Double Bass fdeck preamp techie question...

[drurb]

Yup, sent him one today. It'll be fine, I'm sure. I'm just in a nervous mood today anyway - watching the polls and all.

Francis is a prince! A fine, scrupulously honest human being! Fear not!

 

[drurb]

Any chance either of you can expand on that? I gig 5 - 8 times a week with mine, and after nearly a year of use it seems pretty well built. The pots feel solid, the case is metal, the jacks are good, and IMO they've crammed a whole bunch of stuff into those little boxes. (6 bands of eq and gain for two channels) The Fishman pre that I have, by comparison, is made of plastic and has eq sliders that sure don't feel particularily sturdy. It also has a dc input jack that has never properly worked for me (and others apparently). That's probably neither here nor there - I have no idea what you think of the Fishman pre's, drurb.

I really am curious how you would have designed it differently.

In my experience, the poor design had much to do with the parts that were chosen. In my case, the op-amps were about the cheapest one could buy. IMO, not suited for audio use. The circuit, overall, had very poor dynamic range. I spent about 10 hours trying to trade off the "level" controls (potentiometers at the input) against the gain controls inside the box. I could never get a satisfactory amount of overall gain without overload. So, for sure, if it were up to me, I would have chosen much better op-amps and would have tailored the active and passive circuit elements to produce much better dynamic range. I understand that K&K tries to provide a great deal of bang for the buck. They are good people who are dedicated and have a helpful staff. IMO, the tradeoffs they made just don't work. That's my $0.02. YMMV.

 

[velvetphil]

Francis got back to me - as I suspected he was just super-busy. Looking forward to the preamp, will post my thoughts when I receive it!

 

[MT Spaces]

This is a great little black-box thread here Folks . Learning is Good. Thanks for starting it up VelvetPhil.

..... I have a radical suggestion. Get a good single piezo pickup, run it into fdeck's pre-amp and sell the other stuff on ebay ....

You know, I've been thinking of doing this anyway ...... And thanks for the advice you guys! Think I'm going to pull the trigger on the HPF regardless...

I'm glad you didn't get upset with me for making my suggestion! ....

Bravo Doc .... You didn't upset someone .... A momentous historical event .... Just like yesterday's Presidential Election ! Just Kiddin' ... But it does seem like sometimes Folks don't always take so kindly to your erudite knowledge like VelvetPhil just did . You know I always listen up Doc.

... The best bridge-wing pickup I have ever used is the Rev. Solo. It has to be properly fit to the bridge wing but I have found it to be well worth it ....

Me too. Now that I have my fit tuned and then fine-tuned again several times ... It's All Good .

Back to topic. I got roped into playing my Kay for a regular weekly gig (even with pay ) with some young rowdies doing loud "alt-country." I have ventured into the realm of the real-loud and the raggedy-edge-of-feedback. I run the Rev Solo into my AI Coda, run an external Wizzy M-Line, and also a post-eq direct-out to the PA. I use the Coda's HPF set at 11 o'clock or noon. I have memorized The 13 Commandments Of The Omniscient Toad .... http://www.talkbass.com/forum/showpost.php?p=5450657&postcount=17 .

I have applied many of The Commandments but still am fighting some feedback, especially open E and E on the D string at 2. I have never seen the open Garbo E string vibration amplitude grow bigger and bigger on me before ... kind of cool but scary . What is that frequency ??

Finally the questions .... If I put an FDeck box between the Rev and the Coda, can I then have both phase reversal (from the FDeck box) and HPF (from the Coda)? The Coda can't do both (time for a design change maybe). Is the phase reversal function on the FDeck box like a notch-filter? Can it be adjusted for problem frequencies? Would the FDeck box help the sound and/or amplification in any other ways than just the availablity of HPF and phase reversal?

Thanks for any feedback y'all might have .

