Author Topic: Mars 5-10 stereo - update  (Read 1257 times)

Offline Ampdog

Re: Mars 5-10 stereo - update
« Reply #15 on: April 07, 2019, 09:18:40 AM »
Karel,

Ah! Well done!

In the past I noticed that the 5-10 tone controls are somewhat compromised; not a true log-configuration, as is evident from your analyses. Since the input these days is likely to be from low output impedance devices (not a crystal pick-up as was then), one could decrease the tone stack values say some four-fold to make matters more practical. That would take one to 500K potentiometers plus associated components.

You are one ahead of me right now in that my flippen Spice program will not work. Thus I cannot model for different values, but will calculate with pocket calculator to find new values and contact you later, perhaps by PM so that you can put these through your simulation program first. [E.g. the response with controls set at mid-position should be a straight horizontal line, without the 6 dB deviation found by you. (though it seldom is because of making pots true logarithmic in pactice, plus the even greater difficulty of making ganged log pots to track.  Ah well ....)]           
Audio must be the only branch of engineering where lack of basics' knowledge is considered a superior form of wisdom. (Anon)

Offline fredeb

Re: Mars 5-10 stereo - update
« Reply #16 on: April 11, 2019, 02:04:27 PM »
Wow ! Lots of interesting facts . Thank you FD , Ampdog and Karel .
Check pm from me Ampdog .
...evolution is the gradual development and stratification of progressive series of wholes, stretching from the inorganic beginnings to the highest level of spiritual creation.
Jan Smuts

Offline Ampdog

Re: Mars 5-10 stereo - update
« Reply #17 on: April 12, 2019, 06:25:01 AM »
With passive tone controls the variable resistors would invariably be of the log taper type. A very preliminary estimate of whether the frequency response will be flat in pot middle position, can be made by checking whether he following relationships are true (referring to Karel's circuits on the left of the graphs):

R1 = 10 x R3
C2 = 10 x C1
C4 = 10 x C3

Unfortunately response at frequency extremities can never be mirror images. In the cut positions (control sliders at R3 and C4 ends) the response will flatten out more than at the opposite sides, i.e. 'boost' will be more than 'cut'.

Symmetrical responses are only possible in feedback circuits e.g. the well-known Baxandall circuit. The responses of channels in stereo would also track better. (Ganged linear pots track better than log ones.) Then R5 there is on the low side; it interferes with the symmetrical operation of the bass pot. It should be at least 6 times the pot value.

 
Audio must be the only branch of engineering where lack of basics' knowledge is considered a superior form of wisdom. (Anon)

Offline Ampdog

Re: Mars 5-10 stereo - update
« Reply #18 on: April 15, 2019, 11:40:13 AM »
Further to previous post:

Said 'proper' operation of tone controls of log fashion is further only so if nothing else is hung onto the circuit internally or if e.g. the load it feeds into is not high enough. (There is no end to the variations found in practice - goodness knows for what purpose or for whose hearing - lame old topic again!). Most such circuits are best fed from a low input impedance, succeeded by a high load impedance.

Just for general knowledge. And should it be necessary to point out again: At flat settings any properly configured tone control circuit has zero amplitude variation and zero phase shift in its pass band.

[Sorry to seem to always play the policeman; not my purpose. But I wish someone would for a welcome change put up and indicate precisely how tone controls affect (usually meant negatively) sound quality instead of lamely perpetuating ancient folly. The electronics are dead simple.]   
« Last Edit: April 15, 2019, 11:45:48 AM by Ampdog »
Audio must be the only branch of engineering where lack of basics' knowledge is considered a superior form of wisdom. (Anon)

Offline Mars

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Re: Mars 5-10 stereo - update
« Reply #19 on: July 06, 2019, 04:57:57 PM »
Schematic



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Offline Den123

Re: Mars 5-10 stereo - update
« Reply #20 on: July 06, 2019, 06:10:30 PM »
Hey Mars.
Nice clean and simple design. Looks great.

Offline Mars

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Re: Mars 5-10 stereo - update
« Reply #21 on: July 06, 2019, 08:44:06 PM »
Thanks to the Stern company :cool:

www.valve-radio.co.uk/literature/stern-mullard-5-10-amplifier-and-control-unit/


.... with a bit of GIMP editing. The numbering follows the original Mullard circuit... so credit is due there too!

www.r-type.org/articles/art-003e.htm
« Last Edit: July 06, 2019, 08:46:15 PM by Mars »
OEM manufacture of Tube Audio
Power and Integrated Amplifiers
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DIY Kits
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Offline fredeb

Re: Mars 5-10 stereo - update
« Reply #22 on: July 07, 2019, 09:19:03 PM »
Wow Karel ! That valve-radio.co.uk is a super interesting site . Amazing seeing all the vintage equipment .

Thank you kindly Sir .

:)
...evolution is the gradual development and stratification of progressive series of wholes, stretching from the inorganic beginnings to the highest level of spiritual creation.
Jan Smuts