitute for the large “Volume” control. It goes quiet but not to zero, i can still hear it but pretty quiet.
8 ) Did the “protection” activate at any time while doing these tests? No it did not

The right channel of the power amp section is working fine on both channels. the amp only goes into protection if the R channel input is connected to the power amp input. I connected the L channel to the R channel power amp input and did the same tests, and again was all fine.

If you need me to try anything else let me know.

Thanks

[elecdonia]

Could hear music from each line-level input on L channel
Large “Volume” knob works perfectly to control L channel
No pops, clicks or anything else, sound is crisp and clear
"Loudness knob" as volume control goes quiet but not to zero, i can still hear it but pretty quiet.
“Protection” did not activate at any time

Thanks! Excellent test results. These confirm the fault is only on the R channel and is caused  by a fault inside IC401. No need to worry about any capacitors or other parts being the cause of the loud pops and protection mode.

I worked out a simple and reversible way to bypass IC401. It is done entirely on the function(2) PC board.

To gain access to the function(2) PC board I recommend removing the rear panel. Remove every screw from the rear panel. Note that some may be fine thread screws and others may be coarse thread. I make a diagram as I remove them to remind me where to put them back in during reassembly.

After removing the back panel it should be very easy to unplug the entire function(2) PC board and lift it out of the chassis.

With function(2) PC board on the workbench, locate jumper wires labeled J406 and J407. Clip each jumper wire in the middle and bend up the ends.
Next locate 10uF electrolytic capacitors C461 and C460. They are near the diagonal connector W401. Unsolder the + wire of each capacitor from the PC board and lift these wires up out of the PC board. Note that the wires to unsolder are the wires farthest away from connector W401. Note that the - wire  from each capacitor remains connected as it was to begin with. You will only be unsoldering the + wire of each capacitor.

I use "solder wick" to remove as much solder as possible before attempting to pull the wire out of the hole in the PC board. I also recommend brushing rosin flux onto the PC board pads you will be desoldering before you apply heat.  There's plenty of instructions for desoldering here on eevblog if you haven't done much of this yet. The goal is to unsolder these capacitor wires without damaging the foil pads on the PC board. 

Final step is to solder on two new jumper wires. You may use thin insulated wires of the type often used for breadboard circuit construction.

One new jumper wire goes from upper end of J406      to        + end of 10uF capacitor C461

Other new jumper goes from upper end of J407         to          + end of 10uF capacitor C460. 

That's it.

Now you will be able to use the "Line 1" inputs (the function selector switch no longer does anything).
The "Pure Direct" switch must stay in "off" mode.
The "Loudness" control is now the volume control.

Note: There is another small (reversible) mod which lets the "Loudness" control reduce volume all the way to zero. This mod requires soldering a couple of jumper wires onto the PC board which holds the "Loudness" control. But this mod is optional if you can tolerate being unable to reduce the volume to zero.

Ultimately, if you manage to find a working Function(2) PC board this will fix the original problem and restore complete functionality to the amplifier.

[tiggerlator]

Could hear music from each line-level input on L channel
Large “Volume” knob works perfectly to control L channel
No pops, clicks or anything else, sound is crisp and clear
"Loudness knob" as volume control goes quiet but not to zero, i can still hear it but pretty quiet.
“Protection” did not activate at any time

Thanks! Excellent test results. These confirm the fault is only on the R channel and is caused  by a fault inside IC401. No need to worry about any capacitors or other parts being the cause of the loud pops and protection mode.

I worked out a simple and reversible way to bypass IC401. It is done entirely on the function(2) PC board.

To gain access to the function(2) PC board I recommend removing the rear panel. Remove every screw from the rear panel. Note that some may be fine thread screws and others may be coarse thread. I make a diagram as I remove them to remind me where to put them back in during reassembly.

After removing the back panel it should be very easy to unplug the entire function(2) PC board and lift it out of the chassis.

With function(2) PC board on the workbench, locate jumper wires labeled J406 and J407. Clip each jumper wire in the middle and bend up the ends.
Next locate 10uF electrolytic capacitors C461 and C460. They are near the diagonal connector W401. Unsolder the + wire of each capacitor from the PC board and lift these wires up out of the PC board. Note that the wires to unsolder are the wires farthest away from connector W401. Note that the - wire  from each capacitor remains connected as it was to begin with. You will only be unsoldering the + wire of each capacitor.

I use "solder wick" to remove as much solder as possible before attempting to pull the wire out of the hole in the PC board. I also recommend brushing rosin flux onto the PC board pads you will be desoldering before you apply heat.  There's plenty of instructions for desoldering here on eevblog if you haven't done much of this yet. The goal is to unsolder these capacitor wires without damaging the foil pads on the PC board. 

Final step is to solder on two new jumper wires. You may use thin insulated wires of the type often used for breadboard circuit construction.

One new jumper wire goes from upper end of J406      to        + end of 10uF capacitor C461

Other new jumper goes from upper end of J407         to          + end of 10uF capacitor C460. 

