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Home > Archive > Electrical Engineering > August 2006 > guitar amp
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| Lost'n Found 2006-08-08, 3:25 am |
| Hello. I want to ask about few things that have been bothering me recently a
lot.
1) I've seem some solid state guitar schematics. My question is, why don't
they ever use op-amps in solid state amplifiers?
2) I've seen some tube schematics tubes are used, and on the gird of the
input stage tube, there is a resistor (about 100k-500k) that goes from the
grid straight to the ground. My question is, if they want high input
impedance, why would they put a resistor and not just connect the input to
the grid resulting in very high input impedance?
3) Assume there is a capacitor before the input stage, and we want to have
lots of negative feedback. Does it matter were we feed the signal back to
increase the bandwidth of the amplifier?
Thank you for your response!
| |
| Salmon Egg 2006-08-08, 3:25 am |
| On 8/7/06 8:17 PM, in article o4SdnUJdiZXbn0XZnZ2dnUVZ_s2dnZ2d@comcast.com,
"Lost'n Found" <omakke1@comcast.net> wrote:
> Hello. I want to ask about few things that have been bothering me recently a
> lot.
>
> 1) I've seem some solid state guitar schematics. My question is, why don't
> they ever use op-amps in solid state amplifiers?
I find that hard to believe. Are you sure? How old are these schematics? It
may be tradition. It may be that you are seeing stuff designed by musicians
who took to electronics as a hobby.
>
> 2) I've seen some tube schematics tubes are used, and on the gird of the
> input stage tube, there is a resistor (about 100k-500k) that goes from the
> grid straight to the ground. My question is, if they want high input
> impedance, why would they put a resistor and not just connect the input to
> the grid resulting in very high input impedance?
Vacuum tube amplifiers? Again I am flabbergasted. Of course there are
audiophile nuts that claim outlandish benefits to the use of tubes. At best
they are misguided.
You also have to describe the schematic better. The input impedance you
mention (about 100k-500k) is high, especially if driven by some kind of a
magnetic pickup. It may be part of RC coupling. Some shunting resistance is
need to keep stray capacitance from limiting the audio bandwidth.
>
> 3) Assume there is a capacitor before the input stage, and we want to have
> lots of negative feedback. Does it matter w[h]ere we feed the signal back to
> increase the bandwidth of the amplifier?
You always have to worry about becoming unstable and that might depend on
where negative feedback is inserted.
>
> Thank you for your response!
>
You have more homework to do.
Bill
-- Ferme le Bush
| |
| Lost'n Found 2006-08-08, 3:25 am |
| Thanks for your reply. Yeah, the schematics could be old.. . .
About the input impedance, I read that magnetic pickups have an output
impedance of average 500k. Here is another form of the question: if you have
a mosfet, would you need to have a resistor running from the gate to the
ground? Or can you simply connect the input to the the gate?
"Salmon Egg" <salmonegg@sbcglobal.net> wrote in message
news:C0FD5BFF.37BAF%salmonegg@sbcglobal.net...
> On 8/7/06 8:17 PM, in article
> o4SdnUJdiZXbn0XZnZ2dnUVZ_s2dnZ2d@comcast.com,
> "Lost'n Found" <omakke1@comcast.net> wrote:
>
>
> I find that hard to believe. Are you sure? How old are these schematics?
> It
> may be tradition. It may be that you are seeing stuff designed by
> musicians
> who took to electronics as a hobby.
>
> Vacuum tube amplifiers? Again I am flabbergasted. Of course there are
> audiophile nuts that claim outlandish benefits to the use of tubes. At
> best
> they are misguided.
>
> You also have to describe the schematic better. The input impedance you
> mention (about 100k-500k) is high, especially if driven by some kind of a
> magnetic pickup. It may be part of RC coupling. Some shunting resistance
> is
> need to keep stray capacitance from limiting the audio bandwidth.
>
> You always have to worry about becoming unstable and that might depend on
> where negative feedback is inserted.
> You have more homework to do.
>
> Bill
> -- Ferme le Bush
>
>
| |
| TimPerry 2006-08-08, 3:25 am |
| Lost'n Found wrote:
> Hello. I want to ask about few things that have been bothering me
> recently a lot.
>
> 1) I've seem some solid state guitar schematics.
how many?
>My question is, why
> don't they ever use op-amps in solid state amplifiers?
you haven't seen enough i guess.
