Effective OP-AMP Input Impedance, JFET vs. BiPolar

Frequently asked questions regarding powering your pedal.

Re: Effective OP-AMP Input Impedance, JFET vs. BiPolar

Postby DrNomis » 04 Sep 2011, 22:23

matt239 wrote:Right. The Lo input Z is supposed to be part of the magic with the Fuzz Face, though I think a fuzz with a buffer in front can also sound good.
Why not just shape the pre-fuzz tone with filtering? That way you can choose the precise frequency response desired, & even make it switchable or adjustable.. :)

So for a general purpose device:
I'm not really seeing a compelling reason NOT to use a 1M pull-down resistor, 150 Ohm series resistor, & an LM833.

Right? :D



The Lo input Z of the Fuzz Face is responsible for the bassiness of the resulting tone, due to the very heavy load it presents to the guitar, but there's more, rather than causing the clipping to be mushy, it acually causes the clipping to be very sharp, regardless of whether Si or Ge transistors are used, when the input is driven by a Lo Z Source, such as a buffered output, the Lo input Z of the Fuzz Face has much less of a loading effect because the buffered output can drive it, so as we increase the input signal level, the Fuzz Face clips the signal more and more asymmetrically, which is why the Fuzz Face earned a reputation for not playing nice with other pedals..... :hmmm:
Genius is not all about 99% perspiration, and 1% inspiration - sometimes the solution is staring you right in the face.-Frequencycentral.
User avatar
DrNomis
Old Solderhand
 
Posts: 6899
Joined: 16 Jul 2009, 05:56
Location: Darwin,Northern Territory Australia
Has thanked: 123 times
Have thanks: 401 times

Re: Effective OP-AMP Input Impedance, JFET vs. BiPolar

Postby kleuck » 05 Sep 2011, 00:43

matt239 wrote:Right. The Lo input Z is supposed to be part of the magic with the Fuzz Face, though I think a fuzz with a buffer in front can also sound good.
Why not just shape the pre-fuzz tone with filtering? That way you can choose the precise frequency response desired, & even make it switchable or adjustable.. :)

So for a general purpose device:
I'm not really seeing a compelling reason NOT to use a 1M pull-down resistor, 150 Ohm series resistor, & an LM833.

Right? :D

Actually, this is not (at least alone) the low impedance of the FF, but the fact that the source, ie the guitar, is part of the nfb, this is what gives the FF his sensibility to the guitarist's play (cause resistance of the pickups are actually impedance, variable with frequency etc), pot, cable etc.
Randall Aïken said :
Q: Is there any advantage to using solder with a 2% silver content?
A: Yes. Silver solder keeps werewolves away from your amp.
User avatar
kleuck
Cap Cooler
 
Posts: 469
Joined: 16 Nov 2008, 00:24
Location: France
Has thanked: 44 times
Have thanks: 31 times

Re: Effective OP-AMP Input Impedance, JFET vs. BiPolar

Postby matt239 » 05 Sep 2011, 23:36

OK guys, this isn't a Fuzz Face thread! :lol:

- Another thing to keep in mind when designing inputs for guitar; the pull-down resistor will be in parallel with the guitar's controls from signal to ground, so for instance in a Strat with a 250k vol & 250k tone (only one tone control is in the circuit at a time, right?) - even with a 1M pull-down resistor the actual resistance to ground "seen" by the pickup will be 111k !
And in a Tele with 1M vol & tone, the pickup "sees" 333.33k.

So, if we start using a lower value pull-down resistor, say 250k, then the Tele pickup sees (1M,1M,250k, parallel) = 166.666k
The Strat p/u sees (250k,250k,250k, parallel) = 83.33k !

If we go to a 100k pull-down resistor then:
Tele p/u sees 83.3K
Strat p/u sees 55.55k !
You get the idea.

Also these parallel resistances would lower our "node impedance" giving us less reason for concern about "high node impedance" related noise, Right?? :?:
matt239
Solder Soldier
 
Posts: 225
Joined: 11 Sep 2010, 19:54
Has thanked: 62 times
Have thanks: 5 times

Re: Effective OP-AMP Input Impedance, JFET vs. BiPolar

Postby DrNomis » 06 Sep 2011, 00:28

matt239 wrote:OK guys, this isn't a Fuzz Face thread! :lol:

- Another thing to keep in mind when designing inputs for guitar; the pull-down resistor will be in parallel with the guitar's controls from signal to ground, so for instance in a Strat with a 250k vol & 250k tone (only one tone control is in the circuit at a time, right?) - even with a 1M pull-down resistor the actual resistance to ground "seen" by the pickup will be 111k !
And in a Tele with 1M vol & tone, the pickup "sees" 333.33k.

