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are there reverb units you can use in place of tanks?

 
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George
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PostPosted: Sun Jun 05, 2016 7:11 pm    Post subject: are there reverb units you can use in place of tanks? Reply with quote

that connect by the rca leads?
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NickS
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PostPosted: Mon Jun 06, 2016 11:52 am    Post subject: Reply with quote

Interesting idea. It will depend on the circuitry - did you have a particular amp model in mind? You can buy RCA-to-jack leads. Levels might be an issue, you might need attenuation somewhere for best results.
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George
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PostPosted: Mon Jun 06, 2016 12:18 pm    Post subject: Reply with quote

it strikes me as something that could really help open up a lot of older amps without fx loops, but i don't know how any of that stuff would work in practice.

the particular amp in question is the new vox ac15ch head ive got. love the tone, hate the spring reverb(!) - the volume and effect of it must be heavily subdued by the circuit somewhere. i've swapped the stock tank out for a longer 2 spring version (correct matched impedances etc) that sounds huge and drippy in fender circuits but insipid in the vox.

major tangent below!
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the reverb circuit of which is as follows (my pcb is stamped for an ac15c1 as well):



on other similar circuits people seem to point toward changing or jumpering the various ferrite beads in the output section (R62, R63 or R64) which is just before the output, but there's nothing confirmed out there for me to do without experimenting, so i might try out a jumper cable on R63 and/or R64.

any suggestions? Laughing
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sunshiner
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PostPosted: Mon Jun 06, 2016 1:38 pm    Post subject: Reply with quote

Time to start fannying about with fender-styled amps?
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Fakir Mustache
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PostPosted: Mon Jun 06, 2016 3:22 pm    Post subject: Reply with quote

I would expect some level problems, apparently he didn't have any:

Link

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NickS
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PostPosted: Mon Jun 06, 2016 3:31 pm    Post subject: Reply with quote

Well, the Vox AC15C1 reverb drive stage seems to have quite big gain of around 75 (R30/R29) although this will be slightly reduced by the current feedback through R41, and the reverb return amp stage has gain of around 20 (R52/R45).

The return amp stage has significant top cut (R52 in parallel with C37) starting at around 2.8 kHz, and bottom cut (C35/R45) operating at around 340 Hz; and the drive stage also has bottom cut (C21/R29) operating at around 280 Hz.

The ferrite beads are to eliminate RF pickup. If you want more high end on your return, changing the C37 560 pF to something smaller (say 150 pF) will have more effect than shorting out the ferrites.

If you wanted to use an external reverb pedal without modding the amp I think your best bet would be to use an attenuator on the output with a high-pass element to counteract the top cut and probably an attenuator on the input as well. Or maybe just suck it and see.


[edit: remove unnecessary "then"]


Last edited by NickS on Mon Jun 06, 2016 4:00 pm; edited 1 time in total
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George
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PostPosted: Mon Jun 06, 2016 3:35 pm    Post subject: Reply with quote

looks like im going to get the best/easiest result by using an aby box where it splits into

a: delay -> reverb -> normal channel (low gain)
b: boosts/ts -> top boost channel (med-high gain)

once you start driving the preamp tube (which sounds great!) the reverb sounds awful so the above should hopefully solve that issue if it's just on the top boost channel. plus, even an fx loop or decent reverb tank solution would be placed before power tube breakup. modding the reverb circuit can come later if this doesn't work out.
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George
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PostPosted: Mon Jun 06, 2016 3:37 pm    Post subject: Reply with quote

wow thanks for the reply nick!

good to know people with knowledge are around for when numpties like me are about to blow their amps up.
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Bacchus
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PostPosted: Mon Jun 06, 2016 3:57 pm    Post subject: Reply with quote

NickS.

The S stands for Science.
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George
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PostPosted: Wed Jun 08, 2016 8:43 pm    Post subject: Reply with quote

George wrote:
looks like im going to get the best/easiest result by using an aby box where it splits into

a: delay -> reverb -> normal channel (low gain)
b: boosts/ts -> top boost channel (med-high gain)

this worked really blooming well tonight. when using drives and boosts in channel a, the reverb and delay in channel b didnt get muddy or boomy, but still a bit louder in the mix on account of the power tubes being pushed harder by channel a. pretty much responded how i'd want it to.
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Brandon W
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PostPosted: Wed Jun 08, 2016 9:49 pm    Post subject: Reply with quote

pretty sure this has nothing to do with your question but how amazing is this..

T-Rex
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NickS
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PostPosted: Wed Jun 08, 2016 9:59 pm    Post subject: Reply with quote

Having trouble finding the RCA connectors on this tank.
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Fakir Mustache
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PostPosted: Thu Jun 09, 2016 5:26 am    Post subject: Reply with quote

George wrote:
George wrote:
looks like im going to get the best/easiest result by using an aby box where it splits into

a: delay -> reverb -> normal channel (low gain)
b: boosts/ts -> top boost channel (med-high gain)

this worked really blooming well tonight. when using drives and boosts in channel a, the reverb and delay in channel b didnt get muddy or boomy, but still a bit louder in the mix on account of the power tubes being pushed harder by channel a. pretty much responded how i'd want it to.
If you use a regular overdrive for the top-boost channel, then that should have a regular volume knob and you can use it.
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I only buy synths with mini keys as I like the shortscale synths.
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George
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PostPosted: Thu Jun 09, 2016 8:27 am    Post subject: Reply with quote

but i want to push that channel hard cos it sounds fantastic. i had the top boost channel volume (gain) set a little lower than the normal channel though for that reason yea. sounds more spatial with cleans but less so when the dirts pick up
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