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Thread: How it works

  1. #1
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    How it works

    20180210_172046.jpg

    In my quest for understanding how the tube amp works I have coloured the layout drawing for my build have I done it right ? Also it got me thinking about the negative feedback circuit am I right in thinking that a portion of the output signal gets fed back to the second cathode of the preamp tube and would i be correct that this would only be active in the circuit if the 4 ohm output was being used as it isnt connected to the 8 ohm output ? If it is active in both outputs wouldn't the amount being fed back differ depending on which output was being used?

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    No, you have not done it right. Don't mean to be rude but no one thinks about layout drawings like that. If you can not read schematics it is a must for any kind of analysis. Try this:
    https://robrobinette.com/Reading_Tub...Schematics.htm
    The feedback is active no matter which output you use, and the voltage at the 4 ohm tap stays the same no matter which output you are using.
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    Ha yeah just checked out the link (and bookmarked it!!) Think I'm in for a few late nights digesting that but obviously essential can't help but wonder if you gave two amp builders a circuit schematic that they had both never seen before and got them to build an amp from it how different (or similar) the amps would be ? And therein lies the art I guess!! Thanks though given me a lot to think about

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    Old Timer J M Fahey's Avatar
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    Quote Originally Posted by Jarvini View Post
    Ha yeah just checked out the link (and bookmarked it!!) Think I'm in for a few late nights digesting that but obviously essential can't help but wonder if you gave two amp builders a circuit schematic that they had both never seen before and got them to build an amp from it how different (or similar) the amps would be ? And therein lies the art I guess!! Thanks though given me a lot to think about
    If both amps are built with same schematic and using same parts then results will be identical.
    Builder in that case only mounts and solders, assuming both are competent .
    Juan Manuel Fahey

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    I meant if they just had the schematic and nothing else no idea of a finished design so they worked from scratch picked their own blank chassis their own components, wire, circuit board layout , valves , grounding scheme, wire dress, surely they wouldn't build exactly identical amps

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    Supporting Member eschertron's Avatar
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    Quote Originally Posted by Jarvini View Post
    Ha yeah just checked out the link (and bookmarked it!!) Think I'm in for a few late nights digesting that but obviously essential can't help but wonder if you gave two amp builders a circuit schematic that they had both never seen before and got them to build an amp from it how different (or similar) the amps would be ? And therein lies the art I guess!! Thanks though given me a lot to think about
    Quote Originally Posted by Jarvini View Post
    I meant if they just had the schematic and nothing else no idea of a finished design so they worked from scratch picked their own blank chassis their own components, wire, circuit board layout , valves , grounding scheme, wire dress, surely they wouldn't build exactly identical amps
    Hence the 'art' of amp building idea. Keep in mind that Juan's "competent" builder would have a great deal of background on voltage ratings, e-field generation and coupling, leakage, and all the technical fundamentals that lie behind lead dress, proper grounding, signal isolation, etc. that make a good layout different from a noisy or parasitic-oscillation-prone one. Think about giving a photo to two different painters. If they've learned their art from the same master, then their paintings will be similar. In our case, the "master" is physics. There's no way to deviate from ideal too far before the result is catastrophic. Someone who hasn't learned to paint makes bad art. Someone who hasn't learned the rudiments of electronic theory makes a bad amp.
    So for the sake of argument, discard amp building as art. When a civil engineer builds a bridge, every choice they make is based on the charts, graphs, and tables that provide data about the materials chosen. The engineer cannot willfully disregard those constraints. There are similar constraints in amp building. As long as the constraints are understood and obeyed, the amp functions properly. And as two bridges that are built with exactly the same specs and materials will look pretty similar (form follows function!), two amps built to the same schematic with the same parts will end up pretty close.
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    If it still won't get loud enough, it's probably broken.
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    Quote Originally Posted by glebert View Post
    Distortion is a form of signal degradation. It is pretty easy to define what a good "clean" signal is, but trying to achieve just the right kind of "broken" can be pretty maddening.

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    Yeah point taken!!! be an interesting experiment though just to hear them but then two amps built with exactly the same components would probably sound different anyway due to tolerances so maybe not!!

