I don't know how else to interpret this than as a statement that your guitar amplifier is even noisier than the guitar volume pot. If you had written '4) I've never been in a room quiet enough to actually hear thermal hiss from the guitar volume pot', I would have thought 'fair enough' and would have left it at that.
By the way, the Ampeg GT-10 in this thread https://www.diyaudio.com/community/...nts-for-bc169b-and-2n4062-transistors.396192/ is in fact noisier than the guitar volume control. It has a bipolar input stage biased very far above the noise optimum. Replacing it with a JFET and getting rid of carbon composition resistors at critical places fixed that.
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I don't know how else to interpret several of your recent comments other than increasingly hostile disparagement.MarcelvdG said:
I suggest you stop assuming that everyone who touches a guitar is somehow much less intelligent or much less knowledgeable than you.
I have no interest in dealing with more passive-aggressive comments from you.
Have a nice day.
-Gnobuddy
I just don't like the way you write things that are inconsistent, and when I point out that they are inconsistent, put the blame on me. That has nothing to do with you playing electric guitars.
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Absolutely right - the drop in signal to noise in that Ampeg was probably 20db or so - I wish I had measured it precisely before and after - from 40-ish to 60-ish db.
This was maybe the noisiest guitar amp I've used, but all guitar amps are very noisy compared to, say, decent mic preamps. I have used many, many, guitar amps over the years and they are all noisy, but I don't agree that it's not important. A lot of music is mixed so that the whole dynamic range is maybe 10-15db. In that case, you're not going to hear the noise floor. But if you are playing a guitar amp with a clean tone in a quiet studio at moderate volume, they are all maddeningly noisy, some much more so than others. Noise piles up fast when you're recording.
I just find it a little funny that there are so many retired engineers and technicians on the forums writing thousands of words about things that can be settled through empirical testing. Once in a while, someone will be motivated to make a youtube video testing something, and it becomes the first google hit when you look that thing up. But you have to be motivated to spend hours on that.
It would be nice if someone wanted to test the signal to noise ratio of guitar amps at the different stages (which is easy to do, recording the signal and measuring in Audacity). I have done it (including on the Fender tube amps discussed here) but I'm not motivated enough to rerun that and post results. I have done literally every possible modification that effects signal to noise. Somebody can be the hero that exhaustively and empirically documents this issue.
Obviously you put your focus on some kind of distortion and less on noise. Other people fhere in this thread focus on noise as well, me included. I did extensive research on that topic in the late 60ies/early seventies an at that time decided that about 90dB S/N should be sufficient. You should check your own attitude towards others here to understand why you provoke responses you do not like.
I've seen some people mentioning guitar tone controls. Does that mean that there are also adjustable filters built into a typical electric guitar and if so, does anyone know what the schematic of a typical electric guitar looks like?
For guitars with passive pickups (which is what the vast majority of guitars use), tone controls are variable passive RC LP filters. There may be one dedicated tone control for each pickup, or there may be one shared tone control at the guitar output.
Also, wiring diagrams are generally used instead of schematics: https://rb.gy/hjffd
Also, wiring diagrams are generally used instead of schematics: https://rb.gy/hjffd
So typically a 47 nF or 50 nF ceramic or mica capacitor in series with a 250 kohm potmeter wired as an adjustable resistor, shunting the pick-up. Sometimes two pick-up tone controls share a common capacitor, sometimes not. At maximum volume and with the tone potmeter set to the maximum resistance, some 0.36 pA/sqrt(Hz) of thermal noise current gets injected into the pick-up by the volume and tone potmeters. OK.
Except maybe there is usually a guitar cord and and amp input more or less connected to the same node as the pickups and guitar pots, at least when the volume control is set to '10.'
Of course. I'm interested in the impedance and noise of the guitar itself, as that determines how the amplifier has to be designed to keep it from reducing the signal to noise ratio by more than x dB.
