Transistor replacements- what matters?

[ballooneater]

I am embarking on a new project- the Roland Jazz Chorus amp.  Unfortunately, this will require some high-power devices that I'm not familiar with.  Normally, I'd go the 2N5088/2N5087 for my NPNs and PNPs, but after wading through the datasheets of these transistors, I realized that they just won't cut it.

The list of the transistors and their characteristics can be found at http://matthew.kloiber.googlepages.com/TransistorSubs.txt. (you can ignore the diodes on there)

To find replacements for these, what specifications are the most important?

[Minion]

What Mostly Matters is voltage and Hfe , But also Power disipation and package style/Pin layout , especially for High power devices.....

Are you planning on building a Roland Clone?? or re-building an allready built roland amp?? Have you ever built an amp before?? a Discrete one??

how experienced are you at amps??

Cheers

[ballooneater]

I found a schematic for one on SchematicHeaven, so I guess you could consider what I'm doing a clone.  I've build the "Ruby" amp, but I don't think that's nearly the same as what I'm doing now. 

As far as experience goes, I'm well-researched, but this is my first hands-on time with a powerful amp.

[Minion]

Do you mean this schematic.....

http://www.freeinfosociety.com/electronics/schematics/audio/rolandjazzchorus.pdf

[SISKO]

Any time i look for power transistor replacement what i take care of is: Collector to Emitter Voltage (Vce), Collector current (Ie), Power dissipation, range of operation in frequency and the package unless im building the project from scracht (ie, no replacement to original).
But always i look for this specs i end with the same transistor or its american substitute if it was assian 
Keep an eye in hfe if  you got 1 or more pair of transistor so they are closely matched

[ballooneater]

Do you mean this schematic.....

http://www.freeinfosociety.com/electronics/schematics/audio/rolandjazzchorus.pdf

That's the one!

[Minion]

If that is the one then I don"t want to discourage you but it is an extremely ambitious project and not that I am doubting your electronics skills but are you sure you are up to the task and have really thought about it hard??
The reason I ask is because if you had the amount of knowlege and skill needed to successfully build a project like this you would allready know how to determine what Transistor replacements you would need...

The Preamp section looks difficult enough to design a PCB for, but should be doable if you have some PCB design experience, ( there aren"t any specs on the schematic for the reverb Tank) , there are also a Lot of other considerations when designing a PCB for a discrete Output stage which are totally different than when working with Small signal curcuits, Like you have to keep the audio signals away from the Power rails , you have to know what Transistors need heatsinks, and how to Bias each stage of the Ouput stage, You have to know how to Calculate heat disipation in each Transistor so you can attach a sufficient heatsink....You are also going to have to definately get an Osciliscope ( if you don"t have one) to debug the curcuit.... Pluss the cost is going to be pretty high , I would estimate about $200+ without speaker or chassis.....(Good Power Transistors are expensive and you will also need some Big filter caps and a 2 x 24v 200Va Power transformer which are also fairly expensive ,also a sufficient Heatisnk for the 2 output Stages and the Regulators is going to need to be Fairly big and expensive)

You can probably simplify the design to some degree which would make it easier and much cheaper without sacrificeing quality (Maybe even improve it)...Like instead of have 2 fairly Complex and expensive output channels you could replace the 2 discrete output stages with a Power Amp IC like the LM3886/3875 (Ive built several Guitar amps with these and they are very good), they run off the same voltages as the output stage in the schematic put out 50w, sound great and are cheap and easy to build and take up a very small amount of space , which would negate the need to find replacement transistors (Transistors Which might or might not work in a Particular curcuit).....
Also you can replace the more complex Discrete voltage regulator that is in the PSU with an IC like the 7815/7915 or lm317/337 which will save a lot of trouble in bulding and cost...