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    Old Timer Tom Phillips's Avatar
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    Quote Originally Posted by Jarvini View Post
    Yeah point taken!!! be an interesting experiment though just to hear them but then two amps built with exactly the same components would probably sound different anyway due to tolerances so maybe not!!
    Yes. They could sound different due to component tolerances. However, if the tolerances were properly specified on the original schematic, then any two amplifiers would not sound significantly different. ( Keeping in mind Juan's comment about competent builders)

    It is interesting to note that if you give the same identical amplifier to a group guitar players and you tell them that one of the amplifiers has a specially selected type of capacitors (even though it does not) then a high percentage of players would probably pick the "special" amplifier as the better sounding one.

    Edit: Think of a schematic as the language of electronics. Once you learn how to read and create schematics you can understand and convey electronic information very efficiently. Without the schematic you are in a position similar to writing a thousand words to convey what can easily be understood by a simple picture.
    Last edited by Tom Phillips; 02-10-2018 at 09:30 PM.
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    I think you are all misunderstanding what I first meant!! I didn't mean that two different amp builders would interpret the circuit differently and build a different circuit than each other!! I meant what size chassis they would use what brand of capacitors what type of resistors valve placement transformer choice wire choice solid core or braided star ground bus ground steel or aluminium chassis eyelet board or turret board !! A circuit schematic wouldn't specify anything other than values,tolerances and voltages all the electronic information surely the two amps would be made of completely different brand and type components thus producing 2 different sounding amps that apart from both following the same electronic blueprint would in effect be different

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    It would probably look different inside, I don't think anyone will contest that.
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    That's what I meant that despite following the same schematic they would look different !!!
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    Old Timer J M Fahey's Avatar
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    Quote Originally Posted by Jarvini View Post
    I think you are all misunderstanding what I first meant!! I didn't mean that two different amp builders would interpret the circuit differently and build a different circuit than each other!!
    NOBODY said you said so, you are just trying to change the meaning of what you *actually* said, which was exactly:
    wonder if you gave two amp builders a circuit schematic that they had both never seen before and got them to build an amp from it how different (or similar) the amps would be ?
    and which is quite clear and simple to understand.
    What you are talking about boils down to something like "a Fender Tweed Bassman built by my Cousin Joe, who already built 40 amplifiers, sounds better/worse/brighter/darker/cleaner/dirtier/different than one built at Fender Factory in 1960, even if they use same value components as specified in schematic".
    Well they will sound amazingly similar, and hard to pick in blind testing.
    Any possible difference may be due to component tolerance, but that may work for/against any of them, old or new, and in any case does not depend on "builder´s hand" as you are trying to imply.
    You keep talking about "Art" ,
    And therein lies the art I guess!!
    , not sure what your intentions are, are you trying to justify some would-be "booteeq builder" charging $2500 for what is basically a $400 Ceriatone/Weber/Hoffman/etc. kit , implying his sound better because of his "Art" ?
    It does not work that way.

    Now you are trying to twist its meaning by adding new parameters, but in any case they are not significant as you think.
    We are talking differences in sound, which is what matters.
    Let´s see the new variables you added, one by one, wondering about whether they affect sound/tone significantly (meaning they can be pickwed in a blind test) or not:
    I meant what size chassis they would use
    Nn
    what brand of capacitors
    No.
    If you said *type* then you might have had a point, but you said *brand* , so ....
    what type of resistors
    No.
    Old style carbon comp may hiss more, that won´t change *sound* and I fail to see extra hiss as a "feature".
    valve placement
    No
    transformer choice
    If all competent , basically no.
    You may use a way undersized or underspec´d one but that woukld not be "competent".
    Now using standard commercial ones such as original Fender (yes, you can buy them for your own builds and price is very reasonable) to Classic Tone to Heyboer to Hammond to (gasp) 3X as expensive Mercury Magnetics, and all others in same class, commercially available, they all sound about the same, Manufacturer´s sugarcoating notwhitstanding.
    Can´t imagine anybody crazy enough to use a Japanese handmade $3000 Audio Note silver wire wound transformer

