Thanks both for the circuit suggestions. I'll go look them up and put them on the consideration list. Thanks to everyone else who chipped in too
Apologies for the technical vagaries. I shall of course be the tea boy on this project and am limiting myself to 'designing' and building the pre. I'm just checking I'm not going to be a position of it being almost done and someone saying 'why didn't you use this far superior circuit?'. Any suggestions I pull in will go to the engineer for proper review and consideration. That said I shall come back with less rubbish info for you all to assist with that.
Last edited:
Sure. It's for 2 channel HiFi and I'm going to need around 300W x 2 into 8 ohms. I'm aware that my voltage is a little low. If I can't get that then I can't but it's the aim. I will be chucking the existing boards out and having new ones made up to fit the chosen circuit, heatsink, moutings etc.
Found some pics of the transformer, on the internet and on my phone. But in none of them can you see the label clearly I'll come back with the info as soon as possible.
Found some pics of the transformer, on the internet and on my phone. But in none of them can you see the label clearly
I'll come back with the info as soon as possible.
Last edited:
Yeah I thought that might be the case re output power vs voltage. No, I've not measured it. It's away at the workshop at the moment but I understand that we need to get parameters from that before much more progress can be made. I don't want to bug the engineer who probably has other work to do but I'll get a picture of the transformer label and/or measurements from it asap and come back.
Last edited:
I couldn't possibly comment, but will send you a PM
My plans have moved on a little. I've decided that chasing 300W into 8 with the rails I have is not practical and have moved to plan B. Plan B is to take an old but most excellent 500W a side amp we have kicking around with terminal rot, make new boards, use existing transformers and possibly output devices and find it a case and heat sinks. It's a little more power than I need but it's the best option on the table by far and I am a firm believer in headroom and future options. That was originally inspired by "what can we put in the existing box" and for sure it'd all fit quite nicely but I'm not sure that's a viable option from the thermal perspective.
So, this could become two projects. One to sort that big old amp out and another to get best use out of the existing case, cooling and +-60V rails. I'm thinking maybe look at two channels of 100W class A as a better fit. That may not be viable but it's my current line of thought / investigation. The thing was originally doing 500W in total A/B so I'll take a look at the thermal type viability.
The other option for the chassis I might look into if I want something off the peg is VZaichenko's NS series, which have been mentioned. They look OK.
My plans have moved on a little. I've decided that chasing 300W into 8 with the rails I have is not practical and have moved to plan B. Plan B is to take an old but most excellent 500W a side amp we have kicking around with terminal rot, make new boards, use existing transformers and possibly output devices and find it a case and heat sinks. It's a little more power than I need but it's the best option on the table by far and I am a firm believer in headroom and future options. That was originally inspired by "what can we put in the existing box" and for sure it'd all fit quite nicely but I'm not sure that's a viable option from the thermal perspective.
So, this could become two projects. One to sort that big old amp out and another to get best use out of the existing case, cooling and +-60V rails. I'm thinking maybe look at two channels of 100W class A as a better fit. That may not be viable but it's my current line of thought / investigation. The thing was originally doing 500W in total A/B so I'll take a look at the thermal type viability.
The other option for the chassis I might look into if I want something off the peg is VZaichenko's NS series, which have been mentioned. They look OK.
Last edited:
Using the given chassis, heat sinks and power transformer, you might build four power amplifiers (two output pairs each) and bridge each two of them to get the desired output power from the given DC supply rails. I think, in this case you'd have to abandon your 1943/5200 devices and switch to more beefier ones, like MJL1302A/3281A, though.
Best regards!
Best regards!
If he does in fact have +/- 60V supplies mono-bridging wouldn't be required. This would be capable of producing 200W+ into 8 ohms which would be a powerful amplifier. I can't see an manufacturer running this voltage to multiple single output pair amps like this one though.
Do we know? Or is it 60-0-60Vac? He still keeps some secrets on this...
I'd say also. But he's the one who believes in 300 watts/ch
.Edit: The Pictures Show 20 output devices. So there are five single amplifiers with two pairs each.
Best regards!
Last edited:
Yes that would be dual output pairs. Still not enough output devices for a reliable amp at this power level. I'm curious what the actual measured voltage would be.
