Gainclone heaven ?

[Nick]

How is the power going to enter the amplifier module? Theresoes not seem to be a lot of space left on the "backpanel"?

Coen hi,

You made me smile asking this, I have two options worked out and I'm trying to decide which to go for.

Option 1 is to run an umbilical into the back of the amp module. I left space  to mount a cable gland on one side of the speaker posts. Internally i was going to run the 16 ac power lines to the rectifiers through 15mm plumbing copper tube (earthed to PE ) and under the amp modules. The issue is the possibility of ac hum from the wiring so close to the modules and the cable run is long at 1m in total from transformers to rectifiers.

Option 2 is to run the ac psu wires through the side of the PSU and amp cases just behind the front panels. To do this i would link the two cases with bolts and spacers (bolts are in the pictures). This approach gives a very short and direct  run for the ac wiring away from the modules. If i take this option was planning to insulate the fixings that join the cases, I don't want case hum being transferred from the PSU Case to the Amp case, Iv had a real problem with case and transformer induction fields in my current one box amp. The two cases will be electricly connected but only via their binding points to PE.

Option 2 is my favourite at the moment.

Nick.

[PeterSt]

Is it a most stupid idea to put the rectifiers and all in the Supply case ?

[Scroobius]

IIRC I had that conversation with Peter Daniel and he recommends the rectifiers to be next to the amps. I think it was to keep the earthing arrangement inside the amp as short and simple as possible.

I have a very similar arrangement to Nicks (just 4 amps though not balanced  -  yet!) exactly the same boxes. I have an umbilical arrangement using the back panels (and it was a pain to install). If I was doing the same again I would probably opt for option 2.

P

[Nick]

Is it a most stupid idea to put the rectifiers and all in the Supply case ?

Peter hi,

I had stayed away from putting the rectifies in with the transformers in part because of the reasons Paul gave regarding the earthing but also because of a problem I had with my current amp build.

In my current amp, the rectifier boards are close to the transformers also when I built the rectifier boards I fitted the 10µF capacitors that Peter Daniel supplies (they are optional). Well, I spotted that PauIs amp dosen't have the 10µf capacitors fitted so I snipped them out of my amp. What a difference it made to SQ, much better. I figured that the 10µF capacitors were either resonating very badly, which seems unlikely, or they were picking up hum field from the transformers. The clincher for the transformer hum theory was when I tried moving the physically large Mondorf input capacitors in my amp off of the aluminium case bottom (just placed them onto some 8mm foam) this gave a MASSIVE lift in SQ and fixed an oscillation problem when the amp was on without anything connected to the inputs.

So within reason I'm very keen to keep the transformers well isolated from the amps.

A long explanation but hopefully it may prove helpful if anyone is doing a build.

Cheers,

Nick.

EDIT I quoted the capacitor size incorrectly as 47uf above. Now changed to the correct value of 10uf.

[PeterSt]

Haha Nick. I figured that you would (no, could) come up with those 47s as they are related to the DC protection. Now, I was reluctant to say that you'd need output elcos inside the supply case while maintaining the input ones in the amp case.

But since you now bring it up this way, I thought to mention it anyway.

The proper earthing ? sure. But "as short as possible" - not sure. You can almost think like : when too long, make others more long (just create the path you want which goes over the shortest, same wire thickness assumed).

This too I didn't bring up, because I personally think you may encounter massive problems anyway. The oscillation and such.

In the (very) far end the two boxes may imply more problems than it solves. At least in my case (built by Bert and far from a PD design) I can't see things wrong, or it must be an added small third harmonic. NOS1 same story. The only thing important there as far as I can measure, is the output wires not being allowed to be close to the 230 itself (with a "sorry" for the position of the power inlet vs the outputs ). However, there *are* these compartments of course.

Influence of the internal (9 and 12V) AC ? I never saw anything from that. So to that regard it should be OK to have the AC in there.

But you have a nice o'scope, so you can trial and see !

Peter

[Scroobius]

Peter - just out of interest is your amplifier balanced?

[PeterSt]

No Paul ...

[Scroobius]

Nick - I was just perusing the Peter Daniel forum discussing SQ and found the following quote from Peter (you may have seen it but I thought I would post it anyway).

"Please note, that if you have balanced source, the bridged GC will be better than regular one, especially when it comes to dynamics and bottom end extension. But you need speakers that are at least 6 ohm.

The bi-amping is also a big advantage, and the GC will sound only as good as the rest of your system, if it sounds bad, the fault is usually somewhere else"   ;-)

Initially when you posted this I have to say I had my doubts because each GC amp will be looking at 4ohm load but seems as if it should be OK. So now I am even more interested to hear your amp in my system because I am starting to eye up my soldering iron again.

Best
Paul

[Nick]

Hi Paul,

I had seen Peters Daniels comments some time ago when I started with the bi-amp build. Peter comments do sound very promising for bridged / bi-amped though don't they.

My speakers are quite hi nominal impedance, I think at least 8 ohms and could be higher IIRC. Although bridged modules see half the nominal impedance of the speaker they do only have to deliver only half the output voltage level compared to single ended. Also because our amps are bi-amped they must be seeing higher impediance than the overall nominal speaker impedance because they drive the individual speaker drivers which will have a higher individual impedance than the speaker overall.

My main concern is driving so many modules ("8") directly from the NOS1 outputs. In theory the loading of the bridged design per NOS1 output op amp phase should be the same as our current bi-amped builds. I guess that question will have to wait for listening tests.

I have made some progress with the amp, I took the option to join the two cases to route the transformer secondary’s to the rectifiers (option 2 above) and it looks very nice and neat. Next step is wiring up individual modules to pair them into low DC output offset pairs and then start final the wiring up. I think it may take quite a while to wire up but I am keen to take my time and get it nicely done. Have to say I am REALLY interested to hear the end result.

Cheers,

Nick.

Edit fix unwanted smiley

[Scroobius]

Nick - What spec of transformers did you order in the end? rating? any ES screen? any special windings?

Paul

[Nick]

Nick - What spec of transformers did you order in the end? rating? any ES screen? any special windings?

Paul

Hi Paul

They are 625 va AirLinks with 4 x 22 v secondaries. They were custom wound, as you know standard they have 2 secondaries. I did not bother with the primary secondary shield or GOSS emi shield options, your AirLinks seem to work rather well without these options . The price for the custom wind was close to the standard 625 va with 2 secondaries.

Cheers,

Nick.

[Nick]

Hi I spent 18 hours wiring up the Mk II Bi-amped bridged gainclone amp this weekend, I was determined to get it finished.

IT LIVES ! 

 

I'll post some pictures of the build the finished amp together with thoughts about sound quality soon, but for now first imprisons are VERY good,, a game changer, and that is with just a couple of hours ruining in. Definitely worth all effort.

Time to sit down with a glass of wine and listen to some music   

Nick,

[PeterSt]

Looks like a drawing. So beautiful Nick ...

[Nick]

Looks like a drawing. So beautifil Nick ...

Thanks Peter,

It ended up looking a bit more "complex" when the input caps went into the centre between the amp modules, but the sound is in another league which has made the effort worth it  .

Nick.

[Scroobius]

Nick - your amp is looking very nice!. So much so I have succumbed to temptation and have started ordering parts to build one myself!!. I probably have enough parts here to convert my existing amp into balanced mode (except transformers of course) but that would mean an unacceptable period of time without music. Also I think I have a buyer for the existing amp. so I should recover costs.

The layout will be slightly different (I just need to double check I can do it though) and I will be using Blackgate NX decoupling caps as I am using at the moment.

Looking forward to dusting off my soldering iron. 

Do you find the balanced amp generates significantly more heat?

Happy days!!

Paul