Need help adding slave-in jack on Dr103 clone

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dlp
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Need help adding slave-in jack on Dr103 clone

Post by dlp » Wed Jul 12, 2017 11:45 pm

I just finished building a DR103 clone using Mark Huss's diagrams and schematics (thanks Mark) and I'd like to add a slave-in jack. I'm looking to switch back and forth between the Hiwatt preamp and an outboard preamp.

I can't find much info on this mod. From what I can gather I only need to add a jack between the preamp and power amp and it looks like a good spot to interrupt might be either the wiper pin on the treble pot or the wiper pin on the master volume pot.

Can somebody help me out with this please? Thanks
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Stevem
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Re: Need help adding slave-in jack on Dr103 clone

Post by Stevem » Thu Jul 13, 2017 10:53 am

Take a look at the schematic for a Soundcity L/B 120 mk lV .
Most times with good Amps just like it is with sex, it's best to just plug straight in!

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martin manning
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Re: Need help adding slave-in jack on Dr103 clone

Post by martin manning » Thu Jul 13, 2017 11:09 am

The slave input would have to go at the top of the master volume. I would put a 22n cap at the slave input jack, and use a switching contact to disconnect the 22k resistor feeding it. If you can arrange to ground the 22k, that would be even better.

dlp
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Re: Need help adding slave-in jack on Dr103 clone

Post by dlp » Fri Jul 14, 2017 9:27 am

Stevem wrote:
Thu Jul 13, 2017 10:53 am
Take a look at the schematic for a Soundcity L/B 120 mk lV .
Thanks for the suggestion. I looked it over and I don't think I can make that work. I'm not very knowledgeable on electronics so maybe I just don't understand. There is no master volume like I have on mine. There are 2 slave jacks. One jack goes to pins 2&3 of v1 and the other goes to pins 7&8 of v1. The best I can tell (and maybe I just don't understand) the two slave jacks are nothing more than attenuated inputs that go thru the preamp just like the other inputs.
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Stevem
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Re: Need help adding slave-in jack on Dr103 clone

Post by Stevem » Fri Jul 14, 2017 10:58 am

Yes, they are just attenuated.
Most times with good Amps just like it is with sex, it's best to just plug straight in!

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M Fowler
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Re: Need help adding slave-in jack on Dr103 clone

Post by M Fowler » Fri Jul 14, 2017 1:55 pm

Just put in a send and return jacks/and or stero jack between the master volume pot wiper and phase inverter input.

tictac
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Re: Need help adding slave-in jack on Dr103 clone

Post by tictac » Sat Jul 15, 2017 9:42 pm

Maybe a good question would be, "what are you use the slave in for?"

The cathode follower output before the PI would be the most logical place to put an effects loop send/return jacks.

The send becomes a lo-Z preamp out and the return becomes your slave-in (aka power amp in)

The other option would be use the unused 12AX7 triode for a dedicated slave-in. the slave-in jack would go to the input or the triode and the output could be mixed into the PI thru a 220K or so resistor.

TT

dlp
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Re: Need help adding slave-in jack on Dr103 clone

Post by dlp » Sun Jul 16, 2017 6:24 am

martin manning wrote:
Thu Jul 13, 2017 11:09 am
The slave input would have to go at the top of the master volume. I would put a 22n cap at the slave input jack, and use a switching contact to disconnect the 22k resistor feeding it. If you can arrange to ground the 22k, that would be even better.
Are you suggesting the 22n be inline with the incoming signal to the max volume pin of the master pot? I know this picture won't disconnect the 22k or ground it. I'm just trying to figure out where the components go so I can figure out how to make the jack work.
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martin manning
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Re: Need help adding slave-in jack on Dr103 clone

Post by martin manning » Sun Jul 16, 2017 8:34 am

Yes, that's it. The cap is there to keep DC off of the input.

dlp
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Re: Need help adding slave-in jack on Dr103 clone

Post by dlp » Mon Jul 17, 2017 12:45 am

M Fowler wrote:
Fri Jul 14, 2017 1:55 pm
Just put in a send and return jacks/and or stero jack between the master volume pot wiper and phase inverter input.
tictac wrote:
Sat Jul 15, 2017 9:42 pm
The cathode follower output before the PI would be the most logical place to put an effects loop send/return jacks.
Thanks for the ideas. I think you guys are suggesting I bypass V3? I read that 1/2 V3 functions as a voltage reference for the Hiwatt PI. I have no idea what that means. But if you look at a Hiwatt slave amp schematic the ECC83 is wired very close to the same as V3 on the Dr103 in relation to the phase inverter. I'm just wondering if the voltage reference is needed on the Hiwatt.
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martin manning
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Re: Need help adding slave-in jack on Dr103 clone

Post by martin manning » Mon Jul 17, 2017 1:08 am

Mark is suggesting using V3 pin 7 as the return (slave) input, and you could do that, but you would need a ground reference, and it'd be a good idea to block any DC with a cap. Might as well use the top of the MV pot for the input and use it for an input level control. Tictac's idea would require more than just send and return jacks since the DC voltage on V3 pin 3 sets the bias point for the PI.

dlp
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Re: Need help adding slave-in jack on Dr103 clone

Post by dlp » Tue Jul 18, 2017 11:00 pm

martin manning wrote:
Mon Jul 17, 2017 1:08 am
Mark is suggesting...
Thanks for your help. I think this layout will disconnect the 22k and reconnect it to ground.
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martin manning
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Re: Need help adding slave-in jack on Dr103 clone

Post by martin manning » Wed Jul 19, 2017 12:16 am

Cliff TRS jack version:
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dlp
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Re: Need help adding slave-in jack on Dr103 clone

Post by dlp » Wed Jul 19, 2017 7:33 am

martin manning wrote:
Wed Jul 19, 2017 12:16 am
Cliff TRS jack version:
I like the Cliff jack a lot better. But I think we need to move the 22k to the other side to ground the disconnected end.
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martin manning
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Re: Need help adding slave-in jack on Dr103 clone

Post by martin manning » Wed Jul 19, 2017 10:56 am

Either way will work to ground the output of the on-board preamp. I wanted to put both ends of the 22k on the jack, but if it is presently mounted on a board you can leave it there and wire it like the new version. In fact it wouldn't matter much if the slave input went through the 22k to the pot since the attenuation at the max volume setting would only be -0.7 dB (assuming a 250k pot). Your choice based on whatever is most convenient layout-wise.

BTW, if you want to minimize loss of audible bass frequencies you could increase the 22n to 47n, moving the -3 dB roll-off down to 14 Hz from 29 Hz.

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