DIY Amp

firethorn · Aug 29, 2009

Hello Softies.

I've about had it with my guitar amps at home. God bless my dad for "investing" in these amps oh-so-long ago but they're past their prime. Two of my 3 amps have evolved to include a rotary effect. Only thing is they rotate at like once every few minutes.. if you get my drift. The other one is a keyboard/acoustic amp which also has it's problems.

Anyway, I've considered DIYing an Amp many times before but circumstances have finally pushed me to take the plunge.

So.. I need your thoughts.

I'm considering either a Bassman 5F6a replica or a JCM 800/900 replica.

Specs
I have no plans to gig with this but it could be a future option.
Speakers:
a) This will be "full sized" with 4 celestion g12t-75's in 2by2 config. 8Ohms of course. 16 ohms will be too dry for me. 75 watts each.
b) This will be "slightly smaller full sized" with 4 Celestion Tube 10 speakers in 2by2 config. 30W each.
c) 4 Celestion G12H's in a 2by2 config. 30 Watts each.
d) 4 Celestion Vintage 30's in a 2by2 config. 60W each.
e) If costs die die is a problem when I start to make it, some other Eminence speaker.
Cab Construction:
-Birch wood? I've read that it's good and quite standard for non-cheapo cabs. I've seen shops in Eunos/Ubi that sell wood. Birch should be easy to find right?
-Open back. Or make it closed back to get closer to the original sound.
Amp:
-Sure there are a number of parts but it is "relatively" simple. Will be housed in any spare wood I can find and with an enclosure for the board built from any spare metal I can find.
Circuit Board:
-Will be made to order or will be purchased premade online if I can find one that's cheap and accurate. I cannot tahan anymore point to pointing or veroboard.
Additional Features:
-Will be able to split the cab in half for dual guitar input's or even 4 input's via a switch. This is thinking about home usage as well as praticality at home. For the splitting into half, there will be 2 original amp sections. For the splitting into four, 2 will be original, 2 will be any cheap and lightweight and proven amp schematic I can find.

This project is going to be long and drawn out, possibly up to half a year as I slowly gather all the necessary information to get the best deal in terms of price, quality and suitability for my use.... and gather funds. Sound wise (or perhaps psychologically), I'm more for the bassman with the G12T's.

I guarantee you that if I purchase a manufactured amp/cab, I'm still likely to tear it apart to see how it works so unless you have some significant point to note, I'm pretty much set on DIY, at least for this project.

I do not intend to sell this as I have plans for this to be my baby forever and ever, amen. But, touch wood, if anything should happen to me or my family, will the resale value be somewhat similar to cost price or higher?

My stomach is unsettled with the adrenaline pumping through me as I get excited thinking about all the things I can do, as well as the fact that I love to DIY. But I think I've reached the stage in life where I can wait so take your time and if you're thinking about including your life story with your opinion (and if it's relevant), I'm all ears.

Would love to hear some opinions. =)

Cheers,
firethorn.

Breen · Aug 30, 2009

Keep up with updates and pictures as you go along!!!

Awesome stuff I would like to do something like this too one day. There are many Class D or AB designs and schematics on the 'net for small simple stuff that could be cool for home mojo that I would like to get into one day. Alas, I've only held a soldering iron once before, while a friend was busy and I was burning his coil of solder back in secondary school.

Now my brother has electrical knowledge, and my dad has always been into hi-fi and sound systems. I've been trying to get them to synergize. I can cut the wood I think

measure once cut twice right?

Open back definitely.

Tried looking at Ceriatone for the made to order bit?

I believe if you do want to sell it, and it works well, people would pay a decent enough price for you work and mojo. Bring in the red or purple tolex~

All the best! Can't wait to hear more.

eclipze · Aug 30, 2009

wow nice... please post a pic bro

Dongara · Sep 12, 2009

Having built amps in the past I would like to ask you of your experience in electrics/electronics. If you want to build an amp then be patient and start off with a small one - 5 watts or so, then you will find out if you want to take on a larger one or it is just too much trouble.

You are dealing with lethal voltages inside the amplifier. These are not toys like pedals where the most you can get is a shock from a 9 volt battery.

You will lose money on the amplifier if you decide to sell it. You will even lose money on the speakers. People are not going to cover your costs as the amp is a special design and as you would know, Singaporeans are very picky when it comes to tone.

If you compare building versus buying, be prepared for paying double the cost of the equivalent stock amp. Parts are heavy (especially transformers) and they will have to be shipped in so this cost will have to be factored in.

All in all, if this does not presuade you to give up, at least approach the project understanding the difficulties involved.

If you need any advice, feel free to ask.

cheers,

Mark.

firethorn · Sep 14, 2009

Dongara said:
Having built amps in the past I would like to ask you of your experience in electrics/electronics. If you want to build an amp then be patient and start off with a small one - 5 watts or so, then you will find out if you want to take on a larger one or it is just too much trouble.

You are dealing with lethal voltages inside the amplifier. These are not toys like pedals where the most you can get is a shock from a 9 volt battery.

You will lose money on the amplifier if you decide to sell it. You will even lose money on the speakers. People are not going to cover your costs as the amp is a special design and as you would know, Singaporeans are very picky when it comes to tone.

If you compare building versus buying, be prepared for paying double the cost of the equivalent stock amp. Parts are heavy (especially transformers) and they will have to be shipped in so this cost will have to be factored in.

All in all, if this does not presuade you to give up, at least approach the project understanding the difficulties involved.

If you need any advice, feel free to ask.

cheers,

Mark.

I wouldn't say I have substantial knowledge of electronics. Buy I do have some experience. Built a stable but inefficient and bulky power supply out of transformers, 1 low voltage tube pedal, a few other 9v pedals. The only thing I still can't get my head around is SMPSes. I can't find a good and simple tutorial. heh.

I know this is a big difference but I'm thinking big picture here. The safety protocols for dealing with the mains are now familiar to me. I have calculated the costs of the project and it is around S$1300 total (overestimated). About $800 tops (I have yet to cfm shipping) for 4 speakers. Yea. Too good to be true? maybe... if it is, it raises the estimate by $200.The rest is on wood and amp head parts. Amp head wood will probably be made from ply I have lying around.

A genuine 5f6a bassman is way more expensive than this. The new tweed reissues are about 1K odd and they have at most 2 speakers.

Will come up with a detailed list of parts, cost and source when I have the time and once I finalise it.

What is finalised so far though is that the speakers will be 4xG12T-75s, each an individual channel although I'm trying to see how I can come up with something to wire them up in other combinations while live.

From a certain experience I have just had, die die the maximum inputs must be 4. Tone is secondary but is a very close second in this case. 2 guits, 1 bass and 1 mic. I have to test out how the mic will sound going through a bassman. I have read that some performers do this but I have to see for myself. I'm still considering the financial costs, power costs, and real estate costs for putting a bassman preamp and a modified amp section for each individual channel.

Thanks for your offer to help. Will be back....

Dongara · Sep 14, 2009

Are you looking at building a guitar amp or a P.A.?

I know that the Vox AC30's were designed to handle a band, but the output power required to produce the same sound level for bass and guitar vary significantly. A 50 watt tube amp for guitar (think Marshall 50 watt) is similar to a 200 watt SVT. Two guitars into the same amp (two channels) seems possible, but two guitars, a bass and a vocal is just not.

The problem is not the speaker connection, but the four preamplifiers required and three power amplifiers (one for vocal, one for the guitars and one for the bass).

A Marshall amp actually has two channels (preamplifiers) and four inputs (two per channel - one high and low impedance). SVT's and bass amps are often the same (one for active and one for passive inputs). Only P.A.s have more than two channels, or some exotic Mesa Boogies.

