Let’s turn a pig into a princess for less than a dollar minus shipping charges. Really? It can be done! You need one capacitor that will cost you about 35 cents plus shipping.
It’s a shame Crate did not survive as they actually made some fine tube amps. Before digging in here you should know that the V1512 and the Palomino 16 are the exact same amps. They are 15 watt cathode bias push pull amps with an overdriven front end. Both of these amps use the same preamp circuitry of the V32 overdrive channel and that is why they are dirty. If you know the history of tube amp design you will know these Crate amps are tried and true circuitry without the boutique price tag. The basics of tube amp design have not changed since the 1930’s through 50’s when they were considered high tech. Whether it’s a Dumble or a Carr, they haven’t changed. What these designers do is voice them to get a certain tone and charge for it which is just business. These days there are features, USB interfaces, DI outs etc, but the power stages and preamp designs are essentially the same as they have been for 70 years. These particular amps are orphans because they distort when you look at them and no one wants them. And this is why you should own one because they are cheap and sound great if you know what to do with them. So before you shell out 2 grand for a 20 watt 60 year old design try, 100 bucks and a capacitor and see if you are not in the ball park. And remember this, the speaker is going to play a huge part of the sound you are looking for no matter what amp you choose. So there you go.
The web is full of people trying to tame these by using low gain tubes but none of that works and never will because they are designed to be high gain. It is a futile effort in an attempt to clean these up. So don’t be fooled by comments like this one on Craigslist, “I changed a tube to a 12au7 and gave it more head room and it will keep up with a BJ”. What that means is you can move the volume control from 2 to 2.5 before it over drives. The reason they changed a tube is because the amp is dirty and they did not like it and after they changed the tube it is still dirty and now they want to sell it. These amps are dirt balls as designed and will remain so until you remove a gain stage. That’s why you can get them for 100 bucks, the price of a new speaker. They are 15 watt stomp boxes. The only way you can fix this amp is to remove a gain stage. And it is very easy to do as mods go.
As I mentioned this is an easy mod if you have basic knowledge of tube amps. If you can use a soldering iron and know how to safely discharge the amp before working on it this is a piece of cake. And you may be so impressed with your new found abilities that you start other mods and then building tube amps.
Here is your standard warning. If you don’t know anything about high voltage then STAY AWAY from this and get a tech to do it. You could kill yourself. High voltage is not forgiving. This mod can be done at a service shop by a tech for 60 to 80 bucks or less in labor charges. You are on your own and I will have no liability for what you do.
Here we go. All we are going to do is change a coupling capacitor to boost the low end, remove a shaping capacitor, remove a coupling capacitor and remove one half of a tube. You will cut a piece of land pattern off the circuit board. All this can be reversed if you want the 15 watt stomp box back.
Refer to the schematic diagram and pictures.
Step 1. Change C2 coupling cap to a .0047uf 400v or higher voltage cap. Remove C3 completely. This combination will remove the excessive highs from the amp and balance it out. Without this change the amp will have way too much top end.
Step 2. Remove coupling cap C6 completely.
Step 3. Using an Exacto knife or similar, cut the trace on the circuit board at the point indicated with an X. Cut out a piece about 1/16″ wide. You are permanently disconnecting this gain stage.
Step 4. Solder a wire from the grid of J1-B to ground to keep spurious power consumption down caused by a floating grid. It’s bad practice to just let the grid float around and potentially cause issues.
Step 5. Solder a wire from the volume control to the input resistor R37 of tube J2-A using the solder pad of C6. MAKE SURE YOU USE THE GRID SIDE SOLDER PAD or you will blow your amp.
Here are the schematics of the 1512 for you viewing pleasure!
V1512 Schematic and the V1512 Circuit Board
That’s it. That was a lot of fun. All for less than a buck for a capacitor. Now you basically have a clean amp that sounds great and will compete with a Blues Junior. A great studio amp. If you compare the schematics you will see they are similar in comparison. Both amps use a three section preamp and el84 outputs.
There you go. Now a great little grab and go.
This little amp sounds great!