That's it.

Now you will be able to use the "Line 1" inputs (the function selector switch no longer does anything).
The "Pure Direct" switch must stay in "off" mode.
The "Loudness" control is now the volume control.

Note: There is another small (reversible) mod which lets the "Loudness" control reduce volume all the way to zero. This mod requires soldering a couple of jumper wires onto the PC board which holds the "Loudness" control. But this mod is optional if you can tolerate being unable to reduce the volume to zero.

Ultimately, if you manage to find a working Function(2) PC board this will fix the original problem and restore complete functionality to the amplifier.

Thanks for this.

I have done the mod, and will reinstall it into the amp, and let you know how it goes.



I am guessing i can reconnect CB10 with both L and R connected?

[elecdonia]

Thanks for this. I have done the mod, and will reinstall it into the amp, and let you know how it goes.



I am guessing i can reconnect CB10 with both L and R connected?

Yes, go ahead and reassemble CB10 so that both channels are connected to the power amplifier stages.

Your rewiring on the Function(2) PC board looks perfect to me. I would have done it the same way. Should there ever be an opportunity to obtain a replacement IC401 chip it will be easy to restore the original configuration.

I do still think the best possible way to handle the IC401 issue is to keep searching for a "parts" amplifier or for somebody selling a Function(2) PC board. Like you said in an earlier post, the most common failures of gear like this Yamaha A-S500 are likely to be mains transformers with open internal thermal cutouts or toasted main PC boards due to failure of one or more output transistors. In either case the Function(2) PC board would likely be undamaged.

[elecdonia]

The person i got it off said it was working and his wife unplugged it, now it has this fault.

What probably destroyed IC401 in this amplifier was from the user disconnecting or reconnecting line-level cables while the AC mains was connected.   
Today nearly all integrated amplifiers and receivers contain line-level input switching and control chips similar to IC401.
A major problem with external cables connected directly to low-voltage line-level audio switching chips such as IC401 is that ESD (static electricity) and excessive input signals can easily damage the IC chip.

My advice to owners of modern solid-state audio gear is "always switch everything off" and disconnect all AC mains supply cords prior to connecting or disconnecting line-level audio cables.

But of course we sometimes forget to disconnect the mains cables...   Therefore, experienced circuit designers place ESD protection circuits between external cables and sensitive IC chips. Unfortunately the ESD protection for IC401 audio inputs consists only of 470 ohm series resistors (R401, R408). The lines on the attached schematic labeled L1IL and L1IR connect directly to pins on IC401. 470 ohms isn't anywhere near a large enough series resistance to provide useful protection. I would change these series resistors to 4.7k ohms. This won't cause a noticeable reduction in gain or loudness. I would also consider adding a pair of diodes or zeners connected so that the input voltage cannot go above +7V or below -7V. A diode protection circuit contains 2 diodes which clamp maximum input voltage to the supply rails. A zener protection circuit has a pair of back-to-back 5.6V zeners in series between the input and chassis ground. Replacing a diode is a lot easier than changing out a 100-pin IC chip which might not even be available as a replacement part.

[elecdonia]

This is a block diagram of IC401.
It looks...             complicated

11 stereo line level input channels
8 output channels.
176 analog switches inside IC401 are required just to handle the input selection.
Additionally there is a whole bunch of programmable routing for front/rear left/right, center channel, subwoofer output, etc.
Finally each of the 8 output channels has a digitally controlled attenuator having a 130dB range in 0.5dB steps.

The strangest thing I find about this A-S500 is that only 2 channels of IC401 are used. Yamaha could have selected a much smaller, less expensive, and more standardized analog input switching chip. As for the digital attenuator I would think plenty of 2-channel devices are available to choose from.

[Martin72]

Burr Brown PGA2310 or wolfson WM8816, but if you already have a chip in stock(for mutlichannel amps) produced by your own....

[tiggerlator]

Thanks for this. I have done the mod, and will reinstall it into the amp, and let you know how it goes.



I am guessing i can reconnect CB10 with both L and R connected?

Yes, go ahead and reassemble CB10 so that both channels are connected to the power amplifier stages.

Your rewiring on the Function(2) PC board looks perfect to me. I would have done it the same way. Should there ever be an opportunity to obtain a replacement IC401 chip it will be easy to restore the original configuration.

I do still think the best possible way to handle the IC401 issue is to keep searching for a "parts" amplifier or for somebody selling a Function(2) PC board. Like you said in an earlier post, the most common failures of gear like this Yamaha A-S500 are likely to be mains transformers with open internal thermal cutouts or toasted main PC boards due to failure of one or more output transistors. In either case the Function(2) PC board would likely be undamaged.

Right, connected back up with both L/R channels of CB101 connected to the power maain board and when turned on it still clicks off with a flashing power led. It seems the IC401 need isolating more somehow. If i connect it with the R channel disconnected from the power main board, it works as follows.

