escholl

[quote name='Silent Fly' post='780947' date='Mar 20 2010, 05:26 PM']Can someone of you guys tell me the reasons behind what you say? (Technical reasons, experience, A/B blind tests...)[/quote]
Because passives use those transparent, uncoloring components, transformers. Clearly. As opposed to the flat response, low noise, low distortion, stable input impedance presented by an active input stage, which couldn't possibly sound transparent.

It sounds to me like a lot of people (no offense intended guys) who just haven't set their gain stages correctly, and thus are overloading the input. Or are just using cheap actives. Or both.


[quote name='dannybuoy' post='780980' date='Mar 20 2010, 05:56 PM']A drawback with passive DI boxes is that they don't have a very high input impedance so aren't the best solution for plugging in a passive bass directly as you'll lose a little bit of treble.[/quote]
More than that -- running a passive bass direct into a transformer will present it with a load that has resistance, capacitance, and inductance. Also known as a filter. And not just for highs, depending on how it reacts with the inductance, capacitance, and resistance of the bass pickups and cable, it will reshape the frequency response all over.

[quote name='Moos3h' post='781721' date='Mar 21 2010, 03:54 PM']

Get out.

James [/quote]

:lol:

[quote name='LukeFRC' post='782049' date='Mar 21 2010, 08:23 PM']and yes its a mess inside, and yes my soldering iron did have an argument with one of the jack sockets![/quote]

That's what the case is for -- so no one can see!

Soldering is a lot like learning an instrument. You never feel like you're getting any better at it, until you look back at one of your old projects and have that moment of "wow, i am so much better now!"

Also, my suggestion for next time would be to try some wire looms, as seen in the photo attached. It doesn't really matter, but it just makes things look neater

I usually have the opposite problem...

"Ok, I've packed my bass, now should I bring some clothes with me?..."

i love my cheap bass

can't say I particularly desire any others at the moment though, but then I don't really look.

[quote name='Bankai' post='781005' date='Mar 20 2010, 06:20 PM']Ok. Well referring back to the actual amp head.

If it was a 200W amp (as is the case here) and was being run at full power. Presuming that the signal being fed into the power amp is 0dB, it'd be hitting the RMS bang on. Any fluctuation over 0dB would be more than the 200W RMS?

Or is this not the case? You see the signal coming from my preamp into the power section is usually hitting 10dB on the beat so I'm worried that if I'm running the amp at full it'd be hitting higher than 200W, thus maybe damaging the speaker?[/quote]

Where are you getting this measurement of 10dB from? What nominal input level is the power amp looking for? Is is looking for +4dBu?

The important thing to do is just to listen to your amp -- does it sound distorted? If it doesn't, then you've nothing to worry about. As the saying goes, listen with your ears, not your eyes.

[quote name='LukeFRC' post='775583' date='Mar 15 2010, 07:36 PM']C= 0.21
B= 6.43
E = 5.33

which looks wrong to me!

EDIT 2: arrggh I give up. starting again with another layout that makes more sense and is a wee bit different but at least i know someone else has got it working!


EDIT 3: one day later and half a dismantled effect..... ahh the transistor to ground resistor being 390,000 ohms not 390 ohms may have something to do with that![/quote]

Sorry, I've not been about -- did you get it working in the end?

are these multi-voltage, does anyone know? from what I've read, and the manual, it looks like they aren't, but I would like to be wrong!

[quote name='LukeFRC' post='773321' date='Mar 13 2010, 01:21 AM']EDIT: wee play again. I do like it. As it has more bottom end it comes accross as more subtle. It doesn't 'shimmer' much and doesn't sound great on a guitar but it sounds good. Live and in the mix I'm think it possibly is a good sound.
I wonder... heres an idea.... is the chorus bit of the circuit very good with low end? If I put in a cap smaller that the 1uF in the feed from the op amp to the chorus bit of the circuit would it let give me a more trebly wet sound with the better bottom end i already have? Prob wont do it mind just interested.[/quote]

Try changing the 1uF cap going out of the first gain stage into the effect part of the circuit to something smaller, 0.22uF or 0.33uF perhaps. This won't give you more treble, but it will put less bass through the effect circuitry, and might clean up the sound a bit. Try the 0.33uF to start, if you feel up to it.

I've also just had a thought -- check the connections around the IC1a, make sure those components are all right on the board and there's no loose connections. Most people seem to complain the pedal has too much of a bass roll-off, as you've not found that to be the case but instead have found not enough treble, if may be that the pre-emphasis filtering network is not working correctly for some reason. This is just speculation though.

