I have the schematics but I am having difficulty in finding the specs on this transformer. I was hopping one of you gents could lend a fellow a hand. I will get the chassis measurement tonight and post those up as well but I was hopping for insight into the electrical specs of such and animla as this.
The Amplifier is a Randall B2000 head for bass amplification. I will also attach the Preamp circuts as well in case anyone here is bored.
The Amplifier is a Randall B2000 head for bass amplification. I will also attach the Preamp circuts as well in case anyone here is bored.
I did attach it in the second posting if not I will do it again.
It is a BiAmp design 140 watts on the high end "4 mj15003" and 375 " idicated as 4 but actually 8 Mj15025" at a paltry 8 ohms. I was told when it was new that is was 2 ohm capable and It has proven it self able to do so. I have also run it down to 4 most of its life never a problem.
I know the rail voltage is fiarly high so it would be assumable that they designed it with lower Impedences and such in mind.
Any help you can offer would be fantastic.
It is a BiAmp design 140 watts on the high end "4 mj15003" and 375 " idicated as 4 but actually 8 Mj15025" at a paltry 8 ohms. I was told when it was new that is was 2 ohm capable and It has proven it self able to do so. I have also run it down to 4 most of its life never a problem.
I know the rail voltage is fiarly high so it would be assumable that they designed it with lower Impedences and such in mind.
Any help you can offer would be fantastic.
Hi Kramerguy,
Jaycee has nailed the voltage right on.
For current, just look at the breaker rating and buy a bit larger for headroom. Also, measure the core size and make sure your replacement is at least that big, but still fits. Drilling a couple mounting holes in the chassis may be required.
Still don't see your amp section. What for file size warnings when you attempt to attach a file.
-Chris
Jaycee has nailed the voltage right on.
For current, just look at the breaker rating and buy a bit larger for headroom. Also, measure the core size and make sure your replacement is at least that big, but still fits. Drilling a couple mounting holes in the chassis may be required.
Still don't see your amp section. What for file size warnings when you attempt to attach a file.
-Chris
Hi Kramerguy,
You are allowed one attachment per post. You can have multiple links to images in each post.
If you can not attach a schematic, it is too large to be accepted. You didn't see the error message. The maximum size is given, I can not remember off hand. So, if you reduce the file size, you can attach it.
If you don't mind, could you also forward the schematic to me as well? Send it to bhomester at gmail dot com. If I post my straight email address, spam bots can pick it up. Therefore, the email address is presented in a non-standard format.
-Chris
Yes, I do .....
You are allowed one attachment per post. You can have multiple links to images in each post.
If you can not attach a schematic, it is too large to be accepted. You didn't see the error message. The maximum size is given, I can not remember off hand. So, if you reduce the file size, you can attach it.
If you don't mind, could you also forward the schematic to me as well? Send it to bhomester at gmail dot com. If I post my straight email address, spam bots can pick it up. Therefore, the email address is presented in a non-standard format.
-Chris
Well since I have been running into a wall trying to find a replacement transformer. 8 amps 80v rails + a 65v rail output plus the preamp side which looks to need 12 volts I have been considering stepping into switching power supply type power supplys. I know I could step the voltages down from 80 or 65 using some fiarly standard voltage regulators but finding good quality transformers at this power level has been challening.
Any guidance on how to best achieve this ? I will either have to use 3 SMPS's or get a custom unit made. I am ok with packaging 3 SMPS's in the amp I have loads of room.
I was curious about modifications to the amplifier for proper operation.
as I understand it this is a class AB2. One thing I know that is does better then other Bass Amplifiers I have seen is low frequncy control. It seems to have much stronger and great speaker coupling and control. The lows are cleaner. Maybe some subwoofer guys may find this interesting ??
I hosted the Power supply schematics here.
any input would be great. I have been fixing stuff forever but modding is a whole new paradigm I am not sure I am ready for just yet.
Btw feel free to use the schematics for you own amplifiers. They are public domain now.
http://www.mediafire.com/?sharekey=1aaf83381d3b4a0fd2db6fb9a8902bda]RB2000 Power Supply [/URL]
Any guidance on how to best achieve this ? I will either have to use 3 SMPS's or get a custom unit made. I am ok with packaging 3 SMPS's in the amp I have loads of room.
I was curious about modifications to the amplifier for proper operation.
as I understand it this is a class AB2. One thing I know that is does better then other Bass Amplifiers I have seen is low frequncy control. It seems to have much stronger and great speaker coupling and control. The lows are cleaner. Maybe some subwoofer guys may find this interesting ??
I hosted the Power supply schematics here.
any input would be great. I have been fixing stuff forever but modding is a whole new paradigm I am not sure I am ready for just yet.
Btw feel free to use the schematics for you own amplifiers. They are public domain now.
http://www.mediafire.com/?sharekey=1aaf83381d3b4a0fd2db6fb9a8902bda]RB2000 Power Supply [/URL]
I imagine it would be possiable to run lower voltages. I would prefer not to degrade or change the performance of the amplifier however.
