Hello,
I am currently building SS guitar amp (i have earlier asked here for suggestions). As stated in the earlier post,
please see my details once again..
mostet booster-->phasor-->compressor-->Gt2 clone(tonepad)-->delay-->power amp
power amp :lm3875 datasheet schematic with added input Rf circuit.
Cab: Eminence Gov with pine cab and plywood baffle.
Eminence Governor:"The ultimate expression of that '60s/'70s British sound. Thick, raunchy tone with lots of mids"
www.eminence.com/pdf/Governor.pdf
Problem:
I am not getting much treble when connecting Gt2 directly with the power amp. Gt2 doesn't have any mid control.
and i have found that for each setting there is right bass,too much of mid and lack of treble. it does not have the punch i require.
Then i put the Gt2 output to my small home theater which i think has preamp and there are volume/bass controls only. taking speaker output from home theater has helped increased
the treble but not that much.
so my humble question is whether the o/p of Gt2 is weak enough that it cannot drive power amp directly..if not then,
can i use tone mender from runoff groove prior to power amp
http://www.runoffgroove.com/tonemender.html
No, it's not a "weakness" problem, you are not complaining of lack of volume but lack of highs.
I'd build the tone mender but with the real Fender EQ values (as seen on a Twin, for example) and plug straight guitar>TM>LM3886.
Just like that.
And what you hear is the basic sound that combination can give you.
*After* you test it, then you can add other stages, including the GT2 driving the TM.
But first we need a "reference sound".
Thanks Fahey for your reply.
More specifically when i play strings of my guitar I have found that the response of E A string moderate. D G string very loud. B is medium and for high E string i think i have to break it to make it sound. It's not only for my guitar but also for other guitars i have tried and it is worse when playing a Ibanez guitars.
You are right. Actually volume is pretty loud but again i can not measure whether i am getting the correct loudness/watts.
First I have used a 12 0 12 transformer to drive the lm3875 power amp. Then i use 18 0 18 transformer. But i haven't noticed any significant increase in Volume(there may be but not too much).
earlier i have tried connecting mxr microamp between guitar and power amp. But then also it lacked treble. I just dont know if speaker's own emphasis on mid causing this problem.
I never saw people turning their amp treble full. But I have to make it full but still not getting the required sound. and i thing increasing too much treble from Gt2 making the tone harsh and scratchy.
So the question is whether GT2(tonepad version ) is a true preamp that can drive power amp. or basically it requires another sort of preamp (whether in mixture/PA or power engine from Tech21 which has +-12db eqs).
or there is some problem in my cab chocking treble.
Fahey, I will definitely give TM a try....
Please check these photos..
photos of cab
Divide and conquer.
Just a general thought; you have a long chain from guitar to speaker and if you want to isolate a problem (in this case lack of trebles) then the rule is "Divide et impera" - divide and conquer.
Try driving just your speaker from a known good amp (and say MP3 player) and see if it can produce sufficient trebles - yes/no?
Try feeding the same programme into just the power amp and speaker (ditto) - yes/no?
Keep adding stages one at a time backwards towards the guitar input and testing with the same signal at each stage. Perhaps somewhere you will notice that the last stage you added is eating your trebles, so that is where your attention must be concentrated until that problem is fixed.
Dumb questions - are the strings on your guitar a set, or an odd collection from individual string breakages? How are the pickups and adjustable poles (if any) set?
{Nice looking cab BTW :dbtu: }
Quote from: Roly on October 27, 2012, 03:27:20 AM
Divide and conquer.
Just a general thought; you have a long chain from guitar to speaker and if you want to isolate a problem (in this case lack of trebles) then the rule is "Divide et impera" - divide and conquer.
Try driving just your speaker from a known good amp (and say MP3 player) and see if it can produce sufficient trebles - yes/no?
Try feeding the same programme into just the power amp and speaker (ditto) - yes/no?
Keep adding stages one at a time backwards towards the guitar input and testing with the same signal at each stage. Perhaps somewhere you will notice that the last stage you added is eating your trebles, so that is where your attention must be concentrated until that problem is fixed.
Dumb questions - are the strings on your guitar a set, or an odd collection from individual string breakages? How are the pickups and adjustable poles (if any) set?
{Nice looking cab BTW :dbtu: }
Thank you Roly for your thoughts in my problems.
1. I will connect all those effects circuits later though they are already complete. Now i am only connecting things in this fashion.
Guitar-->GT2-->delay-->Power amp
delay can be bypassed and have no contribution in adding gain or treble. So its neutral.
2. I have tried connecting the power amps and cab with my computer initially to check the response. the treble comparatively less than the full range speakers. but if i make 6khz band of my computer graphic equalizer full, i get some cymbals sound. but still mid is so heavy..I have some solo guitar track. When i listen to normal speaker it has some sharpness but when i listen to governor, its kinda blunt.
