A shiny interior appears to be a very effective way of making a dual mono build with one transformer
That is a 1,000 VA transformer. Do you think it is too small for this AB amp? I have had several high powered comrercial amps that only used one transformer and there was never an issue.
Oh, I hadn't noticed that. Like making a store look bigger by adding mirrors to the walls.
@Terry - It's good practice to tightly twist any pair of wire carrying AC (mains) or signal level. Some even believe wires carrying DC should be twisted too. I can't see your pictures (blocked by my firewall), but I assume Andrew noticed wires going/coming from your xformer. Those seem to be the most critical. If you notice other builds on the forum, you'll see a lot of twisted wires.
Rick
P.S. To get nice, even and tight twists use a variable speed electric drill or screwdriver.
Last edited:
Hi Terry, just looking over the amp pics and the psu does not have bleed down resistors to drain the filter caps.. 6k8 say 4w and 220nf's would do the job.
Just one thing, at power up do you get a grunt from the power transformer? if so add inrush limiter ntc's as this will slow the mass inrush surge that can pop fuse's. if you look at some amps they use ntc's or latch relay circuit's..this can be built around a 2 second timer thus slowing down that turn on surge.
Those who recall old pa amps would of noticed the loud thud or even plop's in speakers at turn on/off even the music signal slowly fading away so relay protection circuits was built in the more amplifiers..
There's information in that book in these's circuits...
Regards A.
Just one thing, at power up do you get a grunt from the power transformer? if so add inrush limiter ntc's as this will slow the mass inrush surge that can pop fuse's. if you look at some amps they use ntc's or latch relay circuit's..this can be built around a 2 second timer thus slowing down that turn on surge.
Those who recall old pa amps would of noticed the loud thud or even plop's in speakers at turn on/off even the music signal slowly fading away so relay protection circuits was built in the more amplifiers..
There's information in that book in these's circuits...
Regards A.
leach superamp
Some amplifier's use different va ratings depending the amps power.. Ive seen folk's who get confused with amplifiers thinking it's a 1000w just because it says 1000w on the case it just means the power transformer is a 1000va.
when building amplifier's we must take in to a count ideal real world usage's and not use under rated transformers that over heat and burn out...Take a 100w per side amplifier bare min say 300 va but again seen have seen 220 va..
Some amplifier's use different va ratings depending the amps power.. Ive seen folk's who get confused with amplifiers thinking it's a 1000w just because it says 1000w on the case
it just means the power transformer is a 1000va.when building amplifier's we must take in to a count ideal real world usage's and not use under rated transformers that over heat and burn out...Take a 100w per side amplifier bare min say 300 va but again seen have seen 220 va..
I repaired a Fender guitar amp rated at 100W that had a power transformer rated at 80VA judging by the size of the one that fit in its place. It was part of the protection scheme - the rail voltage drops when the transformer gets hot so the amp can't make so much power. Guess what was broken? The thermal fuse inside the transformer windings. Junk box fix that had cost me $10 and made my son happy for a year or two.
For home use you can get away with small transformers, just because you typically use so little power. But this is DIY, so we do it right. I've seen something that suggested 50% derating for a capacitive input filter. So, at least a VA rating of at least twice the amp's total output is appropriate. For Class A, I'd think that you'd want at least 3x, but that's another thread.
On a transformer 500 VA+, I use a CL-30 in series with each primary winding (115V) for inrush limiting.
For home use you can get away with small transformers, just because you typically use so little power. But this is DIY, so we do it right. I've seen something that suggested 50% derating for a capacitive input filter. So, at least a VA rating of at least twice the amp's total output is appropriate. For Class A, I'd think that you'd want at least 3x, but that's another thread.
On a transformer 500 VA+, I use a CL-30 in series with each primary winding (115V) for inrush limiting.
Last edited:
That was a long time ago, but I dug a little and didn't find the thermal strip. They claimed 69W 8R and 94W 4R at 5% distortion. It claimed to be a tube amp, not completely false there was a diode connected 12AX7 in the distortion circuit otherwise it's TL072s. For some reason a Google search for Fender Roc Pro 1000 starts off with largely favorable reviews. Then there's one that says "Run, screaming."
Leaving cheesy overrated amps behind and back to Superamps.
Leaving cheesy overrated amps behind and back to Superamps.
Well actually, I did hand twist all of the wires in this amp except the ground wires. That is because they are coming into the star ground from all over the place. Those are the white wires you see in the pics. I guess I may not have twisted them quite as tightly as you do.
I don't hear a grunt from the Tx but I just checked and the woofers do move pretty deeply on start-up.
I have used Thermistors with good results on a couple of my other amps. Maybe I'll try that here.
For the PSU, do you put the 6k8 and the 220nf in parallel with the big caps? I've normally done a CRC on my other amps but decided to just use the two cap for this amp since it sounds fine and I want to get on to something else. I should deal with the turn on thump though. I have some thermistors in the drawer. I also have one of Rods soft start circuits built up and sitting on the shelf. If the thermistors aren't satisfactory, I'll get a little TX and throw that in there.
Blessings, Terry
Please share which wires, specifically, need to be twisted together in the Superamp, if you know.
Thanks, Terry
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.