GAIN Mic Pre / Makeup Amp Kit
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GAIN Build Thread
GAIN Build Thread
Gain PCB is a gain makeup up amp using a single DOA opamp and output transformer or DIP8 dual opamp for electronic balanced out.
Gain PCB runs on a single +V power rail and makes the opamp run in a vintage 1/2v rail configuration.
Example if running a 2520 opamp on +/-16v = 32vdc total. Set the 10k trimpot for 32v from the BD681 reg at +V opamp socket.
GAIN PCB is a cut-down version of our BA Mic pre PCB leaving off the 48v, pad, phase switches and input transformer
Gain PCB is a gain makeup up amp using a single DOA opamp and output transformer or DIP8 dual opamp for electronic balanced out.
Gain PCB runs on a single +V power rail and makes the opamp run in a vintage 1/2v rail configuration.
Example if running a 2520 opamp on +/-16v = 32vdc total. Set the 10k trimpot for 32v from the BD681 reg at +V opamp socket.
GAIN PCB is a cut-down version of our BA Mic pre PCB leaving off the 48v, pad, phase switches and input transformer
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Re: GAIN Mic Pre / Makeup Amp Kit
33R which drives the output transformer.fragletrollet wrote: ↑Sun Oct 31, 2021 6:12 amHello!
See just started above Build thread with schematic above
Any schematic for this one? Is it the RGain or 33R resistor that's supposed to be 1/2w?
Yes correctValue of CL and CZ? Are RZobel resistor only needed if using an input transformer?
As this board makes a bipolar supply from a 48V source, can I just solder wires to the opamp power pins as to further use the bipolar supply for other boards?
No not easily as it is setup like a vintage gain amp to run on a single +V. Use our Dingo kit or PCB if you want to run on +/-V
Yes but with that high impedance you have to watch the output offset of the opamp due to the input transistor current. I don't know of any passive eq that needs that high impedance as they were all made low impedance to keep noise low.Planning to use as makeup gain for some passive pultec boards. They need a high impedance load (at least 470k) and apprx 20-23 db gain. Is the RLoad where I would place my 470k?
Either 5k or 10k will fine.Just install a trimmer for RGain to trim for unity? Recommended value, 5-10k?
Joe
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Re: GAIN Mic Pre / Makeup Amp Kit
Thanks for the feedback.
I have various passive EQ's from Ian @ customtubeconsoles (Helios & Pultec), which are re-designs based on the named units. 470K input impedance is specified in all the gain makeup amps, although differing in how much gain they need. So you're saying other/the original passive designs use low impedance for the makeup amp input? I'm pretty confident in Ian's design choices in regards to these circuits, so a little surprised
Is the JLM Gain pcb running on a reference of 24V, for +/- 24V = 0-48V? So it works fine cascading more Gain pcb's but if you want to add a board that uses the conventional +/- 24V (-24v/0v/24V) this can't be done as the reference is shifted between the two?
I want to add a simplified passive eq (say just two bands, high and low shelf) to my new tube compressor build, and was hoping to add a m/s board using THAT chips, all running from a SMPS instead of a toroid. So I guess I'll have to use a bipolar SMPS like this in addition to the 48V SMPS I allready have installed in anticipation of the GAIN pcb's.
So, how do I "watch the output offset" and make sure it works nicely with such a high input impedance?
And, BOTH 33R resistors should be 1/2W then I presume, both being opamp outputs? The marking on the pcb is a little confusing.
Thanks again and all the best,
Magz
I have various passive EQ's from Ian @ customtubeconsoles (Helios & Pultec), which are re-designs based on the named units. 470K input impedance is specified in all the gain makeup amps, although differing in how much gain they need. So you're saying other/the original passive designs use low impedance for the makeup amp input? I'm pretty confident in Ian's design choices in regards to these circuits, so a little surprised
Is the JLM Gain pcb running on a reference of 24V, for +/- 24V = 0-48V? So it works fine cascading more Gain pcb's but if you want to add a board that uses the conventional +/- 24V (-24v/0v/24V) this can't be done as the reference is shifted between the two?
I want to add a simplified passive eq (say just two bands, high and low shelf) to my new tube compressor build, and was hoping to add a m/s board using THAT chips, all running from a SMPS instead of a toroid. So I guess I'll have to use a bipolar SMPS like this in addition to the 48V SMPS I allready have installed in anticipation of the GAIN pcb's.
So, how do I "watch the output offset" and make sure it works nicely with such a high input impedance?
And, BOTH 33R resistors should be 1/2W then I presume, both being opamp outputs? The marking on the pcb is a little confusing.
Thanks again and all the best,
Magz
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Re: GAIN Mic Pre / Makeup Amp Kit
Pultec EQ are actually fairly low output impedance which usually feeds an audio transformer before the high input impedance of the tube. But since you give me no schematic to go on I cannot advise as I do not know if you are including this transformer or not or which circuit we are actually talking about. But you can make RLoad 470k and see if the output of the opamp you choose to use is sitting at 22v to 26vdc as then it is fine. But most bipolar input opamps draw input current so the higher Rload the most the offset from center on output. If there is a transformer and it is floating secondary into the gain then don't use a blocking cap Cdc and the resistance of 470K will mean nothing as the transformer winding resistance becomes the actual input resistance and little if any offset will happen. Or use a fet input opamp so it has a similar input impedance with no current like a tube.fragletrollet wrote: ↑Thu Nov 04, 2021 4:22 pmThanks for the feedback.
I have various passive EQ's from Ian @ customtubeconsoles (Helios & Pultec), which are re-designs based on the named units. 470K input impedance is specified in all the gain makeup amps, although differing in how much gain they need. So you're saying other/the original passive designs use low impedance for the makeup amp input? I'm pretty confident in Ian's design choices in regards to these circuits, so a little surprised
Yes. If you want to do the same as the gain but with +/-V rails then use our dINgO kit which is the same but runs on +/-V.Is the JLM Gain pcb running on a reference of 24V, for +/- 24V = 0-48V? So it works fine cascading more Gain pcb's but if you want to add a board that uses the conventional +/- 24V (-24v/0v/24V) this can't be done as the reference is shifted between the two?
I Have run many THatcorp the same way as the GAIN you just have to understand and design for -V to be 0v instead.I want to add a simplified passive eq (say just two bands, high and low shelf) to my new tube compressor build, and was hoping to add a m/s board using THAT chips, all running from a SMPS instead of a toroid. So I guess I'll have to use a bipolar SMPS like this in addition to the 48V SMPS I allready have installed in anticipation of the GAIN pcb's.
See above in this replySo, how do I "watch the output offset" and make sure it works nicely with such a high input impedance?
The other 33R is only if you use a dual DIP8 opamp so running electronic balanced out so both 33R can be anything as they will not see a low impedance output transformer primary.And, Both 33R resistors should be 1/2W then I presume, both being opamp outputs? The marking on the pcb is a little confusing.
It is always easier to email me a rough overall schematic first so I can advice the best way to go about making it work as I can always simply most designs and save money for you.
Joe
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Re: GAIN Mic Pre / Makeup Amp Kit
Hi - Looking similar application with passive EQ makeup gain.
A little confused--
RGain - fixed resistor setting the max gain from DOA?
GAIN - 10k Rev log applied to control/trim the gain.
Do I need to have a resistor value inserted into "RGain" if I just hook up the the C10K pot to "Gain" and that is my Gain control?
Thanks,,, wanted to figure this out -- components en route.
Joe
A little confused--
RGain - fixed resistor setting the max gain from DOA?
GAIN - 10k Rev log applied to control/trim the gain.
Do I need to have a resistor value inserted into "RGain" if I just hook up the the C10K pot to "Gain" and that is my Gain control?
Thanks,,, wanted to figure this out -- components en route.
Joe
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Re: GAIN Mic Pre / Makeup Amp Kit
Yes Rgain is in series with the 10k rev log pot or trimpot and just stops the gain pot when it is shorted, putting the opamp into infinite gain which can be bad for it. You can just fit the RGain resistor and short the gain pot terminals together to give the correct set gain for a set makeup passive EQ ampJOETONE wrote: ↑Fri Jan 27, 2023 9:30 amHi - Looking similar application with passive EQ makeup gain.
