OP Amp EQ circuit for Tube Amp

[silverfox]

Not sure if this should go here or elsewhere?

I want to adapt the Channel Input,  EQ, Send-Return and Output circuits from a mixer into a tube power amp build I've completed, (based on the Sunn S100). The EQ circuit already works but is built into the mixer in question. I've got a schematic I'll post as soon as I choose between Stereo or Line/Mic input. Definitely could use help with this but not sure where to post. Here or SS. I'll attach a schematic of the channel in question as soon as I decide which channel to use. (I've been using the Line/Mic input but just realized, after having owned the mixer for a couple years), the two channels in question have different EQ's structures so I'll take a listen to the Stereo EQ portion and decide and post after the 1st.

The EQ circuits are based on OP Amps but already designed. Just need to hack the circuit for a tube amp application.

silverfox.

[PRR]

The main problem putting opamps in tube amps is now you need MORE power supplies. You already have your 6VAC, your 400VDC, maybe your -35VDC bias. Opamps don't readily eat any of these.

A bazillion recent-decades tube amps DO mix opamps in. But this usually leads to a custom PT with extra windings, something hard to find alone. The hack is to add maybe a 40VAC CT transformer (MORE iron to buy and mount!!) for the opampery.

[silverfox]

Thanks PRR, that is the first challenge I encountered. I took the existing mixer apart last night to examine the details and try to find a part number on a transistor. Surface mount and the numbers were so small my daughter couldn't even read them with a magnifying glass. The mixer has a nice little switching PS inside but I'm not ready to scavenge it. The alternative is perhaps a Pultec  style EQ. Just went out to check the spelling and wow! $1600 for a kit of MOJO. http://www.pulteceqp1a.com/

I'll have to spend a few more days looking into some options. I have a few tube based EQ circuits around but that leads to the other side of the equation which is, a boatload of tubes. Hmmm.

regards,

silverfox.

[kagliostro]

Some time ago at DIYItalia was developed this gyrator version of the Equalizer installed on Mesa amp (don't remember the model, it was long  time ago)


http://www.diyitalia.eu/download/file.php?id=8763


http://www.diyitalia.eu/download/file.php?id=8762


I hope this is the last correct/right version


Franco

[jjasilli]

Actually, I think you're in the area of rack mounted gear.  Note that the Mojo mic preamp you cited is a rack mount design.  The guitar amp could be part of the rack or not.  If you want a combo cab, the cab could be designed with rack space(s) at the top, to house speaker(s), amp, & rack gear.


Also, you may be able to get some or all of what you want with an FX loop in the amp.

[PRR]

If you are beyond basic guitar-amp tone controls, need specific EQ, go get a BOSS GE-7(?) graphic EQ pedal, done.

Many things are possible, I could put a hot-tub in the back of my plow-truck; but weeks of welding and caulking may not be the best use of my time; researching and assembling some nice-sound EQ may not be best use of yours. In my career, there *were* a few EQs that I really liked, but even when using less-lovable EQs I could usually get it to sound good enough to get paid.

[silverfox]

After 3 or 4 days, can't remember now cause I'm mind boggled from information overload, after studying Op Amp EQ's and Compressor circuits for hours on end I've reached the conclusion that: ..."may not be the best use of my time; researching and assembling some nice-sound(ing) EQ may not be best use of yours";  as previously stated by PRR. The mixer boards I have are doing nicely. I also have a Compressor that works well.

Now for this- I have a Studiomaster Diamond series mixer that sounds okay but does have a little bit of muddle to the control settings when the LO frequencies are employed a little beyond mid settings. The same for the HI's but they sound tinny. In looking at the Op Amps used, from about 1992 I wonder if changing them out might fix the problem. What's really nice about this mixer being so old, it was prior to surface mount so all the parts are easy to replace and get a value off the surface of. I considered replacing the BA4560 with a Texas Instruments version 4580. Looking at the Data Sheets they both look very similar although the off set voltage is slightly different and I wonder if that wouldn't require some resistor change...

BA4560 Data Sheet: http://elcodis.com/parts/1316842/BA4560.html#datasheet

TI 4580 Data Sheet: http://elcodis.com/parts/1319941/RC4580IDR.html

Thanks for all the advice. I guess I won't be "Going around the Horn" after all... Notice also, I may be changing my font size purely for my own benefit as the smaller default size is too small for me.

Regards,

silverfox.

[HotBluePlates]

Now for this- I have a Studiomaster Diamond series mixer that sounds okay but does have a little bit of muddle to the control settings when the LO frequencies are employed a little beyond mid settings. The same for the HI's but they sound tinny.

The Low frequency pot is at 80-100Hz depending on the model (Low E is at 82Hz), so yes it will sound muddy. High frequency pot is at 12kHz (and guitar speakers drop off sharply after ~6kHz), so yes turning that up will sound brittle.

