jbldriven,
I got my copy of POP back from my apprentice and waded back thru' this entitre thread to see what you'd done and where you are up to.
I particularly took notice of the changes to the bias circuit and the feedback component values. All of these are O.K..
I am still convinced that your problem is in the 12AX7 input stage.
For 60Watts out into 4 Ohms you need about 15.5 VRMS output.
The gain of the whole amp is set by that 33K and 1 K to about 34 (1 + Rf/Rin) - ASSUMING there is sufficient open loop gain
Therefore the Input voltage needs to be 0.46 V RMS. That is 0.65 V volts peak.
With no feedback (this is the worst case condition) half of this needs to appear on the 12AX7 cathodes - that is 0.65V peak. The 12AX7 run at around 1mA each, so the current source emitter is at 220R x 2 x 1mA = 440mV. The base sits 0.6 higher - say at 0.94V.
The cathodes of the 12AX7 will sit at a voltage determined by how much bias is required to set the triodes to 1mA each at the B+ volts you are using. Assume for arguement that its 1.2 volts. The 0.65 signal which is on the cathodes means that the collector of the CCS is swinging down to 1.2 - 0.65 = 0.55V this is below the base voltage. That means 2 things - the transistor goes into saturation and the there will be recovery from saturation problems.
You need to make sure that there is enough voltage across the current source transistor (compliance volts) for it to always be running in its linear mode and that its not saturating or cuttinng off on peak signal swings.
To do this you need to either:
1) maximise the 12AX7 cathode voltage by running high B+ to the anodes (and therefore requiring high bias volts to set the 1mA per triode section).
OR
2) return the current source transistor emitter resistor and the base resistor bottom to a well filtered negative rail (add another RC section from the bias supply).
I have had this problem in the past and have actually seen (on an oscilloscope) the peak off one half of a sine wave INVERT as the current source runs out of compliance voltage.
Cheers,
Ian
I got my copy of POP back from my apprentice and waded back thru' this entitre thread to see what you'd done and where you are up to.
I particularly took notice of the changes to the bias circuit and the feedback component values. All of these are O.K..
I am still convinced that your problem is in the 12AX7 input stage.
For 60Watts out into 4 Ohms you need about 15.5 VRMS output.
The gain of the whole amp is set by that 33K and 1 K to about 34 (1 + Rf/Rin) - ASSUMING there is sufficient open loop gain
Therefore the Input voltage needs to be 0.46 V RMS. That is 0.65 V volts peak.
With no feedback (this is the worst case condition) half of this needs to appear on the 12AX7 cathodes - that is 0.65V peak. The 12AX7 run at around 1mA each, so the current source emitter is at 220R x 2 x 1mA = 440mV. The base sits 0.6 higher - say at 0.94V.
The cathodes of the 12AX7 will sit at a voltage determined by how much bias is required to set the triodes to 1mA each at the B+ volts you are using. Assume for arguement that its 1.2 volts. The 0.65 signal which is on the cathodes means that the collector of the CCS is swinging down to 1.2 - 0.65 = 0.55V this is below the base voltage. That means 2 things - the transistor goes into saturation and the there will be recovery from saturation problems.
You need to make sure that there is enough voltage across the current source transistor (compliance volts) for it to always be running in its linear mode and that its not saturating or cuttinng off on peak signal swings.
To do this you need to either:
1) maximise the 12AX7 cathode voltage by running high B+ to the anodes (and therefore requiring high bias volts to set the 1mA per triode section).
OR
2) return the current source transistor emitter resistor and the base resistor bottom to a well filtered negative rail (add another RC section from the bias supply).
I have had this problem in the past and have actually seen (on an oscilloscope) the peak off one half of a sine wave INVERT as the current source runs out of compliance voltage.
Cheers,
Ian
I've had just the problem gingertube describes in an old balanced pre-amplifier input stage with 6SN7 - the ccs simply ran out of compliance despite the cathode voltage of about 7V - the solution was to run it off of -12V derived from one of the dc filament supplies.
In this application a simple half wave doubler off of a convenient ac filament supply with some filtering or dividing down the bias supply should do the trick.
In this application a simple half wave doubler off of a convenient ac filament supply with some filtering or dividing down the bias supply should do the trick.
kt88 startup problem
Ian I would like to send you the schematic. Kevin made some changes from the original. I think he is away as I'm not able to contact him by phone or email. I myself have only got back in the country. I do not want to post the drawing on the internet due to possible infringments however i need help solving this problem. I can send it to you email direct if that is okay. Therefore if you contact me at shenrich@rogers.com i will forward a sketch of the wave form and a jpeg of the drawing with the changes from the book. I think the drawing could help identify the problem.
Thanks
Ian I would like to send you the schematic. Kevin made some changes from the original. I think he is away as I'm not able to contact him by phone or email. I myself have only got back in the country. I do not want to post the drawing on the internet due to possible infringments however i need help solving this problem. I can send it to you email direct if that is okay. Therefore if you contact me at shenrich@rogers.com i will forward a sketch of the wave form and a jpeg of the drawing with the changes from the book. I think the drawing could help identify the problem.
Thanks
scott (jbldriven),
I've gone through the stuff you've sent and there is a problem with the 12AX7 input stage for sure. Its running way too hot. Too much current. This is because that circuit was originally designed to run off a 300V rail and you have it running off a 540V rail.
For others who have the Kevin O'Connor "Principles of Power" book what we are discussing is his "High-performance diff-splitter" in Fig 6-13 on page 6-14.
So we are going to recalculate its component values.
First choose an operating current for each triode section - If you look at the mu, gm and rp vs plate current curves you will see that 1.1mA is a good operating current for a 12AX7.
Next choose an anode voltage at idle - for a common cathode amp 2/3 of rail volts is a good choice but since you have direct coupled 12AT7 cathode followers hanging off the 12AX7 anodes we will go a bit lower to say around 1/2 rail or a bit over to allow more "operating volts" for the 12AT7.
Your rail is +540V, so we want the anodes at 270 to 300V. That means a 270 to 240V drop across the anode load resistors so they need to be 240V/1.1mA = 218.2 K => use 220K. This has another benefit over the 100K loads shown in your schematic. The gain in this stage will now be 25% higher (gain = mu[ RL / RL + rp], you need to know rp for 12AX7 at 1.1mA is approx 62K).
Ok now a load line shows the bias volts needs to be about -2.1 volts to get the required 1.1mA at 270V on the anode. With the grid at 0V that means the cathode must be at +2.1V. This is the total compliance your current source has to work with. When you have signal volts imposed on that +2.1V you don't want it swinging below the current source transistor base volts. That base volts is set by the emitter volts (voltage developed across the current sense resistor) plus the 0.65 Vbe drop.
Conflicting requirements again - you want to keep the emitter voltage down (to keep the base voltage down) which means a low value of RE (the current sense resistor) but the effective impedance of the current soure (which you want as high as possible) is the RE x Beta of the transistor so yo want RE as high as possible).
Also in order to swamp device thermal effects its recommended not to use less than 400mV across the RE with most guys saying use minimum of 450mV across RE. So RE wants to be 0.45V/ 2 x 1.1mA = 204 Ohms => use 220 Ohms as your schematic suggests. That will give an emitter voltage of 0.48V
So we want a base voltage of 0.48 + 0.65 = 1.13
Now with around 270V on the anodes and 1M2 from each anode to the base and a single "base voltage set" resistor to 0V (the 3K6) on your schematic). Check its value.
Rx / 1M2 || 1M2 + Rx = 1.1 / 270
gives Rx = 2K4
So finally change that 3K6 from base to 0V to 2K4. If you can't find a 2K4 start with 2 off 4K7 in parallel.
Than check your circuit operation.
12AX7 anodes should be between 270V and 300V.
If too low then make that 2K4 a 2K2
If too high make that 2K4 a 2K7
Summary of Changes:
2 off 12AX7 anode load resistors from 100K to 220K - these need to be at least 1W rated.
1 off Current Source Transistor base to 0V resistor from 3K6 to 2K4 (or 2 x 4k7 in parallel)
There - we effectively havent changed your design at all - all we've done is optimised the operating point of the input 12AX7 by changing 3 resistors, which in turn optimised the operating point of the direct coupled 12AT7 cathode follower and we've achieved a 25% increase in open loop gain along the way.
I noted one other problem. The feed back resistor values you are using (33K and 1K) were designed for being fed from the 4 Ohm secondary tap. It looks like you have it connected to the 16 Ohm tap. That means way too much feedback. Shift the feedback feed to where the Black Yellow lead joins the Green lead. That should give you 4 times the closed loop gain in the amp. That will reduce the required input signal by a factor of 4 and that will help the input stage as well.
Cheers,
Ian
I've gone through the stuff you've sent and there is a problem with the 12AX7 input stage for sure. Its running way too hot. Too much current. This is because that circuit was originally designed to run off a 300V rail and you have it running off a 540V rail.
For others who have the Kevin O'Connor "Principles of Power" book what we are discussing is his "High-performance diff-splitter" in Fig 6-13 on page 6-14.
So we are going to recalculate its component values.
First choose an operating current for each triode section - If you look at the mu, gm and rp vs plate current curves you will see that 1.1mA is a good operating current for a 12AX7.
Next choose an anode voltage at idle - for a common cathode amp 2/3 of rail volts is a good choice but since you have direct coupled 12AT7 cathode followers hanging off the 12AX7 anodes we will go a bit lower to say around 1/2 rail or a bit over to allow more "operating volts" for the 12AT7.
Your rail is +540V, so we want the anodes at 270 to 300V. That means a 270 to 240V drop across the anode load resistors so they need to be 240V/1.1mA = 218.2 K => use 220K. This has another benefit over the 100K loads shown in your schematic. The gain in this stage will now be 25% higher (gain = mu[ RL / RL + rp], you need to know rp for 12AX7 at 1.1mA is approx 62K).
Ok now a load line shows the bias volts needs to be about -2.1 volts to get the required 1.1mA at 270V on the anode. With the grid at 0V that means the cathode must be at +2.1V. This is the total compliance your current source has to work with. When you have signal volts imposed on that +2.1V you don't want it swinging below the current source transistor base volts. That base volts is set by the emitter volts (voltage developed across the current sense resistor) plus the 0.65 Vbe drop.
Conflicting requirements again - you want to keep the emitter voltage down (to keep the base voltage down) which means a low value of RE (the current sense resistor) but the effective impedance of the current soure (which you want as high as possible) is the RE x Beta of the transistor so yo want RE as high as possible).
Also in order to swamp device thermal effects its recommended not to use less than 400mV across the RE with most guys saying use minimum of 450mV across RE. So RE wants to be 0.45V/ 2 x 1.1mA = 204 Ohms => use 220 Ohms as your schematic suggests. That will give an emitter voltage of 0.48V
So we want a base voltage of 0.48 + 0.65 = 1.13
Now with around 270V on the anodes and 1M2 from each anode to the base and a single "base voltage set" resistor to 0V (the 3K6) on your schematic). Check its value.
Rx / 1M2 || 1M2 + Rx = 1.1 / 270
gives Rx = 2K4
So finally change that 3K6 from base to 0V to 2K4. If you can't find a 2K4 start with 2 off 4K7 in parallel.
Than check your circuit operation.
12AX7 anodes should be between 270V and 300V.
If too low then make that 2K4 a 2K2
If too high make that 2K4 a 2K7
Summary of Changes:
2 off 12AX7 anode load resistors from 100K to 220K - these need to be at least 1W rated.
1 off Current Source Transistor base to 0V resistor from 3K6 to 2K4 (or 2 x 4k7 in parallel)
There - we effectively havent changed your design at all - all we've done is optimised the operating point of the input 12AX7 by changing 3 resistors, which in turn optimised the operating point of the direct coupled 12AT7 cathode follower and we've achieved a 25% increase in open loop gain along the way.
I noted one other problem. The feed back resistor values you are using (33K and 1K) were designed for being fed from the 4 Ohm secondary tap. It looks like you have it connected to the 16 Ohm tap. That means way too much feedback. Shift the feedback feed to where the Black Yellow lead joins the Green lead. That should give you 4 times the closed loop gain in the amp. That will reduce the required input signal by a factor of 4 and that will help the input stage as well.
Cheers,
Ian
KT88 Project Update
Ian i have sent this message to you by mail with a couple other question not posted. I also sent the circuit showing the voltages.
I made the mods tonight but have yet to do a scope test.
I hooked the unit up to some inefficient bookshelf speakers and notice that the gain has increase by the amount of dial rotation required from the preamp. Success Thanks
I also did some voltage checks from both channel and here are the measurements. Note the original voltages in the schematic were take with no tubes installed and the new measurements are take with tubes installed
Voltages take Nov 23 2006 The first voltage is with tubes out and the second is with the tubes in
B+ Out 605 In571
V+ TO Drive Stage x7 Out 536 In367
Left 12AX7 Pin 1 Out Not Take In 223
Left 12AX7 Pin 6 Out Not Take In 222
Right 12AX7 Pin 1 ? Out Not Take In 228
Right 12AX7 Pin 1 Out Not Take In 235
Standby Switch Out 395 In 391
Bias supply Max Out Neg 24 to Neg 88 In Neg 23 to Neg 87
Bias Set At IN 34 MV
Mods completed
Change 100 k cathode resistor to 220k 1watt 2% metal oxide
Change 3k6 to 2k2 resistor .6 watt 1% metal film.
Tap feedback into Black Yellow wire and Green Wire.
From the measurement taken with the tubes in I am still under the 270 to 300 volts. I have 2k4 and 2k6 resistors available in the shop. Any recommendations or should we test like this.
As for the buzz it was noticeable on the inefficient speakers. By respacing the approach of each wire on the drive circuit board I have managed to reduce it to almost nil. The speakers are probably 82db at one watt so image I will have allot of wire issues to deal with when I hook it up to the horns. I think this will solve most of the buzz or hum problems.
Things are coming together thanks to your help.
Ian i have sent this message to you by mail with a couple other question not posted. I also sent the circuit showing the voltages.
I made the mods tonight but have yet to do a scope test.
I hooked the unit up to some inefficient bookshelf speakers and notice that the gain has increase by the amount of dial rotation required from the preamp. Success Thanks
I also did some voltage checks from both channel and here are the measurements. Note the original voltages in the schematic were take with no tubes installed and the new measurements are take with tubes installed
Voltages take Nov 23 2006 The first voltage is with tubes out and the second is with the tubes in
B+ Out 605 In571
V+ TO Drive Stage x7 Out 536 In367
Left 12AX7 Pin 1 Out Not Take In 223
Left 12AX7 Pin 6 Out Not Take In 222
Right 12AX7 Pin 1 ? Out Not Take In 228
Right 12AX7 Pin 1 Out Not Take In 235
Standby Switch Out 395 In 391
Bias supply Max Out Neg 24 to Neg 88 In Neg 23 to Neg 87
Bias Set At IN 34 MV
Mods completed
Change 100 k cathode resistor to 220k 1watt 2% metal oxide
Change 3k6 to 2k2 resistor .6 watt 1% metal film.
Tap feedback into Black Yellow wire and Green Wire.
From the measurement taken with the tubes in I am still under the 270 to 300 volts. I have 2k4 and 2k6 resistors available in the shop. Any recommendations or should we test like this.
As for the buzz it was noticeable on the inefficient speakers. By respacing the approach of each wire on the drive circuit board I have managed to reduce it to almost nil. The speakers are probably 82db at one watt so image I will have allot of wire issues to deal with when I hook it up to the horns. I think this will solve most of the buzz or hum problems.
Things are coming together thanks to your help.
Now your making progress - congratulations, it should now be running happily and making lovely music. I'd still do the final trim as below.
