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Double Bass fdeck preamp techie question...

velvetphil

velvetphil

Feb 22, 2006
349
1
Los Angeles, CA
#1
Hey all,

So I emailed Francis with this question; he hasn't gotten back to me yet, so I figured I would put it to all of you!

"Hi Francis,

I've been hearing a lot about your preamp from various satisfied customers, and it has pretty much everything I need. The only thing is that I use a K&K Bass Master Pro system. The two piezo elements are wired into a single TRS plug, which goes to a proprietary "blending" preamp with a mono output. There's no phase reversal or high-pass filter, which is why I like your unit better. I'm wondering: could I use both? Put yours in line after the K&K preamp and get the phase and HPF benefits? Is there a downside to using two preamps? Does your unit actually actively boost the signal from the piezo, or just buffer it? Is there a way you can build a box that simply has a passive HPF/bass roll-off along with a phase inverter, that is not a preamp and is impedance-neutral?

Thanks for your time, hope to hear from you soon!

Phil"

Any ideas?

Thanks in advance!

Phil
 
#2
Some things to consider:

1. there is a +3db gain with Fdecks box

2. Not sure how impedence match up will work with two preamps, but it *should* be fine. Fdecks unit has a 10 mega ohm impedence.

I used Fdecks box in line with a tube preamp for some time and it worked quite well. The other preamp also had a 10meg ohm impedence, but with a variable gain.

I think you'd be fine.
 
#3
velvetphil said:
Hey all,

So I emailed Francis with this question; he hasn't gotten back to me yet, so I figured I would put it to all of you!

"Hi Francis,

I've been hearing a lot about your preamp from various satisfied customers, and it has pretty much everything I need. The only thing is that I use a K&K Bass Master Pro system. The two piezo elements are wired into a single TRS plug, which goes to a proprietary "blending" preamp with a mono output. There's no phase reversal or high-pass filter, which is why I like your unit better. I'm wondering: could I use both? Put yours in line after the K&K preamp and get the phase and HPF benefits? Is there a downside to using two preamps? Does your unit actually actively boost the signal from the piezo, or just buffer it? Is there a way you can build a box that simply has a passive HPF/bass roll-off along with a phase inverter, that is not a preamp and is impedance-neutral?

Thanks for your time, hope to hear from you soon!

Phil"

Any ideas?

Thanks in advance!

Phil
Click to expand...

I know fdeck's pre-amp and its design rather well. So here goes. You could cascade these devices in the manner you describe but you'd have to be careful not to overload the input of fdeck's pre-amp with the output of the K&K blender. You would, of course, not have the benefit of loading the piezo with the 10-Mohm input of fdeck's device if it is second in the chain. The fdeck pre-amp is pretty close to unity gain in that IIRC, there is a very slight (but adjustable) gain. No, the circuit cannot be built passively in any practical way. One problem would be that it would behave differently with each different type of pickup connected to it (different impedances, etc.). Another proble would be "insertion loss." That is, a substantial amount of level would be lost. Forget a passive version.

Finally, FWIW, I have found those K&K pre-amp blenders to be among the most poorly designed devices of their type. They are about one notch above a toy. I know, as I spent quite a number of years designing and building similar circuits. 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. :) In all likelihood, your amplified sound will improve.
 
#4
You can use the HPF-Pre anywhere between your bass and your amp's input. I've even tried using it an effect loop, and it worked fine. Gain added by the HPF-Pre is really minimal and nothing to worry about. fdeck did a really good job designing this thing, and headroom is normally not an issue in my experience.

If you want to add a high-pass filter and phase reverse capability to your rig, you will like the HPF-Pre. It's about as simple and as good as it gets. For the price, it's a no brainer.
 
#5
drurb said:
Get a good single piezo pickup, run it into fdeck's pre-amp and sell the other stuff on ebay. :) In all likelihood, your amplified sound will improve.
Click to expand...

You know, I've been thinking of doing this anyway. The TRS output is more trouble than it's worth; i.e. being off-limits to most piezo preamps. Pretty sure I like the wing (Bass Max) element of my system better than the bridge element, so maybe I'll do what you say and grab a used unit somewhere. Also looking at the Fishman Full Circle; any others that work off the bridge wing? I think that's the money spot on my bass.

robgrow said:
I've even tried using it an effect loop, and it worked fine.
Click to expand...

Yeah, this was the other option - get a true-bypass box and switch it in and out depending on need. Though if I use it as my primary pre, I won't need to do this of course!

And thanks for the advice you guys! Think I'm going to pull the trigger on the HPF regardless...

Phil
 
#6
velvetphil said:
You know, I've been thinking of doing this anyway. The TRS output is more trouble than it's worth; i.e. being off-limits to most piezo preamps. Pretty sure I like the wing (Bass Max) element of my system better than the bridge element, so maybe I'll do what you say and grab a used unit somewhere. Also looking at the Fishman Full Circle; any others that work off the bridge wing? I think that's the money spot on my bass.

And thanks for the advice you guys! Think I'm going to pull the trigger on the HPF regardless...

Phil
Click to expand...

I'm glad you didn't get upset with me for making my suggestion! fdeck's unit is a real gem. It's a terrific value for the money and it's a really well-performing circuit. I did some laboratory measurements on the device before it was released for general sale.

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. Check out the discussions and reviews in these threads. Comparing the BassMax to the Rev Solo, on all the basses I've tried it on, I found the BassMax to be "boomy" and unrefined. It tended to make the DB sound like a big BG. The Rev. Solo, on the other hand, is as close to "my bass but bigger" that I have ever gotten with a bridge-wing piezo. I'm so happy with it that I have no pickup G.A.S. and, believe me, I'm not easy to please!
 
#8
velvetphil said:
The TRS output is more trouble than it's worth; i.e. being off-limits to most piezo preamps. Pretty sure I like the wing (Bass Max) element of my system better than the bridge element, so maybe I'll do what you say and grab a used unit somewhere. l
Click to expand...
The split output TRS option is probably more trouble than it's worth.
I suggest you take a soldering iron to that unit and try (a) just the bridge (b) just the wing (c) both wired in parallel - wired to a standard jack - and see which one sounds best.
 
#9
ToneRanger said:
The split output TRS option is probably more trouble than it's worth.
I suggest you take a soldering iron to that unit and try (a) just the bridge (b) just the wing (c) both wired in parallel - wired to a standard jack - and see which one sounds best.
Click to expand...

Hmmm...I actually wasn't thinking about splitting the TRS plug; I just turned the bridge pickup all the way down and loved the sound of the wing by itself. At any rate, I pulled the trigger on fdeck's pre. Looking forward to it! Think I'm gonna sell the Bass Master Pro and pick up a Rev Solo on drurb's recommendation.
 
#10
velvetphil said:
impedance-neutral?
Click to expand...

I don't think this is really how it (er, electronics? physics?) works, but someone will correct me if I'm wrong. The input you plug your bass into is going to have an impedance, and it's not so much a question of matching impedance(s) as it is of deciding which impedance you want for your pickup. Piezos tend to sound "better" into higher-impedance inputs; plugging into a 600K Ohm guitar jack sounds thin and scratchy, while going through a 2M Ohm (or 10M Ohm) input restores the low end and fatness. Because the input loads the pickup, I've always thought it was best to plug first into the thing with the impedance you like--in this case, the fdeck pre. Then go from there.

Of course, all pickups are different, amps are different, and so forth. There's basically no point in using fdeck's pre with an AI amp, for example, if the impedance thing is your main interest, because the 1/4" inputs on the AI are already high-impedance. What I've been doing is plugging my bass into the fdeck box, going from there into a Sadowsky outboard preamp (standard bass and treble, volume pots), and into the effects return jack on an AI Clarus. It sounds remarkably great with both piezo-equipped double basses and passive electric basses (which also benefit from a high impedance input). Going the other way (Sadowsky to fdeck) is not the same, for certain.

OK, DRURB, correct my gross generalizations and inaccuracies! :)
 
#11
Jeremy Allen said:
I don't think this is really how it (er, electronics? physics?) works, but someone will correct me if I'm wrong. The input you plug your bass into is going to have an impedance, and it's not so much a question of matching impedance(s) as it is of deciding which impedance you want for your pickup. Piezos tend to sound "better" into higher-impedance inputs; plugging into a 600K Ohm guitar jack sounds thin and scratchy, while going through a 2M Ohm (or 10M Ohm) input restores the low end and fatness. Because the input loads the pickup, I've always thought it was best to plug first into the thing with the impedance you like--in this case, the fdeck pre. Then go from there.
Click to expand...

Perfecto! You are 100% correct that it is not impedance-matching at all. Rather, it is optimal impedance loading that you are after.

Jeremy Allen said:
Of course, all pickups are different, amps are different, and so forth. There's basically no point in using fdeck's pre with an AI amp, for example, if the impedance thing is your main interest, because the 1/4" inputs on the AI are already high-impedance. What I've been doing is plugging my bass into the fdeck box, going from there into a Sadowsky outboard preamp (standard bass and treble, volume pots), and into the effects return jack on an AI Clarus. It sounds remarkably great with both piezo-equipped double basses and passive electric basses (which also benefit from a high impedance input). Going the other way (Sadowsky to fdeck) is not the same, for certain.

OK, DRURB, correct my gross generalizations and inaccuracies! :)
Click to expand...

No over-generalizations. No inaccuracies. Well stated. Bravo! :)

Of course, the adjustable high-pass filter (HPF) is what sets fdeck's little beauty apart from many other pre-amps and simple circuits that would achieve only desired impedance loading. Many here know how I have ranted about the benefits of filtering infrasonics and the HPF does that very well. The phase-reversal switch is also very useful in cutting feedback in some situations.
 
#12
Ah excellent! The main reason I'm looking at my setup this closely is because I'm primarily a doubler these days. I'm looking for light weight and convenience. To that end, I'm looking at a Markbass F500 head and 12" cab, which has an input impedance of 500k. As I said, I think I'm going to dump the K&K, so it'll end up being the Rev Solo into the HPF pre. Following that, I'm thinking about a variable impedance box like the Radial Dragster going into a Radial I/O input switcher (true-bypass), to go back and forth between P-bass and upright. The Radial I think will give me some flexibility with the sound into the Markbass; worth a shot anyway!

Thanks for the advice everyone!
 
#13
velvetphil said:
Ah excellent! The main reason I'm looking at my setup this closely is because I'm primarily a doubler these days. I'm looking for light weight and convenience. To that end, I'm looking at a Markbass F500 head and 12" cab, which has an input impedance of 500k. As I said, I think I'm going to dump the K&K, so it'll end up being the Rev Solo into the HPF pre. Following that, I'm thinking about a variable impedance box like the Radial Dragster going into a Radial I/O input switcher (true-bypass), to go back and forth between P-bass and upright. The Radial I think will give me some flexibility with the sound into the Markbass; worth a shot anyway!

Thanks for the advice everyone!
Click to expand...


Following the pre-amp/HPF with a variable impedance box seems to provide no advantage of which I can think.
 
#15
Gearhead43 said:
The Radial does not go high enough in impedance to do anything for piezo pickups.
Click to expand...

He wanted to put the radial after the fdeck pre/HPF. In that case, the piezo would be loaded and buffered by the active circuit of the pre/HPF. Following the pre/HPF with a variable impedance box just doesn't seem to provide any advantage. I'm not a fan of such devices in any case.
 
#16
drurb said:
Finally, FWIW, I have found those K&K pre-amp blenders to be among the most poorly designed devices of their type. They are about one notch above a toy. I know, as I spent quite a number of years designing and building similar circuits.
Click to expand...


Gearhead43 said:
+1

I was amazed how cheaply made those POS are.
Click to expand...

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.
 
#17
So Francis hasn't gotten back to me yet; I sent him the cash for his pre via PayPal last Thursday or so. I'm sure he's a good guy and just very busy, but I'm getting a little nervous. Has anyone had bad experiences with him? Or maybe could you just describe your experiences with him? Again, not trying to disparage him, but I'm getting a little nervous.
 

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