Don Voth Electronics Co.

Welcome!

Don Voth has been serving electronics for musicians, professional audio engineers and lighting technicians since 1989. Don started his own business in 2001: the Don Voth Electronics Company, located in Winnipeg, Canada. Technology has evolved over the past 25 years, but Don Voth is still coming up with dynamic solutions; finding and fixing the most difficult and bizarre technical defects.

Velvetone Embassy September 11, 2019

This is a Velvetone Embassy guitar amp. I have never heard of this amp before. Has anyone else seen one before?

I put new tubes in this unit and it sounded fantastic...for about 5 minutes. Then it sounded like shit. I spent forever trying to figure out what the problem was. In fact, I had to draw myself a schematic to figure it out. See below:

It turned out that the preamp would put out ugly distortion after being on for 5 minutes. I traced this problem to the fact that the power supply voltage was dropping way below normal levels. And this was happening because the rectifier tube was being pulled down. And this was happening because the output tube was biased way too hot.

I found a similar schematic on the web, and I determined the correct bias current should be around 30mA. But to get this bias level, I had to install a huge cathode resistor. Such a big resistor would totally suck the life out of the power amp section, so that was unacceptable. So how do I fix this? I put on my genius cap! (Most of you think I am a natural genius, but it is not so; I need a special cap.)

I decided to leave the cathode resistor unchanged so the amp could keep its punch, and then add some negative grid bias with a little 12V power supply. That worked perfect. I got the amp to bias at 30mA and it sounds great and the tremolo still works as well. WOOHOO, we did it again! The only down side is this took so long to figure out I will be losing my shirt on this one. Lucky I have a TEE shirt on.

Don Voth Fixes: Dirty Pot January 2, 2019

In this video, Don Voth explains how he cleans dirty potentiometers.

POS-1 August 21, 2018

Introducing the POS-1, a custom guitar amp designed by Don Voth:

Del Barber with the POS-3 September 7, 2018

Here is Winnipeg musician Del Barber posing with his POS-3. I spent a lifetime (almost!) getting all the bugs out of this baby. When done, it put out about 45W RMS and has 3 speaker impedances. I also gave it a Master Volume and Gain control.

It was a bit of a trick getting it to not hum once the master volume was wired in. What was the trick? Not all grounds are equal in a tube amp chassis. Where you ground the AC is not necessarily the best place to ground the master volume. In fact in this case that was just about the worst place to ground the master volume control. It is all about accumulated ground currents. You want the master volume control to sit on a place where there is very little AC hum currents. The AC ground is not that place. Turns out the input ground point was the best place to ground the Master Volume control. Makes sense when you think about it.

AMEK HX10 September 24, 2018

This is an AMEK HX10 strip. I am told it is a Rupert Neve design. I was told to figure out how to make it work as a standalone strip. I have just finished doing that. I thought it would take me two and a half days to figure this all ou, but I was wrong. So far, I have spent 8 hours on this and I got 90% of everything we need working. The power supplys in the back ground are cheap switching PSUs that have enough jam to easily drive 2 strips and in theory they could drive 4 strips. And you should hear the EQs on this thing...A very effective parametric EQ from Rupert Neve! The hardest part was figuring out why sometimes the switching logic worked and sometimes it did not work. Turns out there was a pin on the CPU that was not being pulled Hi or Low; just hanging there in lala Land. This was the Power Fault pin. So sometimes it would think, "I am in power fault mode" and some times not. It had a mind of its own. I pulled this pin high with a 10K resistor and hence no more indecision. From here on we have to design an enclosure and possibly adding phantom power.

Mesa Boogie Dual Rec Solo Head November 1, 2018

Why do they pay me the big bucks?

I know! I know! Because the Bible tells me so.

...No, it has nothing to do with the Bible. It has everything to do with this Mesa Boogie Dual Rec Solo Head:

This unit came in because it just did not sound right.

I found one bad preamp, two bad rectifier tubes, and noisy effects loop insert jacks. After I repaired and replaced all that, I tested it. The amp hummed in a strange way. I traced the hum back to the input on V2. I tried and tried to eliminate the hum, and could not do it. I consulted with the folks at Mesa Boogie and they suggested that maybe I was expecting too much from this amp. This was a reasonable suggestion; all high gain amps have some hum in them.

Then, I looked a little harder...and found a burned resistor in the filament voltage circuit! This circuit has two 150-ohm resistors that reference the 6V AC to ground. I replaced both these resistors and tested the amp. Now, the hum is normal again. This amp went from being a struggle to play to being a joy to play all because I had this hunch that the hum was just not right...and THAT is why I get the big bucks.

The Hot Box August 30, 2018

This is the Hot Box in use at #BlueRoom #PrivateEar:

It allows you to plug a tube amp into the Hot Box instead of a speaker and then gives you a balanced output that you can send to your recording system. Not a new idea, but my hotbox is a little different inside hence it appears to sound better. One thing it does not have is a reactive load. I am not convinced this [having a reactive load] is a good idea. I have examined the reactive load of another box that does this and I think it is a gimmick and am not convinced that it will give you much, compared to the cost of the reactive components. I will build these units for others on demand, and you can try one before you buy it. Call me if you are interested!

POS-1 August 21, 2018

Watch Joey Landreth, Ariel Posen and Kris Ulrich test out the POS-1, a custom guitar amp made by Don Voth.

Holy Grail August 8, 2017

This is a Holy Grail. Most players say it's a good reverb box. This unit makes a whiny hum. My guess is that all Holy Grails do that.

Except, of course, this one. Why is this one different? An original Holy Grail comes with all metal input/output jacks. As you can see, I have replaced those jacks with plastic Neutrik jacks. Now, why would I do that? Metal jacks make a ground connection to the chassis. Hence, we have 3 ground connections to the chassis: the input jack, the output jack and the power jack. This creates "ground loops." By using plastic jacks, I eliminated the ground loops. After that, I had to add a ground jumper from the output jack to the chassis ground. But not all ground points are the same! Grounding at the output jack nut or the AC ground created noise. So I added the green wire and grounded at the voltage regulator on the PCB, as you can see in the picture below:

Fantastic! Now this piece of Holy Sh** has stopped whining and sounds Wholly Great!

Don Voth Fixes: Crown CTS-4200 October 3, 2016

In this video, Don Voth fixes a Crown CTS-4200.

Don Voth Fixes: Peavey 5150 September 21, 2016

In this video, Don Voth fixes a Peavey 5150.