In over 50 years playing professionally I have seen a lot of things and heard a lot of myths about amplifier tone, what such and such a brand of amp can do where another one can't, etc, etc. I have seen musicians both Pro and Am as well as semi-Pro and hobbyist pay excessive amounts for supposedly legendary guitars, amps, pedals and accessories but this ad for one I came across by accident on Reverb.COM takes the cake.

https://reverb.com/item/6607993-dumble-overdrive-special-1985-black

I know Dumble makes good quality amps, as do Mesa, Marshall, Fender and many other manufacturers but seriously $115,000 (yes that's the asking price) for a 60w Dumble with 1 x 12" speaker is beyond belief. Whether it's tube or solid state is not the issue, nor is whether it is hand-made with p2p wiring and NOS "matched" valves/tubes.

What could it possibly have in it that would make it worth even 1/5th of that price is inconceivable.

The super bright leds will drop the resistance to virtually zero from my tests so far with an old LDR from that original Playmaster 116/7 parts list, but that is probably not really what is required I suspect.

Varying between a few K up to 1/2 meg seems to make more sense too especially with that tremolo circuit where you want to vary the volume level up and down but not turn it completely off. I guess the same goes for that compressor circuit of mictesters that you utilize.

Standard green, yellow, orange and red leds gave varying degrees of resistance with that LDR with red & yellow dropping lower than orange and green. That LDR varies from 10m+ (Dark) down to virtually zero (Light) using a white led.

Quote from: teemuk on March 23, 2008, 01:00:05 AM
There are tons of schematics for LM3886, just search for "chip amp" or "gainclone" and most importantly, read the datasheet. Personally, a chip amp design along these lines is my "favourite":

http://www.elektronika.lt/_sys/storage/2004/11/30/pic1.gif

Why:
- The input circuit is done properly with adequate ground referencing, DC coupling and RF filtering
- Feedback loop has some HF compensation and defines unity DC gain
- Has an output Zobel and an output inductor

Hi Teemuk,

Would you apply the same recommendation to virtually the same circuit using a TDA7293 instead of an LM3886?

Quote from: phatt on August 19, 2017, 04:51:16 AM
Yes standard 5mm Green LED's (wired back to back) hard up against the LDR inserted into a short length of black shrink tube.
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Hi Phil,

I breadboarded up the oscillator Rod Elliot's IC based tremolo circuit (http://sound.whsites.net/project29.htm) which works really well. So as an adjunct to making these LDR/LED units, which LDR did you use? Both Altronics and Jaycar carry the same 2 versions of these CdS cells

One is a ORP-12 equivalent: Dark 10m   to   Light 48k - 140k,

while the other one is: Dark 500k   to   Light 2k8 - 8k4,

I think the ORP-12 was what was used in the old Goldentones and the EA Playmasters 116/117 tremolo circuits

Gavan

Quote from: J M Fahey on December 09, 2016, 07:45:20 AM
Agree on LM3886 opinion, but I guess I found the reason: LM3886 is simpler to use and it boasts 50 or 60W RMS ,
Now TDA7293/4 claim 100W RMS which simply is asking too much from the exact same package.

Thanks to y'all for your explanations.
If I want a 60W "RMS" into 8 ohms output stage which of these chips would be the most suitable:- LM3886, TDA7293 or TDA7294.

TIA

Quote from: J M Fahey on September 15, 2017, 09:20:28 PM
All these chipamps are "powerful Op Amps" , just varying in supply and power output, same design rules apply to all.

JM can you please clarify this. When data sheets (and I quote the LM3886 here) says things like:

"68W cont-avg-output power into 4 ohms" or "38W cont-avg-output power into 8 ohms"

what does the term "cont-avg-output power" mean?
is that their way of saying 68w RMS or 38 RMS?

TIA Gavan.

Quote from: J M Fahey on September 15, 2017, 08:35:42 PM
That said, it *should* work like a plain TDA2050 single supply datasheet example, so "just trust the datashet, not the seller".

The data sheet clearly states that the TDA2050 is a 35W IC so the seller claim of 120w is obviously seller promo "BS".

