Hi all, and thanks for the input!
This is the amp I've got:
https://encrypted-tbn2.gstatic.com/...VSGl15IM54J8pvdUpUI-y4nSmk7I0nA-2y2a_7PzvvdFQ
The transformers have two secondaries each, rated at 31V/250VA. At present, the power supply is wired quite strange (at least to a solid-state novice like me): One leg of each secondary winding is hooked together at a common ground (which is not connected to the chassis at all, but only to the negative speaker terminal and the screen on the input RCA). These ground leads all gather at the serial connection point between the filter caps. These are 10.000uf/50V units, running two-and-two in parallel. The two banks of two caps are wired in series and it is at the connection point between the two that the gounds are gathered. The other legs of the secondary windings are connected to a bridge rectifier, with the cap bank connected between the DC output terminals. So the voltage accross the DC terminals on the bridge is 91VDC, but of course it's +/-45.5VDC if ground is 0. The circuit boards are fed the full 91VDC.
Is this the normal way to construct a PS for a solid state amp?
Again, what I want is an amp that runs a little cooler and a lot quieter. If it also has a bit more power, thet would be a bonus. In valve powered guitar amps, you would generally get a louder and cooler-running amp if you bias the output stage to run in class AB rather than class A. (Very few gutar amps are truly class A, but some cathode-biased designs run very close and very hot). I know that transistors are very different from valves, but thought that maybe the same principals apply.
Thanks again everybody! It's great that you're willing to help out newbies like myself.
Henrik
This is the amp I've got:
https://encrypted-tbn2.gstatic.com/...VSGl15IM54J8pvdUpUI-y4nSmk7I0nA-2y2a_7PzvvdFQ
The transformers have two secondaries each, rated at 31V/250VA. At present, the power supply is wired quite strange (at least to a solid-state novice like me): One leg of each secondary winding is hooked together at a common ground (which is not connected to the chassis at all, but only to the negative speaker terminal and the screen on the input RCA). These ground leads all gather at the serial connection point between the filter caps. These are 10.000uf/50V units, running two-and-two in parallel. The two banks of two caps are wired in series and it is at the connection point between the two that the gounds are gathered. The other legs of the secondary windings are connected to a bridge rectifier, with the cap bank connected between the DC output terminals. So the voltage accross the DC terminals on the bridge is 91VDC, but of course it's +/-45.5VDC if ground is 0. The circuit boards are fed the full 91VDC.
Is this the normal way to construct a PS for a solid state amp?
Again, what I want is an amp that runs a little cooler and a lot quieter. If it also has a bit more power, thet would be a bonus. In valve powered guitar amps, you would generally get a louder and cooler-running amp if you bias the output stage to run in class AB rather than class A. (Very few gutar amps are truly class A, but some cathode-biased designs run very close and very hot). I know that transistors are very different from valves, but thought that maybe the same principals apply.
Thanks again everybody! It's great that you're willing to help out newbies like myself.
Henrik
You and no-one else can get more power than what the supply rails will allow.
re-biasing does NOT give more power.
Your 91Vdc is your power limiter.
Expect an absolute maximum of ~30Vac into a high impedance load.
Into a normal impedance load your maximum is likely to be in the range 20Vac to 25Vac.
i.e. 50W to 78W into 8r0
re-biasing does NOT give more power.
Your 91Vdc is your power limiter.
Expect an absolute maximum of ~30Vac into a high impedance load.
Into a normal impedance load your maximum is likely to be in the range 20Vac to 25Vac.
i.e. 50W to 78W into 8r0
Andrew,
I'm not claiming to be able to do anything at all, that's why I'm on here asking questions that may be very silly.
Like I said, what I want is primarily to improve on what I've got with the aim to reduce hum and idle heat. Can it be done? Could I build the honeybadger, for instance, with the transformers I have?
Cheers,
Henrik
Hum is primarily down to the wiring scheme used, particularly grounds. It has to be right and any amp will hum if its grounds are not optimally configured.
Heat is down to biasing. Class B running say 100 milliamps per channel with one pair of transistors would generate around 4.5 watts of heat per transistor on your rails. So that's 18 watts for a stereo amp. With good heatsinking appropriate to the power rating of the amp (the 50 to 78 or so watts Andrew mentions) the amp would run quite cool under normal use.
Heat is down to biasing. Class B running say 100 milliamps per channel with one pair of transistors would generate around 4.5 watts of heat per transistor on your rails. So that's 18 watts for a stereo amp. With good heatsinking appropriate to the power rating of the amp (the 50 to 78 or so watts Andrew mentions) the amp would run quite cool under normal use.
am I right that this will be your first DIY attempt ?
well, let me ask you, do you have another amp available ?
because these things may take time
and could also go wrong
maybe the best for you is a plug and play module, tested to work and ready for mounting
and then start on another DIY project
if you want more power, then its a whole different project than this
hmm
you have the right box for a bigger amp
but you have the wrong trafo
(I will not suggest series coupling and do the 1000watt thing
)but you probably need a new trafo with higher voltage
but maybe you amp is just not functioning like it should
2x 70watt can be quite powerful, if done right
ouch
with the two trafos you have bridged/balanced would be possiblebut if you can pull it off might be a different matter
Henrik, the type of power supply you describe is called a symmetric supply. As you have correctly deduced, it gives + and - voltage with respect to ground. This is pretty normal in most solid state amps.
