Vintage Bass amp sim/DI - something a bit different.

[anotherjim]

It's an Amp simulator / Direct inject thing -  to be clear it's meant for playing direct into a mixer channel or full range "flat eq" amplification.

Now, by Vintage, I don't mean Ampeg SVT, I mean "whatever" amp came before SVT with big speakers in a sealed cab and flatwound strings on the bass.
This means not a lot of top end at all. Those cabs gave up past 2.5Khz to 3Khz. If slap & pop is your thing, then please move along elsewhere....

Enough top cut EQ to get roundwound strings sounding smoother like flats. This is tougher that it might seem. The tone control on the bass still needs rolling off too to get rid of pesky roundwound overtones, but put the bass tone up full for vintage roundwound growl

Weaker bottom end from un-ported cabs, so bass cut is essential.

Mid range is left intact - that, IMHO, is where the melodic voice of the vintage bass tone resides -  2nd & 3rd harmonics dominate.

Moderate/subtle distortion to bring out growl when you dig in. Not tried with active basses, I only ever use passive meself.

Drive a 10k line input -  it ain't a DI if it can't do that.

I couldn't see anything published that was quite the thing, so this is what I've come up with...



Yes, the CD4007 MOSFETS again! Yay!!!
It's all running from a 5v regulator.
The input needs bias trim since I currently think this is the best sounding and reliable way to get the mosfet in the sweet spot - which is somewhere about 2.5V on the drain pin5.
Reason for the low 5v supply -  so the inverter only needs moderate gain to do it's soft clip thing without any nasty artefacts or hiss.
Conventional Tone Stack thrown away. I like the separated bass & treble better.
The treble cut is tuned a lot lower down than I originally expected it would need to be.

Some bits of the 4007 left over - so Millenium bypass is available. Tie the Gate pin10 to 0v if that's not used.

I'm liking it a lot as drawn so far. Taken to jams & nobody has twigged on that I'm actually using a keyboard amp! Big test is when I get around to putting new SS rounds on the bass.

[Bill Mountain]

Pure and simple.  I bet it sounds great!

Have you thought about adding a balanced out?  I always struggle with figuring the best circuit to go with.

[anotherjim]

I'd copy a balanced out if I'd wanted one from somewhere. Now I thought I saw the Tech21 scheme with a dual opamp somewhere but google doesn't seem to want to find it for me....

[samhay]

Cool.
Not sure how much current it could push, but you could fashion a balanced output out of a complementary pair of the MOSFETS and do away with the Millennium bypass...

>Big test is when I get around to putting new SS rounds on the bass.
Don't do it. Put flats on instead - looks like you really want to deep down.

[Granny Gremlin]

Weaker bottom end from un-ported cabs, so bass cut is essential.

Negatory.  There is actually deeper bass from the same speaker in a sealed than ported (lower extension).  Ported just stays flatter longer before dropping off a cliff (the sealed would be, say,  3-6 db down at that point, but still going).  A more gradual ("natural") rolloff (actually very close to a 1st order filter with the 6db/octaveslope, so you could make it work; just don't cut too much).  ... then again, some vintage units (e.g. the Sunn cabs that were THE bass standard before the SVT came along) were reflex horns; there was some variety out there.

Mid range is left intact - that, IMHO, is where the melodic voice of the vintage bass tone resides -  2nd & 3rd harmonics dominate.

True, that is where the harmonics are, but look at the F response of just about any guitar speaker on the market - see how it is anything but flat with that huge upper mid bump?  That's the F resp shape of vintage bass speakers too, but (e.g. 15s) the bump will be a bit lower. Some flats also have a considerable mid bump compared to rounds with their top end zing. 

Drive a 10k line input -  it ain't a DI if it can't do that.

That is a useful feature, and if it only drives line level that's cool, but technically a DI is intended to drive a LoZ balanced mic input.

[sergiomr706]

So, what you are talking about is a sound like the one that comes from JBs first bassplayers, Bernard Odum and the like? A sound I really like for a deep groove!  ::)Excuse my poor knowledge, but, 5 volts are enough to handle dynamics? Im telling that because most circuits that are said to be very sparky and dynamic are higher voltage, 12 or 18 volts. Thanks a lot,
  Sergio

[anotherjim]

On bottom cut. Also have to deal with small rooms. Many British pub gigs/jams happen in fairly small rooms & the amps will usually have to be against a wall or in the corner. It's a fight to keep bass boom down. This bass control roll-off isn't strong, but the turn over frequency can start high when the 47n is dialled out. Apart from the coupling caps used for bass tone control, it's full range.

Not sure how much current it could push, but you could fashion a balanced output out of a complementary pair of the MOSFETS and do away with the Millennium bypass..

Ah, you mean copy the output to a unity inverter for a cold wire drive? I never thought of that. Level control might be difficult - but would it need one? It isn't that hot that it couldn't be controlled by the mixer gain anyway. Output impedance is high compared to a proper solution, but I think the losses into a mic channel could be made up.
To be honest, I wasn't considering having to plug it direct into an XLR snake box. I would have though you would have a ordinary "flat" D.I. available anyway to plug into.

If I put flats on the bass, I can't also get  Roundwound sound.
The aim is - 
Use rounds, guitar tone up -  like Floyds "Money" or Stranglers "Nice-n-sleazy". Obviously roundwounds picked, but the highs are almost brickwalled out and no boom whatever.
Guitar tone down - James Jamerson.

Sergio, old bass sound isn't all that dynamic - they fought for a fairly constant level. 5v is plenty of headroom. The parts are rail-rail unlike usual opamps. Hard clipping shouldn't happen. I think the dynamics of the bass on tunes like James Browns "I feel good" are in the feel/timing -  not the level. Those players new how to stop a note on time as well as start it. Most players only know how to start notes.
Yes, that sound is EXACTLY one of the things this pedal is aiming for.
So...