What I usually do in situations like this is, find all the mods you can, and try the ones you like the sound of. Then try some new ones, and just play about a bit -- it helps here if you know what you're doing though

[quote name='escholl' post='754278' date='Feb 22 2010, 07:40 PM']That is one that I have personally used, it's an easy read and has lots of illustrations, but includes all the important technical bits you'll want to know. I can't vouch for the others though I'm sure there are some other good ones out there.[/quote]

By the way, I've just remembered the author of that book is the moderator of this forum [url="http://recording.org/studio-construction-forum/"]here[/url]. Not that we here can't help you, but I would recommend browsing that forum as well, and possibly explaining the situation over there to see what (other) people think.

[quote name='LukeFRC' post='771985' date='Mar 11 2010, 07:08 PM']Yay! It works!



I tested it with a 0.015 on the input last night. It clearly wasn't letting the bass through. So I've stuck a 0.1 on the input rather than the 0.033. It probably isnt the same sound as the original but it works fine for me, makes sure there's a bottom end to it (I know idealy you would have some kind of wet dry mod but I havnt got space on the enclosure for another pentometer!

There is a fair volume drop though... would I be right in guessing from what you said that if the 33k resistor in the output op amp was less than 33k it would be louder?[/quote]


A larger input cap shouldn't affect the sound in a detrimental way, it will simply lower the cutoff frequency of the high pass filter that is effectively created by that cap -- in fact, as the pedal was designed for guitar, 0.1 uF is probably a good value to put in for bass, instead of the original. It is a good choice.

You've got the right idea that the 33k resistor affects the volume, however it works in the opposite way. So, if you wanted a louder volume, increase the value of that resistor. This is why when the connection to that resistor was broken, effectively raising the resistance very high, the gain was increased and the distortion occurred. By calculating a ratio of the input resistor (in this case 10k) to the feedback resistor (33k) the gain of the op-amp stage can be calculated, in this case the gain is roughly 3. If you want to increase it, you could try a 39k resistor in place of the 33k, for a gain of roughly 4, or a 47k resistor, for a gain of about 5. You could also try, say, a 47k pot in series with a 10k resistor, which would give you a variable output level.

In case you are wondering, the 6.8k resistor in series with the 0.01 uF cap is there to prevent that gain stage from amplifying too much high frequency noise above the usual audio spectrum, so that can stay as it is and does not need to be adjusted, although it could be if you felt like playing about with the high frequency response.

Also, if you are curious and did want a wet/dry mod, stick a 47k linear pot in place of where the 22k and 20k resistors are next to points A and D on the schematic. Not really needed though, I don't think.

There is also software like [url="http://www.showcuesystems.com"]this[/url] available, but it all depends how much money you want to put into it I suppose. I'm sure there must be a way to make it work with either what you've got already or with free software.

[quote name='tayste_2000' post='770696' date='Mar 10 2010, 05:54 PM']What would be a good piece of software to do that on?[/quote]

Basically any DAW software, Audacity won't do it but Sonar, Logic, Pro Tools, Ableton Live, Cubase, Digital Performer, Reaper, Adobe Audition, FL Studio, etc should all do it, what you seem to need is actually pretty basic. EnergyXT is fun and basic and would probably do it, but I've had problems with it's stability, or at least I did a few releases ago. It depends whether the software supports tempo changes within the project file, all I can say from experience is that Sonar, Logic, and Protools will definitely do it but otherwise are probably overcomplicated for what you need. I've not used many others extensively and so I don't remember exactly if they will do tempo changes.

Really any software that supports tempo changes, supports a metronome click on playback, and supports MIDI file playback, should work fine.

Garageband would work I think, if you've got that. Don't know what the MIDI support is like, as I've only used Logic.


Ardour is supposed to be good, not used that either but it's free so maybe worth a try?

[quote name='LukeFRC' post='771146' date='Mar 11 2010, 12:18 AM']I can't take it out to test (no signal will get through to the second op-amp without the first![/quote]
Doh! I knew that. Honest.

[quote]Checking the 33k resistor and there seems to be a gap on the icb there so no signal gets to either the 33k or .01 cap. Easily fixed.[/quote]

That'll be the problem then. Without those feedback resistors in the circuit, primarily the 33k one, the gain of the op-amp is left at whatever its open loop gain is, probably around 100. In this circuit, it looks like it's supposed to have a gain of about 3 (and not 100), so, that's where your distortion was coming from. With that pcb gap fixed, the problem should be sorted, assuming there are no other issues with the board.

Now to play!

[quote name='LukeFRC' post='771092' date='Mar 10 2010, 11:21 PM']sorry to bother you all again...
tracked down the problem I think. The 4558 chip seems to be funny.
On the [url="http://www.tonepad.com/getFile.asp?id=97"]schematic[/url] it works as two seperate units (op amps???) IC1a seems to be fine, everything doing what it should.
Ground is ok, as is the voltage into this chip. On the IC1b part however we seem to have a wierd fuzzy loudness. input 6 is fine, the signal from the bass, the output 7 however comes out all distorted. IS there a reason it would do this or have i broken the IC somehow?[/quote]

The 4558 is indeed two separate op-amps. Check that pin 5 is definitely at 4.5 volts, and check that there isn't any sort of broken track or dry joint on the 33k feedback resistor (the one just above the 6.8k in the diagram). If everything is in order, but the output of pin 7 is still not what you expect, pull the IC out of it's little socket and then connect your audio probe to pin 6 of the socket. If the input is exactly what you expect to hear on the output, just quieter, then you will need to replace the IC.

