Bridging Hitachi J50/k175 combo? - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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
Reply
 
Thread Tools Search this Thread
Old 8th November 2006, 01:35 AM   #1
diyAudio Member
 
MikeHunt79's Avatar
 
Join Date: Aug 2003
Location: Bristol, UK
Default Bridging Hitachi J50/k175 combo?

Ok, this sort of follows on from another thread where I was asking about heatsinking this setup here.

I've bought two J50/k175 maplin modules in kit form, and all the bits have been soldered to the PCB.

I've also got the caps, toroid, and rectifier, can I plan to use it all as a sub amp. The only thing is, my sub is 4ohm, as it's a car audio one.

Now, if I run this bridged, it will mean this it will run at 2 ohms, and I don't think the J50/k175 combo is capable of that is it?

Is there a way I can bridge this while keeping this at 4 ohms? Or is there a simple mod I could to to get more than 150w at 4 ohms?

My sub is capable of 400w rms, so I'd like to get close to this if possible.
  Reply With Quote
Old 8th November 2006, 08:28 AM   #2
poynton is offline poynton  United Kingdom
diyAudio Member
 
poynton's Avatar
 
Join Date: Mar 2005
Location: A life on the ocean waves when I'm not at home in N. Wales (but I'm not Welsh so no sheep jokes!)
Maplin did a bridging module for this amp.
I seem to remember it gave a rated output of 400W into 2ohm.

I may have 1 somewhere if you are interested.

Andy
  Reply With Quote
Old 8th November 2006, 11:26 AM   #3
djk is offline djk
diyAudio Member
 
djk's Avatar
 
Join Date: Feb 2001
Location: USA
400W/4R is 14A, three pair of J56/K176 on about 90V or so.

This describes a Hafler DH500, a commercial 400W/4R amplifier. It had a large fan-cooled tunnel, and still ran quite warm. Later they bumped it to four pair per channel (XL-600).

The XL-280 used three pair of the J50/K135 on a lower voltage to do 400W in bridge mode (time may be thermally limited to several minutes). About 50V would be right for 400W/4R in bridge mode.

How many outputs do those Maplin modules have?
  Reply With Quote
Old 8th November 2006, 01:27 PM   #4
diyAudio Member
 
MikeHunt79's Avatar
 
Join Date: Aug 2003
Location: Bristol, UK
Quote:
Originally posted by poynton
Maplin did a bridging module for this amp.
I seem to remember it gave a rated output of 400W into 2ohm.

I may have 1 somewhere if you are interested.
Andy
VERY interested. Do you have any more info or pics? I've sent you an e-mail also.
Quote:
Originally posted by djk
The XL-280 used three pair of the J50/K135 on a lower voltage to do 400W in bridge mode (time may be thermally limited to several minutes). About 50V would be right for 400W/4R in bridge mode.
Well this sounds ideal to me, as my toroid is 50V. The only thing is, as sub is 4ohms unbridged, so when I run it bridged, it would run at 2 ohms. If I can somehow find a way of getting these J50/K135's to run at 2 ohms, then I'll be more than happy. I'm not aware so far of anyone running these at 2 ohms, but I'm sure it must be possible with the right bits...

Also, I've only got 2 pairs of J50/K135's. I might be able to get more tho, but they wouldn't be matched - I'm not sure if this will be much of an issue tho, as it's only driving a sub.

Also, heatsinking won't be a problem. I recently aquired over 20kg of alu heatsinks.
Quote:
Originally posted by djk
How many outputs do those Maplin modules have?
I've got 2 modules, and each module has one speaker output.
  Reply With Quote
Old 8th November 2006, 01:59 PM   #5
poynton is offline poynton  United Kingdom
diyAudio Member
 
poynton's Avatar
 
Join Date: Mar 2005
Location: A life on the ocean waves when I'm not at home in N. Wales (but I'm not Welsh so no sheep jokes!)
Quote:
Originally posted by MikeHunt79

VERY interested. Do you have any more info or pics? .
Hi.

This photo may give you an idea of heatsinking for the Maplin modules. The bridging units are on the RHS x2.
[This was the mid-range stereo amp for a disco]

Andy
Attached Images
File Type: jpg maplin.jpg (61.2 KB, 288 views)
  Reply With Quote
Old 8th November 2006, 02:01 PM   #6
poynton is offline poynton  United Kingdom
diyAudio Member
 
poynton's Avatar
 
Join Date: Mar 2005
Location: A life on the ocean waves when I'm not at home in N. Wales (but I'm not Welsh so no sheep jokes!)
This also may be of interest.
It is a stereo PA amp with 2 pairs of J50/K135 per channel
Fanned heatsinks !

