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Relay based volume controls on ebay
Relay based volume controls on ebay
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Old 16th September 2017, 03:26 PM   #1
music4cities is offline music4cities
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Default Relay based volume controls on ebay

Hi,

I neee to replace the volume pot on a Sunfire Classic Vacuum Tube Control Center (preamp), and in doing so add remote control for the vol level.

I have already replaced the original vol pot (which had broken) with a DACt type serial attenuator off ebay and it was a noticeable improvement in clarity and problem free swap out. Better than alps blue velevets (real ones) I have used I think. Anyway Very nice inexpensive unit and the seller laser collection was great to work with. Seems to know his/her stuff.

But to add remote The relay based ladder resistors seem to be the best option, and of course, reduces the number of resistors in the path.

Two questions:

1) any issue with using such a control in a tube preamp? I don't see why but thought I'd ask. The spec output impredance of the pre is extremely low, btw.

1b) The stock pot is 100k; would a 50k present a problem? I know I can add resistors to a 50k if needed. The main issue I guess would be that while the volume is before the main stage for all line level inputs, there is a very good tube driven mm/MC phono stage before it that MAY Have a higher output impedance.

2)

I was wondering if anyone has had experience with any of the ones available on ebay, such as: Assembled Remote volume board 128 steps 2 channel 50K Relays preamp | eBay

Seems more or less a clone/adaptation of known designs. Entire built preamps are also available. Vishay resistors. I don't need the source switching, but it works fine without it apparently. It's 50k ohms but the seller is happy to modify it to 100k to match the stock pot value (or I guess I could if needed after trying it at 50k). I would probably leave the led board buried within the amp case and adapt the ir, running an extension a couple inches to discretely sit behind an plastic window that shows off the tubes. The encoder can be detached from the led display board fwiw.

I would either just wire the relay board into the existing volume pot location using short 1-3" jumper wires -- likely the "safest" route. or perhaps bypass the entire vol section (which is on the power board rather than the main line stage board), tapping into the traces or the headers on the main line stage board, which could possibly shorten the path. The way the pre is laid out, the input traces are pretty long: running from the input selector switch in back, then across the edge of the phono stage board, then across a header to the main line stage, across the width of the line stage board to another header connected to the volume control on the power board, and then back through that header to the actual line stage circuits. Must be at least 2-2.5' of traces, 3 headers, 3 short ribbon wires the signal passes through before hitting the active stage. No sure it really matters though.

Either way I think I can situate the relay board outside the shielded power and transformer area. There is plenty of room in the case for either option.
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Old 16th September 2017, 03:46 PM   #2
music4cities is offline music4cities
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Forgot to mention that the pre has three switched ac outlets on the back I figure I could use one to supply power to the 12vac transformer for the relays control (the actual attenuation is all passive). Plenty of room to add a small 12vac supply as a wall wart or transformer.
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Old 20th September 2017, 04:41 PM   #3
kodabmx is offline kodabmx  Canada
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I just bought this one: Hi-End VOL / 2-Channel Relay Volume Control Board /Stereo volume board | eBay

I'll let you know what I think sometime in October/November.
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Old 16th January 2018, 08:53 PM   #4
IDM is offline IDM  United Kingdom
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Hi,
I wondered if any opinions were reached over the quality of these Ebay really attenuators?

I am also looking for an alternative to my alps potentiometer.
Cheers
Ian
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Old 17th January 2018, 06:33 AM   #5
mchambin is offline mchambin  France
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This design makes a spike when switching.
I wonder if it is noticeable.
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Old 17th January 2018, 07:46 AM   #6
Nico Ras is offline Nico Ras  South Africa
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Spikes in switching results in blown tweeters. The worst spikes is when switching three (or more) relays off and one one. If it is a powerful amplifier expect powerful narrow spikes. Unless the system is designed around make-before-break concept.
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Old 17th January 2018, 09:56 AM   #7
IDM is offline IDM  United Kingdom
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I read somewhere that some of the Ebay relay volume controllers are fine. So its a case of knowing which ones might be ok. I was hoping the original posters might provide some feedback, or indeed anyone else who is using one.

Certainly if it is a case of risking a tweeter, I am not interested :-)
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Old 19th January 2018, 04:33 PM   #8
kodabmx is offline kodabmx  Canada
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I have it here but haven't installed in anything yet. I'll let you know when I do.
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Old 19th January 2018, 06:16 PM   #9
rif is offline rif  United States
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Relay based volume controls on ebay
Quote:
Originally Posted by mchambin View Post
This design makes a spike when switching.
I wonder if it is noticeable.
The 2nd one says "no sonic boom". I'm assuming that's the normal thump? It also has a "dule goal coated" PCB". Something is obviously mixed up in translation.
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Old 19th January 2018, 07:38 PM   #10
kodabmx is offline kodabmx  Canada
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Dual Copper coated board more likely.
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