3. yea tried connecting the speaker from my computer power amp. response is more or less same. But when i connect my computer speaker power amp after Gt2 and taking speaker o/p from that power amp, i have got some treble making the sound more beautiful...
4.I think this is not an issue of guitar. every guitar cant be wrong..
looking for such suggestions..
Mr Fahey likely knows more about speaker stuff but I'd guess these are trying to replicate those famous Celestions?
If so then your observation is correct as their response drops like a brick at around 3kHz.
So unless you have the right preamp/powerAmp to drive it then expect some mismatch with other gear.
This is the problem with just following one part of a very large and complex system.
(Brand name swapping)
Like Bolting a Rolls Royce grill on the front of a VW Beetle may get some looks but I doubt it will make it perform better. :(
The whole system has to work together,, in this case those old drivers need a lot of treble boost in the circuit design to balance it out,, do it right and magic stuff will happen.
Phil.
As a general rule of thumb the top end rolloff of a guitar driver is about 80 times the bass resonant frequency, e.g. 50Hz x 80 = 4000Hz. If you really want some top end (as you do with a synth) then you really need to add a "low reach" tweeter, one that picks up where the main driver rolls off.
{I have seen a pic of a beetle with a fake RR radiator - and it just looked bloody strange :duh }
Quote from: Roly on October 27, 2012, 10:28:05 AM
As a general rule of thumb the top end rolloff of a guitar driver is about 80 times the bass resonant frequency, e.g. 50Hz x 80 = 4000Hz. If you really want some top end (as you do with a synth) then you really need to add a "low reach" tweeter, one that picks up where the main driver rolls off.
{I have seen a pic of a beetle with a fake RR radiator - and it just looked bloody strange :duh }
I do not know much details of my driver but in their datasheet resonant freq mentioned as 101hz
Your speaker has strong low mids, weak high mids and zero treble, as was pointed out above and is mentioned in the Manufacturer's own datasheet, so what you hear from that speaker, driven from a roughly flat source, is what is to be expected.
GT2 is a "SANS Amp" which means WITHOUT Amp.
It's output is flat (the provided treble and bass controls are meant for *minor* tweaking in the mix) and they expect you to plug it into a Recording or Live Sound board, which in turn drives high quality, HiFi *full* range speakers.
So a rollercoaster response like of a guitar speaker is not what they expect.
I suggested starting with the Tone Mender (straight into the chip amp, not even bypassed pedals) as a first step.
Anyway, please remember that even emulating a classic Fender, they were meant to be used with a very light , responsive and Twangy speaker , one of Jensen C or P 10R , 10Q, 12 R/Q or N at most, **very** different from a heavy V30 clone so from the start we are not using the propr speaker.
Of course, let's start with something and adjust marksmanship along the way.
Hint 1) Is there any of those Tube>FET preamps which is clone of a VOX AC 30 or something?.
Hint 2) I bet working with an Italian Jensen would have been easier.
They are considered speakers with too much highs
Just thinking aloud.
Quote from: paku5535 on October 27, 2012, 04:08:21 AM
3. yea tried connecting the speaker from my computer power amp. response is more or less same. But when i connect my computer speaker power amp after Gt2 and taking speaker o/p from that power amp, i have got some treble making the sound more beautiful...
So you get more high end if you substitute another power amp? Is that enough so that the highs are where you think they should be, or is the difference small? Is it beautful or just more beautiful? :cheesy:
I think that for this kind of reference testing, you should have a better amp than a computer speaker one. Get some used 100W per channel studio or sound reinforcement amplifier for a hundred bucks. Something that is 20-20Khz into 4 ohm loads. This can be used as a reference benchmark.
You may have made a mistake in the assembly or a poor solder joint. Lots of gain at low frequencies that rolls off rapidly could point to too much gain (inadequate negative feedback).
Maybe you put an incorrectly valued capacitor somewhere. (Eg mix up picofarads and nanofarads),
You cannot even rule out that you have a bad amplifier IC. You have only reproduced this issue in a single unit that you have built. By some extremely bad luck, you could have a bad chip and tear your hair out looking for problems elsewhere.
Firstly thanks to all of you for sharing your thoughts.
Let me discuss something..
I am a student from India. Basically its my passion to build an amplifier. First of all in India you will not get most of the things required. In India we have the dealer of eminence only and when i bought this speaker they had stock for two speakers, 1. governor 2. some legend series speaker. after watching some reviews and videos I went for governor. I dont know but there is something wrong with the speaker sound. its not that Fender sound not coming good, the marshall type sound is not coming good as well. can you guys please tell me how to detect faulty speaker? I had dreamt of implementing many things including remote foot channel switching etc. But when you are having dull sound coming from it, who like to spend time and money into this!
