you could bypass R2 with a capacitor and have a somewhat similar effect as bypassing a cathode resistor, since it affect the gain ratio dependendt on input frecuency...
i supose thats the idea of bypassing a cathode resistor.

you can use the following formula to find the crossover frecuency (F₀)
F₀=1/(2pi*R*C)
or
C=1/(2pi*R*F₀)

hi there
ive been a bit busy but this weekend i took some time look at the amp
there vas noting to find with the "finger test" so i started to remove IC one by one, after a few removals with no luck i decided to check if the power amp it self was working so i liftet the pins of R83&78 aplyed +- 15volt from the bench supply and a sine signal at IC8 pin7, hooray a nice amplified sine wave output.
back to removing after having removed 6 IC i startet to think why isnothing getting warm
...well 40V (unreguletet) across 270R thats about 150mA, not strange that nothing is warming up. so i connectet my bench supply with no current limit. and yes i got warm...hot it drew 2,5A and IC was smoking.
so problem located. IC10 was of course the last IC to be removed becuase of how they are lined up.
I will also replace IC9

a friend gave me a valvestate vs8100 it did not work, i found out that the -15 volts were not there, i changede C61, C62 &  R101 they were looking suspicious. i now had +8 -6 volts or so. i replaced Zener diodes no change, then i removed TR8-9-10. and then +/-15 volts were on.
then i replaced them and it seemd maintain voltages.
i applyed signal and its output was not pretty. i then saw that problem was IC1. i took awhile since i started applying signal at input of IC8B and halfling my way back through the circuit.
but replacing IC1, it was shortet between + & - pins, it then was up and running.
so i dragged it to a fiends studio to see what i could do and try it with different speakers. it worked for a while, and i played around a lot with settings and then i wanted to try it with another cab, nothing but silence... voltmeter told me no +/-15V.
i tried some of the same procedures from last time but no luck this time and its pissing me off.

i hope someone have had a similar experience or maybe a usefull input.
i attached a schematic

thank you both very much

i knew the ESP page but never saw the articles only the projects...i have now change bookmark to main page.

i have also been wondering how do you know if what minimum load your output is capable of?

I would go with the volume pot for line-out, you could use a buffer or jack-switch to silence the power amp when using the line out.

if you want to use the signal at the speaker wires disconnect it and replace it with a power resistor of equal value, mount it on a heatsink...and no drummer in your amp

hey
I have been wondering when building an amp how do i choose the correct transformer?
I guess first  i should start with choosing output power, lets say 120W_RMS, then amplifier class since it says something about how effective it is, i think that AB is about 70%, not sure.
If so, then 120/0,7= 171VA supply?
How do you determine supply voltages, output power and speaker loads?

Voltages should bee high enough to put out 120W in 8R:
V=SQR(P*R)
V=SQR(120*8 )
V= 31V
but that's only RMS, The peak voltages are then:
V_p=V_RMS*SQR(2)
V_p=31*SQR(2)
V_p=44V

I believe these are important considerations when designing an amp, im not sure if im on the right path here

yeah.......... it not that hard but dig up a schematic and i could help you
it would be best if you put a input buffer  on it

thank you all for your help, unfortunately ive have no time nor monety to realize this project at the time but it will happend and then ill post the result

QuoteI've heard that this is totally fine, and also heard this could mess my heads up.

I've heard I need a splitter box, and also heard I don't need one-but it will make it "sound better".

there's no harm but it could be a impedance problem, this could make your instrument sound darker, less bright.
if the instrument output impedace is larger than the amp in then theres a high frequency loss, roughly said.

QuoteHeard Morely's are garbage, heard they are good.  Heard that the Radial Engineering BigShot ABY Passive Switcher is good, but it's PASSIVE (and I don't really know what that means!)

the splitter box has buffers that will lower your instruments output impedance, this would be an active splitter box
the passive a/b/Y splitter box, when in y-mode is actualy the same as a y cable...

