Although it's not a guitar or Kemper, it's a real pawnshop queen and one of the cleanest Showmans I have ever seen. 100% original and it looks like it was never at a gig. No scuffs on the bottom, and the inside of the chassis is immaculate. It still has the Fender 7025s and RCAs! It's possible this was a salesman's demo amp to demo to music stores along his route.
I can move or delete the post if anyone objects to the amp pics.
That's what I found recently and posted about in a previous thread. As an attenuator, I actually used a 10k resistor in series with a 1k, but the amp I profiled (a cranked Dumble #103 clone set to 4 ohms, with a G12H-100 4 ohm speaker) still clipped the Kemper input, so I tacked a 220 ohm in parallel with the 1k, and that got the signal down enough to do the job. The direct profiles I got with the simple attenuator cable were the best I've gotten with a Kemper. I should have calculated the resistor values in the first place, but I got lazy that day.
I strongly believe that the coloration you'd get using a cheap direct box (especially a passive one, good balanced transformers are NOT cheap) will far outweigh any benefits of using a direct box with a Kemper. You want that connection as simple as possible as any coloration or frequency response issues with a poor direct box would be transferred to the direct profile. But the direct box is the safest route if you do not know about the output stage of your source; a simple attenuator cable connected to a solid state amp with a modern Class D output stage could cause some circuit damage. You have to know what you are doing if you plan to use other than an amp's direct out or a direct box.
MKB, I agree. As a minimum the user would need to understand OHMs law, and the application and implication of it on each external component (including speakers) connected to the amp. As my side job for over 30+ yrs. away from being an EE, I repair amps, have kept logs of the repairs. I can't begin to tell you how many were repaired due to a fried OT, blown transistor outputs including Class Ds due to misuse or not understanding the implications of their connections. FWIW, I built a clone #124 back in 2007.
Then why post it? For bragging rights? Sheesh
The smile face was supposed to be an 8 ohm speaker.
You are missing a very important aspect. In normal operation there is huge amount of interaction between the output transformer of the tube amp and the guitar speaker which acts as a reactive load. This means that the speaker itself has a big impact on the sound of the amp. This is why companies like Suhr or Two Notes produce rather complicated reactive load boxes. They behave similar to a real speaker and help produce the same sound without a speaker attached. A simple load resistor like in your setup may work but in many cases it will sound totally different to the sound with a real cab attached. This is why profiling with the cab conncted will be the preferred method in most cases. If you want a balanced DI signal, simply get a standard DI box. I used the Behringer GI-100 regularly and it worked for me. Make sure the DI signal has a signal attenuation.
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FWIW, a DI box is not much more than an attenuator in parallel with the speaker load. Isolation may be available via a coupling transformer on any decent model, or a coupling capacitor, but it's not necessarily required on an amp that has an OT. Attenuating the amp output signal to an input signal level (into the Kemper) is usually a simple voltage divider. Some models may have switches to select the attenuation, but all this does is change resistor values in the voltage divider.
This was the point MKB was making here.
Also others have posted that they have used the recording output of some amps (non speaker emulated) to feed signal to the Kemper for direct profiling with some success. Such a circuit is often merely a level attenuator with a DC blocking cap, and the cap isn't really needed with most tube amps since the speaker output is transformer coupled anyway.
If the attenuator resistors are chosen wisely (in the 100s of Ohms range or more), then this voltage divider will have a greater impedance than the speaker. The results are very little effect, if any on the speaker dynamics and load impedance.
ie. the attenuator doesn’t matter if it is connected to a real cab, and here's the reason. Per the math of Ohms law, the lowest impedance here, (the dominant value that determines the total impedance), with the DI box and speaker in parallel in this case IS the speaker not the attenuator.
This is also the approach that Kemper used in designing their DI box. Nothing active and nothing reactive, just a straight forward design that does not interfere with the tonal characteristics of the amp to be profiled.
All that is needed to build an attenuator for this case is a little planning and the use of Ohms law. Have fun!
rshull07, check out this thread: Mounting Kemper Remote to rack lid with strong magnets there is a pic of the remote fitting into an SKB 4U rack cover. If it fits in the SKB it should fit in your gator as well using foam and Velcro.
Thanks nightlight, It sounds great and love the chimey chord at the end.
You might want to think about an Online UPS that can provide a true Sine Wave. The standard APCs produce a square wave AC signal that can be hard on gear, particularly sensitive digital gear. I run all my digital gear on a Minuteman Online UPS. If you ever are gigging on a generator, this is even more important, as tube amps can handle the dirty power of a generator just fine, but digital gear can be unreliable, and even damaged by dirty power.
Yes, Absolutely. A true online UPS is the way to go. Although some by pass the UPS circuit when the power is good, then switch over to the UPS when the power is non sinusoidal. The UPS output is similar to the Bang Oulfson Amp in the powered Kempers. Both use an H-Bridge (Class-D) output. Thaks Bigtoe for starting the conversation. I have also used many APCs fro radar sites. All were 750 VA and up to 5kVA, but all were true offline.
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nakedzen wrote:
People, DO NOT put a DI box between your amp and cab before checking it can handle the voltage.
You need to buy a DI box or dummy load that can handle the wattage which is a $200 investment by minimum. You can't use just any $10 di box off the shelf, it's likely you'll destroy the box and your amp. Most DI boxes have been built to handle signal levels (0.1V-1V), not 100W power amps. Want to be safe? Get a load box with line out, like a Hot Plate, and put that between your amp and cab."
Not necessarily true for all DI boxes nakedzen. Understanding how specific models are built is the caveat
My post link below tested a passive type LIVE WIRE SOLUTIOS Model SPDI, and shows that you can use this particular passive DI box in between a tube amp and speaker, IF you understand how your particular DI is made. I have not only profiled a 100W amp, but tested the DI box configuration using a dummy load and a variable power supply up to 40 VDC. This simulates the voltage output of 1) a 200W amp maxed out into an 8 Ohm load, or 2) a 400W amp maxed out into a 4 Ohm load. Another caveat of this testing is that you must be aware of the attenuator setting on this DI box before attempting any testing based on the spreadsheet. This test only applies to this particular DI model, but some other models may work. Understand how it's made is the decision maker.
DI-boxes suitable to create Direct Amplifier Profiles
I doubt very few, if any are profiling 100W or 200W amps maxed out, but what do I know. HTH
The chart is correct and measured the voltages across R1, R2, and R3 while testing the DI box using a dummy 4 and 8 ohm load. The DI box was tested up to 50 W with a dummy load. However, the 0dB setting is really intended to be used as a passive DI box for signals only.
So to avoid any damage to the DI, the attenuator switch must never be set to 0dB for any load greater than 20W conservatively.
The IN and OUT jacks on the schematic were drawn incorrectly. The are not shorting jacks, just paralleled open end jacks.
I have currently direct profiled 9 amps using this method.
I was given, then repaired a broken Live Wire Solutions SPDI Direct Box. This is a passive DI box, but after acquiring the schematic I determined it can be used for direct profiling within power limits and attenuation settings. The attached spreadsheet and schematic list the resistor voltages and the power ratings are based on the attenuator setting at 0, -20 and -40db for 4 and 8 ohm loads at output wattages at 25, 50, 100, 200 and up.
I checked the math against scope measurements into a dummy load. They are correct
For a 0 - 25 W amp MAXIMUM, a 0 dB setting is acceptable.
For a 0 - < 400W amp -20 dB setting is acceptable, 0 dB is unacceptable (@ 400w into an 8 ohm load the wattage is exceeded on R2 10k ohm unless it is increased to a 1W resistor..)
@ a -40dB setting the attenuation is sufficient to use the DI box but the signal may be too attenuated at lower wattages.
I also modified a junk cry baby from a local pawn shop. I had no momentary NO switch on hand, but Lowes had one available. It is configured as a wah/volume. After the calibration, and making the short TS and TRS cables it works great.
I measured the range of the replaced B10k pot with an ohmmeter and adjusted the position of the pot gear so there was an even range from full on to off. This made the calibration easier.
Thanks for the idea! 
I reloaded the profiles and with the cab off the Thiele cabs sound great. I don’t know what the issue was but reloading the profiles worked. Thanks for your suggestions.
Hi thanks for the reply. Yes cab is off, but haven’t reloaded any of my profiles. I was trying different profiles that were already loaded on the replacement power rack. Even the Michael Britt and top Jimi profiles need a little more top end. Playing the same cab thru many different tube amps proves it’s not a speaker/cab issue. Although I only have a few hours on the Kemper, since the initial unit had a defective remote. I will reload my profiles (vibrolux, deluxe, Dumble copy #124) and try again. They sounded great on the first Kemper. Thanks Bob
Marcus, Your cab sounds great. I am also using a home built TL806 cab with an older EVM12L but my cab lacks the sparkle in the top end. Does anyone have suggestions for a supplemental Horn for the top frequencies? The cab handles the lows and mids well, it just needs help on the top end. I haven’t tested the upper range that needs help but it’s just a matter of connecting the speaker load to my scope to determine where to put the crossover knee. Thanks for any suggestions. Bob
The replacement power rack and remote were received on12 October.
No issues with the remote or power rack.
I am a happy Kemper owner.
Thank you Kemper and Sweetwater!
Dean_R I certainly agree. Factory setups just don't work for the players. The sharp notes I was referring to was in reference to retail guitars still on the rack. I should have clarified that, and typically wouldn't play (in particular perform) with a guitar unless it has been properly setup.
An improperly setup nut can also grab a string during bending and hold it sharp. Abrasive chord, correct nut files and a little graphite in petroleum jelly really help with this issue. fwiw, I don't use the Buzz nuts on any of my guitars.
I prefer a lower action and generally use .011s. Fret width has never really been a concern unless playing open chords in the first 3 frets. Then I can hear some notes playing sharp, but a Buzz Feiten nut could fix that. I may be a beginner here on the forum but started playing in 67 and do my own guitar setups and amp repairs (well except for the Kemper).
I'm new to the Kemper forum and recently profiled my 74 Vibrolux at a mid to low volume, turned the cab profile off, added a small amount of reverb and play it thru a home built EV TL806 cab loaded with an older EVM 12L. After all this effort, the biggest factor in obtaining a clean tone was playing on a guitar with single coil PUs, then adjusting the guitar volume settings. The humbuckers sound great but a P-90 turned a little past half way up, or a tele or strat set about the same did it for me. Although I don't use picks, and tend to pluck light or hard depending on the tune. I hope this helps, but believe the biggest factor may be lowering the guitar volume and picking lighter. The Kemper compressor as is, (no tweaking yet, still too new to the Kemper), took away from the sparkle so it was turned off. I hope this helps.
A tone very similar to chris Rea on this tune:
