# Reckhorn F-1 Active Crossover



## Henry666

This is post that I attached to the original brucek post about his modifications.
Nobody has answered or commented, so I will try my luck with a new post.

Hello, I am new to the forum and was wondering if someone could help me with some questions.
All answers are greatly appreciated.

I am attempting to modify my Reckhorn F-1 to get unity gain from the satellite output.
I modified the R3, R12 - change from 3.9K to 10.7K

The problem is that I am using a scythe kama amp with a TEC pre-amp and the volume is still a lot less with the Reckhorn in the chain that without the Reckhorn.

I am new to this modding game and would like to ask, if it is possible to get more than unity gain from the sat outputs? If so, what are the affects on clarity, humming etc. 

Thanks alot and look forward your comments.


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## Lucky7!

Do you have a schematic for the unit? Bit hard to comment otherwise.


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## Henry666

Here is the schematic.

Any thought would be greatly appreciated.


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## Mike P.

> if it is possible to get more than unity gain from the sat outputs?


I'm waiting for a reply from a guy who does F1 modifications, we'll see what he says.


​


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## Henry666

Hello Mike P,

Thanks for the help and looking forward to hearing what information you get.

I am new, so I can't respond to your mail. (I believe)


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## Anthony

You should be able to respond now. After 5 posts, you can PM and post links and images.


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## w1ngs

Looking at the schematic provided; the resistors R3 and R12 set the gain for the subwoofer channels. The two channels are joined together after R1 and R10 but can be separated by cutting a trace and adding a wire so that R1 continues onto VR2 and R10 to VR1 to allow stereo operation.

For the satellite output, gain is set by R18 and R27. All of the gain-setting resistors in this unit will have the effect of increasing gain if their value is increased. With the values shown in the schematic, the satellite gain should be about 1.4. A test with my un-modified F-1 by ear shows that its gain is less than 1 though, so this may be a revised schematic or I'm missing something.

Regardless of all else, you can definitely increase the gain beyond unity quite a ways by increasing the values of R18 and R27. You must consider the gain of the input networks (R35, R5, R38, and R20 for left and R37, R14, R36, and R29 for right). Their gain in the schematic is .322 (for example, R5 and R20 appear as if connected to ground (virtual ground) and thus are in parallel with R38 in the math. A resistor divider is then formed between the parallel resistance of R5, R20, and RR38 and the input resistance R35). This is for the left channel and the same applies to the right.

Once you know the gain of that network you can calculate the gain out of the first op-amp by considering R18 for the left channel and R27 for the right. Consider putting a volt into the input network: 1V * .322 = 322mV. Thus 322mV across R20 or R29 makes 322µA which the op-amp must drop across R18 or R27 to bring its inverting input to zero. 322µA across 6.2k as shown in the schematic makes 1.996V and thus the total gain to this point is 1.996. The reason I calculated 1.4 for the whole circuit on the satellite filter is that you see another resistor divider between the first and second filters because of R63 and R67 for the left channel, and R64 and R68 for the right. The values shown (2.2k and 4.7k) give a gain of .681 and thus .681 * 1.996 = 1.36 (rounds to 1.4).

The total gain of the system once inside your audio system will be slightly less due to the 1k output resistor. This will be reasonably insignificant with most amplifiers, but some will present a low enough input impedance to cause a noticeable effect. For example; if you have an amp with 10k input impedance you will get a reduction in gain by a factor of .909 ((1000+10000)/10000) bringing the complete gain from 1.36 down to 1.24.

This may all seem complex, so if you don't want to do the math you are welcome to experiment with different values for R18 and R27 in the circuit. A good place to start would be to double the resistance and see what the effect is. Then pick a value in between if you find that to be too much gain.

As for hum and noise: the crossover itself is unlikely to generate significant levels of this but it will amplify any junk from the previous piece of equipment by its gain so you have to think of that. I wouldn't worry about it most situations. The only big issue you might run into is clipping in the crossover itself but this is highly unlikely. You'd have to have an output swing from rail to rail, which for an unmodified F-1 this should be around 15 to 18 volts peak (far more than you normally ever see at line level for RCA interconnects).