 

[Gearhead43]

In my experience, the poor design had much to do with the parts that were chosen. In my case, the op-amps were about the cheapest one could buy. IMO, not suited for audio use. The circuit, overall, had very poor dynamic range. I spent about 10 hours trying to trade off the "level" controls (potentiometers at the input) against the gain controls inside the box. I could never get a satisfactory amount of overall gain without overload. So, for sure, if it were up to me, I would have chosen much better op-amps and would have tailored the active and passive circuit elements to produce much better dynamic range. I understand that K&K tries to provide a great deal of bang for the buck. They are good people who are dedicated and have a helpful staff. IMO, the tradeoffs they made just don't work. That's my $0.02. YMMV.

+1 Cheap op-amps, well put.

I would also like to add, that the cheap plastic input jacks constantly break at the solder joints, even if you are very carefull not to put strain on them, especially with the unit mounted on the bass. I never much cared for the overall tonal character of the preamp either.

 

[bolo]

Finally the questions .... If I put an FDeck box between the Rev and the Coda, can I then have both phase reversal (from the FDeck box) and HPF (from the Coda)? The Coda can't do both (time for a design change maybe).

Sure Bob. I suspect you know all this from the sound of your question. The high pass filter on the Coda does not introduce a phase reversal, but the notch filter does. So (1) if you use the notch filter on the Coda and if you also reverse the phase using the HPF-Pre, you would have a notch filter and be back in phase. Or (2) if you use the high pass filter on the Coda and phase reversal on the HPF-Pre, you could have a HP filter w/ phase reversal.

Of course you could turn off the filter button on the Coda and also accomplish option (2) using just the HPF-Pre. High pass engaged, phase reversed.

But these combinations (1) and (2) cannot be accomplished with the Coda on its own. In other words, using just the Coda, you can't have a notch filter in phase, or a high pass w/ phase reversed. Introduce the HPF-Pre and you get these options.

Durn. I had to reread all that like five times.

Is the phase reversal function on the FDeck box like a notch-filter?

Nope, don't think so. But I'm no techie.

Can it be adjusted for problem frequencies?

Nope. It either sounds better with phase reversed or not.

Would the FDeck box help the sound and/or amplification in any other ways than just the availablity of HPF and phase reversal?

If you have a Series III, the HPF-Pre would give you a 10 meg ohm input impedance vs. 1 meg ohm on the Coda. I have not noticed a huge difference between those two impedances w/ my Rev Solo. But others here may have different views.

Thanks for any feedback y'all might have .

That' s a really bad play on words pal.

 

[MT Spaces]

.....The high pass filter on the Coda does not introduce a phase reversal, but the notch filter does. So (1) if you use the notch filter on the Coda and if you also reverse the phase using the HPF-Pre, you would have a notch filter and be back in phase. Or (2) if you use the high pass filter on the Coda and phase reversal on the HPF-Pre, you could have a HP filter w/ phase reversal ..... But these combinations (1) and (2) cannot be accomplished with the Coda on its own. In other words, using just the Coda, you can't have a notch filter in phase, or a high pass w/ phase reversed. Introduce the HPF-Pre and you get these options .....

Most excellent summary Bolo ..... Thanks ! I think I just got smarter . I have been favoring the Coda's HPF to get rid of low-end mud and not using the notch / phase reverse much at all. I think it is time to get one of F Deck's gizmos and use it for the HPF and then switch to using the Coda's notch / phase reversal function to try to tame some specific feedback ranges I've been encountering. Onward into the fog .......

 

[drurb]

bolo is quite correct and to the point. Just to clarify, the phase-reversal is not at all like a notch filter. A Invalid Link Removed (aka band-reject filter, band-stop filter) reduces the amplitude of a relatively narrow range of frequencies. Often, feedback is caused by exciting a specific resonance in the room (or the bass) so cutting the output at this frequency often tames the problem without ruining the overall tonal balance of the sound.

