NAP-140 Clone Amp Kit on eBay

[homemodder]

Cheers Jan, I never realised these pots turn so far. I was afraid I was giving it a big dose of dc and not able to measure it. It sounds great now. Thanks very much for your quick and helpful reply. My next question is a general one realy. I don't know if a pre-amp is neccessary. I never used one on my gainclones or goldmund clone, and although the naimclone sounds good would a pre-amp improve it. (I see their is even a naimclone pre-amp on ebay) Does impedance matching do anything these days. Comments very welcome. Regards Barry

Barry, I and others eagerly await a comparrison with the goldmund modules offcourse.

 

[barry.childs]

I'm trying to upload some pictures of the amp so far. The small transformer will be for speaker protection and poss pre-amp. Compared to the other amps, it is better than the gainclones, but no match for the Linuxguru modded Goldmund clone. (yet!)

 

[homemodder]

Thanks, I personally dont think it can quite match the sound quality one can get from a LTP vas circuit and the goldmund has great advantage in the input Jfets.

Nice build btw

 

[barry.childs]

New development. I've just added a pre-amp and it has boosted everything. In particular,soundstage, stereo seperation and bass. Iv'e included a couple of pictures. It is a balanced output op-amp design (only using unbalanced, but could use balanced on pre-out) Very impressed with results. I was going to buy the naimclone pre but shall not bother now. I wonder what the Goldmund will sound like with a quality pre?

 

[blistard]

@ barry
What preamp do you use now? Did you design it yourself?

 

[ciariello]

overheat ztx653 - ztx753

hi to all i am a new user.I bought 2 nap140 pcbs (tubeshunter on Ebay) i used :
BC550 for Q1 - Q2
2N5551 for Q5
MJ15003 (MOTOROLA)
MJE15030 - MJE15031 (MOTOROLA)
225VA Toroidal Tranformer (NOVATERM)
4 x 10.000mF 63V (Jingshay???)
ALL resistors are Vishay 1%
output resistors are Vishay 7W 0,5%

the ampli WORKS but the ZTX653 - ZTX753 became very very hot (after 20 minutes i read 61-62° on my thermometer)

When i measure the bias current it is 25mA but i can't change it by the trimmer.
I have the same problem on both channel ! ! !

the DC offset is 38mv on channel 1 and -248mv on the channel 2.

I changend all transistors but the result is the same....

plz help me

sorry for my bad english

 

[ciariello]

i attach some picture ...
maybe could be useful to find the problem...

 

[jaycee]

Your MJ15003's look like fakes - Motorola haven't made transistors in a long time, they should be branded ON. Same with the MJE15030/MJE15031 devices.

Get some Acetone, and some paper towel, and wipe the tops of the MJ15003 transistors. If the printing comes off, they are fakes.

 

[osscar]

Counterfeit Transistors

i agree

 

[ciariello]

Your MJ15003's look like fakes - Motorola haven't made transistors in a long time, they should be branded ON. Same with the MJE15030/MJE15031 devices.

Get some Acetone, and some paper towel, and wipe the tops of the MJ15003 transistors. If the printing comes off, they are fakes.

could be the cause of overheating?

if i replace them with ON Semiconductor MJ15003?

on the channel 2 i have 1 MJ15003 Motorola(fake?) and 1 MJ15003 Mospec and on this channel i have a dc offet -248mV

pls i accetp every goods news

 

[ciariello]

Attach the pictures of 1 MJ15003 Motorola (broken) and replaced with MOSPEC MJ15003.
I think this is the same of the other 3 pcs bought in the same shop at the same time

 

[ciariello]

I clean with Acetone top of the MJ15003 transistors and the printing comes off....
FAKES ....
But could be the cause of ZTX overheat?

Sorry for many post fot the same topic but...i can't edit

 

[jaycee]

It is most likely the cause of your problems. I would check also the driver transistors, if these are fakes they may be causing an oscillation, which would cause problems.

 

[ciariello]

could someone send me the RIGHT temperature value of the ZTX (without signal applied)

very very thanks

 

[jaycee]

They should become only slightly warm... you should be able to put your finger on them and not say "ouch!"

 

[ciariello]

mmm....there isn't this risk...i can touch the transistors ZTX without any problems for few minutes...Maybe i worried too.I replace on the channel 2 the Motorola(fakes) with 2 MOSPEC (i think genuine) with the same results.Without signal applied i can read on the thermometer about 48-52°...after 10-15 min power on

 

[ciariello]

i bought MJ15003 - MJ15030 - 15031 "ONSemi" on Distrelec website.
Thursday should give them to me...

 

[U102324]

Ciariello,

I see a very bad thermal contact between the heat sink and transistor mounting plate. This can be the cause of the problem. Measure temp on the transistor mounting plate and then the heat sink. They should be the same or at least very close.

 

[ciariello]

the temperature value on the mj15003 transistors (on both channel)is near to 25-26° (cold...) my problem are the ztx....
the surface of the heat sink and the mounting plane were polished and made smooth.
between the 2 parties, I put a good layer of thermal paste. then the two parts are securely tightened with 4 bolts placed 1.5 cm apart

 

[Ruwe]

Hi ciariello,
First check the current through the 68 ohms resistor in the emitter of ZTX 653. If it is about 8.5-10 mA you're good.

If your bias current is not adjustable most likely the Vbe multiplier doesn't work (the transistor between the ZTX653 and ZTX753). Check the pin orientation and the resistor values around. The voltage for the right bias current is about 2.35-2.38V between the collector of ZTX653 and ZTX753.

One of your channels has DC offset problem. Probably something at the inputs resistors or the feedback resistors. Check the values of the resistors.

... And get rid of the fakes, but I don't believe they are causing the problems.