I hope this is helpful.


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## Henry666

Thank you very much for the reply. I really appreciate it.
I am quite illiterate, when it comes to schematics.
Something I didn't write in my initial post.
I changed the R18 and R27 from 1.5K to 3.9K and the output was still too low.
Should I than go with a higher figure? 
Any suggestions on what for a figure?

Thanks again.


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## w1ngs

Henry: I'm glad I can help.

If 3.9k wasn't enough then there's no trouble going further. I'd try the 6.2k as seen in the schematic on this page. That should get you just over unity gain.

Best of luck.


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## Henry666

Hello W1ngs,

I finally found the time to change the resistors and I would like to report that all is well, but I have encountered a new problem. When hooking up the reckhorn to my system, i experienced a dreadful hum and distortion. I tried to play around with the connections, but to no avail. The amp I am using is the scythe kama bay amp 1100, preamp tcc tc754 connected to a power supply and an REL quake subwoofer. Is this caused by a grounding issue? I don't want to give up on the Reckhorn, but finding it hard not to think, it would be better to get rid of the thing. Any help would be greatly appreciated.


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## w1ngs

Hi again,

This leads to another modification that I feel is absolutely necessary for the Reckhorn: grounding of the chassis.

In the original design the chassis is not grounded or referenced to any particular point; the RCA jacks are isolated with plastic washers. The power transformer is bolted directly to the chassis inside and capacitively coupled hum from the AC line gets into the chassis readily as a voltage potential. Since the chassis is a metal box which is now at some AC potential relative to the guts inside there tends to be coupling of said hum or noise into the electronics. The main coupling is through the potentiometers as they are bolted directly to the chassis and offer no electrostatic shielding; as a matter of fact ordinary panel-mount potentiometers tend to exhibit electrostatic coupling from the track to the case quite well in my experience.

All you have to do here is remove the washers on at least one RCA jack. I do them all out of preference for an even look and a lower impedance ground path. There are two washers on each plug and I remove only the ones on the inside so as to retain the original external appearance and function.

This modification will force the chassis to exist at the same potential as the interconnect grounds where they are connected to the unit. It eliminates the hum and noise problem completely in all situations I've tried.

This post applies to any piece of equipment built in such a way and I have applied it successfully to all sorts of gear. Just make sure the potentiometer cases are grounded to the same reference as whatever signal they're processing and all is well with the world.

I must admit this modification is a pain in the rear to perform but it is well worth the effort.


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## Henry666

Hello, 

thanks again for taking the time to respond. I want to let you know of all the changes, I have made to the reckhorn. I apologize for not mentioning it before. When I changed the the resistors, I also took off the plastic washers on the inside of the rca(s). I also did the following: _I replaced the incorrectly sized filter capacitors (that were originally [email protected]) with a pair of [email protected]_ I took this from the original post from Bruzek on his modifications on the Reckhorn F1. So now everything is out. Have any ideas what could be the problem? 

@Another thing to mention is that I bought the reckhorn second hand, though the seller said it worked it had damage on the control nobs. Everything looks good on the inside, but then again I am no expert.


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## w1ngs

It sounds like you've essentially taken care of all the important stuff. If it's still humming after you removed the insulators then I'm not sure what else is going on.

Good that you got the caps; the original are a disaster waiting to happen given the ratings in use. The power supply voltage is also too high for the op-amps but they seem to have a sense of humor luckily.

It's possible that the hum is the result of the high power supply voltage causing the op-amps to suffer though I doubt this.

What sort of hum are you experiencing? Is it a soft AC-line sort of hum or something with more hiss or buzz to it?


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## Henry666

definitely hiss and buzzing. I read the following on the reckhorn webpage.

Attention: noise sources 
The most units are connected to each other the more disturbances can occur, i.e. from bad or different grounding points. Older amplifiers are mostly grounded on its housing but newer models are not. The F-1 is as well not grounded which is the better solution against disturbances from other units. But connected to some pre- and main amplifiers models or other signal sources you may hear low frequency noise. 

Solution: 
Prepare a 0.3 0.75 mm² isolated wire from F-1 housing to main amplifier. The stripped wire connects to the amplifier ground / GND srew. If not available remove on back side housing screw and put the wire under the screw and put the wire under the screw head and fix it. At the F-1 back side remove one screw and scratch off the rough surface 2-4 mm around the screw hole. Otherwise this anodized surface is non conductive. Then turn the stripped end of the other wire end around the screw head and fix it tightly but do not overdrive. 

More sound improvements: 
1. Move the F-1 farer from other units to find out if disturbances are changing to optimize the final position. Disturbances can be caused by RCA cables. Please check: 

2. If disturbances change when you move the RCA cables find out no nois positions. 
3. All RCA cables must be short. 
4. The plugs must be tight on thze sockets. Loose shield contanct can be pressed slightly for better contact. 
5. All contacts must be clean. 

What do you think? Should I give it a go or is it the same as taking off the washers?


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## w1ngs

The wire jumper idea is essentially doing the same kind of thing as removing the RCA jack isolation. The only big difference is that ground current will be carried through a lead other than the signal ground; this is done on most turntables it improve hum and noise characteristics.

Have you tried plugging the Reckhorn in backwards? Reversing the plug (if it's not polarized) can make a difference if there's something going on with the transformer's insulation.

Sometimes you'll have to try various things to get hum out of a system. You might even have a completely different problem that is due to some other aspect of the system. Check for ground loops due to things like cable TV hookups or various grounded pieces of equipment which may be using separate circuits in the house or even different outlets on the same circuit.


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## Henry666

Hello once again,

So I plugged the Reckhorn into another outlet in another room and then hooked it up to my system. Positive is that the buzzing and hissing are gone, the negative, it sounds like the speakers are mumbled and when I turn up the volume the woofers are not really moving (vibrating) like they should. Is this a problem with my interconnects from the Reckhorn to my other units? I have to admit they are pretty cheap interconnects. I didn't quite uderstand with what you meant by reversing the plug. What would I exactly have to do? Thanks


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## w1ngs

A big change in the sound of the system is not the interconnects unless you've got something wired incorrectly or shorted out. Double-check all your settings and the wiring; see that none of the speakers are connected backwards, etc.

When I said reverse the plug I meant unplug it from the outlet and plug it back in the other way around (this only works on non-polarized plugs but I think the reckhorn's plug is as such).


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## Badbob

Just a couple of things you might think about trying. The first thing I would consider is buying a tester to make sure that all of the wall outlets in your house are phased correctly. It sounds suspicious that just changing a wall outlet would change your symptoms that much. I would do that ASAP. Your phasing in the outlets must be correct for any equipment to work at its peak.

The above step is crucial before you try the next step. If the above is bad and you try the next step, your equipment could be damaged trying a system ground. 

Only, and I mean only after you are sure that your wall outlets are phased correctly, then I would think about running a system ground between all components that actually plug into the wall. DO not run the system ground to the wall outlet unless you know how to do that safely, I think you probably do but I got to say it, preferably you only run it component until all components are connected to the same point. To do this you need to find chassis ground on each of your units. It is best to use a multimeter to do this to make sure on an ohms setting and if you have a three prong plug. Check from the A/C plug ground to an easy to get to screw, usually a good place is on the bottom of the unit if none are available in the rear, and make sure it reads a short, or Zero ohms. Do this for each unit and then run a common ground that connects to each unit in a big loop. That way you neutralize and ripple voltage between components and should let your units all run at their optimum levels. PLEASE, if you aren't comfortable doing this, find a friend that knows how to use a meter and get him to help.

Lastly if none of the above is the cause, it almost has to be a bad cable or a loose component ground or possible a bad or cold solder joint on one of the components you replaced. 

I don't know if you are still playing with this, but even if you are not, I would definitely check your outlet phasing just for you and your family's safety.


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