With that case, heatsinks, and those power supply components.. you could build a very good amp of about 70W into 8 ohms. Look for an amp kit using at least 2 pairs of output transistors per channel, and preferably 3 if you plan driving it hard such as PA duty
With that case, heatsinks, and those power supply components.. you could build a very good amp of about 70W into 8 ohms. Look for an amp kit using at least 2 pairs of output transistors per channel, and preferably 3 if you plan driving it hard such as PA duty
I'm agree with Bimo,
check this very simple one only use 6 transistor:
I got that here http://www.diyaudio.com/forums/solid-state/231662-peeceebee.html
there are many other variant, but this is the easiest one to go
Regards
check this very simple one only use 6 transistor:
I got that here http://www.diyaudio.com/forums/solid-state/231662-peeceebee.html
there are many other variant, but this is the easiest one to go
Regards
Thank you all.
It will be my first DYI solid state amp, although I have built a few tube amps. I was hoping just to buy some kit off ebay, but there are so many designs and I have no idea which is better suited to the components I plan to re-use (transformers and case). The one that John Bali is referring to - is that available as a kit, with the board already printed and all components in a package? I don't mind loading the boards myself, but it would be great to be able to buy as a kit.
regards
Henrik
It will be my first DYI solid state amp, although I have built a few tube amps. I was hoping just to buy some kit off ebay, but there are so many designs and I have no idea which is better suited to the components I plan to re-use (transformers and case). The one that John Bali is referring to - is that available as a kit, with the board already printed and all components in a package? I don't mind loading the boards myself, but it would be great to be able to buy as a kit.
regards
Henrik
I don't know about ebay
but you can check aussie amps
not cheap, but works
Aussie Amplifiers - diyAudio
The best, low cost and trouble free way of getting into solid state audio is with a Chip-amp. This is a sure-fire way to good sound quality that just gets better as your design and assembly skills improve. I support DIY all the way because that is what this forum and the kit sellers here, are about, in as many ways as possible.
However, I can also understand noobs wanting to get started right now without the hassles of learning to lay out PCBs properly. Some of us never get proficient or enthusiastic enough to want to carefully etch and drill PCBs every time we want to make a project.
I suggest you read some threads in the Chipamp forum, follow up on the parts and kit sources at the commercial forums like Audiosector and Chipamp and look at the illustrations, manuals etc. They are great products, compact and attractive.
Then, satisfy your curiosity with all the Ebay chipamp kits based on LM3886, LM3875, TDA7294, LM1875 etc. There's lots out there and quite cheap, even if the design and support is not near as good as our own, if I do say so!
However, I can also understand noobs wanting to get started right now without the hassles of learning to lay out PCBs properly. Some of us never get proficient or enthusiastic enough to want to carefully etch and drill PCBs every time we want to make a project.
I suggest you read some threads in the Chipamp forum, follow up on the parts and kit sources at the commercial forums like Audiosector and Chipamp and look at the illustrations, manuals etc. They are great products, compact and attractive.
Then, satisfy your curiosity with all the Ebay chipamp kits based on LM3886, LM3875, TDA7294, LM1875 etc. There's lots out there and quite cheap, even if the design and support is not near as good as our own, if I do say so!
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Henrik, sorry no kit from me.
But Lazy Cat do: :
http://www.diyaudio.com/forums/vendors-bazaar/225747-vssa-lateral-mosfet-amplifier.html
But I don't know if that one suit with all you have.
It is also not trouble free
Maybe you try chip amp as Ian Finch say, they are easiest one, you even build by PtP
Regards
John
Hi Henrik ! i hope you will see this reply
I have two questions about your amp:
1) which model is ?
2) have you tried reducing the bias ? maybe you will get less heat and more or less same sound
Then i have another question. Do you now the Doxa Model 40 ?
does it sound ok ?
I am sorry ... i should have read all the 3d before asking but i have an offer
Thanks a lot.
Kind regards, gino
Hi and just to say that i agree completely
About cooling there is one thing that i sincerely do not understand
Thanks to pc technology there are fan nowadays that are unbelievably silent
Please if someone can give me a reason not to use them
I see the output transistors mounted in a sort of chimney with internal fins with a silent fan on top or on the bottom
Maybe if the chimney is long and placed vertically it could work fine even without fan, just for natural convection
But i am not an engineer .. well i am not a good one i mean
Thanks and regards, gino
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