cheap pre-amp mod advice - component experts unite!

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lansingxcore

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hello. i want to get into the world of modding my own gear, and i figure i'll start with my art tube mp. (i don't want to hear anybody say i'm wasting my time, buy a better pre, blah blah. i'm in this to learn, and to get the most of the limited resources i have)

i understand that the first thing you'd look for is the tube. apparently they are supposed to have cheap sovtek or chinese tubes, but mine has a JJ ECC83 S, which i have read good things about. (basically the best option for the price.. so i've read. do you have any other/better suggestions?) hey, i got it used, so i don't know if that's what they come with or not.

anyway, the second thing to look at, from what i've gathered, are the op-amps. it has two TL072's, which i gather are fair op-amps, not great but not bad. suggestions for replacements? i did some searching and found the burr brown OPA2134PA to be one option.. is that a good one? i have no idea about these kinds of things.

lastly, what other components are commonly/most effectively modified in a tube mp? i understand that these units are modded fairly often...

thanks in advance!
 
Yeah I think he took down that mod. I did most of it, it's pretty good.

Yes the 2134 is a good swap. The MP is not socketed though, you have to desolder. The Black Lion mod used an even faster chip, which required bypassing or it would oscillate. That's a lot of trouble, the 2134 is plug-n-play.

As for tube, I bought a lot of vintage tubes off eBay cheap and tried 'em until I found good ones.

The rest of the mod was cap swaps, power supply upgrades . . . I did the power supply, not sure if that helped because of course it's impossible to A/B unless you have 2 MPs. I have the Dual MP, so when I modded one channel with tubes & opamps, the different was quite obvious.

One important option in the Black Lion power supply mod was changing a regulator to up the plate voltage and make the tube a little more well-fed, but I dig that tewb sound, so I skipped that.

I can dig out my hard copy & get you part #s if you want them.
 
The JJ tube is an excellant one. Swapping tubes in these plate starved units is not hyper critical. The tube character is very much reduced by these "marketing" driven designs. They can call it a tube pre, but it does not operate in the spirit of true tube gear. It's really a dirty trick on the consumer. Tube swapping is more effective where the tube is operating within its proper voltage windows. For instance, the Vox AD30VT tube plate voltage is +15v. Thats some BS. They don't even have an entry in the manual for changing it. That's because it really won't effect the sound - much - at all. Maybe some, but not much. The opamp and caps, cleaning up the power supply are about all you can do. Pick up some Black Gate electrolytics for the signal path to reduce capacitive distortion. They can be abit costly. The performance of these low end units can be improved to where you can live with them.

Have fun, Bob
 
thanks guys. ok, so to sum it up:

-my tube is fine. but i can always experiment more.

-the 2134's are the best opamp replacement i can get without having to mod more stuff that's perhaps a bit out of my league at this point?

-i should replace the capacitors (yes, mshilarious, part #'s and advice would be fantastic!)

-i should upgrade my power supply (does that not mean replace the whole thing, just certain parts? which parts? and by power supply, are we talking about the wall wart here? i also use my tube mp wall wart to power my old school nintendo, hope it will remain compatible :p )

thanks again so much
 
lansingxcore said:
thanks guys. ok, so to sum it up:

-my tube is fine. but i can always experiment more.
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Well yeah it works, but in my tests, only the obvious dog vintage tubes were worse. The good tubes were tewblicious. The stock tubes were bland and muddy.

-the 2134's are the best opamp replacement i can get without having to mod more stuff that's perhaps a bit out of my league at this point?
Click to expand...

Well with a faster chip, you have to bypass the feedback resistor with a small cap to prevent oscillation. It's not terribly hard, but it's nice not to have to worry about it.

-i should replace the capacitors (yes, mshilarious, part #'s and advice would be fantastic!)
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The caps are pretty simple: replace all the electrolytics with Nichicon UPW or Panasonic FC low-impedance series of the same value. The Black Lion mod didn't recommend any value changes, although sometimes in a PSU you can put in bigger ones. I didn't bother. Also, in modding a preamp it's typical to bypass electrolytic caps in the signal path with small polyester film caps, but again I didn't bother for two reasons: there are a LOT of caps in the MP; and second, the poly film caps help with high-frequency response, and I'm just not looking for sparkling highs out of a tewb pre. What I want is lots of pleasingly warm harmonic distortion.