Most of the noise from a guitar is from coupling of stray EM fields directly into the pickups. Its not hiss but its most of the total audible noise, and its the more objectionable sounding of the two. More so with unshielded single coil pickups that with shielded humbuckers. Some newer passive technologies are best at minimizing that type of noise. However, guitar players may choose unshielded single coils because they prefer the tone.
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Do you mean mains hum or RF signals that get demodulated unintendedly?
I don't think there is much you can do in the amplifier against mains hum picked up by the guitar. You could try to add mains hum with an adjustable amplitude and phase to cancel the picked-up hum, but chances are that there are lots of harmonics and that you only get one harmonic to cancel at a time (and only as long as the guitarist doesn't move). I once built a comb filter that quite effectively suppressed mains hum, but the flutter echo of the comb filter sounded worse than the hum.
I don't see much filtering against RF signals in the few guitar amplifier schematics I have seen on this forum. Usually just a relatively big series resistor at the input with the input device capacitance. I guess a normal RC low-pass is undesired because of the extra load on the guitar.
I don't think there is much you can do in the amplifier against mains hum picked up by the guitar. You could try to add mains hum with an adjustable amplitude and phase to cancel the picked-up hum, but chances are that there are lots of harmonics and that you only get one harmonic to cancel at a time (and only as long as the guitarist doesn't move). I once built a comb filter that quite effectively suppressed mains hum, but the flutter echo of the comb filter sounded worse than the hum.
I don't see much filtering against RF signals in the few guitar amplifier schematics I have seen on this forum. Usually just a relatively big series resistor at the input with the input device capacitance. I guess a normal RC low-pass is undesired because of the extra load on the guitar.
Its mostly AC line related buzz and or hum. Touching the strings can help as the bridge is grounded to the output connector. Makes guitar player go from being antenna to being a shield. Also, moving around the room and or slowing turning around 360-degrees in place to find a null can help too.
Shielded humbucker pickups help, but have a different sound that single coils. LACE pickups (and or whatever else) that came later are reputed to be better yet, but yet another different sound.
Shielded humbucker pickups help, but have a different sound that single coils. LACE pickups (and or whatever else) that came later are reputed to be better yet, but yet another different sound.
I would like to share some practical experience on the Blues Jr amp, which could apply to other similar guitar amps.
First up after a few years of semi regular use, I did notice the amp started to have a crackly noise that would sometime start randomly and as the amp warmed up with use it would get noisier/more crackles. Cleaned all the tube socket contacts, input jack etc..it was better but still the problem persisted. Tightened the contacts in the tube sockets, better but the problem would still present itself once in a while.
Finally I re-soldered all the wiring connections between the main board and the tube socket board and the tube socket pins.
This problem can crop up on PCBs that have been wave soldered, where you have metallic parts with large thermal mass not getting heated enough by the solder wave to get a good solder connections. It may look like a good solder joint but sometimes there is minute cracks between the pin and the board. The amp was working but as the parts heated up in operation this would cause intermittent crackling sound and noise. Once the parts were re-sweated with solder the problem disappeared.
After that I decided to replace all the tubes in the amp, I have JJ types in there now (which I like), but a notable difference was going to a lower noise type 12AXWA in the first position tube (input). Fender's used to use 7025 in that position for lower noise, it's the same type construction as a 12Ax7 but was something like a military spec for lower noise. the 12 AX7WA is similar in the low noise specifications.
One practical thing with the Blues Jr is that it has a master volume control, and generally I tend to bring up the preamp volume up quite a bit , then dial in the master volume to get the output level I need. If the preamp volume is set too low, you end up bring the output volume up more to compensate, but that brings up the noise floor with it. If you have a good solid preamp signal level feeding the rest of the amp, the noise should not be too noticeable.
Cheers!
First up after a few years of semi regular use, I did notice the amp started to have a crackly noise that would sometime start randomly and as the amp warmed up with use it would get noisier/more crackles. Cleaned all the tube socket contacts, input jack etc..it was better but still the problem persisted. Tightened the contacts in the tube sockets, better but the problem would still present itself once in a while.
Finally I re-soldered all the wiring connections between the main board and the tube socket board and the tube socket pins.