Quote from: Psabin8951 on September 12, 2017, 02:27:58 AM
I have an old cream coloured Roland Cube-60

I have two of these Cube 60's. Initially I dispensed with the rev tanks and took a feed from pin 10 of the SIP tank driver IC via a 10k as an Aux send and ran an effects loop using a Chorus Echo 301. I fed the return from the Echo unit into the rev return point. I eventually made a better version of the "send" function which I still use although these days I'm using the RE-20 Space Echo twin pedal instead of the tape based Space Echo.

Just gives you another option.
I can post a schema of the send mod patch if you're interested.

Quote from: phatt on September 01, 2017, 09:36:09 AM
As to your wanting a good amplifier,, you could just build another Cube 60.
Or keep going with "Loudthuds" Fet idea?

I have given some thought to just cloning the Cube's PCB but I did like what the JFET bender sounded like when patched into Rod Elliots IC based guitar preamp.

Thanks for all your thoughts & ideas Phil plus the benefit of your research into the electronics of ss guitar.

Cheers

Quote from: phatt on August 30, 2017, 08:47:33 AM
Here is the Really Cheap Compressor circuit as posted by Mictester at FSB

Thanks Phil,

I have looked at most of these circuits on this forum and I feel grateful that others within it have done an amazing amount of work and research into ss guitar preamp. I don't really use guitar pedals much. I have a BOSS RE-20 reverb unit and a BOSS CE-20 chorus unit which both run in their own separate aux send and returns which I built into my amps.

I guess I should explain my interest in the CA3080 and compressor circuits in general. I'm not really interested in compressors for compression sake itself though. I have been impressed with the JFET bender idea of "Loudthuds" after patching it into Rod Elliot's Project 27 preamp. I'm more interested in the research into the use of that chip as per "Mictesters" spiel on its use to control the gain in the FB network of an IC.

First a little background:

Back in the Tinbeerwah Hall days with Barry & the Rockets I was using a VOX AC-30 Top Boost. When we moved into playing the Maroochy Pub I swapped it for a Blackface Super Reverb as I wanted a brighter edge with less mid-range hump than I was getting with the VOX. When I eventually moved back to Melbourne in 76, for the next 8 years or so used a Mk 1 Mesa Boogie up til about 85 when I started to use my original 2SK117 FET based Roland Cube 60 (original model - even the terminals are Wire-Wrap) which I bought as a practice amp. I replaced that horrible Roland speaker with a Celestion and it virtually fixed the whole sound of the amp in one fell swoop. I took it to use on a couple of small bar gigs and I've been using it (sometimes 2 for large concerts – I have another model of the same sort of vintage) ever since then after making some minor mods to the circuit. Thanks to Qantas dropping it last year on a flight to Brisbane to play the GO Show concerts it has not been working optimally (the bastards f..kd it) and owing to the number of times the PCB has been removed for minor mods & repairs I doubt that it will ever be the same as it was or as reliable.

The Cube was great using guitar straight in (no pedals) to the firstt stage (OD channel and driving the second stage (Normal channel). Responded similar to a Fender Deluxe or Super Reverb and cleaned up after backing off the guitar vol pot. It also had a similar punch factor like the AC30.
After 32 years of never having to replace a tube I figure it doesn't really owe me anything besides which I can always get backline hired for major concert gigs. But I still need a decent reliable amp.

However I'm now interested in moving into the SS IC-based guitar arena. I like Rod's guitar amp project and as part of my checking out of IC systems I've just built up the L5 preamp but I've yet to test it. I rather liked mictesters idea of using the CA3080 to control the gain in the FB network so I was curious as to how you found the EH Blackfinger circuit both noise & response-wise.

I would dearly love to get an IC based front end that responded similar to that Cube 60 or the Fender Deluxe & Super Reverbs with the punch of the AC30 to use with a decent power amp like Rod Elliots.

Quote from: phatt on August 19, 2017, 04:51:16 AM
Yes standard 5mm Green LED's (wired back to back) hard up against the LDR inserted into a short length of black shrink tube. The LED's I had on hand were water clear green but the frosted ones work the same.
Phil.

I haven't been able to see mictesters circuit, so did he use a vactrol and did you use your green leds with ldr instead of the vactrol.
thnx mate.

Quote from: phatt on August 19, 2017, 04:51:16 AM
Well small world, I used to frequent an open mic gig at Yandina (old Bowls club house on the main street) about 7 years ago. I was told it had run for many years but it's folded now. Your mate Barry likely remembers it?

Yes Phil. Barry vaguely remembers that there was an OM night but he never went to it.