I have 2 of these amplifiers "they are composite units for use with bass guitar built in preamps,compression circutry,equlization and Direct Balanced output" I found the problem as being sevral shorted transistor pressumably from a bad speaker cab at some point.
I have used the transformer out of my good amplifier and the amp works correctly when the known good unit is in. I also get zero to no voltage or very weak voltages out of the transformer when powered up. I replaced sevral components several of the MJ15024 5 were shorted. I tried bypassing the thermal limiter and still no go. the transformers smeels harshly and looks to have been very hot.
My assumption is that someone bypassed the speakr proection circut at some point as evidecned by soldering irregulatitys on the juntion for the speaker protection breaker. Why they would do this I am unaware as I have loaded my good head own to 2 ohms running lots of cabinets and had zero issues.
The history of the amp is unknown I bought it as a DOA for spare parts and to repair. However I would love o get it functioning again.
Any insite is greatly appreciated.
I have 2 of these amplifiers "they are composite units for use with bass guitar built in preamps,compression circutry,equlization and Direct Balanced output" I found the problem as being sevral shorted transistor pressumably from a bad speaker cab at some point.
I have used the transformer out of my good amplifier and the amp works correctly when the known good unit is in. I also get zero to no voltage or very weak voltages out of the transformer when powered up. I replaced sevral components several of the MJ15024 5 were shorted. I tried bypassing the thermal limiter and still no go. the transformers smeels harshly and looks to have been very hot.
My assumption is that someone bypassed the speakr proection circut at some point as evidecned by soldering irregulatitys on the juntion for the speaker protection breaker. Why they would do this I am unaware as I have loaded my good head own to 2 ohms running lots of cabinets and had zero issues.
The history of the amp is unknown I bought it as a DOA for spare parts and to repair. However I would love o get it functioning again.
Any insite is greatly appreciated.
megajocke said:
Hi Kramerguy,
Forget looking for a transformer the same as yours. It will be a custom wind, or you may get lucky finding a customer transformer. Don't bet on it.
Therefore, you are stuck with two transformers if you want to go that route.
Make sure your main power transformer is rated for all the power used by everything with a 25% margin minimum.
I hate people like that.
The workmanship you describe is unfortunately very common in music band world. I especially hate it when these morons say something like "Hey!, it's good enough for rock 'n roll!". Typically, those repairs are not "good enough for rock 'n roll!". TV techs seem to be like this as well. Not all, but the overwhelming majority are.
It sounds like you have some options open to you. I think National Semiconductor has a design utility on their site that will work out what you need, give you the schematic complete with parts list. It will also give you the PCB artwork. You can then order the boards, or complete boards and parts in a kit you assemble. Can't be any easier than that!
Just click here on the upper right where it says "WEBENCH® Designer" where it says "Start Design" in green reverse. If you create an account, it will even save your designs. Of course you can download everything about your design as well.
If nothing else, you should try it to get an idea on how this works. I am going to try this for running tube heaters. It will allow a soft start also, to reduce the inrush current in the heaters.
-Chris
Forget looking for a transformer the same as yours. It will be a custom wind, or you may get lucky finding a customer transformer. Don't bet on it.
Therefore, you are stuck with two transformers if you want to go that route.
Just buy the transformer for your 80 volt rails. Then your idea of using switching regulators for the lower voltage rails is quite good. This should work very well. Additionally, you can add effective protection to limit the fault currents. The higher frequencies involved make filtering out the ripple easier with smaller values of inductance and capacitance.
Make sure your main power transformer is rated for all the power used by everything with a 25% margin minimum.
Welcome to the world of "hackers". In the service lingo, that means an uneducated, heavy-handed, overconfident destroyer of equipment that is positive they can fix anything.
I hate people like that.
The workmanship you describe is unfortunately very common in music band world. I especially hate it when these morons say something like "Hey!, it's good enough for rock 'n roll!". Typically, those repairs are not "good enough for rock 'n roll!". TV techs seem to be like this as well. Not all, but the overwhelming majority are.
It sounds like you have some options open to you. I think National Semiconductor has a design utility on their site that will work out what you need, give you the schematic complete with parts list. It will also give you the PCB artwork. You can then order the boards, or complete boards and parts in a kit you assemble. Can't be any easier than that!
Just click here on the upper right where it says "WEBENCH® Designer" where it says "Start Design" in green reverse. If you create an account, it will even save your designs. Of course you can download everything about your design as well.
If nothing else, you should try it to get an idea on how this works. I am going to try this for running tube heaters. It will allow a soft start also, to reduce the inrush current in the heaters.
-Chris
Quick off-topic post here....Kramerguy said:
The forum software doesn't like attachments to be too many 'layers' down from the main directory/root/whatever. I couldn't post attachments from my normal 'HiFi' folder but had no problems when I moved the file to the Desktop (temporarily).
It was a bit of a head-scratcher for me, and may not be your problem at all....
Back to our scheduled program..........
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