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Old 13th July 2010, 08:08 AM   #541
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Quote:
Originally Posted by barry.childs View Post
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.
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Old 13th July 2010, 08:35 AM   #542
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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!)
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File Type: jpg 005.JPG (674.1 KB, 1020 views)
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Old 13th July 2010, 08:53 AM   #543
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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
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Old 14th July 2010, 10:29 AM   #544
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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?
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Old 18th October 2010, 08:42 PM   #545
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@ barry
What preamp do you use now? Did you design it yourself?
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Old 27th October 2010, 07:18 PM   #546
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Default 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
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Old 28th October 2010, 06:33 AM   #547
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i attach some picture ...
maybe could be useful to find the problem...
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File Type: jpg 02012008878 [800x600].jpg (108.2 KB, 402 views)
File Type: jpg 02012008873 [800x600].jpg (102.4 KB, 373 views)
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Old 28th October 2010, 11:08 AM   #548
jaycee is offline jaycee  United Kingdom
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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.
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Old 28th October 2010, 11:23 AM   #549
osscar is offline osscar  Latvia
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Counterfeit Transistors

i agree
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If time is money then I'm out of time
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Old 28th October 2010, 02:23 PM   #550
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Quote:
Originally Posted by jaycee View Post
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
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