You could have two amps, one for the guitars and one for the bass/vocals, but one amp for all is not viable. I would suggest a cheap P.A. head for the bass/vocals (bass player may not like it though) and run that through two of the Celestions. At least that would be a cheaper and lighter option than two complete systems.

cheers,

Mark.

Hope this clears things up

firethorn · Sep 14, 2009

Dongara said:
Are you looking at building a guitar amp or a P.A.?

I know that the Vox AC30's were designed to handle a band, but the output power required to produce the same sound level for bass and guitar vary significantly. A 50 watt tube amp for guitar (think Marshall 50 watt) is similar to a 200 watt SVT. Two guitars into the same amp (two channels) seems possible, but two guitars, a bass and a vocal is just not.

The problem is not the speaker connection, but the four preamplifiers required and three power amplifiers (one for vocal, one for the guitars and one for the bass).

A Marshall amp actually has two channels (preamplifiers) and four inputs (two per channel - one high and low impedance). SVT's and bass amps are often the same (one for active and one for passive inputs). Only P.A.s have more than two channels, or some exotic Mesa Boogies.

You could have two amps, one for the guitars and one for the bass/vocals, but one amp for all is not viable. I would suggest a cheap P.A. head for the bass/vocals (bass player may not like it though) and run that through two of the Celestions. At least that would be a cheaper and lighter option than two complete systems.

cheers,

Mark.

Hope this clears things up

Oh no. You mistake my intentions.

I do intent to have a preamp and and amp section per channel per speaker. It will all be in one amp head enclosure (not confirmed, as I have mentioned previously, I need to do some calculations). Each input to each preamp+amp to ONE speaker.

Only thing is if it's suitable for all of them to be using the bassman circuitry (which I understand some people use for vocals). I have to test this out for myself and check the pros and cons for this. It would make it somewhat easier, a lot more versatile and definitely a lot more cooler though.

And the GT-75's, at 75W per speaker, it should have no issues of loudness with common uses.

I would say it's a guitar amp + speaker solution (not a combo) with the slightly added versatility to be also used as a PA (as compared to the standard guitar amps which can also be used as PAs btw).

seekz · Sep 14, 2009

THe GT75 is a very loud speaker!
I used to have one, didn't liked it
sounds too boomy and mid scooped

Dongara · Sep 15, 2009

firethorn said:
Oh no. You mistake my intentions.

I do intent to have a preamp and and amp section per channel per speaker. It will all be in one amp head enclosure (not confirmed, as I have mentioned previously, I need to do some calculations). Each input to each preamp+amp to ONE speaker.

Only thing is if it's suitable for all of them to be using the bassman circuitry (which I understand some people use for vocals). I have to test this out for myself and check the pros and cons for this. It would make it somewhat easier, a lot more versatile and definitely a lot more cooler though.

And the GT-75's, at 75W per speaker, it should have no issues of loudness with common uses.

I would say it's a guitar amp + speaker solution (not a combo) with the slightly added versatility to be also used as a PA (as compared to the standard guitar amps which can also be used as PAs btw).

Got you now.

Problem is still going to be that the bass will need at least 150 watts worth of high efficiency speaker to be able to reproduce the same volume for the bass notes (especially if you are using a five or six string bass - bassman's were designed for four string basses). The Celestions won't cut it and you will still need at least a 100watt head driving it.

The cab will weigh a tonne with four bassman amps in it. This seems to be what you are suggesting. The transformers alone will cost you an arm and a leg to buy and send. Would be better to have a dual amp - one tube and one IC. The tube for the guitar and the IC for the vocals/bass. Use the Celestion 75's for the guitar if you like and a pair of higher efficiency P.A. speakers (150 watts each) for the vocal/bass channels (something like the Celestion Truvox - 200watt P.A. drivers).

This will reduce the cost of your head, reduce the weight and produce a more even tone for the vocals/bass.

firethorn · Sep 15, 2009

Ok.

This is very embarassing. Under the illusion that the bassman is/was for basses, I have totally forgot that bass speakers are usually designed specifically for basses.

