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Author Topic: Randall RG100 hybrid  (Read 32847 times)

allan_belt

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Re: Randall RG100 hybrid
« Reply #15 on: April 26, 2012, 12:58:22 AM »
Not that I know of.
And I have searched, that and many other things.
I laugh when people say "you can find *anything* on the Net"
Yea, sure !!!  Keep searching !!!
You'll find (maybe) *some* of what anybody posted ... and what never was, never was.
You'll find lots of stuff on classic 40 years old tube amps, little on modern tube ones, almost nothing on SS ones.
Closest solution would be getting some classic discrete 100W into 4 ohms power amp kit and mod it slightly to add the mixed mode feedback.
You'd save 90 or 95% of the work.
Good luck.
Yes i spent a lot of time searching for something close .. and i found on eproject with PCB and Layout of a 100W RMS power amp.. but .. i don't know if it will work  :o
maybe i'll sepend more time learning how to add the mixed feedback..

allan_belt

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Re: Randall RG100 hybrid
« Reply #16 on: April 26, 2012, 01:07:42 AM »
Hello from Peru and congrats for the Randall Hybrid .. recently finished this project only have two issues:
1. Couldnt find the 2n5484 Jfet so i replaced them with 2n5457 i wonder if both have the same gain???
2. tested the sound out of the preamp section into another guitar amp and the sound is great!!! punchy and Heavy  :dbtu: but when i connected to the power amp section presented here the sound is weak and too trebly for my taste, is it normal??

on my experience with power amps the transistor ones are most pleasing sounding for guitar, and adds a little distortion to the signal when driving hard.. anybody know a 100 watts transistor power amp project with pcb and layout?? please let me know...
thanks for the project and please post some advances or maybe an audio demo..  :tu:
Allan Belt.

Re 2/ above?
What do you mean exactly?
If you plugged into the front (Where you normally insert a guitar ) then yes a big big difference would be heard as you have two preamps in series.

If you like it use it that way and save a power amp build. :tu:
Sorry i meant i plugged on another power amp (Effects return)

Re poweramps.
If 100watts or more is desired then yes plenty of circuits abound if you take time to search.
Rod Elliot site ESP has some good big amp circuits.
yeah i just found one in rod Elliot's site but i did't tried it yet.

But at 50 watts or less just use a chip ,,I have built and use an LM3886 chip which is a serious 40~50 ish watt output.
Phil.
I think i need more Power because of the volume drop on  the Extra Sustain mode.    And maybe Transistor based Power amp adds a little distortion of its own at a certain level  :tu:

J M Fahey

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Re: Randall RG100 hybrid
« Reply #17 on: April 26, 2012, 04:02:45 PM »
Start by linking to the project you found.
Schematics are easy to find, worst case you use one from a commercial amp (such as the Randall itself).
PCBs are the problem ... that's why I had to learn to roll my own.
Or bite the bullet and buy a chipamp kit, which can be modded.
*or* (heresy), buy/get/beg some dead "known" amp (Peavey/Fender/Laney/Crate/etc) from a garage sale, Craigslist or even ... a dumpster and use it as a half built kit.
Why a "known" one? : to easily get its schematic, and often a layout .
And commercial guitar amps usually already include mixed feedback. ;)

allan_belt

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Re: Randall RG100 hybrid
« Reply #18 on: April 30, 2012, 08:47:05 PM »
Start by linking to the project you found.
Schematics are easy to find, worst case you use one from a commercial amp (such as the Randall itself).
PCBs are the problem ... that's why I had to learn to roll my own.
Or bite the bullet and buy a chipamp kit, which can be modded.
*or* (heresy), buy/get/beg some dead "known" amp (Peavey/Fender/Laney/Crate/etc) from a garage sale, Craigslist or even ... a dumpster and use it as a half built kit.
Why a "known" one? : to easily get its schematic, and often a layout .
And commercial guitar amps usually already include mixed feedback. ;)

Here the project:
http://www.eleccircuit.com/circuit-power-amp-otl-100w-by-transistor-2n3055-with-pcb/
the Original Schematics of the Randall RG100 ES .. i don't know if its right to post it here.. so i won't ..
give me green light and i'll post it   :dbtu:

J M Fahey

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Re: Randall RG100 hybrid
« Reply #19 on: May 01, 2012, 12:03:02 AM »
No problem.
I have posted it earlier myself, but don't remember the link, so repost.