As per your suggestion, I will build tonemender and connect it. One of my friend has a Marshall MG 30 amp, I will test my speaker disconnecting his. I think that will give some sort of indication. What do you think? Because I cannot tolerate this anymore. its been three or more months i have been working on this without attending college and still its a garbage.
:( :( :( :( :(
which vox clone you are referring?
Hi Paku, don't worry, you must go step by step.
First of all, I understand your situation very well, I'm from Argentina, we have many good things but also lack some specific for this business.
Just for your information, I make my own speakers, go figure, and sell them to other amp makers.
2) sad but true: a plain flat SS amp sounds dull when driving a guitar speaker.
Tube guys have it easier, their amps , even if *very* simple, sound good even "flat".
And the simplest ones, such as the Champ, which has no EQ, are used with a very light, thin paper cone, tiny voicecoil, 6" (or at most 8") speaker which by itself is very trebly, typically including an 8 to 12 dB peak around 3500 Hz.
Does it mean you can't get good sound?
Yes you can, but *you* must add the treble boost.
Doubly so, because you chose a very good and eficient but somewhat dark guitar speaker.
Try to build this preamp, which is a *good* SS amp, and *very* Marshall.
So much so, that ZZ Top used it both live and at the Studio. :o
(http://music-electronics-forum.com/attachments/2552d1212538675-3005.gif)
Look that it has *two* treble boosting circuits:
1) C1 R5 in parallel with R4 , boost 9 or 10dB above 450Hz, I mean *all* frequencies above , so , say, 1000 or 3000 Hz also get boosted that much.
Others would say it cuts low mids and bass below 450Hz ... in the end it's the same.
The guitar goes from muddy boomer to cleaner and brighter.
2) C3 rises high frequencies above 800 Hz at 6dB/octave so it's 12dB up at 1600Hz and 18dB at 3200 Hz.
3) Your friend's MG30 must certainly sound quite good with your speaker.
In fact, your friend will want to keep it ;)
4) GO TO COLLEGE. When you get back home you continue with your amp.
Good luck.
Hello Fahey,
Thanks for your reply. I will implement preamp section. But can I change the pot values to regular values like 10k,47k,100k etc?
@paku5535
GO TO COLLEGE!
The Marshall circuit that JM posted is a nice straight forward amp - effective without getting excessively complex; but I'd make a couple of comments.
The input resistance of only 330k might be fine if you always use a stomp box or have an active guitar, but from some of the stuff I've been doing lately with guitar buffers and splitters it has been driven home to me again how important a high input impedance/resistance is for a passive guitar, at least one megohm.
I've been fooling around with FET buffers that present 2 to 3 megohms and on A/B tests there is a clear difference in the upper register, the natural resonances of the pickup are less damped and even my cheapie test guitar (a $100 Strat copy) sounds richer and more lively with the higher impedance. So I'd bump R1 up to 1 megohm.
You ask about scaling the tonestack pots. As a general rule if you increase the resistance in a tonestack you need to reduce the capacitances to keep the profiles in the same place. In this case however the 100k input impedance/resistance of the power amplifier means that you would be better off going down to the next locally available pot values and scaling the capacitance up. An invaluable tool (and a lot of instructive fun) is Duncan's Tone Stack Calculator, a free programme specifically for such tinkering with various guitar amp tonestacks.
Oh, and GO TO COLLEGE! :dbtu:
Thanks Roly for your reply...
yea, its time to attend college. I think i need to stop my project works for some days since my exam is almost knocking the door. I will start after the end of this semester with fresh mind. I will continue posting in this page then. Hope i will get the same help and support from you guys.
Hi paku.
Those *are* very common pot values, no need to substitute.
I think what confuses you is that old notation for many parts *tried* to use a 0 / 1 / 2 / 5 scale; thus 50K, 1M, 250K, and so on, while modern designers try to write a "normalized scale" value, so 4K7 , 22K, 220K , etc., same as resistors and capacitors.
But it's the same:
22K=25K
4K7=5K
1M=1M (in that case, no change)
Remember that in any case, a pot is *not* a precision part, usually has 20 or 30% tolerance.
From my experience, the tone control values are low enough as to drive properly any reasonable power amp; and the apparently way too high 1M Master Volume pot (100K Audio /Log would be much more reasonable) was chosen *on purpose*.
This, together with the "anti" brightness cap to ground (C7 : 220pF) makes the amp lose some highs when used at a lower volume and sound less buzzy.
Roly's suggestion on increasing R1 to 1M is spot on.
