how to reduce power in a deluxe reverb

[chris shaw]

Guys
Greetings from UK
I've just built my first amp - an ab763 deluxe reverb clone, and .... its really loud
I play coffee shop gigs in small rooms, often alone
Is there a good, harmless, preferably switchable way to drop power by 50 or even 75/80%
I could build a champ but gigs vary, drummers etc. etc.
If you couldv keep it simple or draw me a picture that would be great-- It was my first build and quuite traumatic!!

[booj]

looks like a good place to use THD Yellow Jackets.

THD Electronics

[rudutch]

perhaps an inefficient speaker? like 95db / spl

[olddawg]

Weber attenuator? Mount it on the bottom of the cab?

[Chuck H]

Look at the following diagram. It sounds quite good for a purely resistive attenuator. You can build it in a seperate chassis and mount it right in the cabinet. I use the Arcol aluminum housed resistors and Ohmite rheostats from Mouser in a Hammond 3x4x6 aluminum "utility case". -2db to -20db attenuation, easy to mount, easy to use and cheap to build.

Chuck

[HTH]

You could cathode bias it, but you wouldn't lose much volume overall.

A simple 1M log master volume is the best solution wired before the PI (typical pre-PI master).

I know opinion is divided on this type of master, but I find them to be very natural sounding and to maintain the core amp tone (unless you're using them at bedroom levels). For the gigging musician, this is the best way forward imo.

[olddawg]

Look at the following diagram. It sounds quite good for a purely resistive attenuator. You can build it in a seperate chassis and mount it right in the cabinet. I use the Arcol aluminum housed resistors and Ohmite rheostats from Mouser in a Hammond 3x4x6 aluminum "utility case". -2db to -20db attenuation, easy to mount, easy to use and cheap to build.

Chuck

Chuck....What kind of variable load does a tube amp see with this circuit? What is the max dissipation it can take? I would love to use this as a built in feature in 18 watt clones etc. Will it take 50 watts?

[J M Fahey]

Chuck H: excellent design, congratulations !!
A little math:
Setting-Amp sees-Attenuation.
"10"-----6 ohms-----SS amp: none (constant voltage source)
---------------------------Tube: 20% of the power flows through the resistors
"0"-------8 ohms------20 dB
Gentle on the amp, *very* useful.

[Chuck H]

Will it take 50 watts?

That depends on what size resistors and rheostat you use. Just for safety and to control heat I use a 50watt 10r, a 25watt rheostat and a 10watt 1r and call it good for 25 watts. I only use it in a seperate chassis for "tubes hanging" amps, also to control heat. In a "tubes sticking up" type build I would mount it in the amp chassis itself though. But I would try to keep it away from the filter caps, even though IME it doesn't get all that hot. In fact I'm putting one in a custom build for John Tristao from CCR (singer) thats going to be 4 x EL84's. I'll be mounting the resistors on the "outside" of the chassis with the transformers, tubes etc. It's a "tubes up" build with a 4/8 switchable output impedance. So I'm using a 50watt 10r, another 25watt 10r (added in parallel for the 4 ohm setting), a 50watt rheostat and a 15 watt 1r. If I wanted to sure it would take 50 watts I would probably use a pair of 50watt 20r in parallel to replace the 10r resistor, a 50watt rheostat and a 15watt 1r. By the way, you don't need the 1r at all. But most rheostats are kinda glitchy and the 1r seems to smooth this out a lot.

The reflected impedance for the 8 ohm unit (shown above) swings from 8 ohms at full attenuation up to about 10 ohms in the middle and then down to 6.5 ohms turned up all the way. Perfectly safe for an 8 ohm secondary. Besides, since the speaker is getting most of the current in the full up position, any speaker impedance rises to over 30 ohms at certain frequencies. So that 6.5 ohm is kind of a misnomer if you get my meaning. I would always include a bypass switch. It's a good system and has a far less radical impedance swing than other attenuators I've checked out. My own "stand alone" unit does use inductors and caps to more closely emulate a speaker load and sounds a little better than the purely resistive design, but only with high amounts of attenuation.

I hope you enjoy it.

Chuck

P.S. Thanks Fahey. The circuit just occured to me one day when I was designing an amp for the 2009 Winter NAMM show. Dean Markley liked the amp I was working on but thought it was too loud (20 watts !?!) I thought other attenuators were either too complicated and/or had too much impedance swing in their range. After developement I discovered that the early Weber stuff works on a similar design principal. I'd like to try one sometime. My personal 'homemade' one uses the same circuit but with the R. Aiken speaker load circuit in place of the 10r. It works very well.

[chris shaw]

need more simple picture

chuck h
than ks chuck , it sounds really good judging by other peoples comments but I really am a beginner and have relied on layout pics to enable me to build -any chance of a more 'for dummies pictorial diagram-- what to solder where type picture
really sorry for my ignorance and I appreciate your time

[Chuck H]

Does this help?

This view would be looking at the components as you would solder them.

You can arrange the components however you like really. Or do it just like this.

HTH

Chuck

[chris shaw]

You could cathode bias it, but you wouldn't lose much volume overall.

A simple 1M log master volume is the best solution wired before the PI (typical pre-PI master).

I know opinion is divided on this type of master, but I find them to be very natural sounding and to maintain the core amp tone (unless you're using them at bedroom levels). For the gigging musician, this is the best way forward imo.

hth
sometimes gigs arent far off bedroom level but I'm willing to give your idea a go

I know where PI circuit is but am unsure about exactly where and how to connect master volume 1K log pot in this (also how big does pot need to be )
the circuit i followed was as follows:- https://taweber.powweb.com/store/6a20_layout.jpg
does the pot simply go inline before pin2 of v6 ?
I am a very inexperienced builder so simple and basic is good for me (which pot connection to where, does it need earthing etc. a picture is even better!!! --- got any tips ?
thanks
hope your weather is getting better -am in sheffield and its thawing here

[HTH]

hth
sometimes gigs arent far off bedroom level but I'm willing to give your idea a go

I know where PI circuit is but am unsure about exactly where and how to connect master volume 1K log pot in this (also how big does pot need to be )
the circuit i followed was as follows:- https://taweber.powweb.com/store/6a20_layout.jpg
does the pot simply go inline before pin2 of v6 ?
I am a very inexperienced builder so simple and basic is good for me (which pot connection to where, does it need earthing etc. a picture is even better!!! --- got any tips ?
thanks
hope your weather is getting better -am in sheffield and its thawing here

its thawing here in Newcastle, but still not moving much from around 0degrees. I've caught the flu thats going round and feel like hell

anyway, for your amp I'd just break the connection between the two 200k channel mixer resistors where they feed the input to the PI via the 0.001 cap.

a 1M log pot will do the job.

[chris shaw]

top man
get well soon
all the best for 2010
chris

[Kagliostro]

give a look to this link, read all

Disconnecting one output tube in a push pull amp

and consider this

http://www.el34world.com/Forum/index....0;attach=4084

Kagliostro