Amperes required by LM1875 Guitar Power Amp

[exztinct01]

1) that design has errors, triple check it against the schematic.
2) that design has way too wide tracks, way too close.

I haven't reviewed that layout yet, I just assumed it was good but I actually am going to check it tomorrow. Also, when I see a layout like that, I first build it on a software pcb designer to be able to edit or improve the design.

3) I was worried about your printed picture which showed blank areas along some tracks, or a thick one with a very thin parallel one, maybe it was just a picture reflection, but etchings look very good.

There are no blank areas there, etching was actually good except for some unintended track bridges coz I didn't recognize them soon. I was too careless that time. But I removed those bridges using my handrill.

Also, wow! for the protection advice. I already knew that pcb's needed protection from oxidation but I somewhat kept on ignoring them since all I've been doing before are small projects with cheap components. But for a power amp, especially a guitar amp which I intend to use for a long time, durability and reliability is very important. Also, I think it's a good practice to protect my pcb even though I'm only a beginner since complex circuits with more costly components are surely coming in the future.

Although, I do pray for a permanent math instructor job so I can afford a professionally made pcb. It's hard to spend money when after every semester, you don't know if you will be rehired. 

[exztinct01]

question: that tree rosin you showed me, does that call for a specific tree (e.g. pine)? i think we have some type of tree rosin here we call "kamanyang", but it's not pine. Still, if that calls for a specific tree, I'll be searching for it here.

Add: Here is another shot of the pcb I etched. Some solders don't look too good since I don't have a good iron tip right now, but I tested the amp and it worked and sounded good. Also, I already tested for shorts and dc in the output but found none.

[J M Fahey]

Well, you tried to solder on very dirty and oxidized copper, that makes it very hard work for the soldering iron.
You should have polished it bright with steel wool, or *very fine* sandpaper.

In fact, I recommend you disassemble that board, pull out as much solder as you can (melt it and *quickly*  swipe it out with a dry cotton cloth) and lightly sand it with 600 grit sandpaper, what car paint shops use.

No kidding.
Otherwise if you have any problem, you won't know whether it's a real problem or just poor soldering.

I checked "kamanyang".
It *is*  a tree rosin, and should work, but the name applies to the most expensive there is, the incense rosin used in Church ceremonies, specially Catholic and Orthodox Church.

Not sure what you mention is the real thing (which would be like using $80 a bottle Stolichnaya Vodka when a project calls for $1 a bottle "denatured alcohol") but **maybe** in Philippines the word became generic, meaning any cheap rosin.

The one I mention must be available for cheap , a couple U$ a kilo at the neighbourhood hardware shop, plumbers use it to help solder lead plumbing pipes, go figure.
It should also be available for cheap at a local small chemical supply shop, the kind which also sells unbranded detergent and clothes washing soap in bulk, rat poison, floor cleaner/deodorant, caustic soda, muriatic acid, etc.

Real kamanyang should be available at a Religious objects/Santeria shop or a New Age one, to be burnt over coals and "send bad spirits away".

IF some Spanish use remains, what you want is "resina de pino" , while kamanyang is "incienso".

[exztinct01]

Well, you tried to solder on very dirty and oxidized copper, that makes it very hard work for the soldering iron.

xP
I didn't really know it was oxidized by how it looks  :duh
how stupid of me  :loco

and our kamanyang is not expensive, well maybe the one used in churches here are, but many are sold cheap and bought by some healers
so I guess the name just became generic here

[exztinct01]

Update: Just finished desoldering components from and sanding my amp and PS pcb. Still waiting for the tree rosin to dissolve completely.
BTW, I bought that kamanyang and what they gave me are two different items sold together. Vendors say they are burnt together. In the attached image, the darker ones on the left feels and looks like wood bark or anything related to wood, and the left ones colored yellow looks like crystals but are brittle. the woodlike ones are called kamanyang and the crystal like ones are incenso according to the vendors






I put them inside containers separately and poured ethyl alcohol, and will try to see which is the tree rosin, or maybe both will give me what I need,

[exztinct01]

I just tested my P27 preamp in breadboard, connected to my LM1875 power amp and it worked good. But I used old, used and all linear pots for the preamp so I'm planning on purchasing some pots for it tomorrow before I put it in pcb. So, which among those 5 pots should be log and which should be linear?

Also, is it necessary to shield the preamp from the power amp?

[J M Fahey]

In general, volume/bass/treble/master should be Log/Audio, Mid is usually Linear.

As of shielding preamp, not high gain here so it's not *mandatory*  but it never hurts, it may keep unintended FM radio away.

[exztinct01]

in ESP P27A, there is a 10 ohms resistor in series with the return path from the preamp. What's its purpose? Is it for isolating the preamp's common?

Also, is it necessary to connect the preamp's and the power amp's common? or can I just use a shielded wire, connect the shield ONLY in the power amp's common, NOT in the preamp's common? This way, their only common connection is through the power supply.