EQ center frequencies from Studiomaster's site, though they don't list specs for the Diamond series anymore.

If you're plugging your guitar directly into this, then the sound is what it is. It is inflexible and suited to EQ of several sound sources to get them out of them out of the way of each other. It is not suited to shaping/creating a guitar's sound. Changing opamps won't change that because the parts around the opamp are what fix the frequency band to be altered.

[silverfox]

Ah, that explains that. I have a Behringer mixer that sounds better due to the compressor and the Mid Shift but it's newer and the slider controls are already wearing out. Haven't tried to spray them yet.

Thanks for the explanation.

silverfox.

[HotBluePlates]

You still haven't said Yes/No about whether you're plugging direct into this mixer and using it in lieu of a guitar amp/preamp.

If you are, using a simple EQ pedal might be a good idea to give you flexible EQ options for your guitar. Some forum members have talked about an inexpensive EQ pedal in this thread.

And while I don't always use it, I have a ParaEQ pedal with radically-more flexibility than the fixed-frequency EQ in your Soundcraft (and probably Behringer) mixer. It offers the same parametric EQ capability of all but the most-capable mixers/consoles or outboard EQ's.

[silverfox]

From the top: "I want to adapt the Channel Input,  EQ, Send-Return and Output circuits from a mixer into a tube power amp build I've completed, (based on the Sunn S100). The EQ circuit already works but is built into the mixer in question."

I'm using an Amp Emulator for the preamp section, (AdrenaLinn III). This raises a question that I'll get to. At any rate, I may soon be building the preamp section. So far I've settled on this design for the power amp and really like it. I still have to change a couple values in the schematic as I'm running 6L6 in the output section, 1/2 of a 12AX7 as the PA driver and using the bias circuit Sluckey employed on his Sunn rebuild so this schematic is close but not exact.

The question I've had for some time now relates to the improved sound I get whenever I patch a mixer into the effects loop. I don't understand what it is about either the standard Marshall tone stack or for that matter the EQ built into the Amp Emulator that can't be made to sound as good as adding the mixer. When I add the mixer the sound gets that changy ringing distortion and it seems to be the final touch needed to eliminate any trace of digital sound. At least to my ears. I suspect the mixer signal is over driving the EF806 better than the Emulator.

So that's what I've got going on at this particular point in time.

regards,

silverfox.

[HotBluePlates]

From the top: "I want to adapt the Channel Input,  EQ, Send-Return and Output circuits from a mixer into a tube power amp build I've completed, (based on the Sunn S100). The EQ circuit already works but is built into the mixer in question."

Yep, I recall that. It seems clear to you because you already know you're using it for guitar. Notice you're talking about plugging semi-pro-audio equipment (mixer's channel input, EQ, Send) into a tube amp.

Now a little about me:
Starting in the late 90's I got my hands on some McIntosh tube monoblock power amplifiers. I did have a tube preamp for them at one time, but it was oriented to tape or phono inputs and had EQ I didn't feel I needed. CD player levels are hot enough to go almost directly into the monoblock power amps, but then I'd have no volume control. So I used some tube microphone preamps, in line-level mode, between the CD and the power amps to offer the the volume control I wanted.

So that's also using recording/mixing equipment into a "tube power amp" but not for guitar. And not everything that ever got posted on this forum is about a guitar amp.

See how there could be confusion if you don't state exactly what you're doing with your setup? Further, guitar EQ is generally very-different from full-range EQ for recording or music reproduction.

I'm using an Amp Emulator for the preamp section, (AdrenaLinn III). ... improved sound I get whenever I patch a mixer into the effects loop. I don't understand what it is about either the standard Marshall tone stack or for that matter the EQ built into the Amp Emulator that can't be made to sound as good as adding the mixer. When I add the mixer the sound gets that changy ringing distortion and it seems to be the final touch needed to eliminate any trace of digital sound. At least to my ears. I suspect the mixer signal is over driving the EF806 better than the Emulator.

First mention of all this.

The Adrenalinn is essentially a pedal, and has at most a -10dB output level, which is not enough to drive a guitar output section on its own. So no wonder you like the extra drive from the mixer. Output levels are found in the back of the manual.

A different part of the manual states its amp emulations sound better running into flat, full range amplification (like a mixer feeding PA speakers or going direct into a recording channel then to tape/disk).

[silverfox]

I think at this point I'm going to open a specific Post related to the power amp in question. I think the amp would benefit from a tuning, so to speak and I would like to better understand the input levels best suited driving it and preamp interfacing. First I'll do some reading though on Pedals and signal levels. The schematic also needs to be finalized.

Thanks for all your assistance, you've been most helpful,

silverfox.