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Renioo 14th February 2013 07:29 PM

Small Amp, Renioo Project

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 :)

Bigun 14th February 2013 07:45 PM

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

Renioo 14th February 2013 07:55 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?

Bigun 14th February 2013 08:18 PM

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 ?

Bigun 14th February 2013 08:29 PM

As for tube amplifier - I'm not sure which you prefer, tube or transistor. But it sounds as if you like tubes. You can get output transformers for around $40 (e.g. Hammond 125E).

Renioo 14th February 2013 08:33 PM

It's symmetrical 32-32 V AC.

Yes i already have big ang good heatsink, maybe I would also consider using some cooler inside the chassis.

Renioo 14th February 2013 08:42 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.

Bigun 14th February 2013 08:55 PM

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 14th February 2013 09:06 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?

wahab 14th February 2013 09:31 PM

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.

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