Add 100pF in parallel with it, to kill RF, or you'll have an unexpected backing track while playing.
You will love this little preamp <3)
PS: here you have the Marshall Lead 12 driving a couple "big" speakers (similar to what you have), instead of the tinny tiny original 10" (G1025).
Now you know why it was used to record !!!
http://youtu.be/QW303lSUTxI (http://youtu.be/QW303lSUTxI)
Thnks Fahey..
Yea i know 4.7k alternatively written as 4k7. But we have available pot values of 1k,10k,47k,100k,470k. Thats the reason i am asking here.
taking only the preamp section with chipamp yield the same result?? Not to mention now, but if i find this preamp beautiful can i add fx loop to it, since i have some pedal that need to be added after drive.
video link posted by you sounds good :)
Thanks
If you do *not* find 22k or 25K pots *at all*. use 47K but change parts as follows:
Vr3/Vr5=47K
C9=.001 (1000pF)
R13=22K
C11=.1
C10=.01
Vr4=10K
What I did: this is what Roly called "scaling": moving all impedances up or down *the same amount*.
Here we are doubling impedance, so resistors double and capacitors halve.
Tone control frequencies remain the same (that's the idea).
In this particular case, no big deal, because anyway we will keep that 1M master volume pot (try to get an audio/log type).
hello,
Today i picked my cab and went to my friend house to check with his MG30DFX. Now i quite surprised that the speaker contains more treble than his(though high freq response). but unfortunately it lacks freq just before that. and the bass response is pretty poor compared to his G10. overall the speaker lack some 'x' thing i dont know and sound thin.
overall impression: my friend prefers my speaker, but i like his.is thinness due to pine cab? although his speaker rated at 4ohm, mine one is 8ohm, but for both speaker we are getting almost same loudness for an equal volume. My speaker seems to be more efficient. I think with good and careful preamp design treble will not be any issue. yea "Divide et impera"
Thanks Fahey for calculating those values.
paku
Just a though here: I just have bought a Trademark 120, which is based on the GT2 circuitry as far as preamp is concerned (but the cab sim is only active on the dedicated "sansamp" output, and as it's a combo supposed to work by itself, it has 3 bands active EQ).
First thing is either to feed a Hifi power amp and flat response speaker with the cab sim on, or bypass the cabsim part of the sansamp and drive a power amp and guitar speaker.
One other thing I noted is that the tweed voicing has a tendency to produce weak sound on the light strings (highE-B-G) compared to the other voicings. As a consequence, it needs (and I mean really needs) some EQ tweakings. Don't be mistaken, to add body to these strings you need both more trebble and more mids. So back off the bass a lot on the GT2 when using the tweed voicing or put an external EQ, especially if you are using a guitar with vintage humbuckers (less of a problem with active pickups or single coils).
Hope that helps even if I'm not able to advise on technical stuff.
Actually I pinched the term "scaling" from an excellent little article on "Tone Control Scaling" by Randall Aiken;
http://www.aikenamps.com/ToneControlScaling.html (http://www.aikenamps.com/ToneControlScaling.html)
Just a couple of points that come to mind paku; as a rule of thumb with tonestacks in general we try to drive them from a circuit that has no more then one-tenth the characteristic impedance of the tonestack, and load their output with no less than ten times that impedance. You often don't get the full 10:1/10:1, but you get the general idea that tonestacks like to be driven from a low impedance and output into a high impedance.
When it comes to testing a speaker (or anything for that matter), as @QReuCk implies, we want the driving amplifier and listening environment to be as neutral as possible to isolate just the factor (in this case the speaker) we are interested in evaluating. To this end a stereo or "Hi-Fi" amp is a better source because it can be set to have a flat response, while most guitar amps (especially Fender's) can't be set to have a flat response.
Hi paku , you're welcome :cheesy:
As you see, your speaker can reproduce treble .. if you supply it with lots of it ;)
Not surprised because of the lack of bass in your friend's amp; commercial designers (such as myself) often get a sample of what speaker they will use, and tweak design, eq, etc. , until they get the best response from that combination.
If you work the other way, you will most probably have a surprise at the end.
I'm quite sure that MG30 was optimized for that G10 speaker.
You do the same, first build the Marshall preamp as-is, then you tweak it.
If you watch the video I posted with "good" speakers (such as yours) and the watch the 1000 others on YT using the very light original speaker (a G10-25) you'll see there is a big difference, the G10 was almost unbearably thin and trebly.
Dear paku, here you have a video of one of my *old* amps (this one is 23 years old) , which uses a preamp quite similar to Marshall Lead 12, but driving a 100W amp.
http://www.youtube.com/watch?v=FNehpDVExU8
Now you know why I suggest you build one ;)