So, if we start using a lower value pull-down resistor, say 250k, then the Tele pickup sees (1M,1M,250k, parallel) = 166.666k
The Strat p/u sees (250k,250k,250k, parallel) = 83.33k !

If we go to a 100k pull-down resistor then:
Tele p/u sees 83.3K
Strat p/u sees 55.55k !
You get the idea.

Also these parallel resistances would lower our "node impedance" giving us less reason for concern about "high node impedance" related noise, Right?? :?:



Now, I'm guessing that if we make the pulldown resistor 10M instead of 1M, the resistance seen by the pickup should be more than 111k?..... :hmmm:

Sorry about the Fuzz Face posting btw, but it was kind of relevant, it is a good illustration of what effect the input impedance has on the source impedance.... :thumbsup
Genius is not all about 99% perspiration, and 1% inspiration - sometimes the solution is staring you right in the face.-Frequencycentral.
User avatar
DrNomis
Old Solderhand
 
Posts: 6899
Joined: 16 Jul 2009, 05:56
Location: Darwin,Northern Territory Australia
Has thanked: 123 times
Have thanks: 401 times

Re: Effective OP-AMP Input Impedance, JFET vs. BiPolar

Postby matt239 » 06 Sep 2011, 00:52

DrNomis wrote:Sorry about the Fuzz Face posting btw, but it was kind of relevant, it is a good illustration of what effect the input impedance has on the source impedance.... :thumbsup

Yeah, I was just teasing about the FF posts. :D and yes it was a good example. :)
matt239
Solder Soldier
 
Posts: 225
Joined: 11 Sep 2010, 19:54
Has thanked: 62 times
Have thanks: 5 times

Re: Effective OP-AMP Input Impedance, JFET vs. BiPolar

Postby matt239 » 06 Sep 2011, 05:39

If you go to to 10M resistor, the resistance seen by the p/u is more than 111k, but still <125k. (123.46k)

So perhaps we reach a point of diminishing returns using a bigger R than 1M.
I've seen some designs with a 2.2M. 10M is almost an open circuit..

We don't really get into trouble until we go = or < the value of the guitar controls, but then it happens fast.
Probably can't hear a lot of difference between a 470k pull-down, & a 1M, but we're probably changing the tone quite a bit with a 100k.
(Our resistances form part of an RC low-pass filter with the cable capacitance.)
matt239
Solder Soldier
 
Posts: 225
Joined: 11 Sep 2010, 19:54
Has thanked: 62 times
Have thanks: 5 times

Re: Effective OP-AMP Input Impedance, JFET vs. BiPolar

Postby kleuck » 06 Sep 2011, 10:41

matt239 wrote:.
(Our resistances form part of an RC low-pass filter with the cable capacitance.)

RLC low-pass actually.
Randall Aïken said :
Q: Is there any advantage to using solder with a 2% silver content?
A: Yes. Silver solder keeps werewolves away from your amp.
User avatar
kleuck
Cap Cooler
 
Posts: 469
Joined: 16 Nov 2008, 00:24
Location: France
Has thanked: 44 times
Have thanks: 31 times

Re: Effective OP-AMP Input Impedance, JFET vs. BiPolar

Postby matt239 » 08 Sep 2011, 04:55

RLC ! :wink:

2 other points:

1 - I'm thinking that, if necessary, diodes would be as cheap/simple for protecting an op-amp as a BJT transistor and it's associated components.
Google "protection diodes" and "diode clamps" check out "differential protection diodes" (the diodes are connected anti-parallel from inverting to non-inverting inputs.)

2 - While guitar pickups are considered "high Z" compared to dynamic microphones, they are low Z relative to our discussion here. (6k to 12k vs. our many-mega-Ohm op-amp input)
A transistor buffer would not be necessary for "impedance conversion" to present a relatively low Z to our op-amp input. - Right?

These 2 items, plus the parallel resistance of the guitar controls with our pull-down resistor, affirms for me the utility and appropriateness of connecting directly to an op-amp as our input, with a 680k to 1M pull-down resistor, 150 Ohm to 1k series input resistor, and maybe the addition of protection diodes.

