Diy preamp for Amplifier IRFP240/IRFP9240

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mprivitera1

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#1
Hello guys ,
I built this " POWER AMP " http://www.diyaudio.com/forums/solid-state/162043-mosfet-amplifier-irfp240-irfp9240-77.html

I look for a DIY preamp to match it . I saw these Chinese ;
HIFI DIY Preamp kit base on NAIM NAC152XS Pre-AMP for NAP140 amp L155-1 | eBay
JC-2 Preamplifier Class A Dual differential FET input PER-AMP Kit DIY | eBay
Class A SE MOSFET pre-amplifier PCB based on Aleph P ! | eBay

you recommended what ??? You know other DIY preamp ? ... I await your help.
I forgot, the final 10 000 ohms input impedance !
🙂
 
#2
Virtually all Ebay preamplifier products will suit your amplifier or any other of the typical kits/finished modules on sale. Be aware though, that the Naim and JC-2 clone models and many other clone designs are only copies of a small part of the original designs and don't have anywhere near their performance as they as they are. Otherwise, any commercial preamplifier should also suit but you might find them a bit too expensive.

The preamplifier output impedance is usually low, at around 200R or at least < 1k. It does not need to match the amplifier which generally is >10k input impedance. The preamplifier input impedances will be high at even 47k or more but the player input impedances will also be much lower than this. There is seldom any need for concern if you are assembling Ebay kits that are intended for direct connection between source and amplifier if they are standard designs.
 
#3
Ian Finch said:
Virtually all Ebay preamplifier products will suit your amplifier or any other of the typical kits/finished modules on sale. Be aware though, that the Naim and JC-2 clone models and many other clone designs are only copies of a small part of the original designs and don't have anywhere near their performance as they as they are. Otherwise, any commercial preamplifier should also suit but you might find them a bit too expensive.

The preamplifier output impedance is usually low, at around 200R or at least < 1k. It does not need to match the amplifier which generally is >10k input impedance. The preamplifier input impedances will be high at even 47k or more but the player input impedances will also be much lower than this. There is seldom any need for concern if you are assembling Ebay kits that are intended for direct connection between source and amplifier if they are standard designs.
Click to expand...

Ok I got it, thanks .

but there is another DIY kit , not eaby ?
 
#8
mprivitera1 said:
.....but there is another DIY kit , not eaby ?
Click to expand...
Sure, there is Aliexpress selling the same stuff! 😀 Then there are kits from Indonesia, Thailand and Malaysia sold on Ebay and local Asian on-line sellers' markets. If you mean from European or North American suppliers, you may not like the prices as they will be very different for kits supplied from local businesses because of vastly different economies and costs. You need to feel generous when you buy a similar product for 2 or more times the price and have to pay additional, higher freight charges as well. Look around - Google is your friend and you don't need others to show you what you can buy on the internet.

People who want good products with guaranteed high performance and good sound quality, will pay thousands, not just a few tens of dollars. If you want a DIY kit that you can roll the parts to suit your own experiments, it won't matter what you buy as long as it has the basics of a low-noise gain stage, in/out connectors, a volume control and accommodates the components you want to experiment with. If you don't want Opamps, that leaves very few kits other than tube or hybrid designs and other discrete transistor classics from Ebay. Most other kit manufacturers have moved on from these, decades ago and note that it won't be long before the old transistors with leads are fully obsolete and only junk and fakes arew available.

If you want to talk about preamplifiers, this is the the wrong forum. This one is for conventional, solid state power amplifiers. You need to read and post on the Analog Line-level Forum where the topics are mainly about preamps and the kit options will be discussed on many threads - it's just a very confusing forum title 😕 Analog Line Level - diyAudio
 
#11
Ian Finch said:
Sure, there is Aliexpress selling the same stuff! 😀 Then there are kits from Indonesia, Thailand and Malaysia sold on Ebay and local Asian on-line sellers' markets. If you mean from European or North American suppliers, you may not like the prices as they will be very different for kits supplied from local businesses because of vastly different economies and costs. You need to feel generous when you buy a similar product for 2 or more times the price and have to pay additional, higher freight charges as well. Look around - Google is your friend and you don't need others to show you what you can buy on the internet.

