[QuadList] Merlin vs stock Ampex

[Don Norwood]

Hi Park:

I agree that the EE mode is what you need for this test.  Just wanted to be 
sure of what we were looking at.

I'm guessing that the sweep is 6 MHz with 3.58 being the short marker.  That 
would make the response seem appropriate.  1343 is somewhat overpeaked which 
could enhance detail at the expense of s/n.  It also exhibits some rather 
serious ringing, possibly as a result of the excessive high frequency.  1325 
does not have the ringing and appears to be a "normal" response.

Several things come to mind.  I'm still curious about the amplitude of the 
signal between 5 and 6 Mhz shown in 1343.  That's why I wondered about the 
signal coming out of demod.  Do the demod outputs of the two machines look 
the same?  That's the only way to be sure that you are comparing apples to 
apples with the rest of the processing.

There may not be a way to get color burst on the sweep signal.  Some 
generators will, some won't.  But if it won't, then it would be important to 
go back to the multiburst signal (which I would now guess is also 6 MHz) and 
look at both machines with color burst present on both.  This is important 
due to the way that the TBC processes the chroma information, so we're not 
comparing apples to apples unless both machines have color burst present 
(and the demods are equal).

Don


----- Original Message ----- 
From: "C. Park Seward" <park at videopark.com>
To: "Quad List" <quadlist at quadvideotapegroup.com>
Sent: Tuesday, December 22, 2009 7:52 PM
Subject: Re: [QuadList] Merlin vs stock Ampex


Hi Don,

I was looking to compare just the electronic section so the pictures were 
made in EE so as not to influence the result with tape and head issues.

Both machines have the "good" 4.5 MHz filter.

I don't know the frequencies of the packets but here is a sweep. It has no 
burst.


Best,
Park

C. Park Seward
Visit us: http://www.videopark.com



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On Dec 22, 2009, at 4:21 PM, Don Norwood wrote:

> Hi Park:
>
> More questions than answers....  What are the frequencies of the mutiburst 
> packets?  Also, how are the measurements made (EE or playback)?  For some 
> reason, 1328 has no color burst, so I'm not sure if the waveform is 
> "valid" to compare to 1340.
>
> The performance of the 1200 is related to which filter is installed in the 
> signal system.  The best is 4.5 MHz, and the response should be virtually 
> flat to that point.  Based on that, I'm guessing that this is not a 
> "standard" multiburst with the top packet at 4.2 MHz.  But if the packets 
> are higher frequencies, how are the higher frequencies getting past the 
> filter?  A more revealing test is to use a 5 MHz sweep instead of 
> multiburst.  In any event, for comparison, both machines need to have the 
> same filters.
>
> Then you get into what part of the system is doing what.  It's good to 
> look at the output of the demods to be sure that they are both correct and 
> identical, and then compare it to the output of the machine.  That way you 
> establish whether differences are in the signal system or in the 
> processing.
>
> Don
>
> ----- Original Message ----- From: "C. Park Seward"
> Subject: [QuadList] Merlin vs stock Ampex
>
>
>> Here are some pics I took of the two machines. Same test signals, same 
>> scope.
>>
>> Can you guess which one is which?
>>
>>
>
>
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