1073 eq hf rolloff

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Steffen

Well-known member
Joined
Jun 3, 2004
Messages
399
Location
Germany
close to finish my 1073 knockoff but there´s one thing. that damn hf rolloff in the eq section (around 6dB down@20k!!!)

allready tried the mod from phoenixaudio

http://www.phoenixaudio.net/tipsntri.htm

but it turned out that the critical parts are the 470p (1st inverting amp) and 108p (2nd inverting amp) feedback caps (from output to input)

removing these or decreasing capvalues solves the prob...but then the circuit is not stable (oscillation at high eq boosts) ...argh


any advice? where are the neveslutz? :green:

steff
 
with the 108p and 470p removed the response is flat to over 60 kHz.

changed it to 47p and 100p and removed the basis-collector 47p cap

I must admit that oscillation happens on the unboxed pcb. will see what happens when the board is mounted in the case this afternoon (pots grounded etc.)

steff
 
fixed it....since the pcbs are mounted in the case and the pots are grounded the oscillation problem went away :thumb:

here´s my new baby - 1073/1176 combo, carnhill iron, selfmade inductors....sounds sweet ;-)

steff

comboguts.jpg
 
[quote author="radiance"]As always it looks ultra neat!
A lot of relay switching going on I see.....[/quote]


yepp...the complete input section is fully relay switched. when you go under 20dB gain the input switches automaticly from mic to line. when line input is active I use the 10468 reverse, which is also switched by relay

[quote author="radiance"]
May we see the front as well?[/quote]

sure, watch the action movie :green:


http://www.diygallery.de/forum/109_0909.AVI
 
[quote author="matthias"]why do you use so much relais??
to avoid contact problems or volume drops or to "extend" the rotary switch??[/quote]


12 good quality relays are cheaper than a 4 layer elma :shock:
I´d need 4 layer because I use the 10468 also for line in (reverse) and prim/sec must be flipped when selecting line input.
 
great work Steff
... but then we expect nothing less from the Jedi Master

sorry, but I have nothing to add to the "oscillation at high eq boosts"
tk could be right about -6dB being too much

perhaps you have two roll-off points ?
 
Wow a real beauty! :grin:

Any problems with pops from the relays?

there's another way to do the line in with the 10468, just add a -30dB pad infront of the transformer (in 1200ohm position), two serieal resistors + one over the transformer, you have to try out the serial/parallell values as you get both high / low roll offs with too high or too low loading at of the transformer input. Think I tested with two 6k8 + 1k over the transformer, the 1k was enough to get a flat response.
 
[quote author="Tekay"]Wow a real beauty! :grin:

Any problems with pops from the relays?

there's another way to do the line in with the 10468, just add a -30dB pad infront of the transformer (in 1200ohm position), two serieal resistors + one over the transformer, you have to try out the serial/parallell values as you get both high / low roll offs with too high or too low loading at of the transformer input. Think I tested with two 6k8 + 1k over the transformer, the 1k was enough to get a flat response.[/quote]

no problems with pops.

every relay got it´s own protection diode to prevent switchoff voltage spikes. non audio circuitry like relays, led meter etc... are connected via a dirty ground path to the psu to keep swichnoise and other crap away from audio ground. the switch itself is a MBB version.

...and thanx for the kind words guys....the box really roxx...I´m happy :grin:

steff
 
man, :thumb: , i love you layouts!! neat relay switch also :thumb: :thumb:

:sam: :sam: :guinness: :guinness:
 
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