People who want good products with guaranteed high performance and good sound quality, will pay thousands, not just a few tens of dollars. If you want a DIY kit that you can roll the parts to suit your own experiments, it won't matter what you buy as long as it has the basics of a low-noise gain stage, in/out connectors, a volume control and accommodates the components you want to experiment with. If you don't want Opamps, that leaves very few kits other than tube or hybrid designs and other discrete transistor classics from Ebay. Most other kit manufacturers have moved on from these, decades ago and note that it won't be long before the old transistors with leads are fully obsolete and only junk and fakes arew available.

If you want to talk about preamplifiers, this is the the wrong forum. This one is for conventional, solid state power amplifiers. You need to read and post on the Analog Line-level Forum where the topics are mainly about preamps and the kit options will be discussed on many threads - it's just a very confusing forum title 😕 Analog Line Level - diyAudio
Click to expand...

thanks for your advice .......

Administrators, you can move in " Analog Line Level"
 
#12
Hi guys,

I built this prototype of electrical schematic of Apex BJT preamp. I used parts I have at home, capacitors 68p instead of 82P, BC547C in place BC550C ..... I do not know if I'm wrong?
There are tensions by test / check ... at what points?
if I connect it with no box, I have to connect the "0"

Thank you
apex_b10.jpg

20160210.jpg
 
#13
mprivitera1 said:
Hi guys,

I built this prototype of electrical schematic of Apex BJT preamp. I used parts I have at home, capacitors 68p instead of 82P, BC547C in place BC550C ..... I do not know if I'm wrong?
There are tensions by test / check ... at what points?
if I connect it with no box, I have to connect the "0"

Thank you
apex_b10.jpg

20160210.jpg
Click to expand...


..gran nice preamp, high good range, good midrange, very detail and smooth sound. One thing that has not convinced me is the low range, slightly spread out .... and a little swollen .According you is possbile to do something about this? .... Maybe use quality transistors Philips type ??
tahnks:up:
 
#16
Hello,

I bought the assembled JC2 knockoff and really like it. Does everything well and is dirt cheap. Add a $15.00 or junk box transformer, fuse holder and cord and within an hour you have a very nice sounding bare board preamp. Another hundred on a box, switching and jewelry and you have something nicer to look at. Could use a power on delay to eliminate some thump but I jus turn that on first then the power amp.
I recommend getting regardless because its so cheap.

Other than that consider a 6SN7 based preamp. A Tubcad CCDA or similar design will have all the nice sound of the JFET pre but a little darker with fuller tone and more punch. At the higher cost and maybe some struggle to get it quiet. Of course then there's the cost and obsession of tube rolling, but that's part of the fun. That may cost you over $300.00 DIY, for me it's worth it YMMV.


Once you hear the JFET or 6SN7 you'll question the value of opamps as preamps.
 
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#17
One thing that has not convinced me is the low range, slightly spread out .... and a little swollen
Click to expand...
Impossible to comment on subjective descriptions which have no translation on the Real World, specially in the Audio domain.

FWIW "spread" usually applies, statistically speaking, to a range of measured or calculated values, or describing, say, jam on a toast, not the case here, and "swollen" , among others, to some anatomical parts, not the case either.

Check for the proper use of those words, such as:

https://en.wikipedia.org/wiki/Spread

What Causes Swollen Ankles and Feet? - WebMD
 
#19
I want to clarify ; I completed this pre with BC550C and BC560C ( unknown brand ) as required by progetto.Esso does not provide an output capacitor, try this can be dangerous for the presence of DC , but it can be unvantaggio for sound. The power amplifier , however , provides a coupling capacitor of 1uF input . As I said at the top , the sound of this preamp is really very interesting , but I "only" a limit , I think my only , at low frequencies ..... them feel not very deep . Can be due to use of BJT unmarked ...?
 
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