As a matter of interest (to me at any rate) how did you find the noise floor in your Slackfinger circuit and how useful was the compression factor in it. I notice that the EH Blackfinger and the Morley Tel-Ray VCO pedal use similar implementations of the CA3080 in the FB network of an IC stage to achieve their comp setup as indicated by mictester as the preferred way of utilizing the OTA.

I never got a chance to use those 2 pedals live. I used to use an MXR Dynacomp many many years ago (back in the 70's). After using it on an album session at TCS in Melbourne I hated the sound of it when I listened to the playback and stopped using it after that. However as I have a few of these chips I thought I would experiment with them especially after playing with Rod Elliots Proj 27 and adapting it to use loudthuds JFET bender idea. I was impressed with the results.

Cheers Gavan

Quote from: phatt on August 16, 2017, 08:29:47 AM
For a while I'd given up on comp circuits but then that clever chap mictester at FSB posted his RSC (really simple compressor) circuit only using a dual opamp and a couple of LEDs.

The black finger circuit like a lot of others that use LM3080 the parts count is often high.

While the RSC circuit is dead simple, The hardest part is making the LDR and LED package.

Oh yes,,  I was in Nambour Qld but moved to Bairnsdale Vic,, long story.
Basically the music was great, lots of open mic gigs in East Gippsland, meet some great people but it's just far too cold and I'm an outside kinda bloke so I came back to the Sunshine Coast so I'm in Morayfield ~40 Khm's north of Brisbane.
I just looked up Macedon,, ouch mate that's probably even colder than East Gippsland,, you Victorians are obviously a tough bunch. Ice on the window is hard enough for me and if I never see Snow in my whole life I've missed nothing. I likes me sunshine a lot higher in the sky in winter. <3)
Phil.

I must bboard that RSC up - standard 5mm green LEDs I think you said. The high parts count is not so much of an issue in lieu of my research into comp ideas. I noticed that you used LEDs as a switchable option in your LNC version of the ROSS. I thought of trying that whole CV section from Q1,2,3 & 4 in the LNC as the CV section for the 3080 in your slackfinger circuit. At the moment I'm really just compiling ideas.

I lived up at Noosa in the mid 70's - we played up there for a couple of years. Barry still lives in Yandina and he and I still keep in contact regularly. One of my old schoolmates lives at Mooloola and the band's ex roadie is down near Caloundra. It used to be a great place until they Sufferers Parasited it.

Gavan

Quote from: phatt on February 07, 2011, 08:04:14 AM
I finally got a working schematic.
Bear in mind this is all on the BBoard and still siffting through some ideas but this at least will work as shown.
It was Glitching or clamping hard off in a cyclic LFO kind of way but added R7 (1m2) seemed to sort the random hickup problem.

I know this was a long time ago Phil, but I found this pic of an SS EH blackfinger. Your R15 1.5m looks like it was a 2.2m on the EH pcb. and R5 & R6 could possibly be the 390k & 680k that are on the pcb but not found on the blackfinger schematic where they are marked as 120k but no 120k's are visible on the pic.

If it's of any interest I do have some 3080's. I could always post you a couple (I'm up near macedon), are you down in gippsland or still in nambour?

Quote from: Loudthud on April 17, 2015, 05:54:14 PM
The JFET is used as a variable resistor in a region where it's resistance changes at different current levels. MPF102 JFETs were used because they had a bendable resistance in the right range.

I post this as it may be of some interest to those following this thread.

On researching that presumably "CRATE" overdrive circuit idea in US patent 5647004 filed by St. Louis Music, I came across Scholz's US patent 4627094 which uses an N-Ch JFET (possibly a 2n4340) to vary the gain in the compressor IC (probably a TL072) using the gate's bias voltage being varied by a DBX 2252 rms level detector chip - see fig 2a in the patent. Not exactly the same structure as yours Loudthud I know, but it would obviously lend weight to that JFET variable resistor concept. 

I guess this patent this was the original circuit idea for one of the Rockman models. I know they used TL072's in the little headphone rockmans as I have two of them (a model 1 & a model 2), and the JFET used in those was a 2N4340 although those models don't use the DBX chip.

I have circuit tracings of the 2 models that I did using Express PCB's schematic program if anyone is interested in copies but I have not verified their complete accuracy - they were only used as guide for my curiousity