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Old 8th June 2013, 12:54 PM   #31
JMFahey is offline JMFahey  Argentina
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It will probably work, and in fact each half looks very much like one of my standard power amps (so called Lin type amp) , but:
1) 200W/8 ohms? NO WAY
Max peak voltage on the speaker would be 52V , and that with a regulated PSU .

With the one shown, considering at least 20% loss, it would be 52x.8=41.6V Pk .
You will have extra 10% loss into the emitter resistors, so this leaves you with 41.6x.9=37.5V Pk=26.5V RMS=87W RMS.

Which is also confirmed by the power transformer rating:
40VAC @ 4A= 160VA rating, good for a 100W amp, tops.

2) it does not have short circuit protection, which can be forgiven in a Home Hi Fi amplifier or even in a "fixed" installation PA (think a Church or a Theater) but never in a Musical Instrument amp which travels a lot and gets plugged/unplugged many times.

3) for that kind of power, search for the ApexAudio schematics around here, but the ones with short protection.
Rodd Elliott also has suitable amps.

EDIT: to be more precise, *one* of them has short protection, the other one does not , the Author makes tha unwarranted assumption that "if one current limits, the other is protected too" which is very dubious.

No need to bridge when you can easily get 200/8 with conventional circuits.
Hint: you'll need around 65/70V rails for that.

Last edited by JMFahey; 8th June 2013 at 01:02 PM.
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Old 12th June 2013, 07:34 PM   #32
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JMFahey thank you for everything!

My choice is made and I opted for the latter scheme. I drew my circuit and it remains only controlling me if the design is ok. For information the output will be darlingtons TIP142 - TIP147 and small signal transistors BC546 and BC556.
In a short time I started directing the preamplifier and amplifier. If all goes well I'll post the drawings of PCBs, of course I will make a report on the sound.

Regards!
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Old 13th June 2013, 07:06 AM   #33
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Quote:
Originally Posted by JMFahey View Post
3) for that kind of power, search for the ApexAudio schematics around here, but the ones with short protection.
Rodd Elliott also has suitable amps.
To which project on Rodd Elliot's website are you referring to? 68, 101 or 117??
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Old 13th June 2013, 07:57 AM   #34
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Quote:
Originally Posted by funk1980 View Post
To which project on Rodd Elliot's website are you referring to? 68, 101 or 117??
The schema in post #30.
HI-FI amplifier for bass guitar
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Old 13th June 2013, 08:11 AM   #35
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Quote:
Originally Posted by Project16 View Post
The schema in post #30.
HI-FI amplifier for bass guitar
Thanks! But I was actually curious to which project JMFahey was referring on ESP Projects Pages - DIY Audio and Electronics
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Old 13th June 2013, 08:55 AM   #36
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I've built a simple bass guitar preamp for my "bass teacher" using a TL071 as non-inverting amplifier (gain of 11 times).
It works with a single 9V battery, 10 MOhm input impedance (it's designed for passive instruments, basses and upright bass).
Regards,

Roberto
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Old 13th June 2013, 11:43 AM   #37
JMFahey is offline JMFahey  Argentina
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Quote:
Originally Posted by funk1980 View Post
Thanks! But I was actually curious to which project JMFahey was referring on ESP Projects Pages - DIY Audio and Electronics
I was referring not to a specific one, but in a general way, considering Rodd Elliott a good designer, with his feet firmly in the ground.
And his designs are simple and robust.

See that rather than concentrating on minute distortion levels or incredible slew rate or perfect 100KHz squarewaves (nothing against, of course) he cares more about "muscle" .... which is proper in the hot, sweaty and overdriven Music Instrument world.

I'd start by building this one
100W Guitar Amplifier (Mk II) Figure 2 ;
100W is a very popular power level , good for rehearsal and Club/Pub shows, and yet compact, light and inexpensive.

It's enough to get even (not drown, of course ) with a normal drummer, and a Guitar player using , say, a Tiny Terror, a Blues junior or a Classic 30 , just to name a few small band popular tube amps.

Or if SS, someone using a Bandit, a Valvestate 40 or 65, or one of the many 60/65W 1x12" amps (Princeton 112, Performer, Roc Pro, etc.).

Couple it to 2 x 10" woofers, maybe add a Piezo tweeter if you are into heavy slapping and you are good to go.
Or a 4 ohms 15" .

For a *louder* band, (say, your Guitar player uses a Twin, or a 50W Marshall into a 4x12" or similar and your drummer's "other job" is being a sparring for Mike Tyson) you'll need 250 to 300W.

In this case 300/500W Subwoofer Power Amplifier Fig1 is fine.
See that basically it's the exact same design as the 100W one with added "muscle".

He didn't draw a short protection here because this particular one was meant to be mounted inside a powered enclosure, but of course you can use the one from P68 .
It's only adding 4 resistors, 2 diodes, 2 small transistors, connected the same way (sensing emitter current and clamping driver base current about a certain level, around 8A).

Read all he says about dissipation, adding more transistors if used with +/- 70V and 4 ohms, heatsinking, wiring, fusing, etc.
Lots of practical advice, that's what I like abour Rodd's projects.

Not many go into "small" but important details as deburring properly the heatsinks or mica type and thickness.
Which he mentions in his:
Project 101 - High Power, High Fidelity Lateral MOSFET power amplifier

Here you trade higher cost transistors for simplicity, but that's your choice, of course.

MosFets have no second breakdown and are robust enough to be protected by simple fuses.

As of Project 117 , it was meant more as a joke, he actually calls it "insane" and does not recommend building it.
Me neither, at those power levels simple Class AB is a thermal Inferno .... literally.

No normal Bass player needs that kind of power.

I've posted pictures of some of my customers who do, but they generally buy (or have custom made) some cool preamp, and drive big commercial PA amps.
But we are talking packed Football stadiums here.
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Old 13th June 2013, 05:00 PM   #38
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Quote:
Originally Posted by JMFahey View Post
I'd start by building this one
100W Guitar Amplifier (Mk II) Figure 2 ;
100W is a very popular power level , good for rehearsal and Club/Pub shows, and yet compact, light and inexpensive.
The preamp section from that one sounds quite good for bass too, I used one for a few years on hundreds of gigs.
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Old 16th June 2013, 03:22 PM   #39
Jsixis is offline Jsixis  United States
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I got to play through the 800 watt mark bass head and a david eden 4-10 cab.
Awesome bass head and for 600 bucks or around that it can not be beat.
Never had to turn it above 10 o clock position with the gain and pre set around 9 o clock positions. (active bass of mine is hot)


Quote:
Originally Posted by mortron View Post
This may be off topic, but I play through a Markbass LittleMark II and its a class D... This amp slams. Have you married yourself to using FETs?

There is a lot of debate on this and that regarding class D, but for bass guitar, its beautiful and the head is small. I use it with a 1x15" cab or a 6x10" and never need to turn past 12 o'clock... I compete with a dimed Marshal JCM900/1960a and a drummer who hits like Bonham on one of Bill Brufords old kits - loud as hell... Headroom is key in a bass rig IMO.
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