Seriously...what do all you DIYers think of the DIY work on this:
mshilarious
Banned
It looks like a standard upgrade recipe with reasonable execution. Some of his science is wrong, especially regarding the bypass caps--see #5 and #6 here:
http://uk.geocities.com/cyrilb2@btinternet.com/downloads_5.html
So you can't simply have bypass caps "calculated to carry the majority of the signal, leaving only the bass to the Nichicons.", it doesn't work that way. But Muse are still good, low distortion electros, and probably a good improvement over the original.
It's also questionable whether the audio quality of feedback caps that are far above the audio range is important. No harm there though . . .
I would not have used Muse for the power supply, although they probably will work OK, they weren't designed for that. There's also more than one type of Muse cap; some are 85C and some 105C, I'd definitely want the 105C in a power supply.
Oh, and his comment about manufacturers not using feedback caps--he may need them to solve a problem he created--if the original opamps were very slow, they may not have been capable of much high-frequency gain, and thus no oscillation. So I wouldn't go ragging on the Tascam engineers too bad; chances are they knew what they were doing.
I would worry that he's calculated the cap values a little too lean, based upon one of his comments--even small amounts of low frequency attenuation can accumulate across stages, and the research above shows that larger caps tend to have less distortion than smaller caps, so I'd want to see an analysis of frequency response, ideally pre vs. post mod. Again, him vs. Tascam, they weren't that stupid.
Soldering job looks OK but I see a spot or two that could stand some defluxing, if you are particular about that. I am not.
Lastly, I would want to know the difference in draw between the new opamps and old, to see if the power supply is possibly stressed near or beyond its rating.
http://uk.geocities.com/cyrilb2@btinternet.com/downloads_5.html
So you can't simply have bypass caps "calculated to carry the majority of the signal, leaving only the bass to the Nichicons.", it doesn't work that way. But Muse are still good, low distortion electros, and probably a good improvement over the original.
It's also questionable whether the audio quality of feedback caps that are far above the audio range is important. No harm there though . . .
I would not have used Muse for the power supply, although they probably will work OK, they weren't designed for that. There's also more than one type of Muse cap; some are 85C and some 105C, I'd definitely want the 105C in a power supply.
Oh, and his comment about manufacturers not using feedback caps--he may need them to solve a problem he created--if the original opamps were very slow, they may not have been capable of much high-frequency gain, and thus no oscillation. So I wouldn't go ragging on the Tascam engineers too bad; chances are they knew what they were doing.
I would worry that he's calculated the cap values a little too lean, based upon one of his comments--even small amounts of low frequency attenuation can accumulate across stages, and the research above shows that larger caps tend to have less distortion than smaller caps, so I'd want to see an analysis of frequency response, ideally pre vs. post mod. Again, him vs. Tascam, they weren't that stupid.
Soldering job looks OK but I see a spot or two that could stand some defluxing, if you are particular about that. I am not.
Lastly, I would want to know the difference in draw between the new opamps and old, to see if the power supply is possibly stressed near or beyond its rating.
H
hilarypaprocki
New member
"So you can't simply have bypass caps "calculated to carry the majority of the signal, leaving only the bass to the Nichicons.", it doesn't work that way. But Muse are still good, low distortion electros, and probably a good improvement over the original."
Actually in this case it kinda did. When I switched to Muse caps, they were so slow in anything above the bass I actually couldn't add tracks to the tracks that had been recorded. There was no front edge to any of the notes. I could not catch the beat, to play along. Honest, I added the polypropylenes so that I could play the darn tracks.
When I first added the Wimas, I guesstimated an average value for about 500hz by itself, as if the electrolytic weren't there. This helped, but didn't fix it. When I moved to a value that would go down to about 250Hz by itself, the problem was fixed. So although theory says that paralleled capacitors don't "cross over", in this case they actually did.
As for the feedback caps, this is a technique that was told to me by the man who runs Benchmark Audio. What you want to do is keep your gain curve under the open-loop gain curve (it's published) -- if you don't, you're running open loop at rf frequencies, and that's bad. It's just bad hygiene to not have your amplifiers operating linearly under all circumstances. I have stories.