A phase-reversal switch simply flips the waveform upside-down. That is, if the speaker cone went "out and in," then it now goes "in and out." This is useful in taming feedback induced by interaction of the speaker output and the bass itself. If the amplified sound is "in-phase" with the acoustic output of the bass, it can reinforce the vibration which, when amplifed, will reinforce it further, which when amplified.... You get the idea. That's why you see the vibration of the string continue to grow.

Flipping the phase in such a situation would cause the amplified output to tend to cancel the vibration of the bass. In reality, the amplified output is neither perfectly in or out of phase with the bass and it varies across frequency. So, the phase switch simply lets you choose the polarity that gives the best overall result. You'll find that, understandably, in many situations flipping the phase switch leads to no discernible difference. In others, however, it can really be a lifesaver!

I'm never without my fdeck HPF/pre. Well, okay, I don't sleep with it under the pillow--- yet.

 

[drurb]

Bravo Doc .... You didn't upset someone .... A momentous historical event .... Just like yesterday's Presidential Election ! Just Kiddin' ... But it does seem like sometimes Folks don't always take so kindly to your erudite knowledge like VelvetPhil just did . You know I always listen up Doc.

Thanks! I think.

 

[MT Spaces]

... Just to clarify, the phase-reversal is not at all like a notch filter. A notch filter (aka band-reject filter, band-stop filter) reduces the amplitude of a relatively narrow range of frequencies. Often, feedback is caused by exciting a specific resonance in the room (or the bass) so cutting the output at this frequency often tames the problem without ruining the overall tonal balance of the sound.

A phase-reversal switch simply flips the waveform upside-down. That is, if the speaker cone went "out and in," then it now goes "in and out." This is useful in taming feedback induced by interaction of the speaker output and the bass itself. If the amplified sound is "in-phase" with the acoustic output of the bass, it can reinforce the vibration which, when amplifed, will reinforce it further, which when amplified.... You get the idea. That's why you see the vibration of the string continue to grow.

Flipping the phase in such a situation would cause the amplified output to tend to cancel the vibration of the bass. In reality, the amplified output is neither perfectly in or out of phase with the bass and it varies across frequency. So, the phase switch simply lets you choose the polarity that gives the best overall result. You'll find that, understandably, in many situations flipping the phase switch leads to no discernible difference. In others, however, it can really be a lifesaver!

I'm never without my fdeck HPF/pre. Well, okay, I don't sleep with it under the pillow--- yet.

I'm kinda late here to Thank You Doctor Les !! I was outta-town up in Butte Montana USA this week-end officiating a high-school girls volleyball tournament. The pay is way-better than what I get for playing bass (at least at my rookie level) and it was real-fun. Plus the scenery ain't bad either ... Montana has some some pretty landscapes and athletes .

I will be getting one of Francis' Black Boxes ('specially since you personally tested'n'oscilliscoped it out with your electronics-type thinking-brain). I can tell you right now.... I won't be sleeping with it under my pillow either. It will sit on top of my Coda ..... Doing it's high-pass thing on my Rev Solo and I'll switch the Coda from HPF to "notch" and get rid of that troublesome low-open-E feedback deal I seem to have been getting in that one tavern room that I will be playing in every Thursday night throughout The Winter.

Then, if I understand Bolo Steve and you correctly, I can flippedy-do the Francis' Box switch to either be in-er-outta phase. If all that don't work to solve my issues .... Well then .... I'm just gonna pour gasoline on all the electronic stuff, lite-a-bic, tell the loud alt-country boys to KMA, and go back to playing only acoustic bluegrass on my basses .

P.S. ..... Thanks again Doc .... If I ever have a bout with bummer psycho-acoustics and start hearing voices and bad-bass-playin' in my head again ..... I'll give you a shout (or is that a different psycho-type of book-learning out of your field of expertise ?) .

 

[Jake deVilliers]

You're going to love what FDeck's unassuming little black box does for your sound Bob. It makes it both thicker and cleaner, whatever the instrument.