>
> 2) I've seen some tube schematics tubes are used, and on the gird of
> the input stage tube, there is a resistor (about 100k-500k) that goes
> from the grid straight to the ground. My question is, if they want
> high input impedance, why would they put a resistor and not just
> connect the input to the grid resulting in very high input impedance?
DC grid bias is needed for proper operation as a (sort of) linear amplifier
>
> 3) Assume there is a capacitor before the input stage, and we want to
> have lots of negative feedback. Does it matter were we feed the
> signal back to increase the bandwidth of the amplifier?
negative feedback is used to reduce amplifier instability and in some cases
improve linearity.
negative feedback in both tube and SS amplifiers is primarily intended to
help the power amplifier. section. (as in low voltage gain / large power
gain)
for proper operation, it matters how all elements of the system are designed
and constructed.
>
> Thank you for your response!
yw
| |
| jclouse 2006-08-08, 5:25 pm |
| In article <C0FD5BFF.37BAF%salmonegg@sbcglobal.net>, salmonegg@sbcglobal.net
says...
>
>On 8/7/06 8:17 PM, in article o4SdnUJdiZXbn0XZnZ2dnUVZ_s2dnZ2d@comcast.com,
>"Lost'n Found" <omakke1@comcast.net> wrote:
>
>
>
>Vacuum tube amplifiers? Again I am flabbergasted. Of course there are
>audiophile nuts that claim outlandish benefits to the use of tubes. At best
>they are misguided.
Chet Atkins was misguided? Surely not.
jc
| |
| Salmon Egg 2006-08-08, 5:25 pm |
| On 8/8/06 1:48 PM, in article 12dhu54h4fq1i0e@news.supernews.com, "jclouse"
<jc@the.web> wrote:
>
>
> Chet Atkins was misguided? Surely not.
Chet Atkins has been gone a while and I do not know about his electronics
knowledge. I do know he was an innovative guitarist.
By misguided, I mean not knowing, like the song from Annie, Get Your Gun:
anything tubes can do, solid state can do better. In terms of high fidelity,
ss can be better. Certain ways of using tubes can give distortions that
produce certain special effects easily--but that is not the same as hi-fi.
Bill
-- Ferme le Bush
| |
| jclouse 2006-08-08, 8:25 pm |
| In article <C0FE5538.38361%salmonegg@sbcglobal.net>, salmonegg@sbcglobal.net
says...
>
>On 8/8/06 1:48 PM, in article 12dhu54h4fq1i0e@news.supernews.com, "jclouse"
><jc@the.web> wrote:
>
best[color=darkred]
>
>Chet Atkins has been gone a while and I do not know about his electronics
>knowledge. I do know he was an innovative guitarist.
>
>By misguided, I mean not knowing, like the song from Annie, Get Your Gun:
>anything tubes can do, solid state can do better. In terms of high fidelity,
>ss can be better. Certain ways of using tubes can give distortions that
>produce certain special effects easily--but that is not the same as hi-fi.
Depends on one's interpretation of the word better.
Technical-wise (as measured with instrumentation)
you are likely correct. However.. as sounding better
to the earpans, this is subjective, and indeed tubes
when implimented without too much negative feedback
can sound quite lovely and "warm". This has been the
the subject of many "debates", and of course the
decision on which is "better" lies with the person
doing the listening and applies only to that person.
All that said, I prefer a tube preamp and solid state
power amp with minimum feedback.
jc
| |
| Salmon Egg 2006-08-08, 8:25 pm |
| On 8/8/06 3:51 PM, in article 12di5amccdn8q08@news.supernews.com, "jclouse"
<jc@the.web> wrote:
> Depends on one's interpretation of the word better.
> Technical-wise (as measured with instrumentation)
> you are likely correct. However.. as sounding better
> to the earpans, this is subjective, and indeed tubes
> when implimented without too much negative feedback
> can sound quite lovely and "warm". This has been the
> the subject of many "debates", and of course the
> decision on which is "better" lies with the person
> doing the listening and applies only to that person.
> All that said, I prefer a tube preamp and solid state
> power amp with minimum feedback.
In hi-fi, the best you can do is to reproduce a waveform. A distorted
waveform may sound better to some. I have no quarrel with that. But that is
introducing artifacts. Then the art is to introduce distortion we and others
like.
This distortion is like adding spice and other adulterants to perfectly fine
natural food to make it taste better. Isn't that why we charbroil steaks
instead of eating them raw?
