I installed AD826 opamps in my Yamaha CD Player (CDC-745) a few months ago. All of my CD’s sound much better from top to bottom …. until I played Pink Floyd's Dark Side of the Moon with the volume up a bit, that is. There’s a resonating sound (synthesizer?) on this CD, e.g. after the intro on “Time”. It's a lower midrange/upper bass sound. It never caused a problem before but it’s very pronounced with the new opamps and at approximately 9:00 on the volume dial, it sounded like the drivers were coming out of their frames and the roof was falling in. I could actually see the speakers vibrating. Fortunately, I turned it down quickly and don’t think my speakers are damaged. Has anyone else had a problem like this after replacing opamps? Is this the dreaded opamp resonance I’ve read about?
Sounds to me like their going into spuratic occilation, I replace some in a Pioneer cd player once, they did the same thing, very dangerous for your power amp and speaker, do'nt use them, try something a bit more stable, the way you can see it happening is if you hook up a scope to the output and play that same cd.
For you can try the very cheap but nice sounding OP275, they are stable, or AD825, but they are single smd and you need brown dog coverter boards for them but great sounding if you want the AD826 sound.
Cheers George
For you can try the very cheap but nice sounding OP275, they are stable, or AD825, but they are single smd and you need brown dog coverter boards for them but great sounding if you want the AD826 sound.
Cheers George
Some tunes on Dark Side of the Moon has extremely low bass! I think they have recorded EKG signals even! Have you tested this with the original opamp?Stew said:
BTW: Have you heard the cover of the Dark Side of the Moon? Extremely good sound quality, very much alike the original. The recording is amzing!
The Moon Revisited by Magna Carta
No. RR8916 2 Road Runner
I've had Burr Brown 2604 Opamps oscillate on me. The're a real pain sometimes.
I was told to put a small capacitor, 12pf or so, across the inputs of the opamp. This done the trick for me. Not sure if you have the same problem but you could try it and monitor the opamp output with a scope. Probably a good idea to use a dummy load instead of a speaker and maybe keep the volume down.
I was told to put a small capacitor, 12pf or so, across the inputs of the opamp. This done the trick for me. Not sure if you have the same problem but you could try it and monitor the opamp output with a scope. Probably a good idea to use a dummy load instead of a speaker and maybe keep the volume down.
Value for Bypass Capacitor
Thanks for the replies. This is all new to me and I appreciate the help. The datasheet for the AD826 suggests using two 0.1 uF caps in parallel from each power supply pin to ground. From the above replies and searching this site, I gather that it’s common to put a capacitor between pins 4 and 8 instead. Would a single 0.1 uF capacitor between pins 4 and 8 be a good choice? Are metalized polypropylene caps a good choice?
Thanks for the replies. This is all new to me and I appreciate the help. The datasheet for the AD826 suggests using two 0.1 uF caps in parallel from each power supply pin to ground. From the above replies and searching this site, I gather that it’s common to put a capacitor between pins 4 and 8 instead. Would a single 0.1 uF capacitor between pins 4 and 8 be a good choice? Are metalized polypropylene caps a good choice?
Re: Value for Bypass Capacitor
the purpose of the 100nF bypass capacitors is to produce a low impedance ground return for high frequency garbage which makes its ways on the power supply rails -- in this case, you are best off with a ceramic surface mount capacitor -- if you are going to parallel it with anything a 1 uF tantalum.
i am going to hazard a guess that perhaps one of the solder joints is high resistance but not completely intermittent.
Stew said:
the purpose of the 100nF bypass capacitors is to produce a low impedance ground return for high frequency garbage which makes its ways on the power supply rails -- in this case, you are best off with a ceramic surface mount capacitor -- if you are going to parallel it with anything a 1 uF tantalum.
i am going to hazard a guess that perhaps one of the solder joints is high resistance but not completely intermittent.
The power supply by-pass caps won't help much if it is an occillating opamp, it's the high speed of the opamp itself being excited to go into occillation by high frequency input noise from the previous stage (dac noise maybe?).
But then you could try the caps doesn't cost much and will lower power supply noise.
Cheers George
But then you could try the caps doesn't cost much and will lower power supply noise.
Cheers George
georgehifi said:
"Pulsating DC component" is a good description of what it sounded like. It sounded like the cones were going to blow out of my speakers and the roof was going to fall in. Scary!!
I thought the AD826 was supposed to be pretty stable? Did you try bypassing with a small capacitor?
Background Info
For some background information:
My CDP is a Yamaha CDC-745 with a YAC514LSI DAC (Pro-Bit, S-Bit Plus). The DAC is followed by a "Twin Balanced Processing Circuit", followed by a 3rd order LPF, followed by output buffer amps. The original opamps for the "Twin Balanced Processing Circuit" were JRC 2068DD. The original output buffer opamps were JRC 5532D. I replaced all four with AD826.
I'm very much a novice at all this and greatly appreciate the advice!
For some background information:
My CDP is a Yamaha CDC-745 with a YAC514LSI DAC (Pro-Bit, S-Bit Plus). The DAC is followed by a "Twin Balanced Processing Circuit", followed by a 3rd order LPF, followed by output buffer amps. The original opamps for the "Twin Balanced Processing Circuit" were JRC 2068DD. The original output buffer opamps were JRC 5532D. I replaced all four with AD826.
I'm very much a novice at all this and greatly appreciate the advice!
Yes the only way, the op275 are a cheap way $6aus each very smooth big sound. (almost shall I say tube sound)
The AD825 also smooth and big, but with more detail and stronger dynamics, but can be up to ten times the price with adapter boards, remember they are single smd your going to need 4 of them and two Brown Dog adapter boards. (If your doing 4 you need 8xad825 and 4 Brown Dog's)
If you have a system that can get harsh go with the OP275's.
If your system has no faults go with the AD825's, remember they will not gloss over any hard sounding components like the OP275's can.
And yes they are stable, even unity gain stable, which I know that the AD826's are not in my experience, (they are evil).
Cheers George
The AD825 also smooth and big, but with more detail and stronger dynamics, but can be up to ten times the price with adapter boards, remember they are single smd your going to need 4 of them and two Brown Dog adapter boards. (If your doing 4 you need 8xad825 and 4 Brown Dog's)
If you have a system that can get harsh go with the OP275's.
If your system has no faults go with the AD825's, remember they will not gloss over any hard sounding components like the OP275's can.
And yes they are stable, even unity gain stable, which I know that the AD826's are not in my experience, (they are evil).
Cheers George
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