Author Topic: Mars 5-10 stereo - update  (Read 14098 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



Parts list:



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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 »
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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

Offline Mars

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Re: Mars 5-10 stereo - update
« Reply #23 on: October 07, 2019, 06:47:52 AM »
Hi All,

I checked with admin, and got an OK to post an update on the kit on the Valves page.

I have a client building a Mars 5-10 preamp and a power amplifier combo on separate chassis. The amplifier is as above, but the pre-amplifier departs from Mullard design. More details later. Here is some photos of the build:

Raw chassis from engineers:



Customer spay job:



Tube layout:



Transformers mounted:

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Offline fredeb

Re: Mars 5-10 stereo - update
« Reply #24 on: October 07, 2019, 11:26:25 PM »
Looks Kool Karel . I like the Hammerite finish . The gold on the transformers look a bit gaudy , perhaps a layer of thinned bitumen would knock it back slightly ?

Interesting layout , looks good and will show off all the valves well , looks logical for wiring too .

It's difficult to read the purple text , but from what I can make out :

1. EZ81 rectifier
2. EF86 input voltage gain
3. ECC83 driver
4. EL84 PP output

Well ... I guess that is what a 5 10 is .   :giggle:

Interested to hear about the pre you're planning .
...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 Mars

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Re: Mars 5-10 stereo - update
« Reply #25 on: October 18, 2019, 08:42:28 AM »
Next is the pre-amplifier design. My favourite dual pots (ALPS 27) only goes up to 500K audio taper, so I am sticking to tone controls designs that uses 500kA or lower.

Cruising over to an excellent site ( http://www.angelfire.com/electronic/funwithtubes/Amp-Tone-A.html ) I chose this design:



Note that the output termination resistance is 500k ohm, so a triode directly after the tone controls are needed.

The next limitation (if you can call it that) is the volume control. I tend to use 100kA pots for attenuation. This is mostly for the direct input line level signals ( the volume pot is usually after the selector switch).

In this case we are looking at this signal flow:

source -> selector -> triode -> tone controls -> triode -> volume pot -> output to power amplifier.

Depending how we design the second triode circuit, we can use lower value pots if we want to. For this design I am sticking to a 12AU7 dual triode to lower the output impedance of the tone control circuit.

Did I miss anything? Does anybody have qualms about a volume pot directly on a preamplifier output?



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Offline Mars

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Re: Mars 5-10 stereo - update
« Reply #26 on: October 18, 2019, 09:15:46 AM »
proposed tone control and output configuration:

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Offline El Sid

Re: Mars 5-10 stereo - update
« Reply #27 on: October 18, 2019, 05:52:05 PM »
Thanks Karel! I was about to scratch around for some tone circuit ideas for my guitar amp (too dumb/lazy to work it out for myself) so you have saved me some PT

Offline handsome

Re: Mars 5-10 stereo - update
« Reply #28 on: October 18, 2019, 07:06:53 PM »
Volume pot on the output means variable and potentially very high output resistance (25K max in this case). You ideally want a low output impedance to avoid high frequency roll off from cable capacitance and your power amp input capacitance. Why not just use the Alps 500K pot as the output of your tone control? That way your ECC82 will give you a steady ~10k output impedance Its still too high for a modern preamp, you ideally want less than 1k....

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Offline El Sid

Re: Mars 5-10 stereo - update
« Reply #29 on: October 18, 2019, 08:06:34 PM »
Volume pot on the output means variable and potentially very high output resistance (25K max in this case). You ideally want a low output impedance to avoid high frequency roll off from cable capacitance and your power amp input capacitance. Why not just use the Alps 500K pot as the output of your tone control? That way your ECC82 will give you a steady ~10k output impedance Its still too high for a modern preamp, you ideally want less than 1k....

Sent from my SM-A750F using Tapatalk

I.e. replace the 470k resistor with the Alps pot?