845 Monoblocks,

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JohnG
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845 Monoblocks,

Post by JohnG » Wed Jun 27, 2018 7:30 pm

Keeping this new thread in context, as a follow up reply to my statement on the Owston thread, claiming the Slagle AVC was not delivering the same Bass Quality, equivalent to the Bass being produced when the 845 amp is being driven by the source, and the inbuilt balance controls on the amps are used to adjust volume.

Nick asked
"What's the input impedance of the 845 amp" ?

I have spoke to the engineer, he has told me it is 50K input impedance, I think he also said the output resistance and input impedance are a match, giving me a brief description on how to measure the output resistance using a multimetre.

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Nick
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Re: 845 Monoblocks,

Post by Nick » Wed Jun 27, 2018 8:05 pm

Ok, just wanted to check it wasn't too low for the AVC's, but 50k is fine.

I would be interested to know how you can measure the output impedance of the AVC's with a multimeter. Apart from anything else, the output impedance will depend on the impedance of the source and the volume setting.
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Re: 845 Monoblocks,

Post by IslandPink » Wed Jun 27, 2018 8:25 pm

Well if the conversation included having a signal generator to drive the pre-amp , then one could imagine ( as you would ) that two alternative loads ( eg. 1M and 20k ) could be put on the secondary and the multimeter used to measure voltage.
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Re: 845 Monoblocks,

Post by Nick » Wed Jun 27, 2018 8:29 pm

IslandPink wrote:
Wed Jun 27, 2018 8:25 pm
Well if the conversation included having a signal generator to drive the pre-amp , then one could imagine ( as you would ) that two alternative loads ( eg. 1M and 20k ) could be put on the secondary and the multimeter used to measure voltage.

Yes, but that would only measure the output impedance when driven by the signal generator. You would have to perform the operation with the actual source.
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Re: 845 Monoblocks,

Post by JohnG » Wed Jun 27, 2018 8:50 pm

There is a mix up into the device the engineer discussed with me.
We only spoke about the 845's , there was not a discussion about the methods of measuring the AVC.
As I said, I "think" the output resistance and Input impedance on the 845's are a match, a explanation of how to measure the output resistance using a multimetre was offered. I was told to expect a reading of 47-50K. The instruction to achieve this reading on a multimetre was not understood by myself.
In the short term, I can keep it simple, I'll bring the AVC as well to Owston, and a listen will confirm my assessment, as being accurate or not.

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Re: 845 Monoblocks,

Post by IslandPink » Wed Jun 27, 2018 9:55 pm

Nick wrote:
Wed Jun 27, 2018 8:29 pm
Yes, but that would only measure the output impedance when driven by the signal generator. You would have to perform the operation with the actual source.
Umm... maybe I should have made it clearer that the sig gen would feed in its signal before the final stage driving the AVC.
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Re: 845 Monoblocks,

Post by pre65 » Mon Jul 09, 2018 4:01 pm

Are there any photos of these 845 amps ?
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Re: 845 Monoblocks,

Post by JohnG » Mon Jul 09, 2018 8:47 pm

Had a play in a few editing softwares, I got there with the correct sized attachment.

The 845's taking their first steps in the Big, Wide, World. Ahh ar'nt they cute.
845's-Day-One-AT-Forum.jpg

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Re: 845 Monoblocks,

Post by IslandPink » Mon Jul 09, 2018 9:07 pm

They mean business !
Can we get a close-up ?
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Re: 845 Monoblocks,

Post by JohnG » Mon Jul 09, 2018 10:44 pm

Best I can do tonight
845-Mono-AT-2.jpg

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Re: 845 Monoblocks,

Post by Cressy Snr » Mon Jul 09, 2018 10:48 pm

They were rather good at Owston. :)
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Re: 845 Monoblocks,

Post by simon » Tue Jul 10, 2018 6:26 am

Photos of the insides please :-)

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Re: 845 Monoblocks,

Post by JohnG » Tue Jul 10, 2018 7:25 pm

Got to respect the designer on that one. He has used his own circuits, and some are not in use in any other amp.
He assured me if anything happens to him, all the design notes and schematics are mine.

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Re: 845 Monoblocks,

Post by ed » Tue Jul 10, 2018 8:06 pm

what's it got in it's pocketses.....
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Re: 845 Monoblocks,

Post by simon » Wed Jul 11, 2018 4:55 am

Fair enough John. Not much new in the valve world though.

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