... Unless I've got everything completely ass-backwards... which is entirely possible.. :lol:

So, have I got you guys talked into this topology now? :lol:
matt239
Solder Soldier
 
Posts: 225
Joined: 11 Sep 2010, 19:54
Has thanked: 62 times
Have thanks: 5 times

Re: Effective OP-AMP Input Impedance, JFET vs. BiPolar

Postby DrNomis » 08 Sep 2011, 07:01

Well the way I see it, anything is worth a try and in Electronics there is more than one way to achieve the desired results, that's what's so great about this fascinating subject and it get's even more fascinating with regards to stompbox designing/building.... :thumbsup
Genius is not all about 99% perspiration, and 1% inspiration - sometimes the solution is staring you right in the face.-Frequencycentral.
User avatar
DrNomis
Old Solderhand
 
Posts: 6899
Joined: 16 Jul 2009, 05:56
Location: Darwin,Northern Territory Australia
Has thanked: 123 times
Have thanks: 401 times

Re: Effective OP-AMP Input Impedance, JFET vs. BiPolar

Postby kleuck » 08 Sep 2011, 10:00

I try to make my circuits as simple as possible, "less is more" (and more buffers is....more noise when you use 3 or 4 pedals at the same time)so i do not use any buffer (except in...buffer pedals haha) but i do not always use the same input resistance, depends on the design and purpose of the circuit (as we all make TBP pedals now) so it's between 500K and 1M for AOP-based ones, sometimes 100K, and 1M for transistor-based circuits (fet in the input generally)
Randall Aïken said :
Q: Is there any advantage to using solder with a 2% silver content?
A: Yes. Silver solder keeps werewolves away from your amp.
User avatar
kleuck
Cap Cooler
 
Posts: 469
Joined: 16 Nov 2008, 00:24
Location: France
Has thanked: 44 times
Have thanks: 31 times

Re: Effective OP-AMP Input Impedance, JFET vs. BiPolar

Postby phatt » 09 Sep 2011, 10:07

matt239 wrote:RLC ! :wink:

2 other points:

1 - I'm thinking that, if necessary, diodes would be as cheap/simple for protecting an op-amp as a BJT transistor and it's associated components.
Google "protection diodes" and "diode clamps" check out "differential protection diodes" (the diodes are connected anti-parallel from inverting to non-inverting inputs.)

2 - While guitar pickups are considered "high Z" compared to dynamic microphones, they are low Z relative to our discussion here. (6k to 12k vs. our many-mega-Ohm op-amp input)
A transistor buffer would not be necessary for "impedance conversion" to present a relatively low Z to our op-amp input. - Right?

These 2 items, plus the parallel resistance of the guitar controls with our pull-down resistor, affirms for me the utility and appropriateness of connecting directly to an op-amp as our input, with a 680k to 1M pull-down resistor, 150 Ohm to 1k series input resistor, and maybe the addition of protection diodes.

... Unless I've got everything completely ass-backwards... which is entirely possible.. :lol:

So, have I got you guys talked into this topology now? :lol:



Matt Your the one asking ,,, Not me.
No it is all very much dependent on a lot of variables.

Note* kleuck's * last post where he is down to 100k depending on what is happening. ????

Matt,,,,Go build some circuits ,,, then get back with results.

FWIW, I USE LIVE my home built equipment that gives me no great noise issues>>>
Has more treble than any guitar player would ever need>>> Has incredible sustain>>>Delivers amazing tonal options,,,,
Yet no one here is interested?

I often compete against some big name Amps at our local musicians club; Fender twins, Fender cyber Deluxe, Carvin Legacy, Line 6 Crap ,,, to name a few.
Yet They come and Ask ME? Go Firure :popcorn:

Meanwhile checkout the Mesa VTwin Schematic for more clues.
Note the opamp buffer has 1 meg input yet the triode (V1 clean mode) has 220k on the grid. :hmmm:

Shoved in between the buffer and Valve is a 10k pot WTF????? :shock: :shock: :shock:

Again I say ,,, Go figure??? :scratch: :scratch: :scratch: :scratch: :scratch:

Trust me I use a circuit based on the clean channel of the V Twin and it's just a stunning unit and leaves me in no doubt that many roads can lead to the same result. :secret:
You need to build a few circuits before you get the joke,, haha. 8)
My circuit setup is fine tuned for my own needs and will not suit everyone,,, but again I stress they come ask me,,,, not the other way round,,,, 8) 8)

I've learned that It pays great rewards to read between the lines. :secret:
Phil.
phatt
Transistor Tuner
 
Posts: 1064
Joined: 04 Aug 2010, 06:17
Location: Morayfield SE Qld AU
Has thanked: 0 time
Have thanks: 270 times

Re: Effective OP-AMP Input Impedance, JFET vs. BiPolar

Postby kleuck » 09 Sep 2011, 11:54

phatt wrote:
Note* kleuck's * last post where he is down to 100k depending on what is happening. ????