The volume works up to about number 1(if there were numbers) then the loudness takes over. The input selector still lights up and does need to be on line 1.

Simon

[tiggerlator]

I noticed the power section is on a seperate board. Would it be possible to use it just as a power amp with a dual phono input from a pre amp/signal? How would i do this? or would the protection system make this not possible?
thanks

[elecdonia]

I noticed the power section is on a seperate board. Would it be possible to use it just as a power amp with a dual phono input from a pre amp/signal? How would i do this? or would the protection system make this not possible?

     How to use a separate preamp/control unit with your modified Yamaha A-S500:

Connect the “Line Outputs” from the preamp/control unit to “Line1” of the Yamaha A-S500. Keep the bass, treble, and balance controls centered on the A-S500. Set the A-S500 “Loudness” control at full clockwise or reduce it by 1/4 turn if the system plays louder than you want it to. Note that you will use the selector, volume control, etc. on the preamp/control unit. The A-S500 will act only as the “power amplifier” with this setup. You will control everything with the preamp/control unit.

The mod you just installed into the A-S500 also gives it limited “integrated amplifier” functionality for using it all by itself, but with only one line-level input from the pair of RCA jacks labeled “Line 1.”  The 4 controls in the middle of the A-S500 front panel (Bass, Treble, Balance, Loudness) are also still fully functional.

However, the A-S500 “Input selector” control and the large “Volume” knob no longer operate because they require IC401.

The Yamaha A-S500 contains a “phono stage” but since the function selector switch is inoperative without IC401 it would require some additional rewiring to make use of the A-S500 phono stage. Note that all of the source input switching and selection is performed inside IC401.

     Glossary:
Preamplifier (also known as “Control Amplifier): Provides source selection switching (CD, Tuner, Tape, Aux, Phono) volume control, and optionally bass/treble controls and balance control. Many preamplifiers include a “phono stage.”

Phono stage: A specialized low-noise high-gain equalized preamplifier stage which is used only with a turntable. This stage takes the 1-5mV low-level signal from a phono cartridge and raises it to “line-level.” Phono stages have a fixed gain. They don’t have their own volume control. They simply convert the millivolt level signal from a turntable into a standard “line-level” signal.

Power Amplifier: Takes “line-level” input signal and raises it to a much more powerful signal to drive a loudspeaker. Most power amplifiers do not have a volume control. Rather, their gain is fixed, often at 29dB.

Integrated amplifier: The “preamplifier” and “power amplifier” are combined in one physical unit.

[tiggerlator]

I noticed the power section is on a seperate board. Would it be possible to use it just as a power amp with a dual phono input from a pre amp/signal? How would i do this? or would the protection system make this not possible?

     How to use a separate preamp/control unit with your modified Yamaha A-S500:

Connect the “Line Outputs” from the preamp/control unit to “Line1” of the Yamaha A-S500. Keep the bass, treble, and balance controls centered on the A-S500. Set the A-S500 “Loudness” control at full clockwise or reduce it by 1/4 turn if the system plays louder than you want it to. Note that you will use the selector, volume control, etc. on the preamp/control unit. The A-S500 will act only as the “power amplifier” with this setup. You will control everything with the preamp/control unit.

The mod you just installed into the A-S500 also gives it limited “integrated amplifier” functionality for using it all by itself, but with only one line-level input from the pair of RCA jacks labeled “Line 1.”  The 4 controls in the middle of the A-S500 front panel (Bass, Treble, Balance, Loudness) are also still fully functional.

However, the A-S500 “Input selector” control and the large “Volume” knob no longer operate because they require IC401.

The Yamaha A-S500 contains a “phono stage” but since the function selector switch is inoperative without IC401 it would require some additional rewiring to make use of the A-S500 phono stage. Note that all of the source input switching and selection is performed inside IC401.

     Glossary:
Preamplifier (also known as “Control Amplifier): Provides source selection switching (CD, Tuner, Tape, Aux, Phono) volume control, and optionally bass/treble controls and balance control. Many preamplifiers include a “phono stage.”

Phono stage: A specialized low-noise high-gain equalized preamplifier stage which is used only with a turntable. This stage takes the 1-5mV low-level signal from a phono cartridge and raises it to “line-level.” Phono stages have a fixed gain. They don’t have their own volume control. They simply convert the millivolt level signal from a turntable into a standard “line-level” signal.

Power Amplifier: Takes “line-level” input signal and raises it to a much more powerful signal to drive a loudspeaker. Most power amplifiers do not have a volume control. Rather, their gain is fixed, often at 29dB.

Integrated amplifier: The “preamplifier” and “power amplifier” are combined in one physical unit.

problem is, i can still only use the L channel. If i connect the R channel of the CB101 connector, the amp still clicks off with the power led flashing.

[elecdonia]

If connecting R signal to either L or R input of power amplifier at CB101 causes "protection" then we need to check a couple of items on the other end of the cable that connects to CB101.

Also it is very important to make sure the "Pure Direct" button is released.