-i should upgrade my power supply (does that not mean replace the whole thing, just certain parts? which parts? and by power supply, are we talking about the wall wart here? i also use my tube mp wall wart to power my old school nintendo, hope it will remain compatible :p )
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No, not the wallwart, but the regulator portion of the supply that is inside the unit. Actually other than cap swaps, and an optional voltage regulator swap, the only other change was to replace the diodes with UF4002.

Looking over this again, I see that Black Lion had resistor swaps and three caps removed. I have to say I didn't go that far, and it already sounds much better. Replace the electrolytic caps and bypass the caps on the input side (C12-15) with .1uf poly films. Swap the opamp for OPA2134. Change the tube if you like, and see where that gets you.

Record something really simple and repeatable, like a few guitar chords, before the change so you can A/B it.
 
im gonna join in the fun! on my tube mp there are 2 op amps. i already desoldered them by clipping the legs and taking them out one by one. i put the sockets in from radio shack and im gonna get the 2134 amps.has anyone put a better wall wart power supply on theres? ive seen where people are using a higher amp power supply on there art- dio converter box. would this help a tube mp?
 
gemsbok said:
im gonna join in the fun! on my tube mp there are 2 op amps. i already desoldered them by clipping the legs and taking them out one by one. i put the sockets in from radio shack and im gonna get the 2134 amps.has anyone put a better wall wart power supply on theres? ive seen where people are using a higher amp power supply on there art- dio converter box. would this help a tube mp?
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Good idea to put in sockets. That way you can try different chips and see what you like best.

If the wall wart you have is the correct rating, voltage and amperage wise, for the circuit, there's no advantage to replacing it. The power supply circuit is probably inside the box (I don't have one, or the schematic) and probably consists of a rectifier, filter capacitors, and a voltage regulator(s). If it's not regulating well, larger caps or upgraded regulator might help.
 
OneRoomStudios said:
Well it's a PDF file...so I'd need an email address or something...It would take way too long to type it all out.
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If you want, I can pm you my email address. Send me the file as an attachment and I'll upload it to a site where it can be downloaded, and post the link here.
 
wow, that is truly complicated! now i'm having doubts as to whether or not i can handle this. perhaps after taking an electronics class at the community college...
 
Well you don't have to make all the changes that are listed in the mod to hear an improvement. That mod basically changes everything. I think you were on the right track before with only making a few of the "major" changes.

crazydoc, mshilarious, Bob's Mods....you all know a whole lot more than I do, maybe you could look over the Black Lion mod and come up with a simplified version that addresses the biggest issues. I know the "weakest link/bottleneck" theory, but there have to be a few simple things you could change that would positively affect the overall sound, right?
 
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This all makes me wonder if other budget preamps can be modded in simpler ways to improve their sound, do many of these sort of pres have socketed op amps?.... how much difference would upgrading the op amps on units such as the dmp3 and the audio buddy make?
 
OneRoomStudios said:
Well you don't have to make all the changes that are listed in the mod to hear an improvement. That mod basically changes everything. I think you were on the right track before with only making a few of the "major" changes.

crazydoc, mshilarious, Bob's Mods....you all know a whole lot more than I do, maybe you could look over the Black Lion mod and come up with a simplified version that addresses the biggest issues. I know the "weakest link/bottleneck" theory, but there have to be a few simple things you could change that would positively affect the overall sound, right?
Click to expand...

Sure, I kind of said this already, but:

1) Change the tube. This is very easy, but also involves getting a different tube, or ideally a few tubes, and experimenting.

2) Change the opamps to OPA2134. A little harder--find some old POS computer card to practice desoldering before jumping in.

I started with just those two and the sound improved greatly.
 
crazydoc, Bob's mods...you guys agree? Is there anything else worth doing?

Also, while on the topic, have any of you heard of or used Ei Elite 12AX7E's? They got a good review at thetubestore.com, but I was wondering if anyone else has an opinion about them.
 
OneRoomStudios said:
crazydoc, Bob's mods...you guys agree? Is there anything else worth doing?

Also, while on the topic, have any of you heard of or used Ei Elite 12AX7E's? They got a good review at thetubestore.com, but I was wondering if anyone else has an opinion about them.
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Those came in the ART Pro MPA I used to have. They were better than the stock MP tubes, but not as nice as the vintage GEs I tried.
 
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