A true 300W DIY amplifier would be a pretty serious amplifier. The marketing department would likely advertise this as 1000W. From my own experience +/-63V rails seem to be the sweet spot for power vs. heat generation. +/-75 V is manageable, but is noticeably warmer. Above that turns into something you need help to move or monoblocks = PITA. 200 - 250W with proper supplies to back them up is a great target.
A true 300W DIY amplifier would be a pretty serious amplifier. The marketing department would likely advertise this as 1000W. From my own experience +/-63V rails seem to be the sweet spot for power vs. heat generation. +/-75 V is manageable, but is noticeably warmer. Above that turns into something you need help to move or monoblocks = PITA. 200 - 250W with proper supplies to back them up is a great target.
Do you know what the VA rating is on the transformer? This is a good voltage to work with in my experience.
Hi all,
Thanks for the continued replies. It's all good stuff and very interesting.
I don't have it here at the moment to check the supplies and I'm no longer planning to go out of the way to do that because the plans have changed. However the existing transformers are 2 x 800VA and in their current power circuit end up producing +- 60V DC rails for the amp. For sure more info might tell us if we can play with series configs and stuff like that but really I'm saying if what I know is I can produce +- 60V DC rails what are the options? Or at least that was what I was asking. Considering all the excellent feedback and advice I've had here and from other sources I'm chucking the transformers as well.
I want 300W because my speakers have a sensitivity of 85dB @ 1W @ 1metre, are rated for 300W and I believe in headroom. That seems reasonable to me.
Bridging ain't a bad idea and it was the plan before we decided to chuck the original amp circuits. After that I saw it as a hopefully unnecessary compromise although retained a bit of an open mind about it.
So yeah. Plan B is now almost certainly going ahead. Plan B is to remake that old but excellent 500W (ish) a side using the case I have, but cutting new circuit boards. In other words it's now basically a completely different project based on different parameters. We may put a new heat sink in. We may cut the transistor count down a bit and reduce power, we may not. Current config is 7 pairs of MJW21193 and MJW21194 per side, which is overkill if anything but it's nice to have the flexibility for future speaker upgrades / occasional PA use.
If it turns out to be impractical to use the existing case then I may return to the original spec in terms of case PSU and heat sink as a side project.
Thanks for the continued replies. It's all good stuff and very interesting.
I don't have it here at the moment to check the supplies and I'm no longer planning to go out of the way to do that because the plans have changed. However the existing transformers are 2 x 800VA and in their current power circuit end up producing +- 60V DC rails for the amp. For sure more info might tell us if we can play with series configs and stuff like that but really I'm saying if what I know is I can produce +- 60V DC rails what are the options? Or at least that was what I was asking. Considering all the excellent feedback and advice I've had here and from other sources I'm chucking the transformers as well.
I want 300W because my speakers have a sensitivity of 85dB @ 1W @ 1metre, are rated for 300W and I believe in headroom. That seems reasonable to me.
Bridging ain't a bad idea and it was the plan before we decided to chuck the original amp circuits. After that I saw it as a hopefully unnecessary compromise although retained a bit of an open mind about it.
So yeah. Plan B is now almost certainly going ahead. Plan B is to remake that old but excellent 500W (ish) a side using the case I have, but cutting new circuit boards. In other words it's now basically a completely different project based on different parameters. We may put a new heat sink in. We may cut the transistor count down a bit and reduce power, we may not. Current config is 7 pairs of MJW21193 and MJW21194 per side, which is overkill if anything but it's nice to have the flexibility for future speaker upgrades / occasional PA use.
If it turns out to be impractical to use the existing case then I may return to the original spec in terms of case PSU and heat sink as a side project.
The 800 VA transformer is perfectly sized for a +/- 60V amp, but if you like it loud and are in a big room this might not be enough for you with the low efficiency speakers.
The 500W amp sounds like a neat project. 7 pairs of MJW21193/MJW21194 isn't really overkill at this power level, but there are better devices available these days. Check out Ostripper's Slewmaster series. 5 pairs of Sanken MT-200 would work well here. It's a great design and very forgiving to work with.
The 500W amp sounds like a neat project. 7 pairs of MJW21193/MJW21194 isn't really overkill at this power level, but there are better devices available these days. Check out Ostripper's Slewmaster series. 5 pairs of Sanken MT-200 would work well here. It's a great design and very forgiving to work with.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.