Quote from: Bassbuddy on April 12, 2010, 01:05:06 PM
Hi
The idea I meant was not using a PA amp but to build a separate preamp in such a way that it can be combined easily with A power amp to make a nice matched couple. I will attach pictures of my amp to show what I mean.
GG

this is what greg ginn of black flag uses, in the old days he plugged his guitar directly into the PA amp and turned up the volume until he reached enough distortion...

yours is looking very good

Quote from: J M Fahey on April 09, 2010, 11:40:57 PM
Just some curiosity: where does it claim "180W", close to the power cord ot to the speaker outputs?

well i cant remember and im not near it at the time but i found this:

Yamaha budget amp
Natural Sound Systems Ltd., Unit 7, Greycaine Road, Watford WD24SB have announced a new budget amplifier. The Yamaha A-320 (8995) has kept costs down (and possibly improved overall quality) by omitting tone controls and filters. Separate Left and Right volume controls combine the functions of gain control and balance, but are friction ganged to work together as required. The amplifier is rated at 30 watts-per-channel into 8 ohms, with a claimed 'dynamic power' of 50 watts into 8, 4 or 2 ohms

here
http://www.gramophone.net/Issue/Page/April%201985/122/851895/

but i dont think its around the speaker connection...havent thought about it before you mentioned it

i wonder how to understand the power rating...dynamic power? same at 2, 4 and 8 ohm

thanks alot ....again
repetitive questions are only to be shure that ive understood it right

Quote from: phatt on April 09, 2010, 06:47:43 AM
180 Watts per channel is probably optomitic,, but if it's very heavy
(due to massive transformer) then could be so.

More likely to be 180 Watt *Total* or 90 Watts per channel.
So that 90 Watts into 8 Ohms will be 65-ish Watts into 16 ohms.
Still above average for a HiFiAmp.

If you use a stereo efx processor then you can run the stereo out to both channels and that would rattle the windows I'm sure.
Phil.

90-70 thats some where around what i thought since it doesnt say watts per channel but i better thought better get a second opinion on it.

about the stereo thing i already thought about it with a dual preamp, one for each power amp with some jack switch thing, example, if only input 1 is used it drives both preamps 1 and 2, but if somethings only conected to input 2 it would only drive preamp 2, if both inputs are used they would each drive their own preamp. preamp 1 would go to left poweramp and preamp 2 would go to right poweramp. or maybe just a flip switch for mono/stereo mode (one preamp driving both power amps or two preamps driving seperate power amp, still dual preamp).

....and yes windows will rattle and neighbours will be annoiyed

this have project has gone a bit on hold due to prblems financing the speakers. :$

by the way... it says to be an 180 w amp 8~16 ohm speakers i guess 180 w a 8 ohms but would this per channel or total? any sugestions? just to get the speakers right dont want to blow em..

So.. basicly i could just put any preamp infront and just use the aux or cd or tape or whatever input... well propably not tho phono input.

if i insist on the tubepre i should then make a buffer at the output so that imp will be low.

well thanks alot for your help...

pd the sound clip in your link cant be found

Quote from: phatt on April 07, 2010, 12:35:44 AM
Do you want to gut this thing to build a complete amp from scrap or do you just want a preamp that plugs into an aux input?
Phil.

well i havent yet decided whether it should be a rebuild or an add on but in terms of preamp would there be alot of difference?
I imagine that if i wanted a preamp for the aux input then there should be some buffer thing since i imagine its low impedance compared to a guitars

Quote from: J M Fahey on April 07, 2010, 09:07:43 AM

Quotemaybe its that simple as to put a preamp before the volumepot,

Something like that.
Mount and wire some jack into both Left and Right volume pots , I assume the amp is salvaged from the trash bin or something like that and not used for Hi Fi anymore.
Do not mess with tubes yet, search the Forum for simple preamp ideas.
There's some info on using an LM386 as preamp, which would drive either a small speaker on its own or your Yamaha to neighbourhood upsetting levels.

i have made tube based stop boxes before so its no new and i am aware of the dangers asocieted to the high voltages used.
its a 180 watts/8 ohm so upsetting the neighbourhood is a guaranty