ESP 100watt amp

[One-way]

Hi there folks,
This is a post I put on the ESP site but havent had much feedback yet. I thought some of you techo toilers may be able to help me.
Im fairly new to full electronics schematic work but have done heaps of stuff with building and wiring guitars, cabs and the like.
I have built the chassis for the amp project out of aluminium and have it drilled for all controls and plugs, switches etc. I bought an unfinished amp project cheaply on my local auction which has given me most of the parts I need for this project.
I hav been studying the schematic for a few weeks now and there is few things that Im not quite sure of. http://sound.westhost.com/project27.htm
-On the pre-amp circuit it shows the 15volt power supply in bottom left corner. Does it connect to the right hand end at transistor BC549? I see there is a 15 volt +/- supply to both op amp 1 and from transistor BC549. I assume these are all connected by supply rails?
-With the +/- 35volt end of the above supply, does this connect to the +/- wires that come from the rectifier to the power amp board?
-On the pre-amp TL072 opamps does it only need connection 1,2,3,4,8 on OP amp1 and 5,6,7 on OP amp 2? Are the other terminals left unconnected?
-On the pic of the pre-amp board it shows 6 electrolytic caps but not on the schematic. What the story here?
Sorry to I am asking so many probably stupid questions but Im learning lots as I go.
Thanks in advance,
Derek

[J M Fahey]

Hi OneWay/Derek.
Do you have an actual ESP kit? I mean, the boards?
In that case your life gets simpler, as basically you have to stuff them as indicated, mount them in the chassis and wire them.
Please read IceFire´s post, it basically explains the Schematic/PCB layout link.
http://www.ssguitar.com/index.php?topic=1080.0
Electrically, all points that get connected between them, indicate so by an unbroken line that touches them, which becomes an unbroken track in the PCB.
Certain points that go to some common point, omit drawing the line (to simplify the schematic drawing) but *name* that point: "+15", "Gnd", etc. ; *all* points with the same name get connected by a track on the PCB.
If sometime a track *must* be cut in, say, 2 or more pieces, they are joined by wire links or flying wires.
Follow the schematic and the PCB point by point and you´ll "see".
You´ve correctly assumed, as an example, that different "+15" points get connected by tracks.
The Op Amps 1 and 2 are part of the same package, an TL072 (*dual* Op Amp), and you´ll see that all 8 pins get connected.
The 6 Electrolytics *are* in the schematic, although Rod Elliott , for some obscure reason, often uses "regular" capacitor symbols. Electrolytics must use their own because they are polarized and that must be shown somehow. I hope the board silkscreen is properly marked or that will be a certain source of error.
If you have the original boards, please scan and post them, both sides, even if already with components on them.
Yes, flatbed scanners can cope very well with 3D objects, at least up to 2 inches high.
The not very well marked electrolytics are: C3, C8, C15, C14, and C12 , C13 (these two properly marked).
Good luck with your project, don´t forget to post.

[One-way]

Hi there JM,
Thanks for clarifying a few things.
I am not ordering the PCB's as I want to build it on Perfboard which I have plenty of.
I will learn a lot more by working thru in a logical sequence and fitting the components and wire jumpers etc.  I see what you mean, between both opamps all 8 pins are conected to the circuit.
I guess I should draw out the circuit on perf template paper which I found by doing a web search so that things make more sense.
When I first started wiring guitars I redrew the circuit so I could follow it and colour coded the appropriate wires.

[J M Fahey]

There´s a couple great little PCB programs (one specifically made to design on Vero/Strip board). Don´t have their names present now, I´ll post them tomorrow. They make your life easier and produce Internet-ready artwork to ease sharing/posting. Bye.

[One-way]

Would 50 volt Bi-polar electrolytic caps be suitable for those extra C3,C8,C14,C15 positions? I looked in my catalogue and they have all those values listed.

[J M Fahey]

Yes, they would be perfect. In fact they needn´t be "bipolars" but only regular (polarized) electrolytics ...... but ......... since they´re unmarked on the schematic and original PCBs are unavailable, fine, just play it safe. Besides, the $ difference will only be a few cents. Those programs I suggested you are "PCB Wizard" (truly a Wizard, watching it  autoplacing parts looks like magic indeed) and "Layout Creator", the King of stripboard designers. As a bonus, it comes preloaded with a lot of excellent projects, just to keep you busy and happy. You´ll want to build them all !! There was another one I haven´t used for a long time, it´s called something like "SBD" (Strip Board Creator). Check it if you wish.
Bye and good luck with your project. Build and test it step by step, without hurrying, say: Power Supply > Power out (you can test it with an MP3 or CD) > any preamp you like.

[One-way]

Thanks for the feedback JM.
I found once I drew out the pre-amp circuit it looks totally different to the schematic layout. The trick I guess, is in doing it in the most economical way to avoid a birds nest of jumper wires and wasting board space. I laid it out on template paper so the three main tracks +15, GND, and -15 are evenly spaced 6 holes apart and are running full length. I used that spacing so it suits the 220uF polarised caps as they are the largest components to mount.
I then set up the opamp chip so supply pin 8 sits on the +15 line.
I am going to use a socket for the opamp mounting.
Can you please confirm the polarity if I used polarised caps for position C3, C8, C14, C15.
I have plenty of the correct values that Ive pulled from the amp project I bought.

[J M Fahey]

OK, I´ll check them and, if time allows it, re-draw or edit ESP´s original one *or* at least tell you, say, "Cxx positive is the pin that touches Rxx", etc. and post it here. Try to get "Stripboard designer" or use a trick I used before PCs :draw a *big* stripboard, at least twice as large as needed, fill a sheet of paper with all those neat little circles and photocopy or duplicate that. At least 20 of them (save the original for future "reprintings"). Use them freely to place first important/big/unmovable components, such as ICs, pots or filter capacitors, and then place around them the smaller components, such as regular R's and C's. Then start penciling connecting lines. If it gets messy, don´t erase major errors (you´ll lose your "mind reference") but re-draw it on another sheet (that´s why I asked you to photocopy many). *Very* soon you´ll get the knack at positioning components , which is the "magic" part. Good luck.

[J M Fahey]

Hi OneWay, here´s the corrected ESP preamp, with nice little red "+" signs indicating the electrolytics' positives.
Good luck.

[One-way]

Hey JM,
Thanks very much for the markings for E caps.
I noticed in the notes (2) that they say opamp supply pins should be grounded.
What would that look like on the schematic? Is this for the +/-15 pins 4 & 8?
Thanks Derek
Notes:
1 - IC pinouts are industry standard for dual opamps - pin 4 is -ve supply, and pin 8 is +ve supply.
2 - Opamp supply pins must be bypassed to earth with 100nF caps (preferably ceramic) as close as possible to the opamp itself.
3 - Diodes are 1N4148, 1N914 or similar.
4 - Pots should be linear for tone controls, and log for volume and master.

[J M Fahey]

Hi One Way.
Just as Ron said in note 2.
You should add two .1uF (100n) ceramics, from the + and - 15 folts tracks, to a ground track not too far, preferably a nice fat one where R3 and C3 are grounded too. Take it easy, it´s not *that* critical, 1 inch (and maybe 2 ) will be close enough. Gainclone builders not only solder their feedback resistors straight to the chip  pins, but even grind away its plastic to place it closer.  Crazy, man. !!!!!

[J M Fahey]

Sorry, I forgot to attach the schematic. Here it goes.

[armstrom]

Just FYI, this is an older version of the preamp. I believe the schematic for the new design is only available if you order the board. If you look at the project page you can quickly notice that the picture of the populated board does not match the schematic. Notable differences are the fact that the populated board shows two dual-opamp ICs while the schematic indicates only one. The output buffer transistor is also nowhere to be seen on the board. It's probably safe to assume that the new op amp is at least used to replace the output buffer and perhaps more.

[One-way]

Thanks guys,
This information has been really helpful and has made it clear in my mind how the schematic works now.
Cheers

[armstrom]

Since you're building this from scratch you could probably save yourself some components and solder work if you use a TL074 opamp and use one of the two spare opamps to replace the output buffer. Since this is a bipolar supply already it would be very easy to do.