Bill
-- Ferme le Bush
| |
| sQuick 2006-08-08, 8:25 pm |
|
"Salmon Egg" <salmonegg@sbcglobal.net> wrote in message
news:C0FD5BFF.37BAF%salmonegg@sbcglobal.net...
> On 8/7/06 8:17 PM, in article
> o4SdnUJdiZXbn0XZnZ2dnUVZ_s2dnZ2d@comcast.com,
> "Lost'n Found" <omakke1@comcast.net> wrote:
>
>
> I find that hard to believe. Are you sure? How old are these schematics?
> It
> may be tradition. It may be that you are seeing stuff designed by
> musicians
> who took to electronics as a hobby.
>
> Vacuum tube amplifiers? Again I am flabbergasted. Of course there are
> audiophile nuts that claim outlandish benefits to the use of tubes. At
> best
> they are misguided.
>
I think you could be misguided with the last remark, though the first one
could be true.
sQuick..
| |
| sQuick 2006-08-08, 8:25 pm |
|
"Lost'n Found" <omakke1@comcast.net> wrote in message
news:o4SdnUJdiZXbn0XZnZ2dnUVZ_s2dnZ2d@comcast.com...
> Hello. I want to ask about few things that have been bothering me recently
> a
> lot.
>
> 1) I've seem some solid state guitar schematics. My question is, why don't
> they ever use op-amps in solid state amplifiers?
They all do these day's. I service them regularly.
> 2) I've seen some tube schematics tubes are used, and on the gird of the
> input stage tube, there is a resistor (about 100k-500k) that goes from the
> grid straight to the ground. My question is, if they want high input
> impedance, why would they put a resistor and not just connect the input to
> the grid resulting in very high input impedance?
The grid is biased for a reason. Why not try connecting your guitar
direct to the grid of an ecc83 & see what happenes. Valves/tubes dont
work like transistors.
> 3) Assume there is a capacitor before the input stage, and we want to have
> lots of negative feedback. Does it matter were we feed the signal back to
> increase the bandwidth of the amplifier?
if you design & test an amp well, lots of neg fb wont be required.
Maybe slide a filtered touch in at the phase splitter stage.
sQuick..
| |
| jclouse 2006-08-09, 1:25 pm |
| MIME-Version: 1.0
Content-Type: Text/Plain; charset=US-ASCII
X-Complaints-To: abuse@supernews.com
Lines: 64
Xref: number1.nntp.dca.giganews.com alt.engineering.electrical:180969
In article <C0FE66A8.38375%salmonegg@sbcglobal.net>, salmonegg@sbcglobal.net
says...
>
>On 8/8/06 3:51 PM, in article 12di5amccdn8q08@news.supernews.com, "jclouse"
><jc@the.web> wrote:
>
>
>In hi-fi, the best you can do is to reproduce a waveform. A distorted
>waveform may sound better to some. I have no quarrel with that. But that is
>introducing artifacts. Then the art is to introduce distortion we and others
>like.
The thing is, tubes are less prone to odd-order harmonic
distortion, which is more irritating to the earpans than
even-order harmonics. Note neither transistors and tubes
are distortion-free, so it could be the lesser of the evils.
>This distortion is like adding spice and other adulterants to perfectly fine
>natural food to make it taste better.
Yes, and each person has his choice of "spice", 57, A-1, or
whatever. Some choose even-order distortion.
>Isn't that why we charbroil steaks instead of eating them raw?
Sorry, I don't see that as a good analogy. Some may prefer
them cooked different ways.
BTW, you said: "Chet Atkins has been gone a while and I do not
know about his electronics knowledge." Note he was RCA's
recording engineer in Nashville for quite a while. Regarding
his choice of amps, one of his favorites was a Musicman RD-50
that used 6L6GC output tubes - the workhorse output tubes in
their power class.
jc
| |
| Salmon Egg 2006-08-09, 9:25 pm |
| On 8/9/06 8:45 AM, in article 12dk0pbb938qkd4@news.supernews.com, "jclouse"
<jc@the.web> wrote:
>
> The thing is, tubes are less prone to odd-order harmonic
> distortion, which is more irritating to the earpans than
> even-order harmonics. Note neither transistors and tubes
> are distortion-free, so it could be the lesser of the evils.
>
>
> Yes, and each person has his choice of "spice", 57, A-1, or
> whatever. Some choose even-order distortion.