There are some other Much easier Guitar amp projects out there , that are better documented and much easier and cheaper to build ....
Ive designed and built amps from 10w up to my latest 100w , I have PCB designs for a couple of them if yer interested ,You can also use one of those power amp IC"s I mentioned above and put a few pedal or effect curcuits in front of it to make an amp that has all the effects and pedals you want built in....

Anyways good luck and if I can help let me know...

[ballooneater]

Thanks a lot for you reply, Minion. 

On the original subject of this topic, I managed to find most of the transistors on MCM's website, so that is no longer an issue. 

Regarding skill/knowledge- I honestly learn best by screwing up.  If it wasn't for flubbing so many pedals, I would have no idea how most of the circuits worked.  I'm not expecting this build to be perfect, but a learning experience if nothing else.

I already designed the PCB (I have a bit too much spare time), so that is not much of an issue.  I was sure to keep the voltage traces away from the audio ones as you mentioned. 

As far as parts go, I've cannibalized some other electronic gizmos and gadgets and have managed to retrieve some heatsinks, transformers (not sure what the voltage is, I'll check that later), large caps (6800uf!), and even 4 power transistors. 

I'll take you up on your offer of other amp PCB layouts.  It couldn't hurt to start out smaller.  Do you have them in EagleCAD format?

[Minion]

Actually the amp PCB"s I have are ready to tranfer B&W images with a Parts Placement sheet...
They are pretty simple , a couple Selectable Diode Overdrive settings , Gain,Tone , and Volume controlls...
The PCB and the Power supply, Preamp and Power amp curcuits all on the same PCB and are only about 4 inches square....

This one uses the TDA2030/40/50 IC (14w,20w,32w) ,It is more of a Practice amp as opposed to a gigging or recording amp....




Just hook up a 2x12v Transformer for TDA2030 2x15v for TDA2040 and 2x18v for TDA2050....

Here is a Pic of my latest head...


It"s a 100w guitar head, with a Tube preamp kit and a 15 band EQ (the EQ isn"t diy) and sounds freaking awesome , if yer into heavey tones... I have a schematic for the Preamp and a schematic for the 100w mosfet power amp and a PCB for the Poweramp and PSU if yer interested....


Cheers

[asfastasdark]

Minion, could you PM me those files? 

[ballooneater]

The 100W is more up my alley- I'm trying to go for a bigger sound than what my current amp has. If you could send me the schematic/layouts either through PM or in this topic, I'd be forever in your debt.

Is there any way these schematics could be modded for bass?  I know I'd have to change some caps and use different speakers, but that's about it.


Sorry for hijacking my own topic....

[Minion]

I sent you a PM with the Info on the 100w amp....

You can probably mod it for Bass by increaseing the size of the Input Caps and any DC Blocking caps in the signal Path....

I have played Bass through this amp and it sounds pretty damn good, even through a Guitar Cab , I just Back way off on the Gain and adjust the EQ to boost the low end and roll off some of the High end....

Cheers

[Zben3129]

reguarding the "need 100w for more volume" thing,

What wattage are you playing through now
What cab (preferrably what speakers)

I own a couple 1x12 closed back cabs. I also own a 10w amp and a 100w amp.

Speaker sensitivity (aka efficency) is something you may or may not have taken into consideration before. It has a GIANT impact on the volume of your amp. If you play a 100w amp through a speaker with 98dB efficiency, and a 10w amp through a speaker with 101dB efficiency, they will have the same volume. Increasing a speakers efficiency by 3dB doubles volume, and multiplying the wattage of an amp by 10 doubles the volume.

My reccomendation is a LM3886 amp, with a TS/BSIAB/Valvecaster/Dist+/whatever preamp. Or you could leave it without a preamp and use pedals in front, either way. With the right speaker, 50w is PLENTY.

I am working on a couple amps right now. One is a BSIAB2 --> LM3886. Sounds killer. Highly reccomend BSIAB2 as a preamp, gives a very marshally sound, good for Van Halen especially I have found.

Zach

[Yazoo]

I am very interested in this and was considering just doing the preamp section. Did you go ahead and build it?