First Amp Build

[GuyLonestar]

Newbie here... greetings!

So, I have an old Cerwin Vega D3 cabinet I'd like to make into an amp. It doesn't have to be more than 25w. I'm hoping it can be used for a guitar OR bass, so I'd need to know if that's feasible.

I'd like to keep it as simple as possible. Like, maybe just create a space inside for something like this (link below - MOD 102 DIY Guitar Amplifier Kit, but appropriate power for the speakers). Can it be that simple? Now that I think about it, I guess I could just buy a small head to sit on top of the cabinet? In any case, I need to replace the subwoofer first, as the cabinet is like 35-40 yrs old and the sub has disintegrated. Will that depend on whether I lean toward mostly guitar or bass?

I have a fairly strong technical background, but not with amplifiers. Not afraid to tackle this with with some help.

https://www.amazon.com/MOD-102-DIY-Guit ... F5YZFEVUG6

Thanks in advance!

[alnight]

Hey, so it sounds like you have an old hi fi speaker you'd like to turn into a guitar amp? While I will not say that can't be done, I would suggest that it might be a poor choice for your first build.

I say this from the perspective of "That's the kind of thing I needed to be warned away from when I started down this rabbit hole, too."

If I may, I would suggest that you start with something fairly simple and well documented. Say, a tweed Champ, or maybe a Deluxe if you're feeling frisky. Get the circuit working in it's natural state first, then use it to experiment with different coupling caps, brands and types of resistors, tubes, and so on. Maybe try some simple mods. This will give you a feel for how the components you choose shape the sound of the amp and give you the knowledge base to go forth and build more interesting stuff in the future.

The simpler the circuit, the less cost is involved in trying out different components.

The first build is all about the education and developing the basic skill set. I totally encourage you to do it. I can tell you from experience that diving headfirst into uncharted waters is not the way to go, unless you really enjoy being super frustrated.

[Raja_Kentut]

Hi,

I agree somwhat to alnight because I don‘t know your building skills, but it seems to be an interesting project to start.
My first builds were similar, an old cabinet (fan heater) and a simple class-A amp…

IMG_1017.jpeg

IMG_1018.jpeg

The hi-fi box looks nice, I would replace the 10“ speaker with a suitable one for guitar (e.g. celestion ten 30) and cut out a window above.
The window closed with a nice metal grille that one can see the tubes and transformers, a backlight in the cabinet that glows orange… and a brass faceplate …

I wish you lots of fun and success with the project ! Please post a picture

[Colossal]

I love that heater/amp!

[GuyLonestar]

The hi-fi box looks nice, I would replace the 10“ speaker with a suitable one for guitar (e.g. celestion ten 30) and cut out a window above.
The window closed with a nice metal grille that one can see the tubes and transformers, a backlight in the cabinet that glows orange… and a brass faceplate …

Well, that idea sounds cool, but probably not feasible, unless I waste the mid range and tweeter, which I suppose most amps, especially bass amps, don't have. I had not looked at the cabinet that closely, but I now find that it seems to be sealed at the back and front (no screws to disassemble the wood). As well, there is a removable fabric 'grill' covering the whole front. Yea, I guess I'd have to revamp the entire box. Wasn't in my plan due to time constraints at the moment. I don't know how to insert an image on this forum... it just gives me the following... img /img (both in brackets) when I click the Insert Image icon. It doesn't allow me to go choose a photo.

Back to the idea of just using it as a speaker cabinet with an external amp head... would the output from the head not just connect directly to the speakers? (assuming proper ohms, power ratings, etc.. Or is there a lot more 'technology' to this than I realize?

[Phil_S]

In general, a hifi speaker is not a good match for guitar. Hifi covers a full spectrum of sound, often 20Hz to 20KHz. (If you are over 40 years old, you probably don't hear very much above 12-15Khz and by the time you are 70, maybe 10KHz.) Look at frequency for the low E on bass and high E string on guitar at 16th fret. You'll see about 40Hz to about 5Khz. For guitar, we get that range from a single speaker. There is also a matter of the response curve. That is why people will tell not to use hifi speakers.

If you want to use what you have, it is probably better to salvage the cabinet and start from there. If the speakers are of any notable brand, sell them on eBay.

To include an image, look below the textbox where you type the message. There are two tabs. The second tab is Attachments. Click on Attachments and you'll see a button to "Add files." Yes, show us what you have.

Head connected to speaker cabinet is typical. You must match speaker impedance to output transformer impedance. Output transformer impedance depends on tube selection, turns ratio, and potentially other factors. Failure to match (within reason) can cause an overload that is fatal to the output transformer.

[WhopperPlate]

Sounds like you outta take a stroll down the FAQ sub forum , and make good use of the search function . Practically every question has been asked at one point or another . A basic fundamental approach will alleviate many of the beginner assumptions. Once you have a firmer grasp then get surgical with your questions .

Fwiw a hi fi speaker and tweeters and electric guitar generally don’t work well , unless you are John Cippollina

[GuyLonestar]

In general, a hifi speaker is not a good match for guitar. Hifi covers a full spectrum of sound, often 20Hz to 20KHz. (If you are over 40 years old, you probably don't hear very much above 12-15Khz and by the time you are 70, maybe 10KHz.) Look at frequency for the low E on bass and high E string on guitar at 16th fret. You'll see about 40Hz to about 5Khz. For guitar, we get that range from a single speaker. There is also a matter of the response curve. That is why people will tell not to use hifi speakers.

If you want to use what you have, it is probably better to salvage the cabinet and start from there. If the speakers are of any notable brand, sell them on eBay.

To include an image, look below the textbox where you type the message. There are two tabs. The second tab is Attachments. Click on Attachments and you'll see a button to "Add files." Yes, show us what you have.

Head connected to speaker cabinet is typical. You must match speaker impedance to output transformer impedance. Output transformer impedance depends on tube selection, turns ratio, and potentially other factors. Failure to match (within reason) can cause an overload that is fatal to the output transformer.

Thanks for the good detail!

[GuyLonestar]

Sounds like you outta take a stroll down the FAQ sub forum , and make good use of the search function . Practically every question has been asked at one point or another . A basic fundamental approach will alleviate many of the beginner assumptions. Once you have a firmer grasp then get surgical with your questions .

Fwiw a hi fi speaker and tweeters and electric guitar generally don’t work well , unless you are John Cippollina

Gotcha! I think I'm good for now in this thread.