I don't want to explain all the trick, as it's my business to sell my pedals, but the trick is to have a lot of interaction between the guitar and the active component, when you use an inverting nfb.
Think of the Tube Sound Fuzz or the Red Llama, a lot of improvements can be done here.
Obviously, the guitar must be a passive one, and connected directly to the pedal to have the whole benefit from this trick.
With my treble boosters, i use a variable filter with a variable pot, the input impedance varies from a "modern" one at low settings (higher volumes and lows) to a low impedance, almost matching the Rangemasters's one (same trick as in the Omega Boost from ROF, but i was using this trick 20 years ago in a treble booster based on the Craig Anderton's one) so when in the real treble booster range, the input impedance is only 50 to 150K (my pedal, don't remember for the Omega)
So, as you raise the highs (lower the lows actually) you are loading more the guitar and taming a little the higher highs.My circuit has obviously also a huge voicing for the higher frequencies as i want i to be usable after a buffer, but it's better with the guitar directly in.
In more common circuits, like the TS9 or DOD308/MXR Disto+ (and derivatives of course), where the sound relies a lot on a noisy and low input impedance AOP, and where you want a limited bandwidth, it makes sense not to use a high input (noisy) impedance as we can use TBP easily nowadays.
Remember : a low input impedance is loading the guitar's electronic, and if it's very often a bad thing, it can also be a very good thing, you just have to know where and why the circuit will be used.
Think of the sound of a Rangemaster preceded by a buffer, and you get the point.
Randall Aïken said :
Q: Is there any advantage to using solder with a 2% silver content?
A: Yes. Silver solder keeps werewolves away from your amp.
User avatar
kleuck
Cap Cooler
 
Posts: 469
Joined: 16 Nov 2008, 00:24
Location: France
Has thanked: 44 times
Have thanks: 31 times

Re: Effective OP-AMP Input Impedance, JFET vs. BiPolar

Postby phatt » 09 Sep 2011, 11:59

mictester wrote:
phatt wrote:OK then if that is the direction the builder wishes to go with then why not a *bootstrapped BJT or FET input*?


There are a few good reasons - bootstrapped stages tend to hiss (though your 4 kHz roll-off would go a long way to mitigate this!), and you need a fairly large capacitor in an electrically vulnerable spot in the circuit. I found that most of the cheap electrolytics (and remember - we were trying to keep things cheap) were really microphonic. I first noticed this with an experimental pedal with a bootstrapped input stage that would suffer acoustic feedback when used at "stage" levels, and would transmit a huge "bang" when the footswitch was operated!

FETs are OK for input stages, but it's too easy to punch a hole through the gate with the slightest ESD. Again, this leads to unreliability. This is why it isn't sensible to put CMOS switches on the inputs of effects (something I've seen lately in some high-priced Boutique rubbish). The most reliable topology was a BJT used as an emitter follower feeding into either an FET or CMOS switch to feed either the effect or the bypass. It's also a good idea to have something similar on the way out of the circuit, and you can also have a nice low output impedance to drive cables if you need to.

The basic Tubescreamer is a design classic, and is probably one of the most reliable music circuits ever made. It causes me great amusement when I see the clueless Boutique Boobs remove the BJT input "for greater clarity" or "more transparency". Looking at some of the Boutique stuff around today, I frequently wonder how much of it breaks, and whether the BBs have the ability to repair under warranty, or do they just strap in another gooped board?


Hi Mic, This post got lost for a while,, but now that it is back.
Very interesting, :hmmm: :hmmm:
A big *Arrh Huh* moment for me. insert big light bulb :idea:
It's a big big help when you read the fine details of people who have gone before.
Your knowledge of the fine detail is greatly appreciated. :thumbsup
Phil.
phatt
Transistor Tuner
 
Posts: 1064
Joined: 04 Aug 2010, 06:17
Location: Morayfield SE Qld AU
Has thanked: 0 time
Have thanks: 270 times

Re: Effective OP-AMP Input Impedance, JFET vs. BiPolar

Postby kleuck » 09 Sep 2011, 12:22

phatt wrote:
mictester wrote:
phatt wrote:OK then if that is the direction the builder wishes to go with then why not a *bootstrapped BJT or FET input*?