Draw was a concern, but the machine worked fine for years.
As for the Low Frequency corner, my target was 5Hz or so on the low end. Whatever you think about that is fine with me. Remember, the guys who design these cards don't necessarily know all the places the outputs are going to be routed to in the final completed product; and I find some insanely large values sometimes, just in case. And further remember, a cap that is ten times the size that it needs to be, has ten times the dilectric, which means ten times the dilectric absorption, which is ten times the badness.
All in all, I thought about a lot of stuff that I didn't talk about there, because it's only guys like you and me who care. And I'm not talking about every consideration that I considered here either, like sticking with 5532's instead of higher-fi chips to keep a balance between good sound and good sound. But since the conversation is in the air, I do want to assure you that I didn't just do some canned procedures here. You might disagree with my decisions but if you was here you mighta done more of what I did.
h
Actually in this case it kinda did. When I switched to Muse caps, they were so slow in anything above the bass I actually couldn't add tracks to the tracks that had been recorded. There was no front edge to any of the notes. I could not catch the beat, to play along. Honest, I added the polypropylenes so that I could play the darn tracks.
When I first added the Wimas, I guesstimated an average value for about 500hz by itself, as if the electrolytic weren't there. This helped, but didn't fix it. When I moved to a value that would go down to about 250Hz by itself, the problem was fixed. So although theory says that paralleled capacitors don't "cross over", in this case they actually did.
As for the feedback caps, this is a technique that was told to me by the man who runs Benchmark Audio. What you want to do is keep your gain curve under the open-loop gain curve (it's published) -- if you don't, you're running open loop at rf frequencies, and that's bad. It's just bad hygiene to not have your amplifiers operating linearly under all circumstances. I have stories.
Draw was a concern, but the machine worked fine for years.
As for the Low Frequency corner, my target was 5Hz or so on the low end. Whatever you think about that is fine with me. Remember, the guys who design these cards don't necessarily know all the places the outputs are going to be routed to in the final completed product; and I find some insanely large values sometimes, just in case. And further remember, a cap that is ten times the size that it needs to be, has ten times the dilectric, which means ten times the dilectric absorption, which is ten times the badness.
All in all, I thought about a lot of stuff that I didn't talk about there, because it's only guys like you and me who care. And I'm not talking about every consideration that I considered here either, like sticking with 5532's instead of higher-fi chips to keep a balance between good sound and good sound. But since the conversation is in the air, I do want to assure you that I didn't just do some canned procedures here. You might disagree with my decisions but if you was here you mighta done more of what I did.
h
sweetbeats
Reel deep thoughts...
Hey thanks for posting!
And BTW, congrats on the final price.
Any chance you'd be willing to go into more detail about the mods you did?
The 388 definitely has a following.
I for one like the 5532. The 300-series is chock full of them and I think its a good sounding unit. I'll have to have another look at the spec sheet for the 5532. Did you use those to change out the 072's or does the 5532 have the drive to replace some of the other chips like the 2041?
And why did you use MUSE caps in the PSU?
And BTW, congrats on the final price.
Any chance you'd be willing to go into more detail about the mods you did?
The 388 definitely has a following.
I for one like the 5532. The 300-series is chock full of them and I think its a good sounding unit. I'll have to have another look at the spec sheet for the 5532. Did you use those to change out the 072's or does the 5532 have the drive to replace some of the other chips like the 2041?
And why did you use MUSE caps in the PSU?
Dr ZEE
Anti-Pro Circles Insider
I've re-read this many times and miserably failed to determine the state of my consciousness.
Am I sleepwalking?, dreaming?, drunk?, in coma? ....
I'm so freakin' -
mshilarious
Banned
Did you happen to measure any of that? You are talking about a perceptive delay that would have to be in the msec range, and certainly would have also been a problem with the original circuit. I mean I know the effect you are talking about with respect to high-frequency clarity and the 'punch' of a bass note, but I think I could manage to play along with a slower amp. C'mon, every cheap bar PA in the world is probably slower than your board, yet somehow musicians manage to find the pocket.