EDIT: I saw the project you found.
Don't like it very much: it uses the obsolete single supply configuration, has no short circuit protection, the feedbark network is unnecessarily complex (and probably wrong) and it's not easy to modify it into a mixed feedback system.
Study this:
http://www.diyaudiotr.com/islecler/tammetin.php?metinid=6&durum=e#sonyorum
It is *very* crude, simplified to the maximum, but it works and can be built.
The PCB is easy to homebuild and works too.
And is very easy to modify to mixed feedback.
It's in Turkish but google can translate the page easily.
http://translate.google.com/translate?sl=tr&tl=es&js=n&prev=_t&hl=en&ie=UTF-8&layout=2&eotf=1&u=http%3A%2F%2Fwww.diyaudiotr.com%2Fislecler%2Ftammetin.php%3Fmetinid%3D6%26durum%3De%23sonyorum
Some small corrections:
1) forget the 150W they claim and even 100W, it can provide honest and loud 70W into an 8 ohm speaker.
2) the supply voltage suggested is not too safe.
I suggest (by experience) not passing +/- 40V rails, which demand a transformer of no more than 30+30VAC (or 60VCT).
3) there is a separate .pdf with the ready to print PCB.
www.diyaudiotr.com/resim/proje/kapibara/pcb.pdf
I recommend the iron on laser thermal transfer process, but it requires some experience.
Meaning, make 3 or 4 PCBs before trying this one.
I suggest not building this amplifier now, but it's good to know what you are getting into.
Start by making an LM386 amp.
Build and enjoy it. It is fun.
Later, build , say, some 15 to 30W with a TDA2003, TDA2030 or even TDA2050.
Build and enjoy.
Later, an LM3886 project. (50W)
Loud enough to play anywhere.
Go step by step, enjoy and learn along the way.

I see you live in Peru. Check what amplifier kits you can buy in an Electronics Shop.
« Last Edit: May 01, 2012, 12:57:33 AM by J M Fahey »

allan_belt

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Re: Randall RG100 hybrid
« Reply #20 on: August 06, 2012, 12:08:11 AM »
i spent a lot of time reading about mixed mode  feedback and it was very interesting  ;)
i need some help with the amp i just made.. based on this schematic found on the TDA 7293 Datasheet..


and would like to modify to mixed mode feedback so i came to this:


So my questions are:
are the modifications i made correct?
What would be the right values of the Resistors and the condenser?

i'm using the amp with 8 Ohm Speaker Cab.
Thanx in advance     :dbtu:
« Last Edit: August 06, 2012, 12:11:13 AM by allan_belt »

J M Fahey

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Re: Randall RG100 hybrid
« Reply #21 on: August 06, 2012, 12:53:19 AM »
Basically yes.
New capacitor 100uFx25V
Resistor on speaker ground= .22 ohms. 7 to 10W
New resistor= 470 ohms.
Do not fit R2 and C2.

allan_belt

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Re: Randall RG100 hybrid
« Reply #22 on: August 06, 2012, 11:47:16 PM »
Basically yes.
New capacitor 100uFx25V
Resistor on speaker ground= .22 ohms. 7 to 10W
New resistor= 470 ohms.
Do not fit R2 and C2.
Great thanks for your support you're so kind..  ;)

i`ll test that config and post the results ..  :tu:

allan_belt

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Re: Randall RG100 hybrid
« Reply #23 on: August 08, 2012, 09:54:44 PM »
Yesterday made the changes to the power amp and the sound is a little bit brighter than before .. but with more output.  8)
I forgot to mention    :-[ that there is a resistor (10 ohm) and a condenser (100n) in series between the two extremes of the output..one to the positive side and the other to ground.