[exztinct01]

first, thanks to all your help for finishing my first guitar amp. It's not yet in a chassis since I don't have the tools  for building it but when I get some money, I will immediately go to a metalwork shop to order a custom build one.

My take on my first build (again, it consists of P27 preamp using TL072 connected via shielded wire to LM1875 single channel where the shield connects only to the power amp, common connection is through the PS)
- Noise is very low, I barely hear it when not playing, even when both Volume and Master Volume are at maximum.
- We actually used it (uncased) in a praise and worship setting since our guitarist was so excited about the amp. Honestly, our drummer plays so loud that our soundman finds it hard to bring the vocals and keyboard up to its level, but the guitar in my DIY amp sounded so clear throughout the hall, with leads singing 
- After about 45 minutes of playing (our guitarist was not using any effect pedals that time, just the amp and guitar at maximum volume both), I touched the heatsink and the IC and HONESTLY, it did not even get warm (being out in the open air of course helped).
- Our guitarist even asks me why there is no gain pot and I don't know what to answer him. All I know is that the preamp already has two volume controls and the Master Volume at max produces a little bit distortion. But he asks for more, I don't know how to add a circuit that will integrate a gain control there.
- After our service concluded, I put my DIY MXR Distortion Plus in front of the preamp, set it with maximum gain and Volume at about 3 then played a song with distorted guitar. Turning the pedal on makes a dramatic increase in volume compared with the pedal off so I don't know how to make the transition from clean to distorted using the DS+ sound good. Some suggested that I try different diodes than the 1N4148's.
- Also, when I tried to increase the pedal's volume (I think it was at 7 and above), the speaker suddenly squealed. That high pitch sound disappears when I lowered the volume. So, how do I remove that squeal? Should I maintain my pedal at low gain or low volume? I avoid having my pedal at low gain and volume coz I don't think I hear distortion at those settings. I believe I hear those distorted sounds clearer at high volume.
- Also, after playing with the pedal, my LM1875 IC and heatsink got warm. Not too hot, just warm. 

Any suggestions, opinions, recommendations, mad reactions are accepted  :trouble

[incurably_optimistic]

- Our guitarist even asks me why there is no gain pot and I don't know what to answer him. All I know is that the preamp already has two volume controls and the Master Volume at max produces a little bit distortion. But he asks for more, I don't know how to add a circuit that will integrate a gain control there.

I've build this preamp and I think of the "volume" control on the schematic as a gain control. This control sets the level of the signal before the second op-amp stage with a set gain and clipping diodes, so using this pot not only changes the volume of the pedal, but also amount of clipping.

If you want more distortion out of this preamp, I think the easiest way is to put some booster pedal before the amp in the signal chain - with hotter signal at the input the diodes would clip more easily. If you want to be able to control the gain of specific op-amp stages, as those work as non-inverting amplifiers, you can lower the values of R11 or R6 to 2,2k (that's the lowest value you should use according to Rod) and wire a 5k resistor in series. Although in my opinion that would be redundant to the volume control.

But keep in mind that I'm as new as you to the area of building amps so take this comment with a grain of salt! Better wait for someone more qualified to answer before you make any changes (and the best idea is to put the circuit on a breadboard and then experiment)

[exztinct01]

oh I know you're still way better than me at this  :lmao:
I don't think I'll be integrating a drive in the amp. If he wants distortion, then I'll build him a TS808 or a Big Muff Pi aside from my Distortion Plus. Or like you said, I may build an AMZ Booster.

I find it a bit bassy though, the preamp. How about you?

[incurably_optimistic]

I didn't have in mind putting a booster in the same box, just add a booster pedal to the end of your signal chain if you want to get your distortion from overdriving the amp rather than from a distortion pedal. I prefer to get distortion from my pedals rather than amp, but I liked the overdrive from this preamp so it's just an idea.

Well, I like a lot of bass from the guitar amp so I actually increased the amount of bass in this preamp  :duh but if you want less, try a bigger value for C6 capacitor for starters.

Think twice before building him a BMP if you don't like bass as this thing has TONS of it and not much of treble response.  :grr Of all the overdrives/distortions I've build one of my favorites is BSIAB II, check it out if you haven't already!

[exztinct01]

BSIAB II, I'll definitely try that 

[exztinct01]

In a system composed of a preamp, power amp, them sharing a power supply, which is better? Isolating preamp from power amp or isolating preamp from direct connection to power supply which means its ground connection would pass through power amp first before going to star ground?

I don't even know if I'm asking the right question  :lmao:

I thought maybe if both preamp's and power amp's common are connected directly to PS, and also with each other, there will be a loop and it will do no good for the system if power amp's return will pass through preamp. Am I getting it right? Please help me fix my brain.  :loco

[incurably_optimistic]

If the ground points of the preamp and power amp are connected to each other directly and also there are two separate connections from the preamp and power amp to the common point, then you're asking yourself for trouble - like you said, you're creating a ground loop and also there's a danger that a high current return from the power amp would travel to the common point through the pre-amp stage, which of course is not desired. You can read more about this in this excellent post: http://www.ssguitar.com/index.php?topic=288.0