    but even so I guess he´d be dissappointed at the abismally small difference, if any at all.
    wire choice solid core or braided star
    No difference at all.
    ground bus ground
    you may have small differences in residual hum, but end result will be very close, again if competent builders.
    There´s many ways to skin a cat, all yield a nice warm overcoat as end result.
    steel or aluminium chassis
    No.
    eyelet board or turret board !!
    Save your exclamation marks
    No audible difference, at all.
    I´d even include well designed PCBs, how´s that?
    A circuit schematic wouldn't specify anything other than values,tolerances and voltages
    exactly, and there´s a reason for that
    all the electronic information surely the two amps would be made of completely different brand and type components thus producing 2 different sounding amps
    As you saw above, basically NO
    that apart from both following the same electronic blueprint would in effect be different
    That´s the point you are trying to stress, nut NO.

    I guess (maybe wrong) that you have been over reading what many "Boutique" builders claim.

    Now getting to the point:

    Sad truth is that since Tube amps are electrically simpler than SS, their technology is well "mature" by now (that´s the understatement of the year, we are still using 60/60 year old schematics, based on 70 year old datasheets) , parts are more error-tolerant (you can see plates get red hot, and turn amp OFF, Silicon junctions die in milli-seconds with no warning) and somebody with no formal training at all can still build a working amp just by following colourful layouts , where even resistor color bands are indicated, all this has resulted in hundreds if not thousands people building and most hopefully trying to sell their products ...... and for a good price I might add.

    2 big problems:

    1) they are all building the exact same 10 or 20 (if that many) Classic circuits.
    FWIW in another Forum there is a thread called "How many 5E3 clones does the World need?"

    2) they have to justify a high price or numbers simply do not add up.
    Fender offers **excellent** and versatile 40/60W Tube amps in various configurations, for about U$1000 , 40W Blues Junior for U$700.
    Other makers (think Bugera/Behringer) offer excellent ones for U$400 or less.

    Then Boutique builders have to justify charging U$2000/3000 or more for , say, 15W amps (although power out is not the main factor here) so they HEAVILY insist on , for us, irrelevant details.
    Irrelevant meaning they don´t cange *sound* , although might be "nice to have", or "nice to look at".

    FWIW I started studying Engineering in 1969, by '71 or '72 was quite advanced, and it being Industrial Engineering, the only branch which specifically cares about the Economy/Management side of things (others focus more on the specifically Technical area of esah specialty) we had Marketing courses.

    One typical assignment/"homework" was splitting us in 5/6 guy/gal teams, each of us was given a 1 pint of generic (unscented of course, no additives at all) Industrial type Detergent (Lauryl Sulfate something) , as plain vanilla and unexciting product as can be, and assignment was to come back in 1 week or 2 with a Publicity campaign designed to make Customers buy "my product instead of others" , pay significantly more than what Market would dictate, and at the same time feel proud and happy about doing so.

    Let me tell you that BS was not only not forbidden, but actively promoted !!!!!

    Talk about used car/snake oil salesmen !!!!!!

    So this Boutique insistence on really irrelevant details makes a lot of sense to me.
    Juan Manuel Fahey

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    Lifetime Member Enzo's Avatar
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    You can use carbon composition, carbon film, or metal film resistors and they all will sound alike. One might be a little nosier than the other, but that isn't tone.

    Parts tolerances affect even factory amps. Those old 5E3 Fenders were made with 20% resistors, caps had even wider tolerances. The schematic says right on it, all voltages within +/-20% That means in any given amp the 100k plate resistor on the input stage could be 80k to 120k and be in spec. Your 400v B+ could be 320v to 480v. usually not that wide, but sure enough, line up a few 5E3 amps when new, and they sounded different. They all sounded like 5E3s, but you could hear a difference.