my question is: should i leave them there or put them away of the circuit?
Tanks ..  Greetings from Peru.      ;)   

J M Fahey

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Re: Randall RG100 hybrid
« Reply #24 on: August 09, 2012, 12:59:02 AM »
*Leave them there* !!!
They are a Zobel network and absolutely necessary.
Yes, the amp will sound somewhat punchier, nothing revolutionary but it helps anyway.
Y ..... Argentina y Perú un solo corazón !!!! :dbtu:
Hasta nos prestaron aviones Mirage en las Malvinas !!! :dbtu:
Gracias !!!!!!  :dbtu:

allan_belt

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Re: Randall RG100 hybrid
« Reply #25 on: August 09, 2012, 10:33:15 PM »
*Leave them there* !!!
They are a Zobel network and absolutely necessary.
Yes, the amp will sound somewhat punchier, nothing revolutionary but it helps anyway.
Y ..... Argentina y Perú un solo corazón !!!! :dbtu:
Hasta nos prestaron aviones Mirage en las Malvinas !!! :dbtu:
Gracias !!!!!!  :dbtu:

Zobel network mmmm i think i'll do a google search to learn about that..

Siempre al  lado  a nuestros hermanos Argentinos.. somos un solo corazón !!!

Roly

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If you say theory and practice don't agree you haven't applied enough theory.

allan_belt

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Re: Randall RG100 hybrid
« Reply #27 on: August 20, 2012, 08:57:44 PM »
http://www.eetimes.com/design/audio-design/4015876/IC-Audio-Power-Amplifiers-and-Zobel-Networks-One-Size-Does-Not-Fit-All

Very good article thank you..  :dbtu:
This last few days i was reading a lot about mixed mode feedback and lastly zobel network or boucherot cell.. and it`s a lot more than one resistor and one capacitor  :duh
i'm not too good with theory .. :-[ but i`m more like an experiment guy hehe..
in practice i found a few things:   ;)
Mixed mode feedback it`s a lot more interesting in Transistor or Darlington transistors based power amps .
Zober network don't have much impact in overall sound (in my opinion).
and following the article you posted sometimes can be dangerous for the IC  :o
i`ll keep experimenting and after some fumes  :lmao: will find what i`m looking for : A powerfull amp with lots of bass and almost the same response   of a Randall amp   lml.
Any comments are wellcome  :dbtu:


phatt

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Re: Randall RG100 hybrid
« Reply #28 on: August 22, 2012, 09:36:29 AM »
Hi Allan,
If you wish to take on high current DC power Amp design then head over to ESP site where you will find pages of darn good advice that might save some fumes and smoke. winky.

http://sound.westhost.com/projects.htm

Don't expect to read them all in one sitting the site is VAST.

The site is a gold mine for those wishing to explore the hidden details of such things as DC coupled Amp design and audio in general.

For guitar amplifiers, the more basic designs may well sound just as good as the more complex designs. 8|
Phil.

allan_belt

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Re: Randall RG100 hybrid
« Reply #29 on: August 24, 2012, 10:43:58 PM »
Hi Allan,
If you wish to take on high current DC power Amp design then head over to ESP site where you will find pages of darn good advice that might save some fumes and smoke. winky.

http://sound.westhost.com/projects.htm

Don't expect to read them all in one sitting the site is VAST.

The site is a gold mine for those wishing to explore the hidden details of such things as DC coupled Amp design and audio in general.

For guitar amplifiers, the more basic designs may well sound just as good as the more complex designs. 8|
Phil.
cool thanks for the link .. now i have something to read this weekend..  :tu: