Hi Bigun,
You can browse Linsley-Hoods book " Audio and Transistor Amplifiers" online by doing a search on " Linsley-Hood 15watt Class AB amplifier'' going through the hits to find
"[PDF] Untitled" with text "gen.lib.rus.ec/get?nametype=orig&md5..." I don't have the Shaw and Baxandall material but it is covered adequately in the book.
Some other material by Linsley-Hood appears on "The Class A Amplifier site The Class-A Amplifier Site
Articles / correspondence there debating Linsley Hood's 15 watt Class AB amplifier give some insight into problems designers were addressing around 1970. His early appreciation is consistent with what is now referred to as a "First Watt" approach.
I would appreciate hearing how you found this material and the book.
You can browse Linsley-Hoods book " Audio and Transistor Amplifiers" online by doing a search on " Linsley-Hood 15watt Class AB amplifier'' going through the hits to find
"[PDF] Untitled" with text "gen.lib.rus.ec/get?nametype=orig&md5..." I don't have the Shaw and Baxandall material but it is covered adequately in the book.
Some other material by Linsley-Hood appears on "The Class A Amplifier site The Class-A Amplifier Site
Articles / correspondence there debating Linsley Hood's 15 watt Class AB amplifier give some insight into problems designers were addressing around 1970. His early appreciation is consistent with what is now referred to as a "First Watt" approach.
I would appreciate hearing how you found this material and the book.
Member
Joined 2009
Paid Member
I find that I prefer to work on the amplifier when I have sufficient time to finish what I've started and these days that is really hard so progress is slow even though I find time to read a bit here and there.
I already checked JLH book before my last posting, and guess what, it says the exact page I want is unavailable - I guess they want to sell books not give them away and I can't blame or criticize them for this.
I was curious about the Leak Delta 70 as it's been a schematic I've liked for quite awhile. I realized that 90% of the effort of building my JLH is in the chasis, the heatsinks, the power devices, the power supply, connectors etc. So I was just mulling over the idea of building the JLH but leaving space in the chasis for a Delta 70 at some point in the future - I'd simply switch between the two of them. Class A for winter, Class AB for summer
I already checked JLH book before my last posting, and guess what, it says the exact page I want is unavailable - I guess they want to sell books not give them away and I can't blame or criticize them for this.
I was curious about the Leak Delta 70 as it's been a schematic I've liked for quite awhile. I realized that 90% of the effort of building my JLH is in the chasis, the heatsinks, the power devices, the power supply, connectors etc. So I was just mulling over the idea of building the JLH but leaving space in the chasis for a Delta 70 at some point in the future - I'd simply switch between the two of them. Class A for winter, Class AB for summer
Dear all,
For a friend of my father, I have been renovating a Leak Stereo 30+,as a present, and although its not accurate, it is a pleasant, amplifier. I suspect it boosts the bass a little (compared to a Quad 306) with me upping some of the capacitors in the Leak, I guess I should learn to use the PC to measure this stuff and replace all the capacitors with the original values before i judge it as I did increase the value of the electrolytic capacitors a lot. I just used cheap capacitors from a German online store. It surprised me how practical this amp is (and I will make more orders from that store), I could consider it a good amplifier for office Music.
I know the Leak Delta 30, its only 15 Watts per channel, and nearly the same circuit, but it would be interesting to know the comparative distortion especially at low power levels, for the simulation, say on a logarithmic from 0.01 to 10 Watts. (ie 0.01W, 0.1W, 1W,10W.) Also it would be interesting to see if this amplifier has a flat frequency response, its harmonic distortion, and how the circuit is sensitive in the frequency response to its capacitance values. I think this amp is a very successful product, from the late 1960's into the mid 1970's, which is why you see so many of them, and leaks earlier transistor models.
Don't get me wrong, replacing the capacitors wont get you something that will make you sell a Quad 303 or a Sugden A21 but its a nice cheap easy to repair (though the output transistors look fiddly to change), amplifier at about 12 UKP broken, plus 30-40 Euros of capacitors.
In my model the diodes are attached to the heat sink, they look like they might be difficult to replace. Are they important to protect against thermal runaway as the heat sinks are tiny?
Regards
Owen
For a friend of my father, I have been renovating a Leak Stereo 30+,as a present, and although its not accurate, it is a pleasant, amplifier. I suspect it boosts the bass a little (compared to a Quad 306) with me upping some of the capacitors in the Leak, I guess I should learn to use the PC to measure this stuff and replace all the capacitors with the original values before i judge it as I did increase the value of the electrolytic capacitors a lot. I just used cheap capacitors from a German online store. It surprised me how practical this amp is (and I will make more orders from that store), I could consider it a good amplifier for office Music.
I know the Leak Delta 30, its only 15 Watts per channel, and nearly the same circuit, but it would be interesting to know the comparative distortion especially at low power levels, for the simulation, say on a logarithmic from 0.01 to 10 Watts. (ie 0.01W, 0.1W, 1W,10W.) Also it would be interesting to see if this amplifier has a flat frequency response, its harmonic distortion, and how the circuit is sensitive in the frequency response to its capacitance values. I think this amp is a very successful product, from the late 1960's into the mid 1970's, which is why you see so many of them, and leaks earlier transistor models.
Don't get me wrong, replacing the capacitors wont get you something that will make you sell a Quad 303 or a Sugden A21 but its a nice cheap easy to repair (though the output transistors look fiddly to change), amplifier at about 12 UKP broken, plus 30-40 Euros of capacitors.
In my model the diodes are attached to the heat sink, they look like they might be difficult to replace. Are they important to protect against thermal runaway as the heat sinks are tiny?
Regards
Owen
I would guess that the diodes attached on the heat sink are surely there for thermal compensation. So taking them off might not be a good idea.
Maybe someone should make a replacement 'modern' pcb to fit into the amp chassis.
I like the sound of this amp even though it doesn't measure as well as modern circuits.
Anyone tried one of these ( the Delta 70 or the Stereo 30 ) on an OB speaker system ?
Cheers.
Maybe someone should make a replacement 'modern' pcb to fit into the amp chassis.
I like the sound of this amp even though it doesn't measure as well as modern circuits.
Anyone tried one of these ( the Delta 70 or the Stereo 30 ) on an OB speaker system ?
Cheers.
After a week with the Leak Stereo 30 plus
Dear all,
I ran with the recapped Leak Stereo 30+ for 1 weeks and just switched back to the Quad 303's (which I recapped a year or two ago). My Quad 303's do sound a lot better, especially in the treble region, and you really notice the realism with ESL's with a good amp such as a Quad 303/306 or my Sugden A28 (which I'm currently replacing capacitors in).
The Leaks sound nice but with well recorded acoustic music the improvement with the Quad 303 is surprisingly big. Since I was using the Tape input I was bypassing the tone controls, on the Leak Stereo 30+, and the improvement with the Quad 303 was so much that I was surprised. The low frequencies are better with the Quad 303, but that is down to capacitor sizes I guess Quad has twice the size of capacitors, this could be fixed as their is space to use a lot bigger than just doubling the sizes as I did for the output capacitor and the power supply in the Leaks and the Quads, but the treble is a different thing altogether, the Leak is more muddy and just less realistic, it even could do with a little high treble boost from the tone controls just to match levels. I would still say the Leak Stereo 30+ is a nice practical amp, one day when I learn more I might make some measurements that will hopefully explain the differences.
Regards
Owen
Dear all,
I ran with the recapped Leak Stereo 30+ for 1 weeks and just switched back to the Quad 303's (which I recapped a year or two ago). My Quad 303's do sound a lot better, especially in the treble region, and you really notice the realism with ESL's with a good amp such as a Quad 303/306 or my Sugden A28 (which I'm currently replacing capacitors in).
The Leaks sound nice but with well recorded acoustic music the improvement with the Quad 303 is surprisingly big. Since I was using the Tape input I was bypassing the tone controls, on the Leak Stereo 30+, and the improvement with the Quad 303 was so much that I was surprised. The low frequencies are better with the Quad 303, but that is down to capacitor sizes I guess Quad has twice the size of capacitors, this could be fixed as their is space to use a lot bigger than just doubling the sizes as I did for the output capacitor and the power supply in the Leaks and the Quads, but the treble is a different thing altogether, the Leak is more muddy and just less realistic, it even could do with a little high treble boost from the tone controls just to match levels. I would still say the Leak Stereo 30+ is a nice practical amp, one day when I learn more I might make some measurements that will hopefully explain the differences.
Regards
Owen
Dear Ashok,
I don't have a Leak Delta 70, and I believe the Leak 70+ is the same circuit.
Looking at the circuits, the only difference between Leak 30+ and Leak 70+ amplifiers is the supply voltage and consequently a couple of resistor values. I would not expect a massive difference in sound.
In my opinion the Leak 30+ sounds nice, and is not unpleasant, and in my opinion bests a lot of amplifiers, and sounds good with a Quad ESL 63. The question left for the reader is do you want accurate reproduction or nice sound. I think (but don't have measurements to justify) the Leak 30+/70+ and Delta 30/70 are nice sound rather than accurate, while the Sugden A28 and Quad 303/306 are accurate rather than nice. On this basis I think Valve/Tube amp fans should look at Leak Delta/Plus amplifiers and see why these where regarded as valve/tube amplifier killers in their day.
Regards
Owen
I don't have a Leak Delta 70, and I believe the Leak 70+ is the same circuit.
Looking at the circuits, the only difference between Leak 30+ and Leak 70+ amplifiers is the supply voltage and consequently a couple of resistor values. I would not expect a massive difference in sound.
In my opinion the Leak 30+ sounds nice, and is not unpleasant, and in my opinion bests a lot of amplifiers, and sounds good with a Quad ESL 63. The question left for the reader is do you want accurate reproduction or nice sound. I think (but don't have measurements to justify) the Leak 30+/70+ and Delta 30/70 are nice sound rather than accurate, while the Sugden A28 and Quad 303/306 are accurate rather than nice. On this basis I think Valve/Tube amp fans should look at Leak Delta/Plus amplifiers and see why these where regarded as valve/tube amplifier killers in their day.
Regards
Owen
Hi Owen,
I agree that the Delta 70 does sound very nice. It is very musical and has that foot tapping quality to the sound. I also don't care if it's accurate or not but it is non fatiguing with time. Albums really sound great on this compared with several other amps I have here. The measured performance is not great but certainly not too bad either ! I now use it all the time . This amp really has very good bass slam ! Deep and tight . However that would also depend on how good the speakers are.
I've never heard the Leak 30+ . If they are similar circuitry then I guess they must sound the same except for lower max power output.
I might add that my unit is an approximate clone and not a real Delta 70 ! I built it as my memory of a Delta 70 I heard in the late 70's wouldn't go out of my mind. This clone proves that my memory of the sound is correct !
Cheers.
I agree that the Delta 70 does sound very nice. It is very musical and has that foot tapping quality to the sound. I also don't care if it's accurate or not but it is non fatiguing with time. Albums really sound great on this compared with several other amps I have here. The measured performance is not great but certainly not too bad either ! I now use it all the time . This amp really has very good bass slam ! Deep and tight . However that would also depend on how good the speakers are.
I've never heard the Leak 30+ . If they are similar circuitry then I guess they must sound the same except for lower max power output.
I might add that my unit is an approximate clone and not a real Delta 70 ! I built it as my memory of a Delta 70 I heard in the late 70's wouldn't go out of my mind. This clone proves that my memory of the sound is correct !
Cheers.
Dear ashok,
I am rather impressed with amps like Sugden's, and the Quad 303. The Leak 30+ is defiantly a bettered by these two in my opinion, but I notice that the Leak easier to listen to amps than many modern amplifiers in the same way the 303 is easier to listen to than the other amps under the bed. The Quad 306 is unique in my collection modern amps not to live only under the bed, but the Sugden's or the Quad 303 is driving the ESL's most of the time, I am curious as to why?
Ashok, have you tried building a Sugden A48 clone? or recapping a Quad 303? What sort of speakers are you driving? I am using Quad ESL 63's and both the Sugden's and the Quads are designed around Quad speakers.
Before I come down definitively in favor of the Quad 303 over the Leak Stereo 30+ I should really change the non electrolytic capacitors in the Leak as I did with the Quad 303 (which I am not sure made that much difference for the Quads), but since I am playing with active cross overs to conventional bass drivers, I will probably stick with power amps, and maybe pick up another Leak 30 (plus) to build a new preamp in one day when the ebay prices return to normal.
Still the Stereo 30+ is a nice amp and I am sure that it will be a gift that's appreciated.
Regards
Owen
I am rather impressed with amps like Sugden's, and the Quad 303. The Leak 30+ is defiantly a bettered by these two in my opinion, but I notice that the Leak easier to listen to amps than many modern amplifiers in the same way the 303 is easier to listen to than the other amps under the bed. The Quad 306 is unique in my collection modern amps not to live only under the bed, but the Sugden's or the Quad 303 is driving the ESL's most of the time, I am curious as to why?
- Is it purely subjective and I am swayed by the better looks of older amps?
- Could it be the lack of a differential stage?
- Could it be the Capacitor coupling working well with ESL speakers?
- Could it be the higher cross talk?
Ashok, have you tried building a Sugden A48 clone? or recapping a Quad 303? What sort of speakers are you driving? I am using Quad ESL 63's and both the Sugden's and the Quads are designed around Quad speakers.
Before I come down definitively in favor of the Quad 303 over the Leak Stereo 30+ I should really change the non electrolytic capacitors in the Leak as I did with the Quad 303 (which I am not sure made that much difference for the Quads), but since I am playing with active cross overs to conventional bass drivers, I will probably stick with power amps, and maybe pick up another Leak 30 (plus) to build a new preamp in one day when the ebay prices return to normal.
Still the Stereo 30+ is a nice amp and I am sure that it will be a gift that's appreciated.
Regards
Owen
Hi Owen,
I have heard a Sugden long ago and remember I liked it though I don't remember it as well as the Leak. That is because I had the Leak at my home for a few weeks. I must have a look at the Sugden A48 circuit . As you say, it might be interesting to try out a clone.
I don't have Quad speakers though I have heard several of them at various other people's houses. They are very nice though they don't go as low as I like.
I have some old Mission 701's that have a been 'upgraded' a bit. I have had several other speakers in my house which have been better in many ways but overall I kind of like the sound I am getting now. With a sub it sounds superb.
The only other speakers I like better are Open Baffles that I'm still toying with.
I also have the bookshelf Mission 780 and a Rogers GS-1. All my other speakers have been given away as I have no space in my present house.
Wonder if anyone else has done a Leak Delta 70 and Sugden A48 comparison ?
I have heard a Sugden long ago and remember I liked it though I don't remember it as well as the Leak. That is because I had the Leak at my home for a few weeks. I must have a look at the Sugden A48 circuit . As you say, it might be interesting to try out a clone.
I don't have Quad speakers though I have heard several of them at various other people's houses. They are very nice though they don't go as low as I like.
I have some old Mission 701's that have a been 'upgraded' a bit. I have had several other speakers in my house which have been better in many ways but overall I kind of like the sound I am getting now. With a sub it sounds superb.
The only other speakers I like better are Open Baffles that I'm still toying with.
I also have the bookshelf Mission 780 and a Rogers GS-1. All my other speakers have been given away as I have no space in my present house.
Wonder if anyone else has done a Leak Delta 70 and Sugden A48 comparison ?
Hmm......the Delta70 surfaces again. This morning I came across the board that I had made . As I said earlier it isn't a direct clone as it uses different transistors and resistor values and a few circuit modifications. It sounds nice but possibly not very 'accurate'. Newer designs are better at transients and have better bass control. However I must fire it up again and see how it sounds against what I am using today. Should be interesting.
That is TO5 package driver transistors. They don't make those anymore, and the pin compatible TO126 plastic package is also very rare. I've been using TO220 tranistors like TIP31C and TIP32C instead of TO5 transistors, but you have to twist the leads around because TO220 is B,C,E and TO126 is E-B-C.
The good news is that TO220 is easy to make a heat sink for, just cut a smidge of aluminum door frame and drill a hole in it. The tab is C, so don't let a heat sink touch anything, or use a mica insulator kit.
Ashok, the biggest sonic limitation on a Leak 70 was probably the original output transistors. Real 5 digit RCA transistors were selected from the 2N3055 process for more Vceo (or less leakage current at test voltage), but they had Ft of maybe 200 khz, which was probably audibly slow. I've used NTE60 output transistors instead, (on a copy of the Leak) which are probable MJ15003 copies, and the faster Ft cleans up the sound some IMHO. See the simulations someone did on Leak Stereo 70 with 2n3055, TIP3055, and something else.
The good news is that TO220 is easy to make a heat sink for, just cut a smidge of aluminum door frame and drill a hole in it. The tab is C, so don't let a heat sink touch anything, or use a mica insulator kit.
Ashok, the biggest sonic limitation on a Leak 70 was probably the original output transistors. Real 5 digit RCA transistors were selected from the 2N3055 process for more Vceo (or less leakage current at test voltage), but they had Ft of maybe 200 khz, which was probably audibly slow. I've used NTE60 output transistors instead, (on a copy of the Leak) which are probable MJ15003 copies, and the faster Ft cleans up the sound some IMHO. See the simulations someone did on Leak Stereo 70 with 2n3055, TIP3055, and something else.
Last edited:
This is helpful, but can the Leak Stereo 70 driver transistors be used in a Quad 303? It looks like the collector emitter voltage is OK, but I,m no expert.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.