Don't worry, it's not that uncommon a fault -- I've done it myself by accident. In case for some reason you can't find the 4558, you can also use an NE5532 in it's place, which is technically a better op amp. Either will work however and they are both cheap (under a quid from Maplin).

If, however, the input at pin 6 with the chip removed is not what you'd expect to hear on the output, then your problem lies elsewhere, and the IC is simply amplifying the problem. From what you've said however, that would seem not to be the case.

Why not just use the metronome function in place of a really long wav file? Most DAWs can include the metronome click on playback, and you can choose where the tempo changes. Then just include the MIDI output parts you need for each song, put them into their own tracks, and put it all together in one project file.

[quote name='LukeFRC' post='769573' date='Mar 9 2010, 07:00 PM']but I think I've found my problem....no signal is getting through the opening 0.033 nF cap. you can hear the bass in the input arm of it, but on the output one not at all, just a popping noise. why would it do that?[/quote]

0.033 nF, or 33 pF, seems awfully small for a cap in this position in the circuit -- are you sure that is the right value? If it was 0.033 uF, which is 33 nF, that would make more sense given the typical input impedance and bandwidth requirements of these types of input stages.

[quote name='LukeFRC' post='768591' date='Mar 8 2010, 10:09 PM']like this?


thing that confuses me is that it was working, abet with a fault.
i tried to fix the fault. put the right cap in the 0.033 nF slot (the first one after the in, second nearest the in on the board) and spotted the 0.01 cap on the out side wasnt there.
Fixed them and it didn't work, went back a stage or two and it still doesn't work... :S


EDIT: should add.

+v linked to battery red
pot's wired in correctly (they did work when it did work)
ground and battery black on the sleave of the in jack.
tip of jack to in
tip of out jack to out
sleeves linked[/quote]

Would you be able to provide some clear pics of the other side? Other than to say check and double check that any multipin and polarized components are in the right way round, there is not much I can say seeing only one side of the board.

the maplin units share common ground and voltage rails, basically a daisy chain in a box -- in most of the more expensive units, the individual outputs are independently regulated and isolated from one another.

I love mine, had it for a few years now, would not gig without it. I love knowing that I can go pretty much anywhere, and just plug my pedalboard into the effects return of whatever backline is there, and get a decent sound.

It is truly a brilliant pedal.

[quote name='CYDbass' post='754408' date='Feb 22 2010, 09:28 PM']I looked at the one from Maplins and initially thought the same as a few here, you must really only get what you pay for at £19. But since reading the couple that said it was ok (combined with my local music shop telling me they were out of stock of power banks and would be for a month) I think I'll take the plunge on one! Will report back tomorrow if I get the chance to go to Maplin! Thanks for the advice everyone, for a first power brick I think I'll risk it [/quote]

Not to confuse things more, but I don't know if anyone has mentioned [url="http://www.johnnyshredfreak.com/store/index.php?main_page=product_info&cPath=8&products_id=12&zenid=82894faf24f38baa0e44724e9b9eed23"]this one[/url]?

Identical in operation to the Diago supply that sells for 60 quid, myself and many others on this forum use them and they are brilliant. Better, IME, than the Maplin one, but that's not bad either. The one linked above however is small, has multivoltage input, and can supply a LOT of current while maintaining a quiet output.

[quote name='jakesbass' post='754148' date='Feb 22 2010, 06:13 PM']Thanks for that, can I ask why that one in particular? I noticed there are a few, have you used that yourself, or had it recommended?
Cheers
Jake[/quote]

That is one that I have personally used, it's an easy read and has lots of illustrations, but includes all the important technical bits you'll want to know. I can't vouch for the others though I'm sure there are some other good ones out there.

[url="http://www.amazon.co.uk/Home-Recording-Studio-Construction-Build/dp/1598630342/ref=sr_1_3?ie=UTF8&s=books&qid=1266593305&sr=1-3"]Buy this book.[/url] Seriously. I know it's not that cheap, but, in the long run it will save you time, money, and tears. Even if all you do is a relatively inexpensive soundproof of the garage, you will still want to get the most for your money.

My Seymour STK-J2 pickup is hum cancelling, sounds amazing too. Had to get it from the US though, but wasn't a hassle.

That looks like the sort of cab which might be designed after reading and believing too many posts on an internet bass forum....

I can't tell if they did it to cater to the wants of people who don't know better (but insist they do), or if they did it just as some sort of ironic inside joke. If ever there was a parody of a bass cab, it might be this.