There are a few good reasons - bootstrapped stages tend to hiss (though your 4 kHz roll-off would go a long way to mitigate this!), and you need a fairly large capacitor in an electrically vulnerable spot in the circuit. I found that most of the cheap electrolytics (and remember - we were trying to keep things cheap) were really microphonic. I first noticed this with an experimental pedal with a bootstrapped input stage that would suffer acoustic feedback when used at "stage" levels, and would transmit a huge "bang" when the footswitch was operated!

FETs are OK for input stages, but it's too easy to punch a hole through the gate with the slightest ESD. Again, this leads to unreliability. This is why it isn't sensible to put CMOS switches on the inputs of effects (something I've seen lately in some high-priced Boutique rubbish). The most reliable topology was a BJT used as an emitter follower feeding into either an FET or CMOS switch to feed either the effect or the bypass. It's also a good idea to have something similar on the way out of the circuit, and you can also have a nice low output impedance to drive cables if you need to.

The basic Tubescreamer is a design classic, and is probably one of the most reliable music circuits ever made. It causes me great amusement when I see the clueless Boutique Boobs remove the BJT input "for greater clarity" or "more transparency". Looking at some of the Boutique stuff around today, I frequently wonder how much of it breaks, and whether the BBs have the ability to repair under warranty, or do they just strap in another gooped board?


Hi Mic, This post got lost for a while,, but now that it is back.
Very interesting, :hmmm: :hmmm:
A big *Arrh Huh* moment for me. insert big light bulb :idea:
It's a big big help when you read the fine details of people who have gone before.
Your knowledge of the fine detail is greatly appreciated. :thumbsup
Phil.

I must say that you do not need any buffer before a TS9 circuit, if it was not for the electronic bypass, and i have yet to punch a whole in a fet (i use a LOT, and in the input bjts of a 4558, it's only a dream), they are indeed very reliable and do not need any bjt to be protected (even mosfets are not that sensible, and very often protected by construction).
As for the output buffer : i CAN'T stand them, because the sound of a passive guitar is a conjunction (among other things) of the pickup's inductance loaded by the capacitance of a cable, an output buffer just KILLS the sound of your axe (resonance peak), best way to emulate a PU in a cable is to use a 50 to 100K pot on the output.
Randall Aïken said :
Q: Is there any advantage to using solder with a 2% silver content?
A: Yes. Silver solder keeps werewolves away from your amp.
User avatar
kleuck
Cap Cooler
 
Posts: 469
Joined: 16 Nov 2008, 00:24
Location: France
Has thanked: 44 times
Have thanks: 31 times

Re: Effective OP-AMP Input Impedance, JFET vs. BiPolar

Postby merlinb » 09 Sep 2011, 13:30

kleuck wrote:
phatt wrote:
mictester wrote:
phatt wrote:As for the output buffer : i CAN'T stand them, because the sound of a passive guitar is a conjunction (among other things) of the pickup's inductance loaded by the capacitance of a cable, an output buffer just KILLS the sound of your axe (resonance peak)

Not so, I say. With true bypass your pickups have to drive a different length of cable depending on whether the effect is bypassed or not, so you get a variable tone depending on the number of patch cords and cable runs that you happen to be using at the time, and the number of pedals that happen to be active at that moment. By buffering the signal at all times, you always get the same dependable frequency response from the pickups, which now only drive the first length of cable. You can then take your favourite (first length) cable wherever you go and always get the same response. An output buffer doesn't kill the sound of the axe, it demonstrably *preserves* it.
merlinb
Solder Soldier
 
Posts: 176
Joined: 18 Nov 2010, 18:39
Has thanked: 0 time
Have thanks: 164 times

Re: Effective OP-AMP Input Impedance, JFET vs. BiPolar

Postby phatt » 09 Sep 2011, 14:08

I'm not much worried about cable loss as I do by design have a buffer in circuit all the time,,But the input matching is interesting to say the least.
Again it depends on circumstances, a one guitar straight to Amp player just needs one good cable and it's fine but YES many pedals and multi connections you are far better off buffering the first active unit full time.

In the specific case of altering the treble of a mag pu it is worth learning how the loading of pu response can affect the bandwidth.
There is a big hump at reso when they look into Hi Z and this might be desired if you want country twang when using a Tele but if you are chasing the classic heavy rock or modern metal sound it may frustrate progress.

By backing off the input Z you flatten out this natural hump and this (in my case at least) is far easier to work with.
The handy byproduct is a lot less hiss and hum when driving loud live levels.

