Small Amp, Renioo Project

Renioo

Member
2012-12-16 1:33 pm
Hi,

My project is to make an all-in-one amplifier, and I already have DAC with tube pre-amp. The idea is to have it all in one case (it's mainly aluminium), which is already done and is waiting for stuff to put in it :) It held wire-assembled DAC and preamp and it was working fine, I'm waiting for my PCB's to have it all in complete order.

But the problem is I have never ever tried myself with power-amps. As I run out of money for proper tube amp ( I know that speaker transformers are very critical and expensive, and it looks like solid-state amplifier for the same price would work just better) I decided to go for quite simple solid-state. I looked at few projects like Jean Hiraga Super-Class A 30W, which are quite easy to assemble and look like they suit me perfect, so I decided to go this way. But I'm not really sure if it's the right way, and if not, correct me :) I'm also not really interested in op-amp's and all that kind of stuff.

I wouldn't even ask, but there's a small problem with Hiraga amp's - power supply. To be honest, I can't afford that big PSU - I already have 400W 35V transformer from my old Kenwood Ka-5500, it had only 2x10 000 uf for filter and worked pretty noiseless.

1. Can I do it with a lot smaller PSU capacitance? If not, I would like you to recommend me something that I can assemble with not big money input. I know there are a lot of projects, but I went completele retard trying to clear this up. It doesn't have to have big power! Even 5W suits me, but I wouldn't mind anything bigger.

2. I thought that speaker-protection from DC Voltage sounds wisely - but does it affect in any big way the quality of sound?

I would also post pics of amp from building etc. if you would help me with choice of power-amp :)
 
I don't think a tube amp needs to be that expensive, go and look in the tube forum as I believe there were some low cost designs there. A simple push-pull would be the most affordable option and there are some reasonably priced output transformers available for a number of suppliers.

For solid state class A I would suggest the JLH 10W - there's a huge thread on that amplifier around here somewhere too. It is quite affordable since it can be built with many 'junk box' parts. It has an output capacitor that will protect your speakers from DC and it is widely held to sound very good (despite the output capacitor).

But you may be equally happy with a solid state Class AB amplifier. It will not run so hot, require less heat-sinking and therefore be less expensive as well as potentially more reliable. There are many designs available. You could use a relay based dc protection module from eBay. I would suggest going here: Greg's Web Site
 
Last edited:

Renioo

Member
2012-12-16 1:33 pm
Don't get me wrong, I'm not into saving every $ I can - for solid-state I already have a good transformer that saves big money. For tube amp it would be another 40$ at least. And then speaker transformers - these are just things that don't exist in solid-state circuit and I can spend them for good mosfets, capacitors or anything.

My point is not have an output capacitor if it's possible, and not to use 'junk box' parts. I would like this amp to have a proper quality, I'm just not aiming for the highest quality.
But if you would convince me to use a tube amp, well I would be happy :)

Edit: I looked at the JHL Update circuit and it doesn't have an output capacitor - am I right?
After changing the voltage to DC from my transformer, I would have around 50V - can I safely drop it to around 25V using CRC filter?
 
Last edited:
The original JLH uses an output capacitor, but there are later versions that use split supply rails and no output capacitor. Then you may want to include a speaker d.c. protection add-on circuit. It's your choice of course.

Transformer - well for a d.c. coupled amplifier you need split rails, when you say you have around 50V do you mean 0 - 50V d.c. or do you mean +/-50V d.c. or something else ?

Remember, you need a BIG heatsink with Class A. Do you have this in your ready-to-go chasis ?
 

Renioo

Member
2012-12-16 1:33 pm
Well, you know I really like what the tube did to my equipment. But it's an OTL preamp, not the one with transformer. I was searching for something interesting, but all these quite cheap output transformers have a narrow bandwidth and don't look like they would do the job.

I really like the somehow musical and warm tube sound, but now I'm looking for good performance - just not to waste money. It can be a little clinical, as my speakers and DAC have a really soft response.
 
I agree with your concerns about avoiding poor performing output transformers, so it seems solid state is the right choice for you.

If you have 32-0-32 you are all set for a split rail supply (do you mean 32 a.c. or d.c. ?)

I like the JLH design, but there are other choices such as a KRELL clone - although I have no experience with those.
 

Renioo

Member
2012-12-16 1:33 pm
It's 32V AC.

I read about this JLH design, mainly about updated version and it seems quite cool. I think I would stay with this one as long as no one would comment about anything else, like this KRELL clone. I would really like to hear some opinion :) Anyway thanks Bigun, you helped me a lot !