Andy
Attached Images
File Type: jpg mosfet1.jpg (81.4 KB, 287 views)
  Reply With Quote
Old 8th November 2006, 02:18 PM   #7
diyAudio Member
 
MikeHunt79's Avatar
 
Join Date: Aug 2003
Location: Bristol, UK
Quote:
Originally posted by poynton

This photo may give you an idea of heatsinking for the Maplin modules. The bridging units are on the RHS x2.
Thanks for the pics... they are worth more than 100 words. Do you know if either of these amps are 2 ohms stable? Or have any more info or specs? I'd basically like to do a 1 channel version of this amp, with 1 pair of modules, instead of a 2 channel one with 4 modules. I'm guessing it does around 300w per channel?

I've got heatsink around the same size as that, but the fins are twice as long, so I'm sure I shuold be fine heatwise. It's good to see what the professionals are using tho.
  Reply With Quote
Old 8th November 2006, 05:14 PM   #8
ilimzn is offline ilimzn  Croatia
diyAudio Member
 
Join Date: Feb 2005
Location: Zagreb
Let me make this simple:
There is no way a single pair of J50/K135 will work into 2 ohms the way you want it to.
J50/K135 are 7A parts. Maximum dissipation is 100W at case temperature of 25C, which, using normal heatsinking methods implies a near infinite heatsink (a quick calculation shows a total thermal resistance of 1.25K/W, considering the resistance of the channel to case plus the isolation material, the heatsink comes out as something below 0.1K/W - this would be enormous.
RdsON is quite high for lateral MOSFETs - about 1 ohm, but this will already imply heavy clipping in an audio amp. Since the amplifier module uses the same power supply for both input and driver stage as for the output FETs, the figure in the datasheet giving saturation voltage at Vgd=0 applies, at 7A this is 12V max - already 84W of dissipation just at the peak of the waveform, and that's not the maximum. Meanwhile, at 7A, you have 14V into 2 ohms PEAK. This means each amp in the bridge contributes about 49W, so you get 98W into a bridged 4 ohm load, and should not use rail voltages higher than about 28V.

Consider what happens if you use the same quick and dirty calculation with a 4 ohm load: at 7A the voltage on the load is 28V, and the power 98W - from a SINGLE module, approximately the same power dissipated per module, but rails are about 42V. In other words, using two mudules bridged into a 4 ohm load gives you exactly the same maximum power just with twice the heat.

In other words, in order to get more power, you need an amplifier with more output FET pairs, although the situation would be slightly better if the output stage had about 12-14V lower power supply rails than the driver stage. And all of this is with a very much oversimplified calculation - real world will be much worse!
  Reply With Quote
Old 8th November 2006, 05:57 PM   #9
diyAudio Member
 
MikeHunt79's Avatar
 
Join Date: Aug 2003
Location: Bristol, UK
Ok, gotcha. The only point in bridging these would be if you were driving an 8 ohm driver, on order to achieve a 4 ohm impedance.

I'll stick to a single driver for now, giving me 150w at 4 ohms.
  Reply With Quote
Old 8th November 2006, 07:31 PM   #10
djk is offline djk
diyAudio Member
 
djk's Avatar
 
Join Date: Feb 2001
Location: USA
A single pair of J50/K135 on 50V will only drive 100W/4R (if you can keep it cool).

100W/4R is at the maximum drain current for the device. The Rds over temperature for this part is 1R7, so the minimum voltage loss will be 12V (plus the front-end loss).

The Hafler DH-120 is built this way, uses 52V, and did 90W/4R (time may be thermally limited to several minutes).
  Reply With Quote

Reply


Hide 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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Has any tried this combo with a MTM mcmahon48 Multi-Way 3 25th March 2009 05:14 PM
Best combo 4 car kensr05 Car Audio 4 24th March 2006 06:45 AM
PSU for SS combo wxn Instruments and Amps 1 23rd December 2005 03:02 PM
best sub + amp combo? Xplorer Car Audio 2 13th June 2004 10:12 PM


New To Site? Need Help?

All times are GMT. The time now is 11:32 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2