PM me. I have replacement pots, whole PCB assemblies, etc.
Squealing sounds more like it. But at those bass frequencies so like flubbing might be a better word lol. Becomes a more straight up tone when the frequency is shifted higher. But is correlated to boosting the gain. Which caps are limited to the eq section exclusively? I don’t mind recapping before resorting to a new pot
The more ideal way is to bypass each rail to ground as close as possible to the opamp. But often times that’s hard to do depending on the layout. I have to say the only time I’ve added the bypass caps is when I’m “upgrading” an opamp…and I probably don’t need to even do it then because I’m not one of these guys that tries to use the fastest opamp. So I’m not using parts that would be prone to instability. But the only way to know is to test the output with a suitable scope and put the opamp to the test with suitable stress test input signals, and that can be time consuming and also not necessarily comprehensive…so it’s just easier to put the cap in, so I do it just because if you are changing anything and using a higher performance part than the original it’s a good idea. But the TL072 is a stable part. A lot of people stick their noses up at it, but I’d argue it’s one of the most widely used audio opamps…you’ll find the 071, 072 and 074 in all sorts of devices, and the critics tend to forget it actually has pretty decent specs. And it’s cheap. And stable. Which is why I was surprised to find an application where one was oscillating. It was in the EQ circuit of my prototype Tascam console, the prototype that led to the M-50 and M-500 consoles. The EQ is very different between those…the EQ on the prototype is very similar to the PE-40 rack-mount EQ unit…but the M-50/M-500 EQ is derived from the prototype EQ…much more simple. And because I found one of the six TL072 opamps oscillating in the prototype I thought I’d mention it as a possibility for the OP’s issue with their M-520 EQ, which I also experienced with one I had in the past. In my case with the prototype I didn’t even need to put in the bypass cap, but simply replacing the old JRC branded opamp with a new TI part resolved the issue.
Yes, the TL072 is pretty good. It has a faster slew rate than the NE5532 but then all the common audio op amps have easily fast enough slew unless you include the 741! The 72 has that "output flip/latchup" issue if overdriven and also distortion rises rapidly if loaded with less than about 2k but all in all a very useful device.
thanks again for the information! SO I'm having trouble sourcing all nichicon brand capacitors and their associated values for the 10 smaller capacitors in the PSU. Is it a problem to mix capacitor brands in this case? Also can I use a bi polar cap in any instance here? You guys are a plethora of info I really appreciate the dialogue here.
Doesn’t matter mixing brands at all. What you want to do though is use quality caps that are low ESR and correct values, and I also generally source 105C temp rated parts vs what you’ll often find as 85C parts. It can be difficult to source 105C non-polar parts. Like none of the Nichicon audio-grade non-polar parts are 105C. So I just get what I can get when I want to audio-grade parts. The Panasonic caps are fine. DO NOT put a non-polar cap in where there was polar, and vice-versa. There are rare circumstances where you can do this, and generally it would be putting a non-polar in instead of polar, because generally a non-polar electrolytic cap will perform better in the signal path than the polar equivalent, but expert circuit analysis is required before doing so…the circuit has to be properly biased for non-polar parts to be used…and generally this would be a consideration in the audio signal path, not in a power supply. In a linear power supply, the caps need to be polar. Keep in mind you can generally increase the voltage tolerance, you just never want to decrease it. So if you’re having trouble finding a 22uF 16V cap, for instance, it’s okay to use a 25V or 35V cap…even 50V. This is especially true in a power supply or even in the audio circuits for parts that are not in the signal path. For parts that are in the signal path, there’s no advantage and sometimes can even be a detriment to put parts in that are significantly higher voltage rated parts, but generally it’s okay to use the next one or two steps above what’s spec’ed as far as voltage rating. And sometimes I’ll do that purposely because the factory part is too close for comfort in my opinion…the voltage rating dictates how long the cap will live if subjected to the maximum ratings. A 2,000 hour 16V cap is rated to last 2,000 hours when subjected to 16V constantly as well as other rated maximums like temperature. If there’s a 16V rated part sitting directly in a 15V circuit I’ll generally increase that to a 25V rated part. Also sometimes the parts list and/or schematic don’t match what’s factory installed. I always go with what’s installed because it’s usually product-development related and revised parts lists or schematics may not be available or or even published. Other times a manufacturer might install a higher voltage rated part just because it’s of no consequence and they had the higher voltage parts in the shelf. But, again, I always compare the as-built assembly with the schematic and defer to what’s installed on the as-built assembly. The good news is Teac did a relatively good job selecting values for parts for this era of equipment. I think there is only one circumstance where I ran across something in a 1980s era Teac/Tascam device where the voltage rating was not appropriate…I think it was in the 244. And I’ve done a lot of recapping and studying of 80s era Teac/Tascam stuff. Hope this helps.
(Here’s some of my background for context) I had never recorded in a professional studio until 2021. My band at the time cut a record to 2inch tape and the engineer made it seem so effortless Leaving that experience i was really inspired so I bought this console for $100 about two and a half years ago, cleaned it, recorded about 12 songs or so. In that span of time I grew an interest in wrenching on audio equipment. Last month I picked up an apprenticeship working as an audio technician mainly repairing keyboards, but we kinda do everything from loudspeaker amplifiers to the occasional guitar amp. Anyhow I ask a lot of questions because I have no formal background in electronics and you guys at this site are very generous with your knowledge. I asked about the nonpolar caps cause somewhere(Reddit I think?) I read you can substitute non polars in place of a polar but not vice versa and I was two caps short of trying to match all nichicons, mouser had the right value but only as a non polar cap. BUT as I’ve learned that isn’t the right way and I can mix capacitor manufactures if necessary. Caps get here today and I’ll finish over the weekend
thanks guys cheers.
Thanks.(Here’s some of my background for context) I had never recorded in a professional studio until 2021. My band at the time cut a record to 2inch tape and the engineer made it seem so effortless Leaving that experience i was really inspired so I bought this console for $100 about two and a half years ago, cleaned it, recorded about 12 songs or so. In that span of time I grew an interest in wrenching on audio equipment. Last month I picked up an apprenticeship working as an audio technician mainly repairing keyboards, but we kinda do everything from loudspeaker amplifiers to the occasional guitar amp. Anyhow I ask a lot of questions because I have no formal background in electronics and you guys at this site are very generous with your knowledge. I asked about the nonpolar caps cause somewhere(Reddit I think?) I read you can substitute non polars in place of a polar but not vice versa and I was two caps short of trying to match all nichicons, mouser had the right value but only as a non polar cap. BUT as I’ve learned that isn’t the right way and I can mix capacitor manufactures if necessary. Caps get here today and I’ll finish over the weekend