I need to go and recalculate everything. But I believe it's still going to be cheaper. The transformers at the the very very very most will costs $150 each. I have to double check though. I'm still trying to reconfirm the wattages based on the schems and the actual tubes.

Dongara:
I'm still thinking GT75's for the vocals as I don't think I'll be in the situation where everything needs to be maxed out - plus it can still be used for instruments. I'm considering Vintage 30's for the other 2 guitar sections. What do you think?

200W for the bass speaker might be a bit of overkill though. My main intention is not to gig. Have to research on this. Thanks for your suggestion.

seeks:
I have the GT75s at around the same price as a Vintage 30. From reviews it does seem that the Vintage 30's sound very good for creamy overdrive situations and are versatile enough to have some semblance of a nice light crunch sound. Wouldn't it be underkill to use those on a 4x12?

From my design of using one speaker per amp channel I think recreating the exact tone is obviously out of the window but I would still like to get as close as possible. Which would you suggest. These are for the guitar speakers though.

Ok, I'm going back to the drawing board again and actually start on the calculations again. It's time to stop looking at the pretty's and start looking at the ugly's.

I'll be back.

seekz · Sep 15, 2009

I think there's a 60 watt version of the V30.
Butt the wattage is not the true measue for loudness
you shud check the SPL ratings instead

By the way, still kinda unclear as to what is it you're trying to build.
A 4 channel amp? or 4 amps ?

Dongara · Sep 15, 2009

I'd use a pair of V30's for the guitar amp section (your bassman/Marshall) with two channells and one 50 watt output trany. Wire the two V30's together - 16 ohms in parallel for a 60 watts. These speakers can handle the 50 watt amp fine.

Wire the two 75's together in parrallel the same way for 150 watts and have a 100 watt amplifier supplying them. Two amps in one head and two sets of speakers in one cab.

Best solution I can think of for you.

cheers

firethorn · Sep 16, 2009

Seekz:
Channel is an ambiguous term here? They are 4 separate inputs and should be isolated in every way as I intend to make it a 1input -> 1 speaker situation. So, 4 amps, in one amp head. Should give the illusion of 4 channels though.

The Vintage 30 is 100dB and the GT75 is 97dB. Vintage 30's are 60W and the GT75's are, well, 75W.

I've just noticed the Vintage 30 specs. The Vintage 30 is 3dB louder but uses less wattage? It should be using twice the wattage right? Is it a misprint? Or am I misreading it.

Dongara:
Wa bro... 16ohms is going to be so dry man. Plus I need 1 speaker from 1 input as I am very unsure how putting multiple signals into one amp and/or then into all 4 speakers will affect tone.

Also, with regards to the power transformer, I can get an off-the-shelf "fixed" solution for less than $100 each and I'm sure I can get it lower once I confirm the effects of changing the transformer. RS-Comp. For the output transformer though... ah.. That one.. hang on.. heh.

Destructos · Sep 16, 2009

I would highly suggest haunting sites like geofex, sloclone forums and googling for DIY class A single-ended (aka SE-amps) hi-fi amps that rate in at around 5 - 10 watts (don't look down on these figures, in pure class A configuration, they can get pretty loud).

The simpler the circuit you can find, the easier it is to troubleshoot and keep mental tabs on high voltage points. 12AX7s typically bias around 280v or so, you can imagine the dangers. Based on what you have described for experience, I highly recommend you don't get too ambitious, for the sake of your safety.

Starting small is also good because you can use smaller transformers. 300++watt power trannies cost a bomb. Class AB tube amps like JCM800 have efficiency ratings of about 55% at best. So a 150 watt output capable head will suck 300 odd watts at best case scenario.
Not to mention the need for high-output capable output trannies, those cost a bomb too.

http://www.instructables.com/id/Guitar-Tube-Amp/
Here's a simple tutorial to get you kick started in the world of DIY tube electronics.
8 watts and should be able to handle speakers as low as 4Ohms.

http://www.duncanamps.com/tsc/
Here is a program for calculating values for tone stack, should you want to understand better how marshall's tonestack reacts compared to a fender or even if you have your own idea for your own tonestack's sound. Interesting stuff.

http://www.electronics2000.co.uk/
This software helps convert pF, uF values. Decodes resistor color codes and vice versa. Very very helpful if you haven't found it out yet.

