I have found that the outputs get leaky with being over driven, and the dual transistor up front can also be a source of offset. It can be one or many of the semi's, including diodes. Its time consuming work to find the source, but it can be resolved if you have time and parts.
You can wire in a 10 or 20K pot across the + - 15 volts and connect the wiper to the input just behind the input cap, and adjust the offset out of you channel this way. But it does not resolve leaky semi's. It just resolves offset.
PPI had this setup for years without issue. Whenever I would get one in I would try and reset the offset as small as possible without causing issue with distortion and power output, and bias alignment.
You can wire in a 10 or 20K pot across the + - 15 volts and connect the wiper to the input just behind the input cap, and adjust the offset out of you channel this way. But it does not resolve leaky semi's. It just resolves offset.
PPI had this setup for years without issue. Whenever I would get one in I would try and reset the offset as small as possible without causing issue with distortion and power output, and bias alignment.
I realized after I posted they were indeed the input gains. I really cleaned the board although it wasn't that dirty. I mainly cleaned off the ton of flux. I'll do the pot trick. Found some 2200uF 50V caps that I can squeeze in place of the 1000uF 50V caps for the 4 channels and then unless theres really something that you think will be a day and night difference in SQ I'll just button and back up and put back in the car.
I'm thinking the way to improve the SQ is going to be with a different HU. Know anyone who could look at the schematic of a Sony CDX R5715X and tell me how to improve the sound?
I'm thinking the way to improve the SQ is going to be with a different HU. Know anyone who could look at the schematic of a Sony CDX R5715X and tell me how to improve the sound?
I did an A/B between the 245 and a small tri-path I built for the home that runs on 12v. The tri-path (15W) had better body to the presentation. The 245 is still sounding "thin". I've been blaming all of it on the head unit so I was surprised the little tri-amp sounded better with less distortion.
Does this point to anything in particular in the 245 to you?
Does this point to anything in particular in the 245 to you?
No warmth or body to the sound. More upper register. Rather brittle, possibly with a high frequency tone over riding any warmth of midrange. Exceedingly bright.
This is on the test bench using single drivers. The exactly reminiscent of the sound is the same in the car. When I used the tri-path the sound had more body and warmth. More accurate representation from low midrange up through the highs.
The high pass filters actually make it worse. This is just on the front 4 channels (actually two as I have them bridged).
I've been blaming it on the HU. When the tri-path was in circuit it wasn't as bad.
This is on the test bench using single drivers. The exactly reminiscent of the sound is the same in the car. When I used the tri-path the sound had more body and warmth. More accurate representation from low midrange up through the highs.
The high pass filters actually make it worse. This is just on the front 4 channels (actually two as I have them bridged).
I've been blaming it on the HU. When the tri-path was in circuit it wasn't as bad.
Humm, Sounds like one or both of those channels are out off spec. Do you have the means to check the capacitors I.E. a LCR meter ?
Whats the offset on those channels ? Is there any DC on the RCA input ?
How big is the power supply your using ? I ask because the Tripath is 90% efficient and the AB Soundstream is about 50% efficient.
Other than that you are comparing two completely different types of amp against one another. Perhaps thats why your hearing a difference. I would need to run some more tests to try and characterize the sonic issue your amp has. Run a frequency bandwidth scan, Distortion check, response flatness. maybe pass a few square waves from 7 K on up to see whats up, and check for crossover distortion.
Many of these old school amps had Crossover notch distortion issues and that might be what your hearing
Just pass some sine waves and visualize them on a O scope, you can't miss the notch's at the crossover point if they are there, Hope this helps
Whats the offset on those channels ? Is there any DC on the RCA input ?
How big is the power supply your using ? I ask because the Tripath is 90% efficient and the AB Soundstream is about 50% efficient.
Other than that you are comparing two completely different types of amp against one another. Perhaps thats why your hearing a difference. I would need to run some more tests to try and characterize the sonic issue your amp has. Run a frequency bandwidth scan, Distortion check, response flatness. maybe pass a few square waves from 7 K on up to see whats up, and check for crossover distortion.
