• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Amplifier Circuit Simulation Services

LesE said:
When used in the protection circuit, the KSC1845/KSA992 will begin turning on when the load is roughly 2.1 to 2.5 ohms depending on the signal level and frequency. As mentioned in a previous post, it's usually good practice to use complementary pairs here and so if you use the KSC1815/KSA1015, the protection circuit begins to turn on somewhere around 1.5 to 2.0 ohms. So, either should work fine and in both cases, they should have no effect for loads above say 2.5 to 3 ohms.
Click to expand...
Would you be so kind to take your drawing and highlight the signal path in yellow?
 
 
Yamaha5000 said:
Thank you! It looks like I should probe with the QA at each TR Base and Emitter to help define where this loss of signal and high distortion is introduced into the circuit? Any additional thoughts?
Click to expand...
First, are you inserting your test signal at AUX or Main In? What is your test signal level? Looking at the spectrum at points within the circuit is not all that helpful. Instead, look at the realtime analog waveform in oscilloscope mode. Also, use your DVM to check some of the DC voltages and compare them to the ones noted on the schematic that I provided earlier.
 
LesE said:
First, are you inserting your test signal at AUX or Main In? What is your test signal level? Looking at the spectrum at points within the circuit is not all that helpful. Instead, look at the realtime analog waveform in oscilloscope mode. Also, use your DVM to check some of the DC voltages and compare them to the ones noted on the schematic that I provided earlier.
Click to expand...
Are you familiar with:
QuantAsylum?
Vintage Audio Review?
 
mbz said:
Did you try the low noise regulated power supply based on that diyaudio thread I sent. The CA-1000 only needs about 100mA which is fine for that voltage regulator.
Click to expand...

mbz said:
I'm tempted to "pimp" the CA-1000 on the bench (refurbing) by adding the low noise regulator, do it on a breadboard for "proof of concept" probably add a switch so can switch between OEM and breadboard, maybe a couple of hours work with design, assembly,installation..
Click to expand...
Have you prepared an integrated schematic?

1726573384402.png 1726573423466.png

1726573590937.png

1726573700253.png
 
Last edited:
@LesE I must take a moment and extend an apology to you for sending that WTF parts list. After further review I can see that I really screwed that up!
Yesterday I went back to both Main Boards and changed all the transistors out to what you provided with the drawing. Now I am anxious this morning to run test on these boards to see what changes are found.
 
Yamaha5000 said:
@LesE I must take a moment and extend an apology to you for sending that WTF parts list. After further review I can see that I really screwed that up!
Yesterday I went back to both Main Boards and changed all the transistors out to what you provided with the drawing. Now I am anxious this morning to run test on these boards to see what changes are found.
Click to expand...
No need to apologize. I should mention that I have changed the drivers from TTC/TTA004 to the MJE15032/33 which preliminarily looks good in simulation. The average power dissipation should be somewhere around 800-900mW which is within the operating limits for the TTC/TTA but a heatsink will likely be required. The MJE devices should be bulletproof in this application. Another possible candidate is the KSC2703 and KSA940. I'll let you know if I see any potential problems with the MJE's.
 
The amplifier should provide just over 30dB of gain and I see on your display that the measured gain is around 46dB so I'll assume that you are applying the test signal to the AUX port. Is this the case and if so, what is your test signal level?
 
LesE said:
The amplifier should provide just over 30dB of gain and I see on your display that the measured gain is around 46dB so I'll assume that you are applying the test signal to the AUX port. Is this the case and if so, what is your test signal level?
Click to expand...
I am connected to AUX. I am sure I don't have something configured correctly in the QA Automated Test.
 
So when you are connected to AUX, you are measuring the contribution of the preamp and the main amplifier. Keep in mind that the specified distortion figures are for the amplifier alone. The large spikes below 1kHz are mostly 60Hz and it harmonics which will hopefully be much lower when you have the entire amplifier buttoned up.

You will want to make sure that your test signal is low enough so that it doesn't overdrive the preamp and high enough that you can hit rated power when the volume control is turned up. Typically, somewhere around 150mV RMS is sufficient. The alternative is to use the MAIN IN to measure the amplifier alone. If you use the MAIN IN, you won't have the benefit of the volume control so you will want to start at a low signal level and increase slowly. By my estimate, roughly 0.6V RMS input signal should produce the rated output of 100W for a 4 ohm load at 1kHz.
 
This is with the unit buttoned up and with the AUX input -1db from clipping.

Issues noticed:Right channel is down 17W from the Left Channel
60hz and it's harmonics is extremely high
I am seeing 40v PP at the output with the scope

The 1khz should be set to 0dbr, I can drop it to that level with adjusting the GEN 1 output level, but that is then less than 1W output. I am missing something with the QA setup and trying to get my mind around it.

quantasylum.com

Basics: Power Amps

This post covers some of the more important points to consider when measuring power amps. From the setup to the measurements, if you are looking to make measurements of amplifiers with your QA401, this is a good starting point. The Load We'll start with the load. Amps need to drive into a load...
quantasylum.com

QA401 Tutorial.docx

drive.google.com drive.google.com

Quantasylum QA401 Audio Analyzer setup tutorial for THD/Power tests

I bought a QA401 audio analyzer about 18 months ago. I have been in the receiver/amp restoration hobby for about four years, learning most of what I know from members of the Marantz forum. I have accumulated a bit of test equipment, but the old faithful distortion analyzers, like HP have...
audiokarma.org

1726601281041.png
 
Last edited:
One thing you can try is to look at the output of the preamp to see if it's clean. If it is, then you know there is an issue in the power amp. If the 60Hz is present at the output of the preamp, then you may need to look at the regulated power supply as a possible source or possibly a bad ground connection or broken ground connection.
 
You must log in or register to reply here.

Similar threads

R
High Current Issue with Complementary 300W audio Amplifier
Replies
2
Views
83
rcs16
R
L
Speaker Load Simulation
Replies
0
Views
250
LinuxGuru
L
G
Denon DRA-750 What on earth is "SSS"?
Replies
8
Views
5K
mhardy6647
mhardy6647
Mike Stehr
Aikido 6SN7 amplifier
Replies
11
Views
6K
Mike Stehr
Mike Stehr
A
interesting thing about overload protection
Replies
8
Views
1K
Alfonsol
A
Back
Top Bottom