Diezel VH4- Channel 3 Preamp Idea

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ReverendBow
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Post by ReverendBow »

Hello all, I haven't been here in a long while.

I have an idea and was wondering if anyone has some input.

I got an idea bouncing around in my little mellon...

I was to build an All tube Diezel VH4 Channel 3 preamp.

I came across a supposed VH4 schematic in the deep dark corner of the web... not sure if it is accurate.
https://stremelguitars.files.wordpress. ... preamp.pdf

The thing that makes me wonder about the schematic:

-The tone Stack BASS is wired (or drawn on the schematic) Oddly
-367VDC on the 12AX7 Plates is pretty cooking

Basically, whittling the preamp, Ch3 down to this...

Image

Sorry it won't let me load the pic into the post

Besides that, think it is worth cooking up?

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Post by bmxguitarsbmx »

That's basically it. It does depend on the year. I'm an amp tech and there are a few versions out there. Others have noted the same.

You are correct that the bass control is weird. Wire it normally.

I've seen preamp voltages down to 385V, nothing as low as shown. The best ones I have seen use 400V on the preamp. Any lower and it sounds very compressed too me. For comparison, Mesa dual rectifiers have preamp voltages 410-415V!

The 3.3M I have only seen 1M or 220k.

the 10uF+470k is all over the place or non-existent. A value of 2n2+47k to 100k is good. This network gives a. lot of compression and so you may want to leave it removed at first. 10uF + 470k won't do anything though, so you can skip that.

The 680k going into the grid of V3a should have a resistor to ground that is the value of the combination of all other channels mix resistors to ground (680k||680k||56k) = ~ 47k. So, connect a 47k to ground from the grid of v3a and you will have an appropriate effects send level.

The post tonestack stage does overdrive in a normal vh4.

I like the Diezel sound, but I don't think it sounds good with voltages lower than 400V. I built a VH4 CH3 preamp with only 350V and it was way to compressed sounding and any gain setting above 1.5 (out of 10) was way too much to be useable. I ended up padding down the v2a drive, which helped, but in the end it didnt sound like a Diezel at those low voltages. So, I converted it to a jcm800 type thing. I get it that it is hard to find a preamp sized transformer that will get you to 400V after filtering, but I consider it mandatory. I hope that is helpful.

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Post by bmxguitarsbmx »

I clicked on the link you provided.

The way that dude drew the schematic shows all the channel switching before the tonestack driver as an SPST relay. It is actually a SPDT relay and each channel grounds between the master volume wiper and the 680k (or 56k in the case of the clean channel).

Great job on your schematic reduction by the way! If you can get 400V, it will sound killer.

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Post by ReverendBow »

Dude, thanks for the reply.

I have a Hammond 269EX transformer from my first tube amp I built (the Firefly). I tore that amp apart and ran the Transformer into a Bridge Rectifier last night. It is doing 396vDC before filtering.

So post filtering, it should be up around 390-400

Also going to be running DC for the heaters
Last edited by ReverendBow on 18 Jun 2022, 07:24, edited 1 time in total.

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Post by ReverendBow »

bmxguitarsbmx wrote: 16 Jun 2022, 20:47
The 3.3M I have only seen 1M or 220k.
I order a 3.3M, probably have a 1M in the stash

the 10uF+470k is all over the place or non-existent. A value of 2n2+47k to 100k is good. This network gives a. lot of compression and so you may want to leave it removed at first. 10uF + 470k won't do anything though, so you can skip that.
I am looking at the schematic and trying to figure out where the 10uf+47k is you are speaking of? Off the V2b cathode, Right before the tone stack going to Ground?
The 680k going into the grid of V3a should have a resistor to ground that is the value of the combination of all other channels mix resistors to ground (680k||680k||56k) = ~ 47k. So, connect a 47k to ground from the grid of v3a and you will have an appropriate effects send level.
I am actually planning to drive a JOYO Cab Sim IR with it, but also would like to drive a power amp through an effect loop return
The post tonestack stage does overdrive in a normal vh4.
Cool, but I can't imagine that V3a provides to much more gain, that stage is setup pretty tame
I like the Diezel sound, but I don't think it sounds good with voltages lower than 400V. I built a VH4 CH3 preamp with only 350V and it was way to compressed sounding and any gain setting above 1.5 (out of 10) was way too much to be useable. I ended up padding down the v2a drive, which helped, but in the end it didnt sound like a Diezel at those low voltages. So, I converted it to a jcm800 type thing. I get it that it is hard to find a preamp sized transformer that will get you to 400V after filtering, but I consider it mandatory. I hope that is helpful.
Thank you very much! I appreciate the feedback. I have a blank board coming and am going to build it Point to point on an Eyelet board, like I have built my amps...
IMG_20220612_161533673~3.jpg

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Post by bmxguitarsbmx »

Cool. Looks good. And that building style will be easily modifiable.

the 3.3M position is just to tame gain. There is a shit ton of gain in the vh4 ch3.