This idea of capacitor "speed" is novel. Sorry, but I am more inclined to trust Cyril Bateman's research. You are claiming to hear a dramatic effect from a change in distortion that Bateman measured at around 0.0003%. It would be trivial to simulate that change and see if you can detect audibility. Or you could have simply measured THD before and after yourself. Listening tests before and after a mod are so far apart in time so as to be useless. Ultimately, if the Muse sounded that bad without help I would just have removed them.
Again, any measurement? You are claiming not only a novel effect of bypass capacitors, but also an effect that is critically dependent on a mere 2x change in capacitance.
Everyone has stories. Of course, if you are running fast chips, you need those caps. But did the original Tascam oscillate? Why or why not? Again, do you think the Tascam engineers were incompetent? I mean, I think they knew how to use an oscilloscope, and I'd be willing to bet they scoped the gain stages. I doubt this was a budgetary issue; ceramic caps are the cheapest on the block, well under a penny in Tascam's likely purchase quantity. My experience with Tascam engineering is that it's pretty good. No, maybe not always the sexiest, fastest possible circuit, but the stuff just worked and didn't break easily. The PCB design, case layout, construction . . . all very good. These guys knew their stuff.
Per stage or input to output? 5Hz at each stage could be grossly inadequate if there are many stages. -3dB at 5Hz doesn't mean 0dB at 20Hz.
Hard to predict that effect without considering the selected capacitor's construction and performance. Rereading Bateman I seem to have scrambled the low vs. high capacitance measurements; that was very dependent on the type and brand of capacitor. So I withdraw that claim.
But you would in essence be trading perhaps 1dB or more at 20Hz for a change of less than 0.001% THD at best. At what point is a loss of bandwidth acceptable to obtain a given reduction in distortion? I think one must set 20Hz at better than -1dB across the entire circuit, then shoot for lowest distortion within that framework, otherwise the bandwidth of the system should be disclosed.
The question becomes whether that change in THD is measurable given the overall performance of the system. It's not difficult to measure bandwidth and THD.
Years ago I did somewhat similar mods on an A&H mixer. But only on half the channels initially. Worried about draw and unable to confirm some aspects of the power supply design, I only changed opamps on half the channels, but I eventually did caps everywhere. I used bypass caps at the time. I did a lot of listening at each stage, and since I always had channels with a lesser stage of mod I had a direct comparison. I believe that mod was worthwhile as a result, and I believe your mod probably is too. But I never would have described the improvement in so dramatic terms as you have used. In the end, sometimes mods are quite a lot of work for a small improvement. That's part of the fun of DIY though.
Dr ZEE
Anti-Pro Circles Insider
...or no improvement at all, or!!!!!!!! - for "improvement" that is "measurable" only by the level of invisible to general public internal desire and/or self-satifaction of the DIYer, and thus is priceless and is NOT for sale.
mshilarious
Banned
But it was for sale, for the price of $1,245. And it's the best Tascam 388 in the WORLD!
Dr ZEE
Anti-Pro Circles Insider
Yes it was. BUT! One needs to see what "it" actually is.
When shopping - see what's for sale, but NOT what is being said about it.
If and When the "words" is the only form of presentation of an item, - sophisticated filtering is required.
Something that can't be and thus isn't for sale by its very nature, can't be sold nor can be purchased.
Having said that, the reality is this: certain thing being said may alter an individual's state of consciousness to the extent of unconscious behavior.
Routine check and maintenance of the state of consciousness seems to be a logical thing to do.
...now, back to my first post in this thread
************
btw, Msh, thanks for detailing through this. What's your source of energy? And - source of patience?
mshilarious
Banned
btw, Msh, thanks for detailing through this. What's your source of energy? And - source of patience?
Patience or petulance? If the latter, I'm pretty sure it's my avatar