    Different speakers sound different, but you proposed the same parts list.
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    I apologise if I have offended anyone with my questions I am merely trying to understand in my own way the how valve amplifiers work and are built as I am building one for myself and I want to do it the best I can
    I unfortunately have not had the years of bench experience that many on here have and no doubt never will have so I have to go about it a different way using books, forums, information from the net enlarging pictures so I can see how its wired etc.
    I am not building my amp so I can open it up every time someone comes round to show them the how its wired and expect them to gasp in awe at the components I have selected, nor am I building it to sell it for an extortionate price I am building it to play it and as such I want it to be built as good as I can possibly build it knowing that I have used the best parts I could afford and using the knowledge I am slowly gaining wired it internally the same way an experienced builder would have done I could easily source a load of cheap Chinese parts and throw it together cross my fingers and hope it sound ok but that's not the way I do things.
    If I were to build a car I would do the same using chromed and anodised engine bay parts genuine body panels decent tyres trick interior the works would that make it a better car probably not but it would be my car and I would know that every nut and bolt whether you can see it or not was the best it could be and on the flip side of that I could build a car using the cheapest pattern parts old rusty nuts worn out interior etc. would it still be a car yes, would it get me from a to b like the trick one yes but I would know that its probably going to fail in the future and I would probably be spending most of my weekends wishing I spent the bit extra when I am stuck out there with my head under the bonnet fixing the cheap part that's gone wrong again.
    I realise that a lot of what you read is marketing mumbo jumbo and used in an attempt to justify the savage prices that the boutique builders charge but things are only worth what people will pay for them I myself would not spend that sort of money when it could be built for a fraction of the price but you need to be that way inclined and do some research and do it properly I know people that cannot wire a three pin plug and because of that they would call an electrician to do it for them and im sure he would charge a fortune for it but whos in the wrong ?
    I'm also pretty sure that the people that spend 10 to 20 grand on an original fender amp are never going to play them and they would probably be awful or go pop anyway if you did unless you are someone like Joe Bonnamassa who no doubt has an amp tech to check and repair them first but in doing so you don't have the original anymore anyway so whats the point?
    An amplifier is just that an amplifier it amplifies what you put into it so a lot of the so called tone comes before it, if you gave Jimi Hendrix a 5 dollar amp I'm pretty sure he could make it rock and still have the Hendrix sound and if you gave a novice a 5 grand boutique amp they would no doubt sound awful.
    If an experienced amp tech was to knock on my door and say "hey do you want a job i'll teach you everything I have learned over the years you can use my workshop and all my equipment while your learning" then I'd be there the same day but it isn't going to happen so I've got to do it my way as im sure many of you did and that involves asking dumb questions, research, debating on forums etc.
    So just to reiterate I'm not trying to annoy anyone I'm just trying to build the best amp that I can for my own pleasure with the peace of mind knowing I've done it correctly and safely with parts and products that are tried and tested surely that's where the fun in all this is?
    we all have to start somewhere and I'm a long way back from most of you on here but you were here once too!!

    But I would like to say thankyou for all the help that I have received so far and I am slowly getting there one dumb question at a time

    scott
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    Lifetime Member Enzo's Avatar
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    No one is offended , Scott. We do want to help. We don't know you very well, so we have to approach the questions with that in mind.

    Think about building that car. You probably wouldn't buy 10 cent Chinese spark plugs on ebay, but would you worry whether the car would be better with Mercedes plugs or BMW plugs, and would either of those be better than Bosch plugs from the store? Maybe a better question would be what would you tell a guy starting into car building if he asked you that?

    I don't know that you are doing it, but we worry about people getting carried away with the tiny details that ultimately don't matter. Like the car: should I take the tire inflator caps off to lighten the tires? In my amp, are Allen Bradley pots better than Ohmite? Beats me, both are excellent. And the plain old CTS pots Fender used are working still on 60 year old amps, and they cost a lot less than my ABs and Ohmites.
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    Thanks enzo I am slowly learning sometimes the hard way getting burned with overpriced unneeded items but I do listen to the advice I'm given and won't make the same mistakes twice!! We never had much money when I was young and so most of the things I had were either things I had found and repaired or just made and I've kind of always carried on like that as I get pleasure using the skills I have learned along the way, now I'm older I have my own little workshop in my garden literally full of all kinds of tools needed for pretty much any project or repair that I need to do and being a dustman you'll be amazed at what people throw away just because of a simple fault that given a little amount of skill and the right tools can easily be repaired (I do this regularly by the way) and as I have now turned to building my own amp i can't help but ask questions in order to further my knowledge on the subject as without it, it could quite easily become the last project I ever do and end up frying myself in my workshop!!
    I've been looking at some gold plated transformer screws what do you reckon?..... ONLY KIDDING......
    Scott

