Buffered inputs.

[catalin gramada]

Hello. Considering a regular passive pickup and a lenght of cable which add say 500pf capacitance arround, where should be better to place a buffer stage, in the guitar or at the amp input, for a low 50-100k input impedance, please? Thinking both positions comes with pros and cons but wanna ask for your opinion, please. Thanks.

[Chuck H]

My first considerations are:

The resonant peak created by passive pickups and cable capacitance has been a factor in the development of guitar and amplifier circuits as they have evolved together for decades. In that light:

It's unlikely that amplifier builders and manufacturers are likely to change to buffered inputs anytime soon. So placing it at the amp would mean that you must use THAT amp to get YOUR sound. Finding yourself in a pickle should you have to plug into a different amp for any reason.

Placing a buffer at an amplifier input shouldn't change anything about the relationship between the pickup and the cable capacitance. So where the resonant peak is lost, there is still the HF roll off. It WOULD make the EQ balance from the pickup more consistent with guitar volume control setting, but it would be a consistent rolled off HF unless another circuit were included with the buffer to artificially boost HF. Since the actual boost required would be different for every pickup I think results might be less than satisfying.

And then what happens when you plug a guitar with a buffered output into this amp with the buffered input and the artificial HF boost? I see things getting inconsistent really fast.

The past and current trends have been toward buffering the guitars output. And for good reason IMO. The thing you're really fighting with a buffered system is the cable capacitance. So the buffer should be placed before that. Along with an additional circuit to correct for the lost resonant peak and HF roll off. Without the extra circuit the guitar would probably sound very flat and hi fi.

JM2C

[Helmholtz]

Hello. Considering a regular passive pickup and a lenght of cable which add say 500pf capacitance arround, where should be better to place a buffer stage, in the guitar or at the amp input, for a low 50-100k input impedance, please? Thinking both positions comes with pros and cons but wanna ask for your opinion, please. Thanks.

If you like the sound of your PUs with cable attached into a high impedance input (>500k) and want to preserve it, I would put the buffer in a housing and place it after the cable before any pedals (exception: Fuzz Face). This eliminates any downloading by the amp and effects and as well as the cables following the buffer. I often use my Tube Screamer in this way as a buffer.
If you build the buffer into your guitar you will need to simulate the cable capacitance by an equivalent capacitor wired in parallel with the PUs before the buffer (in other words across the buffer's input) to reproduce the original sound/resonant frequency.

[catalin gramada]

Thanks for your thoughts gents. Trying the best of both I splitted the cable in two length: one 10 feet piece and one 20 feet piece. I put a tc electronics buffer in between 1M/100ohm. Found best results with the shortest length into guitar side and the longer from buffer to the amp. Both cables are low capacitance Klotz Lagrange 70p/m around but doubling from 10 to 20 feet did a lot of difference for my "high" 220 kohm amp input . Thanks.

[pdf64]

How come your amp input impedances are lower than normal, eg 50k-100k?

[catalin gramada]

It is a ss Peavey tnt130. Two inputs: low one as 44k and high one as 220k. Like this was not enough, saw on the board an extra 100p cap from input to ground, think from stability reason......think.The amp sound pretty good but a 20 feet cable did a mess. Any high harmonics are rolled down and should be large compensated from eq even with a good quality cable

[Enzo]

The tiny 100p cap is to shunt off any RF coming in with the signal.

[catalin gramada]

I bought for my buffer a 9V DC Truetone power adapter, sort of one we charge the phones. I got hum from begining (very little 100hz noise clearly distinctive into a quiet room) but reversed the power adapter into wall socket the hum goes away....Very strange as the adapter have no earthing so no loops can be developed in between...
I remember from pics tnt130 models made for USA market have an additional reverse power switch, very useful for this kind of situations. The models for Europe have not we have to deal with position of the plugs into wall socket.

[Helmholtz]

Thanks for your thoughts gents. Trying the best of both I splitted the cable in two length: one 10 feet piece and one 20 feet piece. I put a tc electronics buffer in between 1M/100ohm. Found best results with the shortest length into guitar side and the longer from buffer to the amp. Both cables are low capacitance Klotz Lagrange 70p/m around but doubling from 10 to 20 feet did a lot of difference for my "high" 220 kohm amp input . Thanks.

Your PUs can only "see" and interact with the cable directly connected to the guitar. What comes after the buffer is "invisible" and thus does not contribute to tone shaping.

[J M Fahey]

Agree.
With a guitar mounted buffer , or a very close one (belt/strap/floor but with a short cable, say no more than 6 ft), the pickup will be loaded by very small capacitance.
Now if buffer is at preamp input, 20 ft away, with your 500pF cable in the middle ... itīs too late for buffer do much good ... if any at all.

[Helmholtz]

Now if buffer is at preamp input, 20 ft away, with your 500pF cable in the middle ... itīs too late for buffer do much good ... if any at all.

In this special case I see the main benefit of using a buffer in isolating the PUs from the relatively low impedance amp input.

(I personally do not like the sound of my strats and LPs loaded by a (cable) capacitance below 1nF. But I use vintage-style (i.e. low inductance) PUs. Hotter, overwound PUs may sound "better" with lower capacitance (shorter) cables. It's all a matter of personal preference and the gear used.)

[catalin gramada]

Your PUs can only "see" and interact with the cable directly connected to the guitar. What comes after the buffer is "invisible" and thus does not contribute to tone shaping.

This is pretty much what I looking for. A ten feet cable into 1M input impedance it is a pretty conservative standard. The rest seems to not be affected at all by 20 feet lengthy and low impedance at the amp input

[J M Fahey]

In this special case I see the main benefit of using a buffer in isolating the PUs from the relatively low impedance amp input

True.
That said, lowish input impedance can easily be solved with no need for adding buffers, internal or external, just rise first Op Amp ground (or Bias) reference input resistor to 1M and call it a day.
The 4560 is bipolar input but has no problem with a 1M resistor; IF you wish you may replace it with a Fet input TL072 ... just for peace of mind, you donīt really need it.

In any case becomes what all others do.

EDIT: Are you using the TNT with a Guitar?
No big deal with the Amp itself, but what speaker are you using?

[catalin gramada]

No, it.s a bass, a Precision. The speaker is original Peavey BW with metallic dust cap

[Chuck H]

With a guitar mounted buffer , or a very close one (belt/strap/floor but with a short cable, say no more than 6 ft), the pickup will be loaded by very small capacitance.
Now if buffer is at preamp input, 20 ft away, with your 500pF cable in the middle ... itīs too late for buffer do much good ... if any at all.

THAT^^^^^^^^^^^^^^^^^^

I think the best, common uses for an in line buffer are

1) In old school recording. Where you have a room with a guy and an instrument and the amp in an iso cab or some other room. It allows the musician to use the same cable length tone they normally would regardless of how much cable is added after the buffer. And other similar situations in a studio where cable length can get out of hand quickly.

2) When you happen to be playing a large stage or venue that requires a lot of cable. The buffer goes from the floor effects board.

But notice that in both of the above cases the buffer is used after a length of cable. If the buffer were used at the guitar or on a belt or strap the sometimes desirable interaction between passive pickups and cable capacitance can't occur.

I don't know what cables you're using but is sounds like your desired level of interaction is ten feet of THAT cable. If you'd like even less interaction you'll need to go with the preamp in the guitar or the belt/strap mounted unit like Juan mentioned.

Does anyone still use wireless systems? I never have, but I would think there would be some buffering advantage there. Hopefully tune-able for a desired pickup/capacitor reactance.?.