>
>
> Sorry, I don't see that as a good analogy. Some may prefer
> them cooked different ways.
I am pointing out that distortion of the "natural" product can make the
product more attractive.
>
> BTW, you said: "Chet Atkins has been gone a while and I do not
> know about his electronics knowledge." Note he was RCA's
> recording engineer in Nashville for quite a while. Regarding
> his choice of amps, one of his favorites was a Musicman RD-50
> that used 6L6GC output tubes - the workhorse output tubes in
> their power class.
What the bottom line appears to be is that "Vacuum tube amplifiers have more
pleasant distortion than do solid state amp0lifiers." That may be and I will
not deny any listener of his favorite distortion. Realize that human ears
also introduce distortion. With double ended amplifiers and feedback there
should be engineering problem getting distortion down to audibly
undetectable levels. Moreover, modern electronic technique allows much in
the way of custom generated distortion based on frequency, nonlinear, and
time dependence.
Bill
-- Ferme le Bush
| |
|
| Lost'n Found wrote:
> Hello. I want to ask about few things that have been bothering me recently a
> lot.
>
> 1) I've seem some solid state guitar schematics. My question is, why don't
> they ever use op-amps in solid state amplifiers?
>
> 2) I've seen some tube schematics tubes are used, and on the gird of the
> input stage tube, there is a resistor (about 100k-500k) that goes from the
> grid straight to the ground. My question is, if they want high input
> impedance, why would they put a resistor and not just connect the input to
> the grid resulting in very high input impedance?
>
The grid intercepts some electrons emitted by the cathode. They will
bias an isolated grid negative in an uncontrolled way. An old technique
was to connect the grid to ground with a very high resistance and use
the grid current to provide a controlled bias (grid leak bias).
A high grid-to-ground resistance, combined with shunt capacitance, will
also result in reduction in gain at high-end frequencies. The same is
true for large plate resistors.
Grid bias is usually privided by a cathode-to-ground resistor. If this
resistor does not have a capacitor across it there is negative feedback.
From the dim past, I think electrometer tubes put the control grid in
the shadow of another element and had extremely low grid currents
permitting extremely high impedance grid circuits.
> 3) Assume there is a capacitor before the input stage, and we want to have
> lots of negative feedback. Does it matter were we feed the signal back to
> increase the bandwidth of the amplifier?
>
I agree with Salmon Egg that stability is an issue. You could create a
nice oscillator. A coupling capacitor and a resistor produce a frequency
dependent phase shift. If coupling capacitors are in your feedback loop
you may have trouble, lots of feedback - lots of trouble. (Op amps don't
have coupling capacitors.) From the dim past, I don't remember that
negative feedback was common other than unbypassed cathode resistors.
A major name in amps said he could produce any tube "warm", or other,
sound identically with solid state and feedback.
[Sorry if this post is duplicated]
bud--
| |
| Igor The Terrible 2006-08-13, 1:25 pm |
|
Salmon Egg wrote:
> On 8/7/06 8:17 PM, in article o4SdnUJdiZXbn0XZnZ2dnUVZ_s2dnZ2d@comcast.com,
> "Lost'n Found" <omakke1@comcast.net> wrote:
>
>
> I find that hard to believe. Are you sure? How old are these schematics? It
> may be tradition. It may be that you are seeing stuff designed by musicians
> who took to electronics as a hobby.
Yep!!
> Vacuum tube amplifiers? Again I am flabbergasted. Of course there are
> audiophile nuts that claim outlandish benefits to the use of tubes. At best
> they are misguided.
You are 50% correct on this one. So far as stereo equipment goes, you
are correct. At best it is mostly noisy junk. Guitar amplifiers are
an entirely different story. They are more responsive, warmer, fatter,
and for harmonic clipping (distortion) nothing can touch them....think
about it... there is a reason WHY there were and still are soooooo many
companies manufacturing stomp boxes attempting to simulate them. Ever
listen to a vintage Marshall 1968 Plexi, JTM 45, JCM 800...? Or any
Soldano? Just listen to them...they speak beyond volumes. 
Of course, solid state amps have their place in music as well. Here I
would say they are better suited for some types of Jazz, Pop, and to a
lesser extent Fusion. So far as digital modeling amps go....they too
are junk; they have a long way to go. For now, there isn't anything
like the real thing. Again, why are they trying to duplicate it on a
chip?
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