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Rod Elliott's Project 27 and Amp

Started by ghoshsubha444@gmail.com, February 27, 2013, 04:54:55 PM

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ghoshsubha444@gmail.com

hello,

I have finished p27 preamp(exactly like the picture) and played a couple of songs with delay and compressor..

nice clean sound... but overdrive is not that good and noisy..So i am not playing with drive.

1.if we only concern about the clean..the clean is little noisy(very little noisy). since we have achieved such low noise in clean, is there any way to cure it completely?? 

2. I am not satisfies with the amount of treble and upper mids... rough :( bass side string's sound are not defined.. they are kind of boomy..What to do in this situation??

i have checked the tonestack with duncun software. compared with fender..bass and mid are in the middle position and treble is full..

I am using OPA2107pa as opamp that i had sampled from Texas.. But BC549 is not available so i had to solder cheap bc547 $0.0009/piece in indian currency(dont know A/B/C?). is this creating the noise?
I have found a pdf from diyaudio_com mostly like modified p27 with input and output buffer..
Can i implement it??(attached)from:
http://www_diyaudio_com/forums/attachments/instruments-amps/142195d1254079176-guitar-amp-design-build-guitar-preamp-1.pdf

looking for your input.

subha

J M Fahey

1) congratulations, you built it well.
2) ***what speaker are you using?***
This amp expects a guitar speaker.
3) you can use the Fender tone stack instead of the P27 one.
Be sure to use also the proper 1M volume control.
If you want tho use your current pots, you must "scale" the values to keep the response.
Since you use 50K tone pots, 1/5 the impedance of the originals, you need to use 5X the original caps, as in .1uF>.47uF and so on.
Obviously use the closest standard value.
As in: if math says .23 to .25 uF, use .22uF and so on (within 20%, higher or lower is acceptable).
4) anyway I suspect your speaker.
4) does the bright switch have any effect?

As of noise, grounding is difficult for the baginner; but practice makes perfect.
You already started te right way.

ghoshsubha444@gmail.com

mobile update:when dialing volume pot the treble is getting even lower. So missing the crunch..

J M Fahey

http://www_diyaudio_com/forums/attachments/instruments-amps/142195d1254079176-guitar-amp-design-build-guitar-preamp-1.pdf

Bad link, repost.


ghoshsubha444@gmail.com

thanks fahey for your reply

I am using Eminence Governor speaker with open Cab.

Yea, enabling the bypass switch, i am getting some treble boost
(1k).... (with some low cut)but the lower  strings (E-A-D-G) lack definition 

I do not know the math..can u calculate it for me with the same pot..since 250k,1M pot are totally unavailable here.

But the crunch is completely missing and with higher gain there so much noise and tone is so Fat ??? :-\...
Thanks

Roly

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

ghoshsubha444@gmail.com

Quote from: Roly on March 09, 2013, 10:15:59 PM
Quote from: ghoshsubha444@gmail.com on March 09, 2013, 11:33:25 AM
http://www.diyaudio.com/forums/attachments/instruments-amps/142195d1254079176-guitar-amp-design-build-guitar-preamp-1.pdf

Non-members cannot download link.  You will have to download PDF then upload here.

hello Roly.Thank you for your interest.

I have already uploaded it named GUITAR PREAMP 1.pdf above the graph picture in my earlier post.

I am uploading it again for your convenience..

J M Fahey

1) the "improved" P27 preamp published in DIY audio is wrong, like most of the stuff published there.
Tons of would-be "designers" which have no clue.
In this case, both buffers won't work, because their inputs are floating unbiased.
Besides, the first buffer is unnecessary because Rod's design *already* has 1M input impedance, and the second one, although not bad if you have a unused spare Op Amp, does not justify adding one when the simple transistor one is quite adequate .... and already tested as working ;)
Please post the link where that "improvement" is published, so I warn them about the errors.
2) here you have the corrected Fender values for 50K tone pots.
You'll need a 250K volume pot , don't tell me they are not available at an Electronics shop.
They might be called "220K" to follow modern conventions, but it's the same.
*Try* to get a Logarithmic or Audio one.
3) to increase the effect of original P27 bright switch, change values to 470 ohms and 0.1uF
In all caps I mention, ceramics and electrolytics (depending on value) are fine, also 25 or 50V types, don't need more.
4) you mention "noise" .... what kind?
5) what power amplifier are you driving with this preamp?


Roly

Maybe he was trying to buffer his one microvolt input signal.   :lmao:

Yeah, one missing input ground reference resistor could be a drafting error, but two looks deliberate.  If I had a spare op-amp I'd be thinking of providing a balanced output before adding noise to the input (not to mention being cautious about second-guessing Rod).
If you say theory and practice don't agree you haven't applied enough theory.

ghoshsubha444@gmail.com

#25
Quote from: J M Fahey on March 10, 2013, 11:06:13 AM

Please post the link where that "improvement" is published, so I warn them about the errors.



I was surfing randomly, so i can't recollect where it exactly was..

I have modified according to your value (tonestack) and please check the attachment
[picure a111].White=Fender,RED= modified according to you.. 

I dont know how to define the noise i am encountering but to be precise it is that noise you can hear when your amp is in high gain distortion setting and you are not playing anything.. :(

I am using LM3875 poweramp[National sample]. Power amp has been tested using computer and there is very low noise even in the maximum volume settings...


Questions:

1. I am using some of my pedals phaser and delay which are controlled by digital switching 7414 and 7476..
When i am connecting power to the control board, noise is being increased.. How to avoid that??

2. I am uploading a picture about my planning on the overall setup. please verify it...

Description:

I am building a pedal board using aluminium chassis where i will have three boards..1.phaser 2.copressor 3.delay so that i can on/off them with foot press. Guitar connection will be first to pedal board-->phaser-->compressor-->to amp(p27/distortion i will build later)-->back to pedal board for DELAY-->to amp-->noise gate(manual on/off)-->power amp-->>speaker.[picure a333]

3.A line out will be great for recording. how to do that??

4. Is it better to use Zener instead of regulator 317or 7809 7805 ,if noise is the concern??

5.Wha are the good alternative of bc549 since it is unavailable?
Thanks

J M Fahey

#26
Well, noise is to be expected the way everything is built and mounted (should I say unmounted? ;) ) now.
You have everything "on the table" (literally) and with some long, unshielded wires to boot.
And you add tons of stuff before even reaching the preamp input, then zig zag back and forth, so you definitely can't blame Ron for this.
Who, by the way, knows his stuff very well.
Just as an experiment, solder a jack to the preamp input with 1/2" max wires, and plug your guitar straight into it; and send its output straight to the power amp.
I bet it works as intended.
Congratulations on building all that stuff :dbtu: :dbtu:, now you need to get a metallic chassis, or an U or al least L shaped piece of aluminum, 1 mm thick is fine, and mount everything there.
Properly grounded of course.

By the way, getting a good layout and grounding is as difficult as the "electronics" design.

But as with everything else, practice makes perfect  :dbtu:

EDIT: and as you see my "5 X corrected" tone control schematic matches very well (center frequency and response) the original Fender one.
You just don't get the same boost value because the pot value is not optimum, but, hey!!, we have what we have. ;)

ghoshsubha444@gmail.com

#27
Quote from: J M Fahey on March 11, 2013, 06:35:46 AM
Well, noise is to be expected the way everything is built and mounted (should I say unmounted? ;) ) now.
You have everything "on the table" (literally) and with some long, unshielded wires to boot.
And you add tons of stuff before even reaching the preamp input, then zig zag back and forth, so you definitely can't blame Ron for this.
Who, by the way, knows his stuff very well.
Just as an experiment, solder a jack to the preamp input with 1/2" max wires, and plug your guitar straight into it; and send its output straight to the power amp.
I bet it works as intended.

I knew looking at the picture you will definitely remark :) :). But to assure you i had test it something like this-

Guitar cable directly soldered to p27-->>p27-->>power amp-->>speaker. May be layout and grounding problems are the issue..Let me observe them carefully :loco..

Quote from: J M Fahey on March 11, 2013, 06:35:46 AM
You just don't get the same boost value because the pot value is not optimum, but, hey!!, we have what we have.

Who knows better than you? ;). But being ignorant i want to know whether it needs further boost to compensate on the second stage...

Please look on my questionnaire on my early post..
Thanks Fahey

newbiediy

Just sharing my newbish "experience".
I also had noise problem when first building my own amp.
But it was BEFORE I put it in a chassis. After putting the whole thing into a chassis and connecting input ground to chassis, it was noiseless.
As far as I know, you should connect only ONE ground point to chassis. Please correct me if I'm wrong.
Sorry for my bad English. We say "laik dis" instead of "like this" in Facebook. :P

Roly

Overall layout

Apart from a grounded full metal chassis you will notice that Rod has added a shield over the preamp board (which may be metal such as aluminium, or single-sided PCB laminate, but must also be grounded); and another shield around the input sockets.

Preamp


Power amp


I'd just like to reinforce the point that Rod Elliott is a very professional and capable designer and frankly a cut or two above the vast majority of people who post circuits to the web. I've had 40-something years in electronics design but I would be very careful about second-guessing Rod or trying to "improve" one of his designs.


Now part of your problem seems to be trying to do too much at once.  Particularly with a new build we try to take each stage a step at a time, identify and correct any problems with that stage before moving on to the next, and in audio amps this generally means starting with the power supply, then the power amp, and so on moving stage by stage back towards the input.

The difference between having boards scattered over the bench, and mounted in a metal chassis, can be very large where picking up external electrical hum and noise is concerned.  The grounded metal chassis makes a very effective electrostatic screen around the assembly.

Now this particular amp design is a little unusual in that it uses some current feedback, and Rod has some particular things to say about how the main amp section should be laid out and wired to avoid instability.  I suggest you read them again closely and mount your power supply, main amp, and output sockets in your chassis then test at that stage that it is working properly.  You can feed a test signal from an MP3 player or similar into the main amp input, and you should be able to get a clean and loud output from your speaker (which must also be properly mounted in its enclosure).

Once you have got to that point you can then add the next stage in front of that and test again, then the next and so on until you finally get to the input sockets.

Before you get too deeply into distributing DC power around your chassis you need to read this thread;

http://www.ssguitar.com/index.php?topic=288.0

Poor distribution and incorrect grounding causes a lot of preventable problems with amp builds, so it's important to have a single chassis signal ground point, and to distribute your power and ground lines radially from there, not daisy-chain fashion as your assembly drawing shows.

It is also important with single point grounding that you use sockets that are fully insulated from the chassis.


Q.1 I suspect that grounding may be the cause of the problem.

You appear to have used hookup wire for the signal interconnects between boards.  Generally speaking it is better to use screened cable for signal interconnects with the screen only connected at the receiving end, the common grounds going around via the single ground point.

Q.3 a line output can be added later using a simple op-amp buffer taking its signal from the input of the main amp.

Q.4 Not really, three pin regulators generally have better noise performance than zeners, but in any case supply lines should be well bypassed with both large value electrolytic caps and some smaller ones such as 0.1uF close to each IC, and particularly right at the input and output of three-pin regulators.

Q.5 Just about any reasonably high gain audio transistor.  The BC549 is a member of  very old family that go back to the BC109, and the main difference in the BCxx9 family are the packages and lead order.  The suffixes A, B and C are the sorted gain ranges being "lowish", "medium" and "high to very high".  Similarly the original BCxx7, BCxx8, and BCxx9 where 'rough", "smooth", and "very smooth" in terms of noise and audio quality, however today even the BCxx9 family are surpassed by audio-specific op-amps that are better in every respect.

The main thing when looking at the data sheet for a possible substitute is that it will withstand the supply voltage and pass the required current, with a safety margin for both, then that it has a gain, hfe, the same or higher.  Then you chose the one with the lowest noise figure, but with modern transistors the noise figure isn't generally an issue except in really demanding circuits such as microphone preamps.


So, start getting the initial parts into a chassis, mains wiring, transformer, power supply, and main amp, and testing each stage as it is completed, then as you add stages in front of the main amp we can deal with the problems as they arise.

HTH

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