A little confused--
RGain - fixed resistor setting the max gain from DOA?
GAIN - 10k Rev log applied to control/trim the gain.
Do I need to have a resistor value inserted into "RGain" if I just hook up the the C10K pot to "Gain" and that is my Gain control?
Thanks,,, wanted to figure this out -- components en route.
Joe
Joe
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Re: GAIN Mic Pre / Makeup Amp Kit
Thanks!
Does IC1 need to be fitted at all if using unbalanced out?
Which 33R & 47pF are not needed if unbalanced out?
The ones closer to IN/OUT
or
The ones closer to GAIN/POWER
Joe
Does IC1 need to be fitted at all if using unbalanced out?
Which 33R & 47pF are not needed if unbalanced out?
The ones closer to IN/OUT
or
The ones closer to GAIN/POWER
Joe
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Re: GAIN Mic Pre / Makeup Amp Kit
JLM Twenty Five Twenty can run on this PCB +/-24, correct?
Just Link C to E?
I assume the 2520 note for the DOA 32v +/-16 rails for this PCB is just for Api-Originals, right?
Just Link C to E?
I assume the 2520 note for the DOA 32v +/-16 rails for this PCB is just for Api-Originals, right?
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Re: GAIN Mic Pre / Makeup Amp Kit
Yes
Yes you can but if you want soft start and extra regulation just fit BD681 and turn trim pot up to full to get about 46v (+/-23v)Just Link C to E?
For most 2520 and clones. Not for our Twenty 5 TwentyI assume the 2520 note for the DOA 32v +/-16 rails for this PCB is just for Api-Originals, right?
Joe
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Re: GAIN Mic Pre / Makeup Amp Kit
Yes, you need IC1 always either a DIP8 or DOA is needed for the GAIN to work.
The ones closer to GAIN/POWERWhich 33R & 47pF are not needed if unbalanced out?
Joe
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Re: GAIN Mic Pre / Makeup Amp Kit
Struggling a bit with this PCB but I know I'm close.
I have the Gain PCB voltage set to DOA @ 22vdc
1k resistor in RGAIN
10k rev log pot: GAIN to wiper, 0v to outer lug
So, with no DOA inserted I read from the DOA PCB pins: +V=22vdc, 1/2=11vdc, Out=10.29vdc?
This correct?
It'll pass audio with the DOA inserted, but not getting any boost in gain/level...
I have the Gain PCB voltage set to DOA @ 22vdc
1k resistor in RGAIN
10k rev log pot: GAIN to wiper, 0v to outer lug
So, with no DOA inserted I read from the DOA PCB pins: +V=22vdc, 1/2=11vdc, Out=10.29vdc?
This correct?
It'll pass audio with the DOA inserted, but not getting any boost in gain/level...
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Re: GAIN Mic Pre / Makeup Amp Kit
But yes with 22v you should have roughly half that at the output of the opamp if running ok. With gain pot shorted and 1k R Gaiin you should have a gain of 11. What DOA are you using that needs so low a voltage of +/-11v = 22v?JOETONE wrote: ↑Mon Mar 13, 2023 2:18 amStruggling a bit with this PCB but I know I'm close.
I have the Gain PCB voltage set to DOA @ 22vdc
1k resistor in RGAIN
10k rev log pot: GAIN to wiper, 0v to outer lug
So, with no DOA inserted I read from the DOA PCB pins: +V=22vdc, 1/2=11vdc, Out=10.29vdc?
This correct?
It'll pass audio with the DOA inserted, but not getting any boost in gain/level...
Can you send me a couple of photos to check over?
Joe
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Re: GAIN Mic Pre / Makeup Amp Kit
Ok, Should V+ be the total voltage? I set to 22v, should that be 44v to get +/- 22 to the DOA? -- the DOA is your Flick.
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Re: GAIN Mic Pre / Makeup Amp Kit
Yes for the flick if running on a 48v regulated rail just turn the trim pot fully up to get about 46v = +/-23v for Flick.
Did you solve the no gain problem?
Joe
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Re: GAIN Mic Pre / Makeup Amp Kit
Still not getting Gain, but voltage readings V+, 1/2V, 0V, Out now look correct.
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