My bad, 10uF +1M off the cathode of v2b. Still it will not do anything at those values (unless you have golden ears). Just trying to point you in the right direction to get the Diezel sound. There have been many Diezel builds over at the Sloclone forums. People have a love hate relationship with this network. The values I recommend are in the range that I think is useful.

You will need to pad the signal after the master volume if you are going to drive effects or the IR device. 680k to 47k would create the level that Diezel actually drive v3 with.

You can definitely leave V3 out. It is for post tonestack clipping. It is subtle, and a vh4 ch3 is already crazy gained out. I skip it most of the time. I will note that the Rev.G and earlier dual rectifiers are sought after because the effects return can be overdriven by turning up the channel master and controlling volume with the global master. The sweet spot isn't to totally saturate it, it is just to give it some juice. This might be where Diezel was influenced, I don't know. The vh4 ch3 is one of my favorites of all time, but it has way too much saturation most of the time. Anything to get a little more headroom like 400V, the 220k(or smaller) instead of 3.3M, and eliminating V3 altogether are good ideas in my opinion

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Post by ReverendBow »

bmxguitarsbmx wrote: 18 Jun 2022, 17:26 Cool. Looks good. And that building style will be easily modifiable.
Thanks. The only amp I built true point-to-point was my first.. the Doug H Firefly. Serious pain in the ass to modify/troubleshoot... I started making my own eyelet boards when I built my second amp, which was a 3 watt using 2- 6AK6s running push-pull with a Marshall style preamp

That board is my 6V6 push-pull amp with a 4 stage preamp... no cathode follower... it doesn't do clean... LOL
the 3.3M position is just to tame gain. There is a shit ton of gain in the vh4 ch3.
Ok, cool. A 1 M will dump more signal to ground.
My bad, 10uF +1M off the cathode of v2b. Still it will not do anything at those values (unless you have golden ears). Just trying to point you in the right direction to get the Diezel sound. There have been many Diezel builds over at the Sloclone forums. People have a love hate relationship with this network. The values I recommend are in the range that I think is useful.
Cool, thanks. I appreciate the input. I think I use to be a member at the SLOClone forum...

I will probably put it in as I already have the parts coming.
You will need to pad the signal after the master volume if you are going to drive effects or the IR device. 680k to 47k would create the level that Diezel actually drive v3 with.
So this is why the diezel VH4 pedal has 2 outputs.... one for front of amp, and one for effects loop return. One is padded for effects level, one is for driving the phase inverter ... correct?

I could put the 47k on a switch... effect level/power amp drive level
You can definitely leave V3 out. It is for post tonestack clipping. It is subtle, and a vh4 ch3 is already crazy gained out. I skip it most of the time. I will note that the Rev.G and earlier dual rectifiers are sought after because the effects return can be overdriven by turning up the channel master and controlling volume with the global master.
I am going to build it with all three tubes... it looks evil!

Pretty sure the earlier Rectifier is an SLO ripoff.

The sweet spot isn't to totally saturate it, it is just to give it some juice. This might be where Diezel was influenced, I don't know. The vh4 ch3 is one of my favorites of all time, but it has way too much saturation most of the time. Anything to get a little more headroom like 400V, the 220k(or smaller) instead of 3.3M, and eliminating V3 altogether are good ideas in my opinion
Ok, I will be able to get the power supply section built as soon as my filter caps show up... also, my fiberglass board for the eyelet board is enroute as well. Need to find/build a chassis to build it in as well... but I have to get the eyelet board layout done to size everything else...

Thank you very much for the input. I appreciate it.

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Post by bmxguitarsbmx »

As far as the outputs between driving effects and driving the power amp, you will have to put those at the end. So, if you include V3, you could drive the power amp with the cathode follower and drive effects normally.

680k+47k voltage divider is a lot. But, that is because of the 400V supply allowing very high voltage swings. A Marshall type preamp with 240v-280v on the tone stack driver would be 470k+47k. But, in your case where you will use V3, the 680k+47k is really to keep from driving the effects send stage too hard.

Your 6ak6 amp sounds really interesting and 3 watts is about all you need on practice days. What B+ did you use? And what Primary Impedance? Looks like 280V and a 22k primary might do it... Is that similar to yours?

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Post by ReverendBow »

Oh man, that 6AK6 was built years ago...

