Is there any point in upgrading outputs in an amp that has no bias control? I have a few smaller car audio amps that lack bias control, but I feel could benefit from a larger better sounding output device.
I know you are suppose to adjust bias when replacing or upgrading outputs but what do you do in a case where there is no bias control?
Are there any downfalls to doing this?
I know you are suppose to adjust bias when replacing or upgrading outputs but what do you do in a case where there is no bias control?
Are there any downfalls to doing this?
So is your suggestion to always use the same output device the amp came with when dealing with fixed bias circuits?
Question is what are you trying to achieve? changing to a "better" transistor doesn't necessary improve anything. It's more important to optimize the amp than just change the transistor. Adding bias adjustment should be very helpful, not so fast in changing transistors just yet.
Do you have the schematic? If you want to improve the amp, you really need to look at the circuit and see what needs to improve.
My experience with my Acurus amp that was biased very cold, increasing the bias sure improve the sound quite a bit. But together with increase the bias, I should change the emitter resistors to match the bias so the resistor drops 26mV to get the optimal Oliver's condition for lowest crossover distortion.
I am guilty of only increase the bias without changing the resistors. I even bought the resistors but too lazy to change it. In my case, I don't listen at loud volume, I am sure I am running my amp in Class A at my listening level. I am building a new amp, I hate to mug around on this Acurus, it's not a bad amp by any standard, so I just leave it alone and serve as the standard to judge my designs. Point is, I would put the bias adjust, make sure you keep the transistor in safe thermal region. Listen and judge whether it's worth increasing the bias. If you hear obvious improvement, then look at the emitter resistors. Come back and read more about the Oliver's condition.
Do you have the schematic? If you want to improve the amp, you really need to look at the circuit and see what needs to improve.
My experience with my Acurus amp that was biased very cold, increasing the bias sure improve the sound quite a bit. But together with increase the bias, I should change the emitter resistors to match the bias so the resistor drops 26mV to get the optimal Oliver's condition for lowest crossover distortion.
I am guilty of only increase the bias without changing the resistors. I even bought the resistors but too lazy to change it. In my case, I don't listen at loud volume, I am sure I am running my amp in Class A at my listening level. I am building a new amp, I hate to mug around on this Acurus, it's not a bad amp by any standard, so I just leave it alone and serve as the standard to judge my designs. Point is, I would put the bias adjust, make sure you keep the transistor in safe thermal region. Listen and judge whether it's worth increasing the bias. If you hear obvious improvement, then look at the emitter resistors. Come back and read more about the Oliver's condition.
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I appreciate you digging further, but I am looking for opinions and answers to the question posed. I do believe different output devices have an affect on overall sound due to my own experience/opinion from swapping them many times over my life.
Other parts have been changed. I changed and upgraded every electrolytic cap in the amp, and also swapped the opamps to one that I prefer.
This particular amp has a few mix-matched outputs from being repaired before I acquired it, so I am changing them anyway. This is why I was thinking about using my favorite device and spending a few more dollars (MJL21193/4), but noticed the amp doesn't have a bias control so I thought I would get some opinions.
Yes, because any replacement could either cause worse performance (if the bias dropped to low or to zero), or excess heat/thermal runaway if went to high.
Fixed bias means its dependent on the device characteristic.
No, changing to your "better" transistor likely will not improve sound. It's a crap shoot on the bias. I don't believe there is "better" sounding transistors. This is not tubes that are half way mechanical devices. It's about matching and optimizing the operating condition of the transistors. Mooly is absolutely right, the new "better" transistor can have higher Vbe drop and make you amp work in class B and you'll really cry over it.
If you want to spend the time tinkering like this, it's better if you buy the book by Bob Cordell and at least read the part of crossover distortion so you know what matters.
Changing to better caps and all does not guaranty you get better sound, again, it's all about the design.
You want opinions, you got it. If I were you, I'll first find out what is the bias of the transistor by measuring the voltage drop over the emitter resistors of the power transistors. Make sure it is not biased too cold. Next, look at the voltage drop of all the resistors and note whether there is big difference in voltage drop between different transistor to check whether the transistors are matching. then report back and let people give you suggestion.
don't blindly changing parts, this is waste of money and work and you might ruin the amp also.
If you want to spend the time tinkering like this, it's better if you buy the book by Bob Cordell and at least read the part of crossover distortion so you know what matters.
Changing to better caps and all does not guaranty you get better sound, again, it's all about the design.
You want opinions, you got it. If I were you, I'll first find out what is the bias of the transistor by measuring the voltage drop over the emitter resistors of the power transistors. Make sure it is not biased too cold. Next, look at the voltage drop of all the resistors and note whether there is big difference in voltage drop between different transistor to check whether the transistors are matching. then report back and let people give you suggestion.
don't blindly changing parts, this is waste of money and work and you might ruin the amp also.
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You're a funny guy. Obviously, I know enough to ask the question I asked. Therefore, I know what an improperly biased circuit can do on both sides of a correct bias setting.
Outputs do affect sound. Period.
Thank you for the verification, Mooly. It's appreciated.
I've had several of these amps. They won't benefit from changing the output devcies - unless doing so increases the bias. Half of the time they sound terrible - when the bias drifts low the crossover distortion is more than a little audible. The real fix is to optimize the bias. Many times there is a Vbe multiplier or whatever in there - just no damn pot. The resistors that set it can often be manually trimmed (by placing one in parallel until the bias goes up to target). It will make the amp sound A LOT better. If there are no emitter resistors to stabilize it they can be added. I had to do that to an old Fultron. Running the bias up with no emitter resistors would have been a disaster the first time it's cranked. A whole Vbe multiplier wth a pot can be added if needed, but that does make a bit more work out of it. If an amp doesn't already have some sort of bias circuit already there I won't mess with it - just save the effort for one that does.
Wg_ski provided the proper solution ...things are exactly as described For cheap amps and for cost reduction the trimmer is not there just a steady resistor Farther more the Vbe multiplier is hardly ever sensing or reacting properly.
Pins are too short or mechanical attachment is very poor
Fix bot hand you have a better and warmer amplifier
As about the outputs expect not much to change but if you gain better reliability then you scored something
Molly you missed the point i think
10 points off your bill
Pins are too short or mechanical attachment is very poor
Fix bot hand you have a better and warmer amplifier
As about the outputs expect not much to change but if you gain better reliability then you scored something
Molly you missed the point i think
10 points off your bill
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