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    g1
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    Ok, in post #14, you mentioned quality and reliability. This is different than 'tone' and you won't get as much argument.
    I like the automotive analogy, let's stick with it. Chrome in the engine bay will not alter much in the reliability department. Pistons made by a reputable brand compared to a cheap asian knock-off will. So there are places where you can make a difference in terms of quality and reliability, as long as we don't expect major tonal magic.
    Someone I know works in the motorcycle industry. He told me when in doubt, stick with upper-midrange quality stuff. I fall back on that when I need to and it has usually served me well, regardless of whether motorcycle related or not. It's not 100% foolproof, but seems ok as a general rule.
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    Bent Member Chuck H's Avatar
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    To be perfectly fair, Juan is being a tad stringent. I'm sure he's done exactly this more than I have, but it's been my experience (as a competent builder ) that two amps that are the same schematically but different physically can indeed sound different due to minor phase errors caused by layout and lead proximity. But it's not a "this is a different amp" difference. It's not even the same difference you would get with a speaker change. So, short of building to a schematic and having incompetent design issues like gross phase errors due to layout and lead dress, Juan is fundamentally correct. And asking the same question different ways won't change the real answer.

    That doesn't mean boutique builders are shysters Juan But it does mean that in the case of vintage designs what you are paying extra for in a boutique build would have to be limited to quality of materials, perhaps even parts made to spec just for the builder that other cloners can't get, quality of workmanship, perhaps an excellent warranty and definitely reputation, which amounts to product sound quality, reliability and support. These aren't insignificant things.
    "I'm just going to perform a bit more scientific investigation, turn it up to 11 and rip of the knob." überfuzz

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  19. #19
    Supporting Member eschertron's Avatar
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    Quote Originally Posted by Jarvini View Post
    I am building it to play it and as such I want it to be built as good as I can possibly build it knowing that I have used the best parts I could afford
    Hopefully you've listened to the other posts about 'good enough' versus 'overpriced'. There are a lot of components out there that you do not want to buy simply because they are the most expensive. So without further clarification,
    best parts I could afford
    becomes an invitation to throw money into an ever-growing hole.

    For my curiousity, is this your first amp, or is this the only amp you'll ever build? I can see the temptation to sink lots of money into the pride of having high-quality components; stick with reliable, well-thought-of parts, and you'll have the cash to build more than one amp, or build a guitar too! Keep posting on your progress, there is help here even if it sometimes sounds gruff and pedantic
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    Quote Originally Posted by Steve Conner View Post
    If it still won't get loud enough, it's probably broken.
    Quote Originally Posted by Justin Thomas View Post
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    Quote Originally Posted by glebert View Post
    Distortion is a form of signal degradation. It is pretty easy to define what a good "clean" signal is, but trying to achieve just the right kind of "broken" can be pretty maddening.

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    It's my first amp so I picked a pretty simple one just one preamp tube, one power tube and a rectifier tube, volume and tone controls it does have a boost switch which works in conjunction with the cathode bias resistor but that's all and if it's a success then I'll try something a bit more complex but i wanted to start at the bottom so to speak and see how I get on I'm going to have loads of parts and wire left when it's done so I'll be well on my way if I do! I have had nothing but help on this forum to be honest which is brilliant I was just worried that I had got on people's nerves asking the same thing over and over I think I am trying to apply what applies to hi-fi as I have spent lots of time building my stereo, older amps and cd players speakers speaker cables and interconnects racking speaker placement and apart from loudspeaker choice none of it really applies to guitar amps it seems so I'm kinda in the dark, I need to get it built and go from there

  21. #21
    Bent Member Chuck H's Avatar
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    Quote Originally Posted by Jarvini View Post
    I think I am trying to apply what applies to hi-fi as I have spent lots of time building my stereo, older amps and cd players speakers speaker cables and interconnects racking speaker placement and apart from loudspeaker choice none of it really applies to guitar amps it seems
    What part of your experience doesn't apply? Did you learn (incorrectly) that the same stereo/hifi amp schematic built by two different people will sound different? All the reasons that make it a misnomer for guitar amps also apply to hifi amps. Everything else you mention culminates, at the very least, in a physical skill and experience set will surely help you on your guitar amp build. Even your experience sourcing parts will get you through that chore more quickly.