The anode voltages on the 12AX7 are now a bit low.
2 ways you can tackle this in either of 2 ways.
Either
1) use lower value anode resistors - say 180K instead of the 220K which would also drop the open loop gain by 4 or 5%
OR
2) drop the current in the 12AX7 sections a bit. Try a 1K8 in place of that 2k2 from the base of the current source MPSA06 to 0V.
If you need it there is the 2 x 3K9 in parallel option (=1K95) to try which gives you a setting half way between what you have now and what I suggest you try next (the 1K8)
I would suggest 2) as being easier and probably the marginally better solution.
Cheers,
Ian
The anode voltages on the 12AX7 are now a bit low.
2 ways you can tackle this in either of 2 ways.
Either
1) use lower value anode resistors - say 180K instead of the 220K which would also drop the open loop gain by 4 or 5%
OR
2) drop the current in the 12AX7 sections a bit. Try a 1K8 in place of that 2k2 from the base of the current source MPSA06 to 0V.
If you need it there is the 2 x 3K9 in parallel option (=1K95) to try which gives you a setting half way between what you have now and what I suggest you try next (the 1K8)
I would suggest 2) as being easier and probably the marginally better solution.
Cheers,
Ian
KT88 Stat up and measurement
Hi Ian, I haven't got a hold of the tech yet to take the actual output measurements. Kevin recommended changing the plate resistor to 390k to increase headroom. Sound good to you? I want to take a measurement to check performance of the amp prior to changing any resistors. I purchase a audio generator and presently looking for a scope. I looking for a textronik 50 to 60mhz dual channel. Anything specific i should watch for?
Hi Ian, I haven't got a hold of the tech yet to take the actual output measurements. Kevin recommended changing the plate resistor to 390k to increase headroom. Sound good to you? I want to take a measurement to check performance of the amp prior to changing any resistors. I purchase a audio generator and presently looking for a scope. I looking for a textronik 50 to 60mhz dual channel. Anything specific i should watch for?
KT88 Hammond 60watt to 120watt circuit
Ian Once i get the 60 watt up to speed, will there be enough gain in the x7 to driver circuit for parrallel set of kt88's in the 120 watt mono block design. Kevin recommended all the same drive stag with the only changes being the output tranny and 2 additional kt 88 in parrallel. Of course i would build the same power supply for each mono block. I have the schematic completed and can forward but i will need to encorporate the resistor value changes as they occur in the drive stage. Any Thoughts ?
Thanks
Ian Once i get the 60 watt up to speed, will there be enough gain in the x7 to driver circuit for parrallel set of kt88's in the 120 watt mono block design. Kevin recommended all the same drive stag with the only changes being the output tranny and 2 additional kt 88 in parrallel. Of course i would build the same power supply for each mono block. I have the schematic completed and can forward but i will need to encorporate the resistor value changes as they occur in the drive stage. Any Thoughts ?
Thanks
Also just starting the 60W 1650P build
Hello Ian, jbldriven:
My very 1st post here.
What a coincidence. I have been mulling over getting back into some tube amp construction for the past 8 months or so. I found Kevin and London Power on the web and ordered the Principles of Power. After a lot of reading, research (including on this site) I settled on building one of these 60 watt 1650P amps from page 5-30.
I have all the components on hand for a build for 2 monoblocks. Questions - I would really appreciate your help:
1) How much difference does the improved diff splitter make?
2) Now that you've built this, how do you like it?
3) Any chance of getting a copy of your revised schematic? I can email you with a copy of the original circuit out of my book so you know I have the book.
I appreciate your time and I still can't believe my luck with your post coming up at this moment!!
Ted.
Hello Ian, jbldriven:
My very 1st post here.
What a coincidence. I have been mulling over getting back into some tube amp construction for the past 8 months or so. I found Kevin and London Power on the web and ordered the Principles of Power. After a lot of reading, research (including on this site) I settled on building one of these 60 watt 1650P amps from page 5-30.
I have all the components on hand for a build for 2 monoblocks. Questions - I would really appreciate your help:
1) How much difference does the improved diff splitter make?
2) Now that you've built this, how do you like it?
3) Any chance of getting a copy of your revised schematic? I can email you with a copy of the original circuit out of my book so you know I have the book.
I appreciate your time and I still can't believe my luck with your post coming up at this moment!!
Ted.
KT88 start up
Right now the final design is not complete with debugging ongoing. Please keep in touch with this post to find out the final result. As for the schematic there has been a series of changes from the book with the power supply, circuit values and the splitter. Kevin recommended the changes however the final settings are not complete. As for how the unit sounds well all i have to compare to is solid state amps, parasound and bryston . Presently I am running my mid horns 2" format JBL 2482 on a bentwood horn 300 hz to 5k. Yes there is a difference i am only using probaly 1 watt average. The presence is better with a bit more airy sound. It will be interesting when i try a feww different tube in the future. We tried the amp on a full range horn system and it worked very well. The bass was deep than another tube amp that produced 15 watts per channel. I don't think i am getting full power out of the kt88's yet thats why i'm looking for a scope. I would like to speak tho kevin before i give out any of his work. If you bought his book he will be very appreciative.
Thanks
Right now the final design is not complete with debugging ongoing. Please keep in touch with this post to find out the final result. As for the schematic there has been a series of changes from the book with the power supply, circuit values and the splitter. Kevin recommended the changes however the final settings are not complete. As for how the unit sounds well all i have to compare to is solid state amps, parasound and bryston . Presently I am running my mid horns 2" format JBL 2482 on a bentwood horn 300 hz to 5k. Yes there is a difference i am only using probaly 1 watt average. The presence is better with a bit more airy sound. It will be interesting when i try a feww different tube in the future. We tried the amp on a full range horn system and it worked very well. The bass was deep than another tube amp that produced 15 watts per channel. I don't think i am getting full power out of the kt88's yet thats why i'm looking for a scope. I would like to speak tho kevin before i give out any of his work. If you bought his book he will be very appreciative.
Thanks
KT88 start up
Ted The amps im building for the 60 watt are stereo with one 278cx transformer and 2 1650 P trannies on one chassis. The 120 watt monos will be seperate units. I plan on using these to drive my 15" altec mid bass horn. What speakers are you using?
Once I'm finished I will probably strat a el34 amp with less wattage or 300b. I have limited knowledge in the designing.
Ted The amps im building for the 60 watt are stereo with one 278cx transformer and 2 1650 P trannies on one chassis. The 120 watt monos will be seperate units. I plan on using these to drive my 15" altec mid bass horn. What speakers are you using?
Once I'm finished I will probably strat a el34 amp with less wattage or 300b. I have limited knowledge in the designing.
6550 project
Hi jbldriven,
The speakers are rather mundane - just a pair of 8" Philips woofers + 2 x 1" dome tweeters + 1 x 5" midrange per sealed enclosure (home-built). I have driven them with a variety of amps, including a 6BQ5 (EL84) stereo amp that I pulled out of a console a while back and replaced capacitors etc. for.
I have done the chassis layout for this 6550 amp (using 1650P outputs and 278X power transformers.)
It will be built as two monoblocks on one chassis, and yes it will be heavy but I put a big handle at each end and it will save on gym fees.
So I am most interested in the splitter, I will probably leave the power supply as-is. Thanks for any help!
Ted.
Hi jbldriven,
The speakers are rather mundane - just a pair of 8" Philips woofers + 2 x 1" dome tweeters + 1 x 5" midrange per sealed enclosure (home-built). I have driven them with a variety of amps, including a 6BQ5 (EL84) stereo amp that I pulled out of a console a while back and replaced capacitors etc. for.
I have done the chassis layout for this 6550 amp (using 1650P outputs and 278X power transformers.)
It will be built as two monoblocks on one chassis, and yes it will be heavy but I put a big handle at each end and it will save on gym fees.
So I am most interested in the splitter, I will probably leave the power supply as-is. Thanks for any help!