Many of these old school amps had Crossover notch distortion issues and that might be what your hearing
Just pass some sine waves and visualize them on a O scope, you can't miss the notch's at the crossover point if they are there, Hope this helps
I only have a DMM. I'd have to send the amp to you for all these rest. All the ps caps have been replaced. I'll try to see if there's any DC on the rca's. I have the DC offset in an earlier post. Basically 3 of 4 are 46mA and one channel is <20mA.
I guess its probably a form of distortion. Not enough to corrupt the sound completely. Just enough that I can't EQ it out with the HU.
No DC on the RCA inputs
I guess its probably a form of distortion. Not enough to corrupt the sound completely. Just enough that I can't EQ it out with the HU.
No DC on the RCA inputs
You need to determine if your meter has enough bandwidth. The owner's manual should tell you.
You will need to check the response of your audio source to be sure it has a flat response. Set all equalizers, the controls and the loudness to off (center position for tone and equalizer controls).
Run the sweep and connect your meter to the RCA outputs. Set the level for ~1 volt. Restart the sweep and watch the meter. It should stay near 1v. If it varies by more than ~0.12v, there may be some sort of equalization in use and you need to remove it or take it into account when checking the amp.
When driving the signal into the amp, you want to do so at a relatively low level. 1-2 volts is enough to get reliable readings. If you do it near full power, you may damage the amp. Some amps will self destruct when driven to full power with a 20kHz sine wave.
Allow the test tone to sweep while getting the output level right. When you have it at the level you want, restart the sweep and watch the meter. Again, you don't want to see more than ~0.12v variation. That's ~1dB.
This is the link to the sweep. There's a limit to the number of downloads so it would be nice if others would allow you to get it first. When you have it, let others know you have it to allow the rest of those who want it to download it. If the downloads max out before you get it, email me and I'll post it again and send you the link via email.
Distribute the sweep freely.
http://s01.11send.com/?01070305842595951544
You will need to check the response of your audio source to be sure it has a flat response. Set all equalizers, the controls and the loudness to off (center position for tone and equalizer controls).
Run the sweep and connect your meter to the RCA outputs. Set the level for ~1 volt. Restart the sweep and watch the meter. It should stay near 1v. If it varies by more than ~0.12v, there may be some sort of equalization in use and you need to remove it or take it into account when checking the amp.
When driving the signal into the amp, you want to do so at a relatively low level. 1-2 volts is enough to get reliable readings. If you do it near full power, you may damage the amp. Some amps will self destruct when driven to full power with a 20kHz sine wave.
Allow the test tone to sweep while getting the output level right. When you have it at the level you want, restart the sweep and watch the meter. Again, you don't want to see more than ~0.12v variation. That's ~1dB.
This is the link to the sweep. There's a limit to the number of downloads so it would be nice if others would allow you to get it first. When you have it, let others know you have it to allow the rest of those who want it to download it. If the downloads max out before you get it, email me and I'll post it again and send you the link via email.
Distribute the sweep freely.
http://s01.11send.com/?01070305842595951544
First I will say Hi and this is a great site full of info. New here, but not to Car Audio.
Hate to dig up a old post but,
I was just wonder is/was/will there any sonic improvements for change in input op-amps to the TL082 or the OP275 on MC245 and upgrading the power suppply Caps on the MC245 or any of the older MC's or D's Soundstream amps.
The reason I ask is I have own 2 MC245, 2 D100II, a MC140x, and a D200 (for first one, not the series II). I had a MC140 but I just sold it and now I want it back all ready.
Thanks for all your help in advance.
Hate to dig up a old post but,
I was just wonder is/was/will there any sonic improvements for change in input op-amps to the TL082 or the OP275 on MC245 and upgrading the power suppply Caps on the MC245 or any of the older MC's or D's Soundstream amps.
The reason I ask is I have own 2 MC245, 2 D100II, a MC140x, and a D200 (for first one, not the series II). I had a MC140 but I just sold it and now I want it back all ready.
Thanks for all your help in advance.
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