    Stick around. Build your amp. Bring questions here.
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    Sorry by building I meant compiling I was referring more to the difference that a set of interconnects can make between an amp and a CD player or how one set of speaker cables can influence bass response or treble clarity.
    This is how far I've got at the moment with my amp build apart from a collection of all the other parts that is
    20180211_234620.jpg
    Nothing has been soldered yet just in case

  23. #23
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    Hi Scott,
    It is prudent to keep in mind that the laws of physics apply equally to the electronics in a guitar amp, a high end stereo and all manor of other electronic devices. Once you understand the basic principles then you can apply them to construct the device the suites your need. As you learn the basic principles it will free you to be creative and to understand why things are done a particular way.

    Attached is an annotated version of your turret board. The added note is there because elevated temperatures shorten the life of electrolytic capacitors. Your layout has an electrolytic cap right next to a power resistor that will heat up as the resistor does its job. Your layout will not affect the initial performance of the amp but it will shorten it's useful life. This is just one of the many things you will learn as your electronics studies progress.
    cathode-r-bypass-cap-space.jpg

    Quote Originally Posted by Jarvini View Post
    S...or how one set of speaker cables can influence bass response or treble clarity...
    Warning. That is pretty much snake oil that is propagated by people who want to sell expensive cables. There is a well known blind test that was done comparing high end speaker cables to plane old coat hanger wire. The story is that the golden ear audiophiles could not tell the difference. Ha!
    Cheers,
    Tom
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    Bent Member Chuck H's Avatar
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    Quote Originally Posted by Jarvini View Post
    I was referring more to the difference that a set of interconnects can make between an amp and a CD player
    Oh. You mean, like gold contacts and cryo treated copper? (Sorry, you'll get nothing but grief here for that stuff )

    Quote Originally Posted by Jarvini View Post
    or how one set of speaker cables can influence bass response or treble clarity.
    The reason you don't hear about this with guitar amps is that the cable runs to the speaker are typically very short. But LF, even for a guitar amp, can very much be affected by long speaker cables of small conductor.

    As to your layout so far... There are indeed some less than ideal things going on. But this is not just WRT guitar amps. That is, they would be less than ideal in a hifi amp (or even a CD player).

    First I'd like to ask if your assortment of resistor types is intentional for their reputed tonal contribution to specific circuits or just what you had on hand in those values.?. I'll guess the former based on the silver plate wire and the TAD caps Grow a thick skin, you're going to get ribbed here sometimes... If we like you But really, the tonal contribution of carbon comp resistors is going to be too small to hear. What won't be too small to hear is the shot noise typical of carbon comp resistors. They are the worst type of resistor for this sort of thing and the worst place to use them would be high voltage dropping resistors, like plate load resistors. Shot noise is, if I've interpreted it correctly, tiny arcs of electricity crossing voids in the resistive element. The end result is a kind hissy sound that borders on crackly. It's especially apparent in higher gain circuits though, so you should be fine with this build using them.

    Then there's the grounding. Right now you have the power tube cathode resistor intentionally grounded with the preamp. That's a no no. You REALLY want to keep high current power amp and power supply grounds OFF the preamp ground buss. Since you've already cut the board you may need to get creative to alter the layout, but that's not the end of it...

    Right now you have the cathode bypass cap physically close and parallel to the cathode resistor. Electrolytic caps HATE heat. That resistor makes a lot. Although this "parallel on two eyelets or turrets" arrangement is common that is likely the reason failure of that cap is common in vintage style amps. Most experienced techs and builders don't do it. Preferring to mount the cap away from the resistor, but ground it in the same place.

    And that's all I can tell from what you have so far.
    The Dude likes this.
    "I'm just going to perform a bit more scientific investigation, turn it up to 11 and rip of the knob." überfuzz

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  25. #25
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    Glad I put the picture up before soldering now !! Looks like some adjustments are needed don't worry I can take a good ribbing and I was expecting some errors with regard to the cathode bypass and electrolytic issue I take it you mean the one for the power tube that I need to alter the grounding for ?
    Really helpful advice though thanks chuck

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