A good explanation here;
http://www.ozvalveamps.org/pickups.htm#Magnetic

A similar tone suck/input Z debate came up some time back on another site and I think a few of the teck geeks got a shock when they actually did some Real World Testing. :oops:

Note the rather low 220k load still retains the basic signature of the PU response.
with a lot of preamp stages this can really help keep it all under control without the need to resort to noise gates and a boatload of other pointless circuitry.
Once you get down to 50k then YES it really bits into the sound/tone produced,, yuk.

My hot rodded VTwin actually uses 330k (not 1 meg) on the input buffer as this helps keeps a lot of unwanted issues all under control.

Also Note the booboo on the Vtwin schematic. R24 is 270k on U1B (powerAmp output drive). Whoopsy try 20k or there abouts,
I just used a pot there for some final gain trim.

Phil.
phatt
Transistor Tuner
 
Posts: 1064
Joined: 04 Aug 2010, 06:17
Location: Morayfield SE Qld AU
Has thanked: 0 time
Have thanks: 270 times

Re: Effective OP-AMP Input Impedance, JFET vs. BiPolar

Postby merlinb » 09 Sep 2011, 14:31

phatt wrote:My hot rodded VTwin actually uses 330k (not 1 meg) on the input buffer as this helps keeps a lot of unwanted issues all under control.

A smaller shunt resistor will reduce sensitivity to hum, but it has virtually no effect on Johnson noise (hiss)- we need to keep these two things separate.
merlinb
Solder Soldier
 
Posts: 176
Joined: 18 Nov 2010, 18:39
Has thanked: 0 time
Have thanks: 164 times

Re: Effective OP-AMP Input Impedance, JFET vs. BiPolar

Postby phatt » 09 Sep 2011, 14:46

merlinb wrote:
phatt wrote:My hot rodded VTwin actually uses 330k (not 1 meg) on the input buffer as this helps keeps a lot of unwanted issues all under control.

A smaller shunt resistor will reduce sensitivity to hum, but it has virtually no effect on Johnson noise (hiss)- we need to keep these two things separate.


Yep point taken.
I probably used the wrong term :blackeye

I'm not up to speed on the really deep stuff some of you blokes have stored away.

Maybe 330k is helping to make the PU's less sensitive to hum pickup from surrounding equipment.
Live gigs are a whole different experience and what might be passable in the back shed can easy turn into nightmare hums an buzzes live.
Phil.
phatt
Transistor Tuner
 
Posts: 1064
Joined: 04 Aug 2010, 06:17
Location: Morayfield SE Qld AU
Has thanked: 0 time
Have thanks: 270 times

Re: Effective OP-AMP Input Impedance, JFET vs. BiPolar

Postby kleuck » 09 Sep 2011, 15:14

merlinb wrote:An output buffer doesn't kill the sound of the axe, it demonstrably *preserves* it.

Merlin, i love your work and you site, but i can't agree on that.
Try a LP Junior in a 5 meters cable straight in a simple vintage amp, and switch to the same cable, a Boss pedal or a buffer, and another 5 meters cable, if you get the same sound, ie the same presence peak, you're lucky, i never did.
I make a buffer with a PU/Cable simulator, wich is only an inductance and a few caps which nails the straight sound, and i agree that you must have one buffer in the chain if you re using long cables or/and a few pedals, but no, buffers in the output do not preserve the sound.
Randall Aïken said :
Q: Is there any advantage to using solder with a 2% silver content?
A: Yes. Silver solder keeps werewolves away from your amp.
User avatar
kleuck
Cap Cooler
 
Posts: 469
Joined: 16 Nov 2008, 00:24
Location: France
Has thanked: 44 times
Have thanks: 31 times

Re: Effective OP-AMP Input Impedance, JFET vs. BiPolar

Postby kleuck » 09 Sep 2011, 15:47

phatt wrote:
Note the rather low 220k load still retains the basic signature of the PU response.

No, it relies heavily on the cable you are using, his length, the pots you have in your axe, if you have two volume pots or a single one : it's a way too simple response.
Randall Aïken said :
Q: Is there any advantage to using solder with a 2% silver content?
A: Yes. Silver solder keeps werewolves away from your amp.
User avatar
kleuck
Cap Cooler
 
Posts: 469
Joined: 16 Nov 2008, 00:24
Location: France
Has thanked: 44 times
Have thanks: 31 times

PreviousNext

Return to Power

Who is online

Users browsing this forum: No registered users and 4 guests