Chandler Tube Driver Rack

[beatnik]

Hi everybody,

I'm in the process of making a layout for this preamp /distortion box. Am planning to fit two channels in 1U rackspace.

http://assets.accordo.it/images/articles/p_a1ab_1.jpg

I have found a schematic on the web and started redrawing in eagle.

I am kind of a noob in circuit theory, so I would really appreciate if some expert eyes could give a look to my schematic and spot eventual mistakes. I am mostly unsecure about potentiometers orientation and jacks normalling.

Obviously any other suggestion/improvement to the design is highly appreciated!

The layout will be public on the forum for self-etchers. Long live diy! Eventually if there is some demand I will organize a pcb batch.

Many thanks in advance

 

[john12ax7]

One possible change could be to use discrete jfets instead of the opamps. A good bit of a re-design though. If you do a straight up clone I might be interested. Never tried the rack but the pedal version is awesome.

 

[beatnik]

Let's start on getting a pretty straight forward replica working, then try more radical mods. the doa idea sounds good btw.

I have a question about the powering supply. On the original schematic I don't have any data about the power transformer.

What voltage do you think are the opamps and tube heaters running?

I attach original schematic too

 

[JayDubrek]

Those opamps run on 4-15VDC while typically a 12AX7 is 6.3V either AC or DC...if you were considering a stereo unit 2 tubes can have heaters wired in series at 12.6V...

 

[beatnik]

So would be ok to run the opamps at +/- 12VDC and the heaters + 12VDC too?

I think I'll choose a dual 15V transformer, what do you think?

 

[john12ax7]

So would be ok to run the opamps at +/- 12VDC and the heaters + 12VDC too?

I think I'll choose a dual 15V transformer, what do you think?

That would work, might as well go +/- 12.6V if you go that route. Another option which a lot of pedals do is to use a 12V wall wart.

 

[alexc]

12AX7 (and the rest of the 12xx7 series) use 6.3V@300mA or 12.6V@150mA heaters.
Either AC or DC.

No need to wire heaters pairs of stereo parts. I would not do that for various reasons.

If you go DC on the heaters, you could use 12VAC secondary or 15VAC secondary.

If you don't use a regulator for the heaters, you will need a voltage dropping resistor
to 'adjust' the dc voltage to be 12.6V. Needs to be of sufficient wattage to handle the
power.

Or you can use a voltage regulator, in which case it needs to be heatsinked to able to handle the power
dissipated by the regulator : voltage drop x the current passing thru it.

For AC, a 12VAC rated secondary may get you close enough to the 12.6VAC heater requirement
or you may also need a dropping resistor.

Since you need around 12VDC regulated supplies for your opamps and what not, I would get
a pair of 12V regulated supply PCBs and use them off a pair of 15VAC secondaries.

If you have the chassis space, even better, a pair of dual 12VDC regulated pcbs -
so each channel has one regulator for heater and one for opamps.
I prefer not to mix them, again for various reasons.

Looks like an interesting project.

 

[beatnik]

alexc thanks a lot for the great info.

i'll make an external psu board regulated with lm317 to adjust voltages to 12.6

am finishing the pcb layout and hope to try a prototipe very soon.

stay tuned!

 

[James Cassidy]

Hey Y’all!
I have 2 Chandler TD Racks (The REV 2’s), and I’m just hoping maybe some peeps out there could hopefully help me with some advice, and guidance.

I’m going to be recapping them both, and firstly just wondering if anybody has a schematic for this version, as I can’t seem to find one.

I’m also just wondering if anyone out there knows which caps would be good candidates for trying out some Wima’s, I’d be super grateful.

Thanks so much! Here’s a few pics.

 

[rock soderstrom]

Hey Y’all!
I have 2 Chandler TD Racks (The REV 2’s), and I’m just hoping maybe some peeps out there could hopefully help me with some advice, and guidance.

I’m going to be recapping them both, and firstly just wondering if anybody has a schematic for this version, as I can’t seem to find one.

I’m also just wondering if anyone out there knows which caps would be good candidates for trying out some Wima’s, I’d be super grateful.

Thanks so much! Here’s a few pics.