Common shops I like to visit for audio parts include Koba in chinatown, SLT and Martin Electronics in Bencoolen square beside SLS.

Helps a lot if you can afford extra 1 or 2 of each component in case of a screw up and shit gets fried. LOL
Have fun and be safe.

-edit-
Awww www.diyguitarist.com is no longer up. I always liked going to that site to check out the numerous projects.

seekz · Sep 17, 2009

One amp into one speaker that would mean 4 amps instead of 4 channels.
Usually when we talk about a 2 channel amp, it means two pre-amp channels
sharing the same power amp.

Why would you want to house all four amps into one "head"
wouldn't the faceplate be very cramped, or wouldnt the chassis
be very cramped up with lots of trannys.

I'm not particularly familiar with speaker ratings, but I assume
a 60 watt speaker just means that it can take/putout 60 watts of output
before it fails ?

SPL is like the efficiency ?? Not really sure, I'm just guessing.

Destructos · Sep 17, 2009

seekz said:
One amp into one speaker that would mean 4 amps instead of 4 channels.
Usually when we talk about a 2 channel amp, it means two pre-amp channels
sharing the same power amp.

Why would you want to house all four amps into one "head"
wouldn't the faceplate be very cramped, or wouldnt the chassis
be very cramped up with lots of trannys.

I'm not particularly familiar with speaker ratings, but I assume
a 60 watt speaker just means that it can take/putout 60 watts of output
before it fails ?

SPL is like the efficiency ?? Not really sure, I'm just guessing.

As far as I know, multi channel amps have one preamp circuit and one power amp circuit.
The channel switching allows you to switch between 2 or more sets of potentiometers which represent your settings (gain, eq, etc).

Speaker power ratings usually means how much sustained power (usually lower than peak power, both are very different kinds of ratings. pls read wiki) can it accept from your amp before the coils overheat.

SPL, or Sound Pressure Level, represents how physically loud your speakers can get. Judging from the posts, the amp might be meant for home practice use. Therefore, it's not really important if you're buying guitar amp speakers nor practical to get a very loud one indeed.
Just look around online for discussion boards regarding some of the speakers that interest you. See if others experience the type of sound you want from it.

Firethorn>> As for inputting multiple signals, you are kinda building a line powered mixer. That kinda adds significantly to the circuit complexity.
I highly suggest you start small first, simple single channel, Class A single-ended amp that takes to effects pedals well (you'd be surprise as to how many DIY circuit designs crap out when you introduce a stompbox into the signal chain).
You'd be surprised as to how good these small things can sound.

seekz · Sep 17, 2009

>Destructo

I guess different amp builders designs them differently.
I got that impression because I recently serviced a boogie maverick
http://www.schematicheaven.com/boogieamps/boogie_maverick.pdf

Destructos · Sep 17, 2009

seekz said:
>Destructo

I guess different amp builders designs them differently.
I got that impression because I recently serviced a boogie maverick
http://www.schematicheaven.com/boogieamps/boogie_maverick.pdf

Thanks a lot for the schem!
No wonder Mesa amps always seem to have an insane number of preamp tubes.
They used triodes to buffer almost everything also, except for FX out which is a discrete opamp.

The idea I had was from an old thread in AX84 regarding a simple mod for dual EQ for one of their beginner amps.
It's an excellent site full of ideas. Got full description and explanation as to why each amp was designed as such with all the maths included.

funtimesman · Nov 4, 2009

funtimesman · Nov 4, 2009

help

or please tell me how and which of the above would go together and how to put them together in a Cigar Box or something....i am really clueless...
thanks

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