Colin's gm70 Boat Anchor monoblocs

Toppsy · Post by **Toppsy** » Tue Jul 24, 2007 1:28 pm

Thought I'd start a new thread in the appropriate place for this DIY amp project.
I have managed to find a way of compressing the pic file size and below is a shot of the assembled amp before the copper plate gets chromed and with no internal components.

Hurrah! it worked and I thought I would have to be a member for at least a week and made 10-odd posting before I could post links.

More pics to follow.

For those interested the graphics on the front are home made water slide transfers copied on a laser copier with special transfer paper bought at my local stationary shop. I'll post details if anyone is interested.

Toppsy · Post by **Toppsy** » Tue Jul 24, 2007 1:40 pm

More pics.

Toppsy · Post by **Toppsy** » Tue Jul 24, 2007 1:44 pm

The final onslaught of pics just to bore you all fully!

Cressy Snr · Post by **Cressy Snr** » Tue Jul 24, 2007 3:00 pm

Now that's what I call nice.

Steve

Toppsy · Post by **Toppsy** » Tue Jul 24, 2007 4:06 pm

Thanks Steve.

I think you have done a very nice job of your OTL amp. Your build skills are definitely improving with each amp you make.

The original intention of this gm70 amp was to build it OTL as suggested by the designer of my electrostatic speakers. "Why have a step down output TX only to step it up with the audio TX of the speaker" so he says. However, Nick had technical design issues with this approach so we went for a conventional output TX. I'm sure Nick can enlighten?

Regards

Colin

Clive · Post by **Clive** » Tue Jul 24, 2007 4:27 pm

Magnificent job! I feel utterly inadequate.

Clive

Darren · Post by **Darren** » Tue Jul 24, 2007 5:07 pm

Wow, wow and wow.....!!!

They do you proud..I must say.

On the transfers, would a laser printer work just as well?

Post by **Nick** » Tue Jul 24, 2007 5:22 pm

The original intention of this gm70 amp was to build it OTL as suggested by the designer of my electrostatic speakers. "Why have a step down output TX only to step it up with the audio TX of the speaker" so he says. However, Nick had technical design issues with this approach so we went for a conventional output TX. I'm sure Nick can enlighten?

Well, it wasn't ever OTL, what we did consider is replacing the output TX stop down and ELS input TX step up with one single step up (but not so much).

I hold my hand up, I was put off the idea by Dave Slagle who argued that it was actually better to have the two TX's. Also it would have made it impossible for me to test and design at home, as I don't have any statics.

There is no design reason why you couldn't try a stepup TX Colin, the GM70 needs to see about 7k load and its swinging about 600v RMS on the primary at full power.

One thing that would put me off the idea, is you would have to have HV connections from the amp to the speaker, and I wonder just how any capacitance on that connection would hit the output stage hard.

ed · Post by ed » Tue Jul 24, 2007 6:16 pm

amp looks awesome in those pics Colin.......bien jouer!!!
I feel a pang of envy coming on, I'll either have to go and write myself a blues song or go and buy a porsche..

what's next??

Ed

Paul Barker · Post by **Paul Barker** » Tue Jul 24, 2007 8:04 pm

I couldn't have made it any better!

Darren · Post by **Darren** » Tue Jul 24, 2007 8:17 pm

Paul Barker wrote:I couldn't have made it any better!

Really??

Andrew · Post by **Andrew** » Tue Jul 24, 2007 8:24 pm

Hi Colin,

Very smart!

Where did you get the shrouds, if you don't mind me asking?

cheers,

-- Andrew

Paul Barker · Post by **Paul Barker** » Tue Jul 24, 2007 8:48 pm

What are you saying about my building Darren? I'm offended

Toppsy · Post by **Toppsy** » Tue Jul 24, 2007 8:54 pm

Thanks for the gracious feedback guys but really the end result is all down to Nick's design. It is a really stunning sounding amp hooked up to my ESL's. The layout really lends itself around the potted TX's and we just fitted the tubes around this. My mate from work gave me two sheets of copper that just happened to be the right size when we started laying out my little cardboard mockups of the TX's.

Nick,

don't think I'll tread the path the suggest. I too have grave concerns the HV connections to the speakers and the amp as it is can be used for any low efficiency speaker rather than just being specific to ESL's.

Darren,

the graphics material is called LAZERTRAN and is for Lazer colour copiers. I think they do similar for printers both inkjet and laser, I'm sure this stuff is ideal for Steve (theshaddow) to add some colour graphics to his OTL amp?

Ed,

you'll have to post us all a download version of the blues song, but then a drive in the Porche, now your talking.

I'm off to the chrome platers tomorrow and then it's on with the internal hook up. Hopefully, with the aid of Nick it should be up and running in a couple of weeks. And to think I've just got new neighbours!! Dam.

Andrew,

by the shrouds do you mean the cases for the TX's? If so all the TX's and chokes were ordered ready potted from AE Europe. Nick has very good relationship with this company. Just do a google search for AE Europe.

Must sign off my son is lurking to get on the PC.

Colin

Dave the bass · Post by **Dave the bass** » Tue Jul 24, 2007 8:58 pm

Phwooaarr!

That looks nice Colin.

(Much nicer than Steves shoddy ol' bits of wood

)

I'm 'orrible I know.

DTB

audio-talk

Colin's gm70 Boat Anchor monoblocs

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