I also have a question about a phono preamp. I have a 3-way selector, so I would like to put a phono stage too. If I have a tube preamp, is the passive RIAA enough, or some small J-fet stage (I've seen a lot on 2sk170) ? I have a small 7.5 or 13V output too and I can use it for this purpose. Would there be a big difference between totally active phono preamp ( I assume that the RIAA correction is somewhere between the FET/tube stages) and connecting the simple one to a proper tube line preamp?
 
The most hyped class A amps , among others the JLH , Hiraga s , profet or F5
are all vastly inferior to class AB high feedback amps that would be class A
biaised , even some of the most basic iterations of Lazycat/Gaborbela s CFB are more worthy of a build than thoses amps that are no more up to current audio sources.
 
Renioo,

There are many choices of solid state amplifier compatible with your transformer and chassis - that's part of the fun of DIY. I may not agree with the opinion of Wahab but I would say there are many happy owners of all the amplifiers he listed. You should be careful not to get stuck in a loop where you feel anguish over the decision. You could build your project in modules, the power supply separate from the amplifier, you can then replace your amplifier with a different design in the future if the fancy takes you.

Phono - I don't have vinyl, don't know much about phono amps. They are generally high gain and need to be low noise. You need active devices in a carefully designed circuit if you want good results. You also need to be very careful with their power supply and the environment you put them in. I think it's a whole extra project.


Wahab, my TGM5 was based on the lazycat amplifier. I've been using it for a year now. I can now say that I don't prefer it over my other amplifiers although the design is good. We all find our own likes and dislikes in the end and they don't match up always.
 
Last edited:
Why is that so? I don't reject that statement, but where is that point in which AB class works better than A? As far as I know, the Class A should give the lowest distortion etc.

The numbers don't tell all. As I said earlier, you may be happy with Class AB. JLH also designed a Class AB amp and said it sounded to his friends every bit as good as his Class A amp. Everyone has their own preferences and opinions and you will not find the answer so easily on this forum - the best answer is what you find out yourself by building and listening. I think you would be pleasantly surprised by the sound qualify of the DX amplifier I linked already and it will also work with your transformer.
 

Renioo

Member
2012-12-16 1:33 pm
Building the amp in the modules which I can simply replace is a really reasonable idea and I would follow that. And I would work on a phono stage after I complete the power-amp, so I wouldn't do so many things at once. I'm going to make a material list this weekend for JLH. I won't feel any regret because of choice of amplifier as I know it's not the best I can find and do. And exploring new choices after it sounds even more interesting :) You helped a lot.

Anyway, I'm still ready to hear any opinion and think about any other project.
 

tinitus

diyAudio Moderator R.I.P.
2005-11-24 1:47 am
the best 50watt classAB will be very hard to beat for any amp
its main limit is ...the limited output

going higher would be better
but then you need more output transistors, and other problems easily pulls it down again

but if you have nightclub disco no 50watt is worth much :D
 
Why is that so? I don't reject that statement, but where is that point in which AB class works better than A? As far as I know, the Class A should give the lowest distortion etc.

Class A is not a guarantee of low distorsion wich is dependant
of the amp global linearity.

Wahab, my TGM5 was based on the lazycat amplifier. I've been using it for a year now. I can now say that I don't prefer it over my other amplifiers although the design is good. We all find our own likes and dislikes in the end and they don't match up always.

True that in a class A amps CFBs are not the best choice
given their poor supply noises rejection.
 
If you are really strapped for cash AND if you have access to junk in a parts box, might want to try to see if you can build the RH84 SE tube amp. Uses EL84 tubes that are inexpensive, old transformers from throw away console stereos, left over chokes from same consoles, and small output transformers usually also from consoles. You can skip the tube rectifier and use 4 diodes and make the rectifier yourself.

I have heard people having built RH84 amps from junk and getting good to excellent performance for $40, though I doubt I have that many spare parts in the junk bin. And with the very low parts count, it is a sweet build.

Currently, I am scrounging new leftover components from other builds, looking for cheap old iron (i am undecided on this as I have a 275-0-275, but the build requires a 300-0-300 and a couple of OPTs, so I might buy new Edcor) and a choke, and I have a rock solid chassis already from an old cassette player. I am needing some sockets and a new gain tube.

Take a look at it, lots on these forums on it too.
 

Renioo

Member
2012-12-16 1:33 pm
I thought about simple EL84 or something similiar, but I have no junk parts to try. Nothing that would suit tubes -no chokes, no transformers, even no tube base left. So it won't be that cheap comparing to what I can spend to be worthy building.
 
Last edited:

Renioo

Member
2012-12-16 1:33 pm
I think about changing the SRPP circuit to an anode-cathode follower as my PCB allows to do it.

I use 6n6p for preamp which would give about 80-90Ohm output impedance in cathode follower. If i would put electrolytic cap 220uf on output, would it safely work also as headphone amp?