This problem can crop up on PCBs that have been wave soldered, where you have metallic parts with large thermal mass not getting heated enough by the solder wave to get a good solder connections. It may look like a good solder joint but sometimes there is minute cracks between the pin and the board. The amp was working but as the parts heated up in operation this would cause intermittent crackling sound and noise. Once the parts were re-sweated with solder the problem disappeared.
After that I decided to replace all the tubes in the amp, I have JJ types in there now (which I like), but a notable difference was going to a lower noise type 12AXWA in the first position tube (input). Fender's used to use 7025 in that position for lower noise, it's the same type construction as a 12Ax7 but was something like a military spec for lower noise. the 12 AX7WA is similar in the low noise specifications.
One practical thing with the Blues Jr is that it has a master volume control, and generally I tend to bring up the preamp volume up quite a bit , then dial in the master volume to get the output level I need. If the preamp volume is set too low, you end up bring the output volume up more to compensate, but that brings up the noise floor with it. If you have a good solid preamp signal level feeding the rest of the amp, the noise should not be too noticeable.
Cheers!
I have a DV Mark Raw Dawg EG in the shop because the customer is complaining about excessive noise. This has a switched-mode power supply and Class D output stage with a claimed output power of 250 watts. (I'm skeptical of that rating, but it does have substantial gain.) So, my question is: What is the typical noise voltage (hiss, hum & harmonics) expected from a solid-state amp of this size?
These are my measurements: With amp volume fully down and nothing plugged in, into a 4 ohm resistive load, I'm seeing about 40mV rms (-25dbm). With amp volume fully up and nothing plugged in, I see about 70mV rms (-21dbm) and when I listen, the sound is mostly hiss. With a guitar with humbucking pickups plugged in with its volume fully up and the amp volume fully up, I'm seeing about 120mV rms (-16dbm) and when I listen, the sound is the usual mixture of hum and gnarly harmonics. These numbers seem reasonable to me, but I'd like your opinions.
These are my measurements: With amp volume fully down and nothing plugged in, into a 4 ohm resistive load, I'm seeing about 40mV rms (-25dbm). With amp volume fully up and nothing plugged in, I see about 70mV rms (-21dbm) and when I listen, the sound is mostly hiss. With a guitar with humbucking pickups plugged in with its volume fully up and the amp volume fully up, I'm seeing about 120mV rms (-16dbm) and when I listen, the sound is the usual mixture of hum and gnarly harmonics. These numbers seem reasonable to me, but I'd like your opinions.
Noise of commercial guitar amps may vary over quite a wide range, so there is no common "gold standard".
Be sure to make your measurements band limited using a soundcard or some good true rms meter.
Measurements using any kind of oscilloscope are pointless here, specially with class-d-amps with their pwm-clock residual at the output,
Be sure to make your measurements band limited using a soundcard or some good true rms meter.
Measurements using any kind of oscilloscope are pointless here, specially with class-d-amps with their pwm-clock residual at the output,
Okay. But will the amp be used with a speaker or recorded direct? Reason I ask is because the amp and speaker comprise a system. Some things that can reduce noise may also affect tone and or playability. So why the focus on a part of the system that may never be used alone?
Mark, this is used onstage with a speaker.
Bucks, I did see a residual clock frequency at 113kHz with amp volume at minimum. But, that was obviously not audible. I made my voltage measurements with a Fluke 45.
I didn't think to ask the customer if he's using single or double (humbucking) pickups. So, that may be part of the problem? Or perhaps he doesn't realize the need to keep such a powerful amp's volume as low as possible?
Thanks for all your quick replies.
Bucks, I did see a residual clock frequency at 113kHz with amp volume at minimum. But, that was obviously not audible. I made my voltage measurements with a Fluke 45.
I didn't think to ask the customer if he's using single or double (humbucking) pickups. So, that may be part of the problem? Or perhaps he doesn't realize the need to keep such a powerful amp's volume as low as possible?
Thanks for all your quick replies.