Ted.
jbldriven,
Increasing the anode loads on the diff amp stage to 390K can be done. This will give you a little more "headroom" as Kevin suggests and increase gain yet again by 10%. You will have to adjust the current source to give about 700uA thru' each side of the diff amp (1.4 mA total) to maintain the anodes at around 270 to 300 Volts.
The current source can be adjusted by changing either the emitter resistor or the resistor from base to 0V. Last time we changed that base to 0V resistor. For best current source performance we want to maintain a minimum of 450mV across the emitter resistor so this time we need to change the emitter resistor instead/as well . The new emitter resistor value should be 390 Ohms. You may then need to change the base to 0V resitor to get the anodes at the right voltage (270 to 300 Volts).
Cheers,
Ian
Increasing the anode loads on the diff amp stage to 390K can be done. This will give you a little more "headroom" as Kevin suggests and increase gain yet again by 10%. You will have to adjust the current source to give about 700uA thru' each side of the diff amp (1.4 mA total) to maintain the anodes at around 270 to 300 Volts.
The current source can be adjusted by changing either the emitter resistor or the resistor from base to 0V. Last time we changed that base to 0V resistor. For best current source performance we want to maintain a minimum of 450mV across the emitter resistor so this time we need to change the emitter resistor instead/as well . The new emitter resistor value should be 390 Ohms. You may then need to change the base to 0V resitor to get the anodes at the right voltage (270 to 300 Volts).
Cheers,
Ian
KT88
Thanks Ian. I have been running the amp on my system for the 300hz to 5k horn. I still seem to be having a gain problem from the starting blocks.
I previously used a parasound 70 watt per channel amp (six output channels total)which supplied 70 watts to each of the following drivers. 15" midbass, 2"format mid horn and 1" format high driver. The gains were set on the crossover at 15"-- plus 2db, 2" -- minus 4db and the 1"-- plus 4 db.
In order to try the amp i am using a 250 watt per channel bryston on the 15" midbass, the 60 watt kt88 tube amp on the 2" and a 100 pioneer watt on the 1" high.
I have had to set the gains as follows to the following. Bryston & 15" midbass minus 2 db, 60 kt88 & 2" at plus 8db and the pioneer & 1" at plus 4db.
The gain for the KT88 tube amps had to be turned up about 12 db plus which i think is a sign of a gain problem.
Therefore i don't thint the amp would reach maximum output before preamp clipping.
The tech with the scope is out of town on a job so i decided it's time to pick up some equipment. I purchased a signal generator and hope to have a scope for this week some time. I have the resistive loads required know for testing. I will let you know the result as soon as test.
I am interest in you comments or thoughts on the gain problems.
Sorry i didn't get back to you soon for some reson the message never posted into my inbox.
Thanks for your input.
Thanks Ian. I have been running the amp on my system for the 300hz to 5k horn. I still seem to be having a gain problem from the starting blocks.
I previously used a parasound 70 watt per channel amp (six output channels total)which supplied 70 watts to each of the following drivers. 15" midbass, 2"format mid horn and 1" format high driver. The gains were set on the crossover at 15"-- plus 2db, 2" -- minus 4db and the 1"-- plus 4 db.
In order to try the amp i am using a 250 watt per channel bryston on the 15" midbass, the 60 watt kt88 tube amp on the 2" and a 100 pioneer watt on the 1" high.
I have had to set the gains as follows to the following. Bryston & 15" midbass minus 2 db, 60 kt88 & 2" at plus 8db and the pioneer & 1" at plus 4db.
The gain for the KT88 tube amps had to be turned up about 12 db plus which i think is a sign of a gain problem.
Therefore i don't thint the amp would reach maximum output before preamp clipping.
The tech with the scope is out of town on a job so i decided it's time to pick up some equipment. I purchased a signal generator and hope to have a scope for this week some time. I have the resistive loads required know for testing. I will let you know the result as soon as test.
I am interest in you comments or thoughts on the gain problems.
Sorry i didn't get back to you soon for some reson the message never posted into my inbox.
Thanks for your input.
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