SS amp building...No treble

[paku5535]

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.

[J M Fahey]

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

[paku5535]

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

[J M Fahey]

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).

[paku5535]

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

[QReuCk]

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.

[Roly]

Actually I pinched the term "scaling" from an excellent little article on "Tone Control Scaling" by Randall Aiken;

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.

[J M Fahey]

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.

[J M Fahey]

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