Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Solid State Talk all about solid state amplification.

Musical Fidelity A1 Integrated repair/upgrages
Musical Fidelity A1 Integrated repair/upgrages
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Thread Tools Search this Thread
Old 5th March 2011, 09:46 PM   #11
spendorspain is offline spendorspain  Spain
diyAudio Member
Join Date: Apr 2005
Location: Spain
Great! I知 looking forward to see your tutorial on the A1 soon, Zen Mod.

Please, I壇 be very grateful if you could give advice regarding the new power transformer on my A1 because I知 still in doubt about its VA size.

I値l probably buy the Nuvotem 0120P1-2-018K which is a 120VA unit with one 230Vac primary and two 18Vac secondaries. If I知 not wrong, to obtain the required 18v-0v-18v ac supply I have to join the two 0v output cables (black and orange) and solder both to the 0V input on the A1 pcb. The other two wires (red and yellow) are soldered each to one of the two 冬 inputs on the pcb. Just to be sure, this is the correct wiring, isn稚 it?

I have a doubt regarding the size. The original A1 transformer is around 100VA, so I think the 120VA will suffice and its 104mm diameter is perfect for the box I have. I will use the amplifier with a pair of small 4 ohms loudspeakers in a smallish room and I listen usually nearfield at low volume, so the limited 20W power is not a problem, but I致e read that the A1 is not at ease with a 4 ohms load. Perhaps in this case a bigger transformer is better, helped by the beefier MJ15003/4 output transistors and a big 0.30コC/W heatsink to cool all down. Will its higher rating and inrush current stress too much the PSU caps and diodes?

What do you think about it? Is there any advantage in going from a 120VA to a 160VA transformer?

Thanks again in advance

Best regards

Attached Images
File Type: gif Nuvotem 0120P1-2-018K transformer wiring.gif (11.0 KB, 449 views)
  Reply With Quote
Old 5th March 2011, 10:25 PM   #12
Zen Mod is offline Zen Mod  Serbia
Official Court Jester
diyAudio Member
Zen Mod's Avatar
Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
Musical Fidelity A1 Integrated repair/upgrages
considering that stock A1 ( if you're lucky not to have one with crippled bias ) is cruising somewhere at 700mA/2 x 22V per channel - that's 30W ; say that rest of circ is drawing some 10W max , so you have around 40W of draw per channel

80W for both - my logic is to use at least 200VA xformer if shared between channels

if you are going for one xformer per channel , 120VA is more than fine

to further refine things - look at ,say, F5 manual ( FIRST WATT HOME) and observe how NP use two bridges (one per winding) ..... old trick , also used by Naim boyz

that way you'll have cleaner audio gnd , less spikes and buzz in xformer

for going completely nutz - use discrete bridges , made with either shottky or fast T0220 cased diodes
my Papa is smarter than your Nelson !
clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa...ゥ by Mighty ZM
  Reply With Quote
Old 6th March 2011, 02:53 AM   #13
jaycee is offline jaycee  United Kingdom
diyAudio Member
Join Date: Apr 2004
Location: Norwich, UK
The original transformer is only 100VA iirc. You would join the black and yellow wires together and connect this to the 0V point.

I wouldn't bother "going nuts" on this amplifier at all. What I would do is replace all of the capacitors, and replace the output transistors (which are MJ2955/2N3055s) with more rugged MJ15024/5 or MJ21193/4 devices. Also as Mark says, build a replacement preamp and bypass the dreadful one in the amp itself.
  Reply With Quote
Old 19th January 2012, 12:33 PM   #14
adespade is offline adespade  United Kingdom
diyAudio Member
Join Date: May 2009
Default Pre-amp layout

Hi, does anyone already have a layout for Mark Hennesey's preamp design
or would anyone be willing to verify mine?

Attached Images
File Type: jpg preamp_mod_vboard_big.jpg (500.2 KB, 389 views)
  Reply With Quote
Old 11th February 2012, 07:24 PM   #15
adespade is offline adespade  United Kingdom
diyAudio Member
Join Date: May 2009
Default Revised Layout

For anyone interested..this is an updated layout
Attached Images
File Type: jpg preamp_mod_vboard_big2.jpg (484.5 KB, 381 views)
  Reply With Quote


Musical Fidelity A1 Integrated repair/upgragesHide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
anyone know the musical fidelity a1 -x amplifier tube shop Solid State 11 26th October 2015 12:38 PM
Musical Fidelity A1 Improvements juluska Solid State 17 8th February 2010 01:37 PM
Improving Musical Fidelity A1 - How to? likeDIY Solid State 4 6th June 2007 09:39 AM
Musical Fidelity A1 modification ilimzn Solid State 5 19th January 2007 01:34 AM
JLH Or Musical Fidelity A1? Jay Solid State 1 16th September 2003 01:40 PM

New To Site? Need Help?

All times are GMT. The time now is 12:05 PM.

Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio