pumpkin has an amplification of ten, thought for F4 without any amplification. What input voltage does your amp need?
Maybe 1 V only?
Maybe 1 V only?
The noise is there with no input signal applied.
10 x Nothing should be Nothing. Even if the A700 has a more sensitive input ?
The Aleph isn't finished yet, the Shuntky / Pumpkins are being built in preparation for the big day.
10 x Nothing should be Nothing. Even if the A700 has a more sensitive input ?
The Aleph isn't finished yet, the Shuntky / Pumpkins are being built in preparation for the big day.
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when your amp has also 20db amplification pumpkins amplification must be reduced.
an older ML I just googled even had 26db amplification.
an older ML I just googled even had 26db amplification.
The amplifier is making an intermittent "Pop" sound with no input attached and with the volume set to maximum.
set gain to 4-5x
try fully open pot , fully unloaded input with any tube preamp (for instance) - and you're looking for trouble
same with Pumpie
try fully open pot , fully unloaded input with any tube preamp (for instance) - and you're looking for trouble
same with Pumpie
As they always say, "You learn something every day".
If I had a signal applied under the conditions mentioned the Power Amp would be pushing over 60W into the speakers so you wouldn't hear the noise anyway. The only problem would be that you would hear the noise during quiet passages.
I'll leave the gain as it is for the time being as the noise may be a function of the increased gain of the A700. I'll see what it is like with the Aleph 4.
Zen-Mod, when you say unloaded input do you mean no signal or shorted input pins?
I would expect an amplifier with shorted input pins to be silent, ie amplifying nothing.
Although I rarely use the amp at full volume there will be occasions when you may wish to do so. I would not expect to hear "pops" from the speakers during the quiet passages...
If I had a signal applied under the conditions mentioned the Power Amp would be pushing over 60W into the speakers so you wouldn't hear the noise anyway. The only problem would be that you would hear the noise during quiet passages.
I'll leave the gain as it is for the time being as the noise may be a function of the increased gain of the A700. I'll see what it is like with the Aleph 4.
Zen-Mod, when you say unloaded input do you mean no signal or shorted input pins?
I would expect an amplifier with shorted input pins to be silent, ie amplifying nothing.
Although I rarely use the amp at full volume there will be occasions when you may wish to do so. I would not expect to hear "pops" from the speakers during the quiet passages...
problem is if you are doing those things* to highly sensitive input , as Pumpkin have ; not thinking about gain , but on sensitivity ... if I'm putting that correctly
* leaving input "open" - without source , where input is projected to work with finite source resistance . that way circ loose programmed gain , because inputs are flapping on breeze .....
I can bet that - if everything is OK - you'll not have any pops or whatever if you connect some source to Pumpkin's input , with pot where it belongs - between source and Pumpie input
Generg ( and few other builders) made similar mistake in past - using Pumpkin set to highish gain , with amps needing just line level for full throttle ..... after setting to moderate/adequate gain , problems were solved
* leaving input "open" - without source , where input is projected to work with finite source resistance . that way circ loose programmed gain , because inputs are flapping on breeze .....
I can bet that - if everything is OK - you'll not have any pops or whatever if you connect some source to Pumpkin's input , with pot where it belongs - between source and Pumpie input
Generg ( and few other builders) made similar mistake in past - using Pumpkin set to highish gain , with amps needing just line level for full throttle ..... after setting to moderate/adequate gain , problems were solved
Andy do you know how to set the gain to 3-4? One way is to change the feedbackresistor from 100k to 38k-41k, or rise the 10k in the inputs to 25-30k....
Is this correct Zen?
Is this correct Zen?
In my current set-up I agree, however, Pumpkins were built to go between my Arcam CD36 (2V output) and an Aleph 4.
If my tuition serves me correctly the Aleph has ZERO gain and requires approximately 26V to drive it fully.
Therefore the Pumpkins 10x gain should do the trick nicely. I might actually need to increase it slightly in order to fully drive the Aleph 4. I really could do with a gain of 15x and an output swing of 30V to give the Pumpkin headroom as well as the Aleph 4.
I don't intend on using the Class A Aleph 4 at 100W (10W is loud enough), but, the whole reason for this project in the first place is because my A700 is Class A up to a point (about 30W) when it changes to Class AB.
My previous pre-amp was constructed using the Borbelly Valve Circuit, although very good, it did colour the signal in a way that I was not very happy with. It has a gain of 15x and is absolutely silent under no signal conditions.
I don't want to enter into a slanging match about gains of various amplifiers. Ultimately when they are all built and tested I will measure the Inputs and Outputs and adjust the gains accordingly.
If my tuition serves me correctly the Aleph has ZERO gain and requires approximately 26V to drive it fully.
Therefore the Pumpkins 10x gain should do the trick nicely. I might actually need to increase it slightly in order to fully drive the Aleph 4. I really could do with a gain of 15x and an output swing of 30V to give the Pumpkin headroom as well as the Aleph 4.
I don't intend on using the Class A Aleph 4 at 100W (10W is loud enough), but, the whole reason for this project in the first place is because my A700 is Class A up to a point (about 30W) when it changes to Class AB.
My previous pre-amp was constructed using the Borbelly Valve Circuit, although very good, it did colour the signal in a way that I was not very happy with. It has a gain of 15x and is absolutely silent under no signal conditions.
I don't want to enter into a slanging match about gains of various amplifiers. Ultimately when they are all built and tested I will measure the Inputs and Outputs and adjust the gains accordingly.
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I stand corrected. As I said, I'll measure everything. All I want is a pre-amp to buffer the already high 2V output of the Arcam CD36 to a level that will drive the Aleph.
I get better noise figures with the volume controls between the Pumpkin and the Amplifier. Do you reckon this is due to the sensitivity of the A700 ?
By the way I haven't even tried the CD player with the set-up yet, I'm just using my Arcam AVR280 to provide a line-level tuner input for testing at the moment.
I get better noise figures with the volume controls between the Pumpkin and the Amplifier. Do you reckon this is due to the sensitivity of the A700 ?
By the way I haven't even tried the CD player with the set-up yet, I'm just using my Arcam AVR280 to provide a line-level tuner input for testing at the moment.
I've decided to stay with the Pumpkin as it is far more tolerant with high input voltages. The Borbely definitely needed an attenuator between the CD player and its input. The Pumpkin is more than happy with a 2V input signal and an attenuator at its output.
Borbely is now for sale on E-Bay - Stunning amp but I need to sell to fund future projects.
Borbely is now for sale on E-Bay - Stunning amp but I need to sell to fund future projects.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
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sounding now ?
Pumpkins do sound much better. Now that I've sorted the problem with Input and Output sensitivities and impedances.
Pumpkins seem happy with Arcam CD36 driving 2V directly into input and then putting 100K ladder pot on the output between pumkin and the power amp.
Borbelys didnt like the 2V input but were happy with the pot at the input.
I prefer the lack of colouration of the Pumkins. The tube Borbely spoilt the sound for me.
Pumpkins seem happy with Arcam CD36 driving 2V directly into input and then putting 100K ladder pot on the output between pumkin and the power amp.
Borbelys didnt like the 2V input but were happy with the pot at the input.
I prefer the lack of colouration of the Pumkins. The tube Borbely spoilt the sound for me.
After a break the Aleph 4 is back on the workbench.
I had a worrying few weeks with all the threads about fake components, I bought my IRFP244s from E-Bay but they would appear to be OK.
Having used many methods of matching the MOS-FETs I eventually chose a batch of 6 and mounted them to the OUTPUT PCB and thought about how to test the matching.
I attached +25V DC to the Common Drains, 0V to the Common Source Resistors and applied a variable +DC to the Common Gate Resistors.
With Vg = 0V I gingerly turned on the +25V and waited for smoke. THERE WAS NONE !!!!
Measuring Vs across each Source Resistor revealed that none of the MOS-FETs were ON - GOOD, that is what I expected.
Measuring Vs across the first of the six Source Resistors I gently increased Vgs until that MOS-FET was conducting about 100mA.
I measured Vs across the remaining Source Resistors to confirm that all MOS-FETs were conducting equally and then left it to warm up.
After 20 minutes the Vs readings are all within 0.7% of each other.
Next step is to try it with the +48V Power Supply and load them up to full idle current to check the matching again.
I'm hoping that the results that I have obtained so far are indicitative of a fairly good match of the MOS-FETs so far.
I had a worrying few weeks with all the threads about fake components, I bought my IRFP244s from E-Bay but they would appear to be OK.
Having used many methods of matching the MOS-FETs I eventually chose a batch of 6 and mounted them to the OUTPUT PCB and thought about how to test the matching.
I attached +25V DC to the Common Drains, 0V to the Common Source Resistors and applied a variable +DC to the Common Gate Resistors.
With Vg = 0V I gingerly turned on the +25V and waited for smoke. THERE WAS NONE !!!!
Measuring Vs across each Source Resistor revealed that none of the MOS-FETs were ON - GOOD, that is what I expected.
Measuring Vs across the first of the six Source Resistors I gently increased Vgs until that MOS-FET was conducting about 100mA.
I measured Vs across the remaining Source Resistors to confirm that all MOS-FETs were conducting equally and then left it to warm up.
After 20 minutes the Vs readings are all within 0.7% of each other.
Next step is to try it with the +48V Power Supply and load them up to full idle current to check the matching again.
I'm hoping that the results that I have obtained so far are indicitative of a fairly good match of the MOS-FETs so far.
Borbelly sold on E-Bay for £50.00 some lucky punter got a real bargain. It cost him almost the same in P&P though.
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