I have taken to trying it on everything electrified that comes through my shop - Nationals, mandolins, guitars and of course DBs, and it improves them all!

"You might not believe this little fella, but it'll cure your asthma too!"

Don't leave home without it........

 

[drurb]

P.S. ..... Thanks again Doc .... If I ever have a bout with bummer psycho-acoustics and start hearing voices and bad-bass-playin' in my head again ..... I'll give you a shout (or is that a different psycho-type of book-learning out of your field of expertise ?) .

LOL! I'm fond of telling folks that I don't deal with "crazies or rats." Just normal-hearing (if not plain old normal) listeners who run in laboratory experiments in an effort to understand how the ear and brain work. If you do start hearing those voices, I can recommend a few folks, though.

fdeck's little wonder-box has to be one of the best deals on the planet. Yes, I did test the hell out of it, both on the bench and in real life. It's a really classy, very well-designed and well-built circuit.

As part of an economic stimulus package, maybe the Feds can buy one for every DB player in the country! Francis would be delighted, our sound would improve leading to more gigs, leading to greater income for the venues, leading to more income for us, leading to improvement of the GNP, leading to greater overall national prosperity, leading to improvement in the overall global economy, leading to world peace-- and all because of a little HPF/pre! I think I'm gonna go call one of those "voices in the head" docs now...

(Got any pics from the voleyball tourney?)

 

[velvetphil]

Got mine, love it. As was suggested by drurb, it sounds great with my Rev Solo - but man, what a pain it was to install that thing (the PU)! Been trying it through the line in of an Ashdown ABM amp and an Acme 2x10 - sounds very natural, much more "woody" than the K&K system but less present in the mids. Another way of saying that is it sounds "flat" in a good way. I think I need to try it with a 12" cab. Any suggestions?

LOVE IT!

 

[drurb]

Got mine, love it. As was suggested by drurb, it sounds great with my Rev Solo - but man, what a pain it was to install that thing (the PU)! Been trying it through the line in of an Ashdown ABM amp and an Acme 2x10 - sounds very natural, much more "woody" than the K&K system but less present in the mids. Another way of saying that is it sounds "flat" in a good way. I think I need to try it with a 12" cab. Any suggestions?

LOVE IT!

I'm honored! You took my advice all the away around. Best of all, you sound happy! Yes, the RS is a pain to fit but I really do think it is well worth it (You'd probably love to see how fast they fit them at Upton's shop).

Here's a tip. With the change of seasons, if you find that it loosens up in the bridge wing, a single layer of cellophane tape over one surface will usually do the trick. Also, once you find the "sweet spot" in terms of positioning, make a small mark with a pencil so you can easily and quickly restore the p/u to that position in case it gets bumped.

Oh, and the relatively attenuated mid-range compared to the K&K is, IMO, a very good thing (the K&K seems to have a mid-range "hump"). You seem to agree.

Enjoy!

 

[velvetphil]

Yeah...that Rev Solo - might have to get it refitted at the Upton shop. Field trip! Saw in your profile you're playing through an EA rig - what's your take on the Wizzy?

And yeah, I always appreciate thoughtful suggestions from anyone - and you seem to have a bunch!

 

[drurb]

Yeah...that Rev Solo - might have to get it refitted at the Upton shop. Field trip! Saw in your profile you're playing through an EA rig - what's your take on the Wizzy?

And yeah, I always appreciate thoughtful suggestions from anyone - and you seem to have a bunch!

If you're within striking distance of Upton's shop, it would be a worthwhile venture. It's fun too! Hey, maybe we can meet there.

I really do like the Wizzy. As you can find in many of my posts here, I also like the parametric tone-shaping section of the iamp200. Yes, it takes a bit of training (I've even posted about a training regimen) to understand how to use it effectively but, like the fitting of the RS, IMO, it is time well-spent.

 

[MT Spaces]

Boy that Francis is quick . In a matter of about 10 minutes last night e-mailing back and forth .... one of his gizmoes is on its way to me. I can hardly wait ... it will be nice to be able to use the Coda's notch filter and get HPFing from the gizmo. Here's hoping .... I may be able to go LOUD and tame the feedback yet.

You're going to love what FDeck's unassuming little black box does for your sound Bob ..... "You might not believe this little fella, but it'll cure your asthma too!" ....

Thanks Jake .... "Asthma" .... You actually hit a nerve there . Lately I have been stuffing foam behind the tailpiece, putting a piece of rubber automotive vacuum hose with slits for the strings on the afterlengths, and plugging the f-holes with 1" diameter black foam backer rod. My bass has asthma and can't breathe . Maybe I can de-foam and open up the air passages if I can figure out how to use the FDeck and Coda boxes features.

Got mine, love it. As was suggested by drurb, it sounds great with my Rev Solo ..... I think I need to try it with a 12" cab. Any suggestions?

VP ..... You might want to listen to your set-up thru a Wizzy 12 M-Line cab. My Kay with the Rev Solo sounds really "natural" and loud through the M-Line and I run the eqs on my AI amp pretty-much flat. Take your bass on a trip to Gollihur Bass sometime. Bob would probably let you plug into EA and AI amps and the Wizzy line of cabs for some test driving .

... As part of an economic stimulus package, maybe the Feds can buy one for every DB player in the country! ...

I like the way you think Doc . I would love to be stimulated. But I forget ..... Are us bass players members of the "Middle Class" or members of the "No Class" ??

.... (Got any pics from the volleyball tourney?) ....

Sorry Doc ..... Can't help you there. I wouldn't want to cause excessively-rapid heart palpitations resulting from tight-spandex shorty-shorts (known in the volleyball world as "bunhuggers") or further contribute to the deliquency of any Dirty Old Men around here .

 

[Jake deVilliers]

Nice Bob!

"Wanna bite of my walnetto?!"

"Would you call my face ruggedly handsome? Would you call my body sexually attractive? Would you call my next of kin?"

What a great show!

Oh, and that's a nice self-portrait of you beside Artie Johnson too!

 

[jonphilpott]

I built a fdeck hpf-pre for my dog house with what i like to call a "fake maxxxxxxxxxxxxxxxxx", its my version of the BassMax (2 piezo disks sandwiched together wired in parallel in the wing of my bridge).

The problem I'm having is that with the piezo plugged into the hpf-pre I'm not getting a lot of gain, with the preamp plugged into my practice-amp (hartke 30watt), I have to have the amp set at full volume to really get an audible signal. Now is this 'normal', or did i build it wrong? and if i built it wrong, does anyone have any advice as to where abouts in the circuit I should look to remedy?

As a side note, I also built the fdeck quick and dirty, and it behaves the same way.

 

[fdeck]

I built a fdeck hpf-pre for my dog house with what i like to call a "fake maxxxxxxxxxxxxxxxxx", its my version of the BassMax (2 piezo disks sandwiched together wired in parallel in the wing of my bridge).

The problem I'm having is that with the piezo plugged into the hpf-pre I'm not getting a lot of gain, with the preamp plugged into my practice-amp (hartke 30watt), I have to have the amp set at full volume to really get an audible signal. Now is this 'normal', or did i build it wrong? and if i built it wrong, does anyone have any advice as to where abouts in the circuit I should look to remedy?

As a side note, I also built the fdeck quick and dirty, and it behaves the same way.

Jon,

A quick sanity check involves measuring a few DC voltages in the circuit. The source terminals of the two JFETs should both be roughly a couple volts above ground. That's a way to be sure that the JFETs are both drawing current. Likewise the output of the last transistor, before the blocking capacitor, should be roughly half of the battery voltage. Note my liberal sprinkling of vague language, because there is some variation from batch to batch of those components.