Why recap? Any defects? If so, replace with the technically identical capacitors. If the aim is to "improve" the sound, I would not do this, the difference, if audible, will be marginal. On the other hand, there is a high risk of destroying one of the very fine (double sided!) PCB traces when replacing the caps.

Just my 2 cents...

 

[abbey road d enfer]

No need to wire heaters pairs of stereo parts. I would not do that for various reasons.

+1

If you go DC on the heaters, you could use 12VAC secondary or 15VAC secondary.

If you don't use a regulator for the heaters, you will need a voltage dropping resistor
to 'adjust' the dc voltage to be 12.6V. Needs to be of sufficient wattage to handle the
power.

According to schematic there is a dropper resistor, 22R. Assuming heaters are in series @150mA, that's a drop of 3.3V, so rectified voltage would be 12.6+3.3=15.9V, which is perfectly compatible with a 12Vac xfmr. With about 2V drop in R2/R22 opamps would be powered at +/-14.

Or you can use a voltage regulator, in which case it needs to be heatsinked to able to handle the power
dissipated by the regulator : voltage drop x the current passing thru it.

A regulator would impose the use of a higher voltage xfmr, since they want to see about 3V to operate correctly; the voltage would be a tad too high for teh opamps, which would require either replacing R2/R22 or using regulators.

 

[drtechno]

So would be ok to run the opamps at +/- 12VDC and the heaters + 12VDC too?

I think I'll choose a dual 15V transformer, what do you think?

I have that transformer on file.

It is a 24VCT @ 6VA

I would build it like they build it and don't jack with modding it (first)

 

[James Cassidy]

Why recap? Any defects? If so, replace with the technically identical capacitors. If the aim is to "improve" the sound, I would not do this, the difference, if audible, will be marginal. On the other hand, there is a high risk of destroying one of the very fine (double sided!) PCB traces when replacing the caps.

Just my 2 cents...

Hey!

Thanks for the reply!

Ya, so basically I have two units, both exactly the same. The one with the old caps(pushing 35years old) doesn’t sound too great. The other unit had the Electrolytics changed/upgraded a few years back, and it sounds soooo much better.

I know part of it is tolerance drift, but I’m pretty certain a recap is going to help it a tonne. It works fine, but just sounds bad. Way darker, hazier, less headroom and punch etc.

Once caps start pushing 25-30 years old in something, especially when they aren’t particularly great, I’m all for getting them out. Especially if a unit sat unused for a long time, which I’m guessing there’s a good chance this one did. If the unit sounded good, it may be a different story, but it doesn’t lol. Also, it’s not so much that its better caps will be the difference, but just getting the old ones out.

The other thing is, since I’m doing it with the one, I’m just going to take the opportunity to Recap both, with all the same type of Caps, and I’m also upping some voltages in a few places, and changing the big Axials to Radials for heat dissipation. I use these for mixing a lot, so if I can get them matched a little better, it could be a bit more ideal if l ever want to use them on a Sterio Track, or Mix etc.

I don’t think I’m going to bother with Wima’s at this point though.

Does anyone out there actually have, or know where I can find a schematic for my unit ? I can’t seem to find it anywhere!

Rock on!

 

[James Cassidy]

Sooo, I guess no one knows where I can find a schematic for the Tube Driver Rev2 Huh?

Also, I just had another question I’m hoping somebody can help me with. Not sure how easy it is to tell, and also sorry if this is a bit of a newb question, as I won’t lie, I’m not super experienced when it comes to schematics, and knowing certain ins/outs about circuits, but you know the 3 big 2200uf/35V Caps, and how there’s the two on one side, and the other one down near the other end by the tube, what purpose are they all playing in the circuit? I’m guessing the two on one side are power supply, and is the other one also power supply, or is it for something else in the circuit?

Thanks Yall’

J

 

[abbey road d enfer]

what purpose are they all playing in the circuit?

Indeed they're all in the PS.

I’m guessing the two on one side are power supply, and is the other one also power supply, or is it for something else in the circuit?

The current draw on the negative rail is larger than on the positive rail, so it takes a larger capacitor.