[samhay]

>Ah, you mean copy the output to a unity inverter for a cold wire drive?

That's what I was initially thinking, but I think you can do something more elegant with a complementary pair like this:



It is quite lossy - voltage gain is about 0.3, but you can feed it via a pot to set level.

You could also use one of the middle FETs with independent S and D as a Cathodyne-type phase splitter.

[anotherjim]

I suppose you could call that supply sensing Sam. I do wonder whether shoot through current is a problem in that scheme - that is voltage dropped over the source resistors can mask out signal wiggle. I have tried something similar and got rather bad full wave rectifier type frequency doubling. As either mosfet turns off, it unloads the resistors and this happens for + and - swings. Does the sim software model the shoot thru?
Cathodyne might be simpler - simply run off existing level control output.
I doubt I'll have time to test it any time soon, so any who want to, have at it!

Strictly speaking it doesn't necessarily need bypass switching. I done it for A/B checking. A slide DPDT is a cheaper alternative to a stompswitch if you don't expect to need to bypass in performance.

Anyway, I'll take to the local jam tonight then in the coming week get some demo tracks done.

[samhay]

>Does the sim software model the shoot thru?
Yes, but you can null this out by biasing the FETs - R2/R4 is your 50k trim.

It was theoretical, so good to hear that it sort of works in reality.
To be honest, any of the options are going to be mediocre at best, and I expect a dedicated balanced driver using e.g. a NE5532 would very likely be worth the extra PCB real estate if balanced output is needed.

[sergiomr706]

Thanks for the explanation Jim, my precission always wears flatwounds and a sponge under the bridge ashtray, so the next thing to try would be something like this, instead of an ampeg simulation.  I ll try to  lay it out with an editor, doesnt seem complicated, not a lot of parts here. Thank you.

[Bill Mountain]

To be honest, I wasn't considering having to plug it direct into an XLR snake box. I would have though you would have a ordinary "flat" D.I. available anyway to plug into.

You bring up a good point that is often lost on a lot of bassists.  Every time I see a new piece of bass gear the first question I have (or see) is whether or not it has a DI (I even did it to you).

I struggle with this question because like you say there are flat DI's out there and who are we to say we could do better???  I'm all for custom tailoring EQ and drive levels to taste but it's going to be hard to make a better DI than Countryman or Radial (or Sansamp for that matter).

You're helping me reaffirm my decision to not concentrate too much on that.  I think I'll pick up a passive Radial for my board for when the club doesn't have one.

I'm definitely interested in demos.

[anotherjim]

my precission always wears flatwounds and a sponge under the bridge ashtray

It appears that you already know what you're doing Sergio. If you are a committed flats player, you may not need C4. Sponge will also be taking some top end out.

If you have a Sansamp - it can be bypassed to work as a flat D.I. To quote Tech21 "The footswitch activates the Tube Amplifier Emulation circuitry. Disengaging the circuitry enables you to use SansAmp Bass Driver DI as a standard active transparent direct box. " So obviously another "tone" box can be used in series allowing you to have it all.

Last nights pub jam was a bit weird - St Valentines day so the more romantic regulars were elsewhere romancing their "other halves" (I brought mine with me as a romantic treat). We were just a 3 piece and had a great time. Played my P bass through a Laney AH100 audiohub combo with the "Vintage". Sound was clear & punchy. Well pleased.

Just been spending some time with "Vintage" plugged into mixer & listening on phones. Getting some ideas for demo pieces.

[samhay]

Sorry to hijack, but Bill, what do you want a flat DI to do?
If you are happy to go active and ditch the transformer, is not difficult or expensive to build a balanced line driver around a dual op-amp. We know how do do high impedance buffers, etc, which we can tack on the input...

[Bill Mountain]

Sorry to hijack, but Bill, what do you want a flat DI to do?
If you are happy to go active and ditch the transformer, is not difficult or expensive to build a balanced line driver around a dual op-amp. We know how do do high impedance buffers, etc, which we can tack on the input...

I have no strong preference either way (active or passive).  I'm just trying to decide on a good basic circuit to tack on to a future build at some point.

But the main thing stopping me is the plethora of adequate DI's in existence (but there aren't many simple active ones made for pedal boards  that easily run off of 9V).  The pedal board friendly ones often have some other preamp or feature attached to them.  Hence why I'd like to build my own one eventually.

I have some TI DRV134 balanced driver chips that I'm hoping to experiment with one day.

[Bill Mountain]

I wanted to bump this because I feel like we got off track and I want to hear more about the circuit from the OP.  I'm looking forward to hearing demos.

[anotherjim]

Not entirely off-track Bill. I found some full Sansamp schemes and they seem to employ RC4580 dual to drive the XLR in an obvious manner (unity buffer to hot and unity inverter to cold).

Anyway, this thing is already boxed & no room for much of anything more.
I like the basic tone so much, I may well develop a more sophisticated SVT type thingy in the future and XLR drive will feature.

Have started recording demo's. Still with worn rounds, then I'll do some with new. I don't have enough basses to dedicate one to flats. Making isolated, unadulterated bass tracks is quite "challenging" even though they only have to be snippets.

[anotherjim]

Demo's are up.
https://soundcloud.com/ashdalestudio/sets/vintage-bass-preamp
Headphones required to get the full bottom end heard properly.
The "bassier" ones sound weirdly like those isolated studio tracks you find on YouTube & such.

[Bill Mountain]

Awesome.  Thanks for sharing these sound great!

[Kipper4]

Nice Jim.
I'm gonna check the chip stocks tomorrow and see if I've ever bought that chip.
I'll breadboard it.