It is a 115/6-0-6 3A transformer back to back with another 115/6-0-6 3A transformer into a voltage doubler. I taped the center of the 2 transformers for the filiment voltage

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Post by ReverendBow »

bmxguitarsbmx wrote: 19 Jun 2022, 21:26
Your 6ak6 amp sounds really interesting and 3 watts is about all you need on practice days. What B+ did you use? And what Primary Impedance? Looks like 280V and a 22k primary might do it... Is that similar to yours?
I went digging into the bowels of an old hard drive...

Image

I used the Bottom Power Section

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Post by bmxguitarsbmx »

Cool. I hadn't seen anyone doing the firefly with pentodes. I have a marshal style build with 12au7 that rips imo. I'd really like to hear what pentodes could do in that wattage range. I feel like 500mW is about what you need to be as loud as string noise, 1watt is killer if you are fine overdriving the power amp, and somewhere above that is minimum for clean tones.

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Post by Reachahighernoon »

I was actually wondering about the post tonestack stage and how much it affects the overall sound of the amp because from what I saw of solid state versions in pedal form the only thing that exists post tonestack is a small booster buffer and the Deep/Presence controls

I designed my own version but of the channel 4, based on the same schematic you posted, if you want I can share it

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Post by bmxguitarsbmx »

Reachahighernoon wrote: 25 Jun 2022, 16:34 I was actually wondering about the post tonestack stage and how much it affects the overall sound of the amp because from what I saw of solid state versions in pedal form the only thing that exists post tonestack is a small booster buffer and the Deep/Presence controls

I designed my own version but of the channel 4, based on the same schematic you posted, if you want I can share it
VH4 ch4 is insane gain. I would say you don't need the post tonestack overdrive. It all depends on your personal preference though. I want a certain amount of percussiveness in the attack even for lead tones. We'll see what ReverendBow says about the levels of gain of ch3 the way he is setting it up. CH4 is very cool. It has so much gain that it sounds synthetic. Very processed, but in a cool way. The level of gain is similar to a evh 5153. Like useful gain values are between 0.9 and 3 for either amplifier and I hate to say it, but the 5153 has a more useable rhythm tone. So, I would say skip the post tonestack clipping for both CH3 and CH4. It just so much gain. But, if you like liquid tones without a lot of attack, the post tonestack clipping might be cool. That being said, It doesn't add a whole lot. Not nearly as much of a tone change as overdriving the fx return on a two channel mesa dual rectifier.

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Post by Reachahighernoon »

bmxguitarsbmx wrote: 25 Jun 2022, 18:19
Reachahighernoon wrote: 25 Jun 2022, 16:34 I was actually wondering about the post tonestack stage and how much it affects the overall sound of the amp because from what I saw of solid state versions in pedal form the only thing that exists post tonestack is a small booster buffer and the Deep/Presence controls

I designed my own version but of the channel 4, based on the same schematic you posted, if you want I can share it
VH4 ch4 is insane gain. I would say you don't need the post tonestack overdrive. It all depends on your personal preference though. I want a certain amount of percussiveness in the attack even for lead tones. We'll see what ReverendBow says about the levels of gain of ch3 the way he is setting it up. CH4 is very cool. It has so much gain that it sounds synthetic. Very processed, but in a cool way. The level of gain is similar to a evh 5153. Like useful gain values are between 0.9 and 3 for either amplifier and I hate to say it, but the 5153 has a more useable rhythm tone. So, I would say skip the post tonestack clipping for both CH3 and CH4. It just so much gain. But, if you like liquid tones without a lot of attack, the post tonestack clipping might be cool. That being said, It doesn't add a whole lot. Not nearly as much of a tone change as overdriving the fx return on a two channel mesa dual rectifier.
It sounds at this point like it's better to overdrive the input if you want more gain

And I wish I could do a tube preamp of a 5150 but for some reason the schematic is a bit too complex IMO

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Post by bmxguitarsbmx »

The gain level is highly personal, I'm just giving my opinion. :)

Yeah, some of those old peavey schematics are a bit tough to look at. There is a simplified version of the block/sig. 5150 out there. Which is my favorite version, though I think all 5150 versions are great. Indulgant amounts of gain for sure! But, great amplifiers.

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Post by Reachahighernoon »

bmxguitarsbmx wrote: 26 Jun 2022, 20:09 The gain level is highly personal, I'm just giving my opinion. :)

Yeah, some of those old peavey schematics are a bit tough to look at. There is a simplified version of the block/sig. 5150 out there. Which is my favorite version, though I think all 5150 versions are great. Indulgant amounts of gain for sure! But, great amplifiers.
I've looked at the schems again, I mean it is doable but that means 3 tubes in a pedal with no clean channel, eh could be worse

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