As a side note, these amps are built better than Blues Juniors in that they use real metal pots, not the cheap plastic jobs Fender puts in the BJ. Fender cheaped out on them and it is just a shame.
Other Mods that are not necessary!
I made a couple further mods that are NOT NECESSARY but helpful to me and you may consider them. I changed the output transformer to a
OT19PP (USA) HC100 version PP Output Xfmr 22VA 8K to 4/8/16ohm for “18 Watt” available from
http://www.musicalpowersupplies.com/
I also installed a switch to let me select 16, 8 or 4 ohms so I have the capability to experiment with speakers I have. The stock output transformer will drive 16ohm speaker and that is fine. This transformer is made in the USA and is high fidelity and a great price. So it does add a wider bandwidth to the amp. But that is not the reason I bought it. The reason was for the taps. In hindsight they had a standard transformer with the taps and I probably should have gotten that one. The speaker itself limits the bandwidth of the amp. I did not try the mod before changing this transformer.
And Matt, the owner of the company was very helpful.
I changed the slope resistor R13 from 47.5k to a 33.2k 1% resistor increasing the mid control range slightly. It was only a guess after running it through Duncan’s tone stack program and I suggest you ignore that until you have had time to play with the amp. This sort of mod must be listened to in order to decide if it is worth it. No numbers or curve set is going to tell you what this sounds like. Use your ears.
I also replaced the 120 ohm 5 watt bias resistor with an aluminum 10 watt bias resistor mounted on the exterior of the chassis and removed the stock resistor from the circuit board. This bias resistor gets hot and it along with the output tubes heats up the control knobs on the operator panel to a point where they are too hot to touch. That helped but only slightly which surprised me and I do not recommend you do it as the effect was minimal by itself.
The most useful change I made outside of removing the gain stage was installing a fan. All these Crate tube amps, the Palomino V32 and V16 and the V1512, are poorly ventilated and the knobs get too hot to touch. So if the knobs are too hot to touch, the rest of the components especially capacitors are cooking towards a slow death. I added a 16cfm 19dba very quiet ball bearing fan and the amp now only gets warm as it should. It was tricky to mount but worth every bit of the trouble. This is a very worthwhile addition you should consider. This fan will add life to your tubes and components by keeping them cooler as well as cooling the knobs and is silent. Cooler tubes and components are quieter tubes and components. And it’s good for your fingers!
SPICE – Frequency response details
The guitar has a frequency response of roughly 80hz to 3.3khz which includes the first harmonic of the high E.
Below are some simplified Spice analyses of the interstage coupling that you are modding and the resultant curves before and after. You can see the circuitry was designed to give heavy emphasis to the high end because this amp was designed to be a high powered stomp box. So lots of treble is needed to provide cut through in a band situation. The treble was provided by cutting the bass. It was not a bad design, just a design to fill a market need of the time.
Default Coupling:
[singlepic id=700 w=150 h=150][/singlepic]
This simplified Spice model of the stock 1512 coupling circuit shows the effect of C3 as a treble boost capacitor in the interstage coupling circuit and the small .001uf coupling capacitor. This leads to heavy treble output of the amp to the point of ear splitting because the mids and lows are reduced by 10db and more from the 3.2khz high end second harmonic of the high E. The red line is the input sweep signal at C2-C3 junction. Green is the top of P1 and blue is theR37 R35 junction. The amp will work like this but can be painful unless you compensate by cutting the treble severely with an EQ.
Modified Coupling:
[singlepic id=713 w=150 h=150][/singlepic] After changing the interstage coupling cap to .0047uf and removing the treble/presence capacitor a much better flatter response is gained and the ear splitting top end is greatly reduced. The curves clearly demonstrate this. The Yellow curve is the input sweep junction C2-R4, Green is R4-R37 (top of P1) junction and Red is R37-R35 junction. If you change this cap to say .047uf it will become so boomy it will have too much bass. So it’s something you can experiment with just to see how an amp is voiced. Unless you want to experiment, just follow the mods here and take my word for it.
That